[PATCH RFC 00/24] Compiler-Based Capability- and Locking-Analysis

[PATCH RFC 00/24] Compiler-Based Capability- and Locking-Analysis

[Marco Elver]

[ Note: Bart and I had concurrently been working on bringing Clang's
  -Wthread-safety to the kernel:
    https://lore.kernel.org/all/20250206175114.1974171-1-bvanassche@acm.org/
  Having both RFCs out should hopefully provide a good picture on these
  design points and trade-offs - the approaches differ significantly. ]

Capability analysis is a C language extension, which enables statically
checking that user-definable "capabilities" are acquired and released where
required. An obvious application is lock-safety checking for the kernel's
various synchronization primitives (each of which represents a "capability"),
and checking that locking rules are not violated.

Clang originally called the feature "Thread Safety Analysis" [1], with
some terminology still using the thread-safety-analysis-only names. This
was later changed and the feature became more flexible, gaining the
ability to define custom "capabilities". Its foundations can be found in
"capability systems", used to specify the permissibility of operations
to depend on some capability being held (or not held).

[1] https://clang.llvm.org/docs/ThreadSafetyAnalysis.html
[2] https://www.cs.cornell.edu/talc/papers/capabilities.pdf

Because the feature is not just able to express capabilities related to
synchronization primitives, the naming chosen for the kernel departs
from Clang's initial "Thread Safety" nomenclature and refers to the
feature as "Capability Analysis" to avoid confusion. The implementation
still makes references to the older terminology in some places, such as
`-Wthread-safety` being the warning enabled option that also still
appears in diagnostic messages.

Enabling capability analysis can be seen as enabling a dialect of Linux
C with a Capability System.

Additional details can be found in the added kernel-doc documentation.

=== Development Approach ===

Prior art exists in the form of Sparse's context tracking. Locking
annotations on functions exist, so the concept of analyzing locking rules
is not foreign to the kernel's codebase.

However, Clang's analysis is more complete vs. Sparse's, with the
typical trade-offs in static analysis: improved completeness is
sacrificed for more possible false positives or additional annotations
required by the programmer. Numerous options exist to disable or opt out
certain code from analysis.

This series aims to retain compatibility with Sparse, which can provide
tree-wide analysis of a subset of the capability analysis introduced.
For the most part, the new (and old) keywords used for annotations are
shared between Sparse and Clang.

One big question is how to enable this feature, given we end up with a
new dialect of C - 2 approaches have been considered:


	A. Tree-wide all-or-nothing approach. This approach requires
	   tree-wide changes, adding annotations or selective opt-outs.
	   Making additional primitives capability-enabled increases
	   churn, esp. where maintainers are unaware of the feature's
	   existence and how to use it.

Because we can't change the programming language (even if from one C
dialect to another) of the kernel overnight, a different approach might
cause less friction.

	B. A selective, incremental, and much less intrusive approach.
	   Maintainers of subsystems opt in their modules or directories
	   into "capability analysis" (via Makefile):

	     CAPABILITY_ANALYSIS_foo.o := y	# foo.o only
	     CAPABILITY_ANALYSIS := y  		# all TUs

	   Most (eventually all) synchronization primitives and more
	   capabilities (including ones that could track "irq disabled",
	   "preemption" disabled, etc.) could be supported.

The approach taken by this series if B. This ensures that only
subsystems where maintainers are willing to deal with any warnings one
way or another. Introducing the feature can be done incrementally,
without large tree-wide changes and adding numerous opt-outs and
annotations to the majority of code.

=== Initial Uses ===

With this initial series, the following synchronization primitives are
supported: `raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`,
`seqlock_t`, `bit_spinlock`, RCU, SRCU (`srcu_struct`), `rw_semaphore`,
`local_lock_t`.

As an initial proof-of-concept, this series also enables capability
analysis for the following subsystems: kfence, kcov, stackdepot,
rhashtable. (Those subsystems were chosen because I am familiar with
their locking rules; rhashtable was chosen semi-randomly as a test
because it combines a bunch of things: RCU, mutex, bit_spinlock.)

The initial benefits are static detection of violations of locking
rules. As more capabilities are added, we would see more static checking
beyond what regular C can provide, all while remaining easy (read quick)
to use via the Clang compiler.

=== Appendix ===

The following pending Clang patch is recommended, but not a strong
dependency:

	https://github.com/llvm/llvm-project/pull/123063

This series is also available at this Git tree:

	https://git.kernel.org/pub/scm/linux/kernel/git/melver/linux.git/log/?h=cap-analysis

Marco Elver (24):
  compiler_types: Move lock checking attributes to
    compiler-capability-analysis.h
  compiler-capability-analysis: Rename __cond_lock() to __cond_acquire()
  compiler-capability-analysis: Add infrastructure for Clang's
    capability analysis
  compiler-capability-analysis: Add test stub
  Documentation: Add documentation for Compiler-Based Capability
    Analysis
  checkpatch: Warn about capability_unsafe() without comment
  cleanup: Basic compatibility with capability analysis
  lockdep: Annotate lockdep assertions for capability analysis
  locking/rwlock, spinlock: Support Clang's capability analysis
  compiler-capability-analysis: Change __cond_acquires to take return
    value
  locking/mutex: Support Clang's capability analysis
  locking/seqlock: Support Clang's capability analysis
  bit_spinlock: Include missing <asm/processor.h>
  bit_spinlock: Support Clang's capability analysis
  rcu: Support Clang's capability analysis
  srcu: Support Clang's capability analysis
  kref: Add capability-analysis annotations
  locking/rwsem: Support Clang's capability analysis
  locking/local_lock: Support Clang's capability analysis
  debugfs: Make debugfs_cancellation a capability struct
  kfence: Enable capability analysis
  kcov: Enable capability analysis
  stackdepot: Enable capability analysis
  rhashtable: Enable capability analysis

 .../dev-tools/capability-analysis.rst         | 149 ++++++
 Documentation/dev-tools/index.rst             |   1 +
 Documentation/dev-tools/sparse.rst            |   4 +
 Makefile                                      |   1 +
 .../net/wireless/intel/iwlwifi/iwl-trans.h    |   2 +-
 .../wireless/intel/iwlwifi/pcie/internal.h    |   2 +-
 fs/dlm/lock.c                                 |   2 +-
 include/linux/bit_spinlock.h                  |  24 +-
 include/linux/cleanup.h                       |  18 +-
 include/linux/compiler-capability-analysis.h  | 407 +++++++++++++++
 include/linux/compiler_types.h                |  18 +-
 include/linux/debugfs.h                       |  12 +-
 include/linux/kref.h                          |   2 +
 include/linux/list_bl.h                       |   2 +
 include/linux/local_lock.h                    |  18 +-
 include/linux/local_lock_internal.h           |  41 +-
 include/linux/lockdep.h                       |  12 +-
 include/linux/mm.h                            |   6 +-
 include/linux/mutex.h                         |  29 +-
 include/linux/mutex_types.h                   |   4 +-
 include/linux/rcupdate.h                      |  73 ++-
 include/linux/refcount.h                      |   6 +-
 include/linux/rhashtable.h                    |  14 +-
 include/linux/rwlock.h                        |  27 +-
 include/linux/rwlock_api_smp.h                |  29 +-
 include/linux/rwlock_rt.h                     |  37 +-
 include/linux/rwlock_types.h                  |  10 +-
 include/linux/rwsem.h                         |  56 +-
 include/linux/sched/signal.h                  |   2 +-
 include/linux/seqlock.h                       |  24 +
 include/linux/seqlock_types.h                 |   5 +-
 include/linux/spinlock.h                      |  61 ++-
 include/linux/spinlock_api_smp.h              |  14 +-
 include/linux/spinlock_api_up.h               |  71 +--
 include/linux/spinlock_rt.h                   |  27 +-
 include/linux/spinlock_types.h                |  10 +-
 include/linux/spinlock_types_raw.h            |   5 +-
 include/linux/srcu.h                          |  61 ++-
 kernel/Makefile                               |   2 +
 kernel/kcov.c                                 |  40 +-
 kernel/time/posix-timers.c                    |   2 +-
 lib/Kconfig.debug                             |  43 ++
 lib/Makefile                                  |   6 +
 lib/rhashtable.c                              |  12 +-
 lib/stackdepot.c                              |  24 +-
 lib/test_capability-analysis.c                | 481 ++++++++++++++++++
 mm/kfence/Makefile                            |   2 +
 mm/kfence/core.c                              |  24 +-
 mm/kfence/kfence.h                            |  18 +-
 mm/kfence/kfence_test.c                       |   4 +
 mm/kfence/report.c                            |   8 +-
 net/ipv4/tcp_sigpool.c                        |   2 +-
 scripts/Makefile.capability-analysis          |   5 +
 scripts/Makefile.lib                          |  10 +
 scripts/checkpatch.pl                         |   8 +
 tools/include/linux/compiler_types.h          |   4 +-
 56 files changed, 1682 insertions(+), 299 deletions(-)
 create mode 100644 Documentation/dev-tools/capability-analysis.rst
 create mode 100644 include/linux/compiler-capability-analysis.h
 create mode 100644 lib/test_capability-analysis.c
 create mode 100644 scripts/Makefile.capability-analysis

-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 01/24] compiler_types: Move lock checking attributes to compiler-capability-analysis.h

[Marco Elver]

The conditional definition of lock checking macros and attributes is
about to become more complex. Factor them out into their own header for
better readability, and to make it obvious which features are supported
by which mode (currently only Sparse). This is the first step towards
generalizing towards "capability analysis".

No functional change intended.

Signed-off-by: Marco Elver <elver@google.com>
---
 include/linux/compiler-capability-analysis.h | 32 ++++++++++++++++++++
 include/linux/compiler_types.h               | 18 ++---------
 2 files changed, 34 insertions(+), 16 deletions(-)
 create mode 100644 include/linux/compiler-capability-analysis.h

diff --git a/include/linux/compiler-capability-analysis.h b/include/linux/compiler-capability-analysis.h
new file mode 100644
index 000000000000..7546ddb83f86
--- /dev/null
+++ b/include/linux/compiler-capability-analysis.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Macros and attributes for compiler-based static capability analysis.
+ */
+
+#ifndef _LINUX_COMPILER_CAPABILITY_ANALYSIS_H
+#define _LINUX_COMPILER_CAPABILITY_ANALYSIS_H
+
+#ifdef __CHECKER__
+
+/* Sparse context/lock checking support. */
+# define __must_hold(x)		__attribute__((context(x,1,1)))
+# define __acquires(x)		__attribute__((context(x,0,1)))
+# define __cond_acquires(x)	__attribute__((context(x,0,-1)))
+# define __releases(x)		__attribute__((context(x,1,0)))
+# define __acquire(x)		__context__(x,1)
+# define __release(x)		__context__(x,-1)
+# define __cond_lock(x, c)	((c) ? ({ __acquire(x); 1; }) : 0)
+
+#else /* !__CHECKER__ */
+
+# define __must_hold(x)
+# define __acquires(x)
+# define __cond_acquires(x)
+# define __releases(x)
+# define __acquire(x)		(void)0
+# define __release(x)		(void)0
+# define __cond_lock(x, c)	(c)
+
+#endif /* __CHECKER__ */
+
+#endif /* _LINUX_COMPILER_CAPABILITY_ANALYSIS_H */
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 981cc3d7e3aa..4a458e41293c 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -24,6 +24,8 @@
 # define BTF_TYPE_TAG(value) /* nothing */
 #endif
 
+#include <linux/compiler-capability-analysis.h>
+
 /* sparse defines __CHECKER__; see Documentation/dev-tools/sparse.rst */
 #ifdef __CHECKER__
 /* address spaces */
@@ -34,14 +36,6 @@
 # define __rcu		__attribute__((noderef, address_space(__rcu)))
 static inline void __chk_user_ptr(const volatile void __user *ptr) { }
 static inline void __chk_io_ptr(const volatile void __iomem *ptr) { }
-/* context/locking */
-# define __must_hold(x)	__attribute__((context(x,1,1)))
-# define __acquires(x)	__attribute__((context(x,0,1)))
-# define __cond_acquires(x) __attribute__((context(x,0,-1)))
-# define __releases(x)	__attribute__((context(x,1,0)))
-# define __acquire(x)	__context__(x,1)
-# define __release(x)	__context__(x,-1)
-# define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
 /* other */
 # define __force	__attribute__((force))
 # define __nocast	__attribute__((nocast))
@@ -62,14 +56,6 @@ static inline void __chk_io_ptr(const volatile void __iomem *ptr) { }
 
 # define __chk_user_ptr(x)	(void)0
 # define __chk_io_ptr(x)	(void)0
-/* context/locking */
-# define __must_hold(x)
-# define __acquires(x)
-# define __cond_acquires(x)
-# define __releases(x)
-# define __acquire(x)	(void)0
-# define __release(x)	(void)0
-# define __cond_lock(x,c) (c)
 /* other */
 # define __force
 # define __nocast
-- 
2.48.1.502.g6dc24dfdaf-goog

Re: [PATCH RFC 01/24] compiler_types: Move lock checking attributes to compiler-capability-analysis.h

[Bart Van Assche]

On 2/6/25 10:09 AM, Marco Elver wrote:
> +/* Sparse context/lock checking support. */
> +# define __must_hold(x)		__attribute__((context(x,1,1)))
> +# define __acquires(x)		__attribute__((context(x,0,1)))
> +# define __cond_acquires(x)	__attribute__((context(x,0,-1)))
> +# define __releases(x)		__attribute__((context(x,1,0)))
> +# define __acquire(x)		__context__(x,1)
> +# define __release(x)		__context__(x,-1)
> +# define __cond_lock(x, c)	((c) ? ({ __acquire(x); 1; }) : 0)

If support for Clang thread-safety attributes is added, an important
question is what to do with the sparse context attribute. I think that
more developers are working on improving and maintaining Clang than
sparse. How about reducing the workload of kernel maintainers by
only supporting the Clang thread-safety approach and by dropping support
for the sparse context attribute?

Thanks,

Bart.

Re: [PATCH RFC 01/24] compiler_types: Move lock checking attributes to compiler-capability-analysis.h

[Marco Elver]

On Thu, 6 Feb 2025 at 19:40, Bart Van Assche <bvanassche@acm.org> wrote:
>
> On 2/6/25 10:09 AM, Marco Elver wrote:
> > +/* Sparse context/lock checking support. */
> > +# define __must_hold(x)              __attribute__((context(x,1,1)))
> > +# define __acquires(x)               __attribute__((context(x,0,1)))
> > +# define __cond_acquires(x)  __attribute__((context(x,0,-1)))
> > +# define __releases(x)               __attribute__((context(x,1,0)))
> > +# define __acquire(x)                __context__(x,1)
> > +# define __release(x)                __context__(x,-1)
> > +# define __cond_lock(x, c)   ((c) ? ({ __acquire(x); 1; }) : 0)
>
> If support for Clang thread-safety attributes is added, an important
> question is what to do with the sparse context attribute. I think that
> more developers are working on improving and maintaining Clang than
> sparse. How about reducing the workload of kernel maintainers by
> only supporting the Clang thread-safety approach and by dropping support
> for the sparse context attribute?

My 2c: I think Sparse's context tracking is a subset, and generally
less complete, favoring false negatives over false positives (also
does not support guarded_by).
So in theory they can co-exist.
In practice, I agree, there will be issues with maintaining both,
because there will always be some odd corner-case which doesn't quite
work with one or the other (specifically Sparse is happy to auto-infer
acquired and released capabilities/contexts of functions and doesn't
warn you if you still hold a lock when returning from a function).

I'd be in favor of deprecating Sparse's context tracking support,
should there be consensus on that.

Thanks,
-- Marco

Re: [PATCH RFC 01/24] compiler_types: Move lock checking attributes to compiler-capability-analysis.h

[Peter Zijlstra]

On Thu, Feb 06, 2025 at 07:48:38PM +0100, Marco Elver wrote:
> On Thu, 6 Feb 2025 at 19:40, Bart Van Assche <bvanassche@acm.org> wrote:
> >
> > On 2/6/25 10:09 AM, Marco Elver wrote:
> > > +/* Sparse context/lock checking support. */
> > > +# define __must_hold(x)              __attribute__((context(x,1,1)))
> > > +# define __acquires(x)               __attribute__((context(x,0,1)))
> > > +# define __cond_acquires(x)  __attribute__((context(x,0,-1)))
> > > +# define __releases(x)               __attribute__((context(x,1,0)))
> > > +# define __acquire(x)                __context__(x,1)
> > > +# define __release(x)                __context__(x,-1)
> > > +# define __cond_lock(x, c)   ((c) ? ({ __acquire(x); 1; }) : 0)
> >
> > If support for Clang thread-safety attributes is added, an important
> > question is what to do with the sparse context attribute. I think that
> > more developers are working on improving and maintaining Clang than
> > sparse. How about reducing the workload of kernel maintainers by
> > only supporting the Clang thread-safety approach and by dropping support
> > for the sparse context attribute?
> 
> My 2c: I think Sparse's context tracking is a subset, and generally
> less complete, favoring false negatives over false positives (also
> does not support guarded_by).
> So in theory they can co-exist.
> In practice, I agree, there will be issues with maintaining both,
> because there will always be some odd corner-case which doesn't quite
> work with one or the other (specifically Sparse is happy to auto-infer
> acquired and released capabilities/contexts of functions and doesn't
> warn you if you still hold a lock when returning from a function).
> 
> I'd be in favor of deprecating Sparse's context tracking support,
> should there be consensus on that.

I don't think I've ever seen a useful sparse locking report, so yeah, no
tears shed on removing it.

[PATCH RFC 02/24] compiler-capability-analysis: Rename __cond_lock() to __cond_acquire()

[Marco Elver]

Just like the pairing of attribute __acquires() with a matching
function-like macro __acquire(), the attribute __cond_acquires() should
have a matching function-like macro __cond_acquire().

To be consistent, rename __cond_lock() to __cond_acquire().

Signed-off-by: Marco Elver <elver@google.com>
---
 drivers/net/wireless/intel/iwlwifi/iwl-trans.h     |  2 +-
 drivers/net/wireless/intel/iwlwifi/pcie/internal.h |  2 +-
 include/linux/compiler-capability-analysis.h       |  4 ++--
 include/linux/mm.h                                 |  6 +++---
 include/linux/rwlock.h                             |  4 ++--
 include/linux/rwlock_rt.h                          |  4 ++--
 include/linux/sched/signal.h                       |  2 +-
 include/linux/spinlock.h                           | 12 ++++++------
 include/linux/spinlock_rt.h                        |  6 +++---
 kernel/time/posix-timers.c                         |  2 +-
 tools/include/linux/compiler_types.h               |  4 ++--
 11 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-trans.h b/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
index f6234065dbdd..560a5a899d1f 100644
--- a/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
+++ b/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
@@ -1136,7 +1136,7 @@ void iwl_trans_set_bits_mask(struct iwl_trans *trans, u32 reg,
 bool _iwl_trans_grab_nic_access(struct iwl_trans *trans);
 
 #define iwl_trans_grab_nic_access(trans)		\
-	__cond_lock(nic_access,				\
+	__cond_acquire(nic_access,				\
 		    likely(_iwl_trans_grab_nic_access(trans)))
 
 void __releases(nic_access)
diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/internal.h b/drivers/net/wireless/intel/iwlwifi/pcie/internal.h
index 856b7e9f717d..a1becf833dc5 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/internal.h
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/internal.h
@@ -560,7 +560,7 @@ void iwl_trans_pcie_free_pnvm_dram_regions(struct iwl_dram_regions *dram_regions
 
 bool __iwl_trans_pcie_grab_nic_access(struct iwl_trans *trans);
 #define _iwl_trans_pcie_grab_nic_access(trans)			\
-	__cond_lock(nic_access_nobh,				\
+	__cond_acquire(nic_access_nobh,				\
 		    likely(__iwl_trans_pcie_grab_nic_access(trans)))
 
 void iwl_trans_pcie_check_product_reset_status(struct pci_dev *pdev);
diff --git a/include/linux/compiler-capability-analysis.h b/include/linux/compiler-capability-analysis.h
index 7546ddb83f86..dfed4e7e6ab8 100644
--- a/include/linux/compiler-capability-analysis.h
+++ b/include/linux/compiler-capability-analysis.h
@@ -15,7 +15,7 @@
 # define __releases(x)		__attribute__((context(x,1,0)))
 # define __acquire(x)		__context__(x,1)
 # define __release(x)		__context__(x,-1)
-# define __cond_lock(x, c)	((c) ? ({ __acquire(x); 1; }) : 0)
+# define __cond_acquire(x, c)	((c) ? ({ __acquire(x); 1; }) : 0)
 
 #else /* !__CHECKER__ */
 
@@ -25,7 +25,7 @@
 # define __releases(x)
 # define __acquire(x)		(void)0
 # define __release(x)		(void)0
-# define __cond_lock(x, c)	(c)
+# define __cond_acquire(x, c)	(c)
 
 #endif /* __CHECKER__ */
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7b1068ddcbb7..a2365f4d6826 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2738,7 +2738,7 @@ static inline pte_t *get_locked_pte(struct mm_struct *mm, unsigned long addr,
 				    spinlock_t **ptl)
 {
 	pte_t *ptep;
-	__cond_lock(*ptl, ptep = __get_locked_pte(mm, addr, ptl));
+	__cond_acquire(*ptl, ptep = __get_locked_pte(mm, addr, ptl));
 	return ptep;
 }
 
@@ -3029,7 +3029,7 @@ static inline pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr,
 {
 	pte_t *pte;
 
-	__cond_lock(RCU, pte = ___pte_offset_map(pmd, addr, pmdvalp));
+	__cond_acquire(RCU, pte = ___pte_offset_map(pmd, addr, pmdvalp));
 	return pte;
 }
 static inline pte_t *pte_offset_map(pmd_t *pmd, unsigned long addr)
@@ -3044,7 +3044,7 @@ static inline pte_t *pte_offset_map_lock(struct mm_struct *mm, pmd_t *pmd,
 {
 	pte_t *pte;
 
-	__cond_lock(RCU, __cond_lock(*ptlp,
+	__cond_acquire(RCU, __cond_acquire(*ptlp,
 			pte = __pte_offset_map_lock(mm, pmd, addr, ptlp)));
 	return pte;
 }
diff --git a/include/linux/rwlock.h b/include/linux/rwlock.h
index 5b87c6f4a243..58c346947aa2 100644
--- a/include/linux/rwlock.h
+++ b/include/linux/rwlock.h
@@ -49,8 +49,8 @@ do {								\
  * regardless of whether CONFIG_SMP or CONFIG_PREEMPT are set. The various
  * methods are defined as nops in the case they are not required.
  */
-#define read_trylock(lock)	__cond_lock(lock, _raw_read_trylock(lock))
-#define write_trylock(lock)	__cond_lock(lock, _raw_write_trylock(lock))
+#define read_trylock(lock)	__cond_acquire(lock, _raw_read_trylock(lock))
+#define write_trylock(lock)	__cond_acquire(lock, _raw_write_trylock(lock))
 
 #define write_lock(lock)	_raw_write_lock(lock)
 #define read_lock(lock)		_raw_read_lock(lock)
diff --git a/include/linux/rwlock_rt.h b/include/linux/rwlock_rt.h
index 7d81fc6918ee..5320b4b66405 100644
--- a/include/linux/rwlock_rt.h
+++ b/include/linux/rwlock_rt.h
@@ -55,7 +55,7 @@ static __always_inline void read_lock_irq(rwlock_t *rwlock)
 		flags = 0;				\
 	} while (0)
 
-#define read_trylock(lock)	__cond_lock(lock, rt_read_trylock(lock))
+#define read_trylock(lock)	__cond_acquire(lock, rt_read_trylock(lock))
 
 static __always_inline void read_unlock(rwlock_t *rwlock)
 {
@@ -111,7 +111,7 @@ static __always_inline void write_lock_irq(rwlock_t *rwlock)
 		flags = 0;				\
 	} while (0)
 
-#define write_trylock(lock)	__cond_lock(lock, rt_write_trylock(lock))
+#define write_trylock(lock)	__cond_acquire(lock, rt_write_trylock(lock))
 
 #define write_trylock_irqsave(lock, flags)		\
 ({							\
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index d5d03d919df8..3304cce4b1bf 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -741,7 +741,7 @@ static inline struct sighand_struct *lock_task_sighand(struct task_struct *task,
 	struct sighand_struct *ret;
 
 	ret = __lock_task_sighand(task, flags);
-	(void)__cond_lock(&task->sighand->siglock, ret);
+	(void)__cond_acquire(&task->sighand->siglock, ret);
 	return ret;
 }
 
diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 63dd8cf3c3c2..678e6f0679a1 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -212,7 +212,7 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
  * various methods are defined as nops in the case they are not
  * required.
  */
-#define raw_spin_trylock(lock)	__cond_lock(lock, _raw_spin_trylock(lock))
+#define raw_spin_trylock(lock)	__cond_acquire(lock, _raw_spin_trylock(lock))
 
 #define raw_spin_lock(lock)	_raw_spin_lock(lock)
 
@@ -284,7 +284,7 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 #define raw_spin_unlock_bh(lock)	_raw_spin_unlock_bh(lock)
 
 #define raw_spin_trylock_bh(lock) \
-	__cond_lock(lock, _raw_spin_trylock_bh(lock))
+	__cond_acquire(lock, _raw_spin_trylock_bh(lock))
 
 #define raw_spin_trylock_irq(lock) \
 ({ \
@@ -499,21 +499,21 @@ static inline int rwlock_needbreak(rwlock_t *lock)
  */
 extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
 #define atomic_dec_and_lock(atomic, lock) \
-		__cond_lock(lock, _atomic_dec_and_lock(atomic, lock))
+		__cond_acquire(lock, _atomic_dec_and_lock(atomic, lock))
 
 extern int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
 					unsigned long *flags);
 #define atomic_dec_and_lock_irqsave(atomic, lock, flags) \
-		__cond_lock(lock, _atomic_dec_and_lock_irqsave(atomic, lock, &(flags)))
+		__cond_acquire(lock, _atomic_dec_and_lock_irqsave(atomic, lock, &(flags)))
 
 extern int _atomic_dec_and_raw_lock(atomic_t *atomic, raw_spinlock_t *lock);
 #define atomic_dec_and_raw_lock(atomic, lock) \
-		__cond_lock(lock, _atomic_dec_and_raw_lock(atomic, lock))
+		__cond_acquire(lock, _atomic_dec_and_raw_lock(atomic, lock))
 
 extern int _atomic_dec_and_raw_lock_irqsave(atomic_t *atomic, raw_spinlock_t *lock,
 					unsigned long *flags);
 #define atomic_dec_and_raw_lock_irqsave(atomic, lock, flags) \
-		__cond_lock(lock, _atomic_dec_and_raw_lock_irqsave(atomic, lock, &(flags)))
+		__cond_acquire(lock, _atomic_dec_and_raw_lock_irqsave(atomic, lock, &(flags)))
 
 int __alloc_bucket_spinlocks(spinlock_t **locks, unsigned int *lock_mask,
 			     size_t max_size, unsigned int cpu_mult,
diff --git a/include/linux/spinlock_rt.h b/include/linux/spinlock_rt.h
index f6499c37157d..eaad4dd2baac 100644
--- a/include/linux/spinlock_rt.h
+++ b/include/linux/spinlock_rt.h
@@ -123,13 +123,13 @@ static __always_inline void spin_unlock_irqrestore(spinlock_t *lock,
 }
 
 #define spin_trylock(lock)				\
-	__cond_lock(lock, rt_spin_trylock(lock))
+	__cond_acquire(lock, rt_spin_trylock(lock))
 
 #define spin_trylock_bh(lock)				\
-	__cond_lock(lock, rt_spin_trylock_bh(lock))
+	__cond_acquire(lock, rt_spin_trylock_bh(lock))
 
 #define spin_trylock_irq(lock)				\
-	__cond_lock(lock, rt_spin_trylock(lock))
+	__cond_acquire(lock, rt_spin_trylock(lock))
 
 #define spin_trylock_irqsave(lock, flags)		\
 ({							\
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 1b675aee99a9..dbada41c10ad 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -63,7 +63,7 @@ static struct k_itimer *__lock_timer(timer_t timer_id, unsigned long *flags);
 
 #define lock_timer(tid, flags)						   \
 ({	struct k_itimer *__timr;					   \
-	__cond_lock(&__timr->it_lock, __timr = __lock_timer(tid, flags));  \
+	__cond_acquire(&__timr->it_lock, __timr = __lock_timer(tid, flags));  \
 	__timr;								   \
 })
 
diff --git a/tools/include/linux/compiler_types.h b/tools/include/linux/compiler_types.h
index d09f9dc172a4..b1db30e510d0 100644
--- a/tools/include/linux/compiler_types.h
+++ b/tools/include/linux/compiler_types.h
@@ -20,7 +20,7 @@
 # define __releases(x)	__attribute__((context(x,1,0)))
 # define __acquire(x)	__context__(x,1)
 # define __release(x)	__context__(x,-1)
-# define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
+# define __cond_acquire(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
 #else /* __CHECKER__ */
 /* context/locking */
 # define __must_hold(x)
@@ -28,7 +28,7 @@
 # define __releases(x)
 # define __acquire(x)	(void)0
 # define __release(x)	(void)0
-# define __cond_lock(x,c) (c)
+# define __cond_acquire(x,c) (c)
 #endif /* __CHECKER__ */
 
 /* Compiler specific macros. */
-- 
2.48.1.502.g6dc24dfdaf-goog

Re: [PATCH RFC 02/24] compiler-capability-analysis: Rename __cond_lock() to __cond_acquire()

[Peter Zijlstra]

On Thu, Feb 06, 2025 at 07:09:56PM +0100, Marco Elver wrote:
> Just like the pairing of attribute __acquires() with a matching
> function-like macro __acquire(), the attribute __cond_acquires() should
> have a matching function-like macro __cond_acquire().
> 
> To be consistent, rename __cond_lock() to __cond_acquire().

So I hate this __cond_lock() thing we have with a passion. I think it is
one of the very worst annotations possible since it makes a trainwreck
of the trylock code.

It is a major reason why mutex is not annotated with this nonsense.

Also, I think very dim of sparse in general -- I don't think I've ever
managed to get a useful warning from between all the noise it generates.

Re: [PATCH RFC 02/24] compiler-capability-analysis: Rename __cond_lock() to __cond_acquire()

[Marco Elver]

On Fri, Feb 07, 2025 at 09:28AM +0100, Peter Zijlstra wrote:
> On Thu, Feb 06, 2025 at 07:09:56PM +0100, Marco Elver wrote:
> > Just like the pairing of attribute __acquires() with a matching
> > function-like macro __acquire(), the attribute __cond_acquires() should
> > have a matching function-like macro __cond_acquire().
> > 
> > To be consistent, rename __cond_lock() to __cond_acquire().
> 
> So I hate this __cond_lock() thing we have with a passion. I think it is
> one of the very worst annotations possible since it makes a trainwreck
> of the trylock code.
> 
> It is a major reason why mutex is not annotated with this nonsense.
> 
> Also, I think very dim of sparse in general -- I don't think I've ever
> managed to get a useful warning from between all the noise it generates.

Happy to reduce the use of __cond_lock(). :-)
Though one problem I found is it's still needed for those complex
statement-expression *_trylock that spinlock.h/rwlock.h has, where we
e.g. have (with my changes):

	#define raw_spin_trylock_irqsave(lock, flags)		\
		__cond_acquire(lock, ({				\
			local_irq_save(flags);			\
			_raw_spin_trylock(lock) ?		\
			1 : ({ local_irq_restore(flags); 0; }); \
		}))

Because there's an inner condition using _raw_spin_trylock() and the
result of _raw_spin_trylock() is no longer directly used in a branch
that also does the unlock, Clang becomes unhappy and complains. I.e.
annotating _raw_spin_trylock with __cond_acquires(1, lock) doesn't work
for this case because it's in a complex statement-expression. The only
way to make it work was to wrap it into a function that has attribute
__cond_acquires(1, lock) which is what I made __cond_lock/acquire do.

For some of the trivial uses, like e.g.

	#define raw_spin_trylock(lock)	__cond_acquire(lock, _raw_spin_trylock(lock))

it's easy enough to remove the outer __cond_lock/acquire if e.g. the
_raw_spin_trylock has the attribute __cond_acquires. I kept these around
for Sparse compatibility, but if we want to get rid of Sparse
compatibility, some of those can be simplified.

Re: [PATCH RFC 02/24] compiler-capability-analysis: Rename __cond_lock() to __cond_acquire()

[Peter Zijlstra]

On Fri, Feb 07, 2025 at 10:32:25AM +0100, Marco Elver wrote:
> On Fri, Feb 07, 2025 at 09:28AM +0100, Peter Zijlstra wrote:
> > On Thu, Feb 06, 2025 at 07:09:56PM +0100, Marco Elver wrote:
> > > Just like the pairing of attribute __acquires() with a matching
> > > function-like macro __acquire(), the attribute __cond_acquires() should
> > > have a matching function-like macro __cond_acquire().
> > > 
> > > To be consistent, rename __cond_lock() to __cond_acquire().
> > 
> > So I hate this __cond_lock() thing we have with a passion. I think it is
> > one of the very worst annotations possible since it makes a trainwreck
> > of the trylock code.
> > 
> > It is a major reason why mutex is not annotated with this nonsense.
> > 
> > Also, I think very dim of sparse in general -- I don't think I've ever
> > managed to get a useful warning from between all the noise it generates.
> 
> Happy to reduce the use of __cond_lock(). :-)
> Though one problem I found is it's still needed for those complex
> statement-expression *_trylock that spinlock.h/rwlock.h has, where we
> e.g. have (with my changes):
> 
> 	#define raw_spin_trylock_irqsave(lock, flags)		\
> 		__cond_acquire(lock, ({				\
> 			local_irq_save(flags);			\
> 			_raw_spin_trylock(lock) ?		\
> 			1 : ({ local_irq_restore(flags); 0; }); \
> 		}))
> 
> Because there's an inner condition using _raw_spin_trylock() and the
> result of _raw_spin_trylock() is no longer directly used in a branch
> that also does the unlock, Clang becomes unhappy and complains. I.e.
> annotating _raw_spin_trylock with __cond_acquires(1, lock) doesn't work
> for this case because it's in a complex statement-expression. The only
> way to make it work was to wrap it into a function that has attribute
> __cond_acquires(1, lock) which is what I made __cond_lock/acquire do.

Does something like:

static inline bool
_raw_spin_trylock_irqsave(raw_spinlock_t *lock, unsigned long *flags)
	__cond_acquire(1, lock)
{
	local_irq_save(*flags);
	if (_raw_spin_trylock(lock))
		return true;
	local_irq_restore(*flags);
	return false;
}

#define raw_spin_trylock_irqsave(lock, flags) \
	_raw_spin_trylock_irqsave((lock), &(flags))

work?

Re: [PATCH RFC 02/24] compiler-capability-analysis: Rename __cond_lock() to __cond_acquire()

[Marco Elver]

On Fri, 7 Feb 2025 at 10:41, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Feb 07, 2025 at 10:32:25AM +0100, Marco Elver wrote:
> > On Fri, Feb 07, 2025 at 09:28AM +0100, Peter Zijlstra wrote:
> > > On Thu, Feb 06, 2025 at 07:09:56PM +0100, Marco Elver wrote:
> > > > Just like the pairing of attribute __acquires() with a matching
> > > > function-like macro __acquire(), the attribute __cond_acquires() should
> > > > have a matching function-like macro __cond_acquire().
> > > >
> > > > To be consistent, rename __cond_lock() to __cond_acquire().
> > >
> > > So I hate this __cond_lock() thing we have with a passion. I think it is
> > > one of the very worst annotations possible since it makes a trainwreck
> > > of the trylock code.
> > >
> > > It is a major reason why mutex is not annotated with this nonsense.
> > >
> > > Also, I think very dim of sparse in general -- I don't think I've ever
> > > managed to get a useful warning from between all the noise it generates.
> >
> > Happy to reduce the use of __cond_lock(). :-)
> > Though one problem I found is it's still needed for those complex
> > statement-expression *_trylock that spinlock.h/rwlock.h has, where we
> > e.g. have (with my changes):
> >
> >       #define raw_spin_trylock_irqsave(lock, flags)           \
> >               __cond_acquire(lock, ({                         \
> >                       local_irq_save(flags);                  \
> >                       _raw_spin_trylock(lock) ?               \
> >                       1 : ({ local_irq_restore(flags); 0; }); \
> >               }))
> >
> > Because there's an inner condition using _raw_spin_trylock() and the
> > result of _raw_spin_trylock() is no longer directly used in a branch
> > that also does the unlock, Clang becomes unhappy and complains. I.e.
> > annotating _raw_spin_trylock with __cond_acquires(1, lock) doesn't work
> > for this case because it's in a complex statement-expression. The only
> > way to make it work was to wrap it into a function that has attribute
> > __cond_acquires(1, lock) which is what I made __cond_lock/acquire do.
>
> Does something like:
>
> static inline bool
> _raw_spin_trylock_irqsave(raw_spinlock_t *lock, unsigned long *flags)
>         __cond_acquire(1, lock)
> {
>         local_irq_save(*flags);
>         if (_raw_spin_trylock(lock))
>                 return true;
>         local_irq_restore(*flags);
>         return false;
> }
>
> #define raw_spin_trylock_irqsave(lock, flags) \
>         _raw_spin_trylock_irqsave((lock), &(flags))
>
> work?

Yup it does (tested). Ok, so getting rid of __cond_lock should be doable. :-)

[PATCH RFC 03/24] compiler-capability-analysis: Add infrastructure for Clang's capability analysis

[Marco Elver]

Capability analysis is a C language extension, which enables statically
checking that user-definable "capabilities" are acquired and released where
required. An obvious application is lock-safety checking for the kernel's
various synchronization primitives (each of which represents a "capability"),
and checking that locking rules are not violated.

Clang originally called the feature "Thread Safety Analysis" [1], with
some terminology still using the thread-safety-analysis-only names. This
was later changed and the feature became more flexible, gaining the
ability to define custom "capabilities". Its foundations can be found in
"capability systems", used to specify the permissibility of operations
to depend on some capability being held (or not held).

[1] https://clang.llvm.org/docs/ThreadSafetyAnalysis.html
[2] https://www.cs.cornell.edu/talc/papers/capabilities.pdf

Because the feature is not just able to express capabilities related to
synchronization primitives, the naming chosen for the kernel departs
from Clang's initial "Thread Safety" nomenclature and refers to the
feature as "Capability Analysis" to avoid confusion. The implementation
still makes references to the older terminology in some places, such as
`-Wthread-safety` being the warning enabled option that also still
appears in diagnostic messages.

See more details in the kernel-doc documentation added in this and the
subsequent changes.

[ RFC Note: A Clang version that supports -Wthread-safety-addressof is
  recommended, but not required:
  	https://github.com/llvm/llvm-project/pull/123063
  Should this patch series reach non-RFC stage, it is planned to be
  committed to Clang before. ]

Signed-off-by: Marco Elver <elver@google.com>
---
 Makefile                                     |   1 +
 include/linux/compiler-capability-analysis.h | 385 ++++++++++++++++++-
 lib/Kconfig.debug                            |  29 ++
 scripts/Makefile.capability-analysis         |   5 +
 scripts/Makefile.lib                         |  10 +
 5 files changed, 423 insertions(+), 7 deletions(-)
 create mode 100644 scripts/Makefile.capability-analysis

diff --git a/Makefile b/Makefile
index 9e0d63d9d94b..e89b9f7d4a08 100644
--- a/Makefile
+++ b/Makefile
@@ -1082,6 +1082,7 @@ include-$(CONFIG_KCOV)		+= scripts/Makefile.kcov
 include-$(CONFIG_RANDSTRUCT)	+= scripts/Makefile.randstruct
 include-$(CONFIG_AUTOFDO_CLANG)	+= scripts/Makefile.autofdo
 include-$(CONFIG_PROPELLER_CLANG)	+= scripts/Makefile.propeller
+include-$(CONFIG_WARN_CAPABILITY_ANALYSIS) += scripts/Makefile.capability-analysis
 include-$(CONFIG_GCC_PLUGINS)	+= scripts/Makefile.gcc-plugins
 
 include $(addprefix $(srctree)/, $(include-y))
diff --git a/include/linux/compiler-capability-analysis.h b/include/linux/compiler-capability-analysis.h
index dfed4e7e6ab8..ca63b6513dc3 100644
--- a/include/linux/compiler-capability-analysis.h
+++ b/include/linux/compiler-capability-analysis.h
@@ -6,26 +6,397 @@
 #ifndef _LINUX_COMPILER_CAPABILITY_ANALYSIS_H
 #define _LINUX_COMPILER_CAPABILITY_ANALYSIS_H
 
+#if defined(WARN_CAPABILITY_ANALYSIS)
+
+/*
+ * The below attributes are used to define new capability types. Internal only.
+ */
+# define __cap_type(name)			__attribute__((capability(#name)))
+# define __acquires_cap(var)			__attribute__((acquire_capability(var)))
+# define __acquires_shared_cap(var)		__attribute__((acquire_shared_capability(var)))
+# define __try_acquires_cap(ret, var)		__attribute__((try_acquire_capability(ret, var)))
+# define __try_acquires_shared_cap(ret, var)	__attribute__((try_acquire_shared_capability(ret, var)))
+# define __releases_cap(var)			__attribute__((release_capability(var)))
+# define __releases_shared_cap(var)		__attribute__((release_shared_capability(var)))
+# define __asserts_cap(var)			__attribute__((assert_capability(var)))
+# define __asserts_shared_cap(var)		__attribute__((assert_shared_capability(var)))
+# define __returns_cap(var)			__attribute__((lock_returned(var)))
+
+/*
+ * The below are used to annotate code being checked. Internal only.
+ */
+# define __excludes_cap(var)		__attribute__((locks_excluded(var)))
+# define __requires_cap(var)		__attribute__((requires_capability(var)))
+# define __requires_shared_cap(var)	__attribute__((requires_shared_capability(var)))
+
+/**
+ * __var_guarded_by - struct member and globals attribute, declares variable
+ *                    protected by capability
+ * @var: the capability instance that guards the member or global
+ *
+ * Declares that the struct member or global variable must be guarded by the
+ * given capability @var. Read operations on the data require shared access,
+ * while write operations require exclusive access.
+ *
+ * .. code-block:: c
+ *
+ *	struct some_state {
+ *		spinlock_t lock;
+ *		long counter __var_guarded_by(&lock);
+ *	};
+ */
+# define __var_guarded_by(var)		__attribute__((guarded_by(var)))
+
+/**
+ * __ref_guarded_by - struct member and globals attribute, declares pointed-to
+ *                    data is protected by capability
+ * @var: the capability instance that guards the member or global
+ *
+ * Declares that the data pointed to by the struct member pointer or global
+ * pointer must be guarded by the given capability @var. Read operations on the
+ * data require shared access, while write operations require exclusive access.
+ *
+ * .. code-block:: c
+ *
+ *	struct some_state {
+ *		spinlock_t lock;
+ *		long *counter __ref_guarded_by(&lock);
+ *	};
+ */
+# define __ref_guarded_by(var)		__attribute__((pt_guarded_by(var)))
+
+/**
+ * struct_with_capability() - declare or define a capability struct
+ * @name: struct name
+ *
+ * Helper to declare or define a struct type with capability of the same name.
+ *
+ * .. code-block:: c
+ *
+ *	struct_with_capability(my_handle) {
+ *		int foo;
+ *		long bar;
+ *	};
+ *
+ *	struct some_state {
+ *		...
+ *	};
+ *	// ... declared elsewhere ...
+ *	struct_with_capability(some_state);
+ *
+ * Note: The implementation defines several helper functions that can acquire,
+ * release, and assert the capability.
+ */
+# define struct_with_capability(name)									\
+	struct __cap_type(name) name;									\
+	static __always_inline void __acquire_cap(const struct name *var)				\
+		__attribute__((overloadable)) __no_capability_analysis __acquires_cap(var) { }		\
+	static __always_inline void __acquire_shared_cap(const struct name *var)			\
+		__attribute__((overloadable)) __no_capability_analysis __acquires_shared_cap(var) { }	\
+	static __always_inline bool __try_acquire_cap(const struct name *var, bool ret)			\
+		__attribute__((overloadable)) __no_capability_analysis __try_acquires_cap(1, var)	\
+	{ return ret; }											\
+	static __always_inline bool __try_acquire_shared_cap(const struct name *var, bool ret)		\
+		__attribute__((overloadable)) __no_capability_analysis __try_acquires_shared_cap(1, var) \
+	{ return ret; }											\
+	static __always_inline void __release_cap(const struct name *var)				\
+		__attribute__((overloadable)) __no_capability_analysis __releases_cap(var) { }		\
+	static __always_inline void __release_shared_cap(const struct name *var)			\
+		__attribute__((overloadable)) __no_capability_analysis __releases_shared_cap(var) { }	\
+	static __always_inline void __assert_cap(const struct name *var)				\
+		__attribute__((overloadable)) __asserts_cap(var) { }					\
+	static __always_inline void __assert_shared_cap(const struct name *var)				\
+		__attribute__((overloadable)) __asserts_shared_cap(var) { }				\
+	struct name
+
+/**
+ * disable_capability_analysis() - disables capability analysis
+ *
+ * Disables capability analysis. Must be paired with a later
+ * enable_capability_analysis().
+ */
+# define disable_capability_analysis()				\
+	__diag_push();						\
+	__diag_ignore_all("-Wunknown-warning-option", "")	\
+	__diag_ignore_all("-Wthread-safety", "")		\
+	__diag_ignore_all("-Wthread-safety-addressof", "")
+
+/**
+ * enable_capability_analysis() - re-enables capability analysis
+ *
+ * Re-enables capability analysis. Must be paired with a prior
+ * disable_capability_analysis().
+ */
+# define enable_capability_analysis() __diag_pop()
+
+/**
+ * __no_capability_analysis - function attribute, disables capability analysis
+ *
+ * Function attribute denoting that capability analysis is disabled for the
+ * whole function. Prefer use of `capability_unsafe()` where possible.
+ */
+# define __no_capability_analysis	__attribute__((no_thread_safety_analysis))
+
+#else /* !WARN_CAPABILITY_ANALYSIS */
+
+# define __cap_type(name)
+# define __acquires_cap(var)
+# define __acquires_shared_cap(var)
+# define __try_acquires_cap(ret, var)
+# define __try_acquires_shared_cap(ret, var)
+# define __releases_cap(var)
+# define __releases_shared_cap(var)
+# define __asserts_cap(var)
+# define __asserts_shared_cap(var)
+# define __returns_cap(var)
+# define __var_guarded_by(var)
+# define __ref_guarded_by(var)
+# define __excludes_cap(var)
+# define __requires_cap(var)
+# define __requires_shared_cap(var)
+# define __acquire_cap(var)			do { } while (0)
+# define __acquire_shared_cap(var)		do { } while (0)
+# define __try_acquire_cap(var, ret)		(ret)
+# define __try_acquire_shared_cap(var, ret)	(ret)
+# define __release_cap(var)			do { } while (0)
+# define __release_shared_cap(var)		do { } while (0)
+# define __assert_cap(var)			do { (void)(var); } while (0)
+# define __assert_shared_cap(var)		do { (void)(var); } while (0)
+# define struct_with_capability(name)		struct name
+# define disable_capability_analysis()
+# define enable_capability_analysis()
+# define __no_capability_analysis
+
+#endif /* WARN_CAPABILITY_ANALYSIS */
+
+/**
+ * capability_unsafe() - disable capability checking for contained code
+ *
+ * Disables capability checking for contained statements or expression.
+ *
+ * .. code-block:: c
+ *
+ *	struct some_data {
+ *		spinlock_t lock;
+ *		int counter __var_guarded_by(&lock);
+ *	};
+ *
+ *	int foo(struct some_data *d)
+ *	{
+ *		// ...
+ *		// other code that is still checked ...
+ *		// ...
+ *		return capability_unsafe(d->counter);
+ *	}
+ */
+#define capability_unsafe(...)		\
+({					\
+	disable_capability_analysis();	\
+	__VA_ARGS__;			\
+	enable_capability_analysis()	\
+})
+
+/**
+ * token_capability() - declare an abstract global capability instance
+ * @name: token capability name
+ *
+ * Helper that declares an abstract global capability instance @name that can be
+ * used as a token capability, but not backed by a real data structure (linker
+ * error if accidentally referenced). The type name is `__capability_@name`.
+ */
+#define token_capability(name)				\
+	struct_with_capability(__capability_##name) {};	\
+	extern const struct __capability_##name *name
+
+/**
+ * token_capability_instance() - declare another instance of a global capability
+ * @cap: token capability previously declared with token_capability()
+ * @name: name of additional global capability instance
+ *
+ * Helper that declares an additional instance @name of the same token
+ * capability class @name. This is helpful where multiple related token
+ * capabilities are declared, as it also allows using the same underlying type
+ * (`__capability_@cap`) as function arguments.
+ */
+#define token_capability_instance(cap, name)		\
+	extern const struct __capability_##cap *name
+
+/*
+ * Common keywords for static capability analysis. Both Clang's capability
+ * analysis and Sparse's context tracking are currently supported.
+ */
 #ifdef __CHECKER__
 
 /* Sparse context/lock checking support. */
 # define __must_hold(x)		__attribute__((context(x,1,1)))
+# define __must_not_hold(x)
 # define __acquires(x)		__attribute__((context(x,0,1)))
 # define __cond_acquires(x)	__attribute__((context(x,0,-1)))
 # define __releases(x)		__attribute__((context(x,1,0)))
 # define __acquire(x)		__context__(x,1)
 # define __release(x)		__context__(x,-1)
 # define __cond_acquire(x, c)	((c) ? ({ __acquire(x); 1; }) : 0)
+/* For Sparse, there's no distinction between exclusive and shared locks. */
+# define __must_hold_shared	__must_hold
+# define __acquires_shared	__acquires
+# define __cond_acquires_shared __cond_acquires
+# define __releases_shared	__releases
+# define __acquire_shared	__acquire
+# define __release_shared	__release
+# define __cond_acquire_shared	__cond_acquire
 
 #else /* !__CHECKER__ */
 
-# define __must_hold(x)
-# define __acquires(x)
-# define __cond_acquires(x)
-# define __releases(x)
-# define __acquire(x)		(void)0
-# define __release(x)		(void)0
-# define __cond_acquire(x, c)	(c)
+/**
+ * __must_hold() - function attribute, caller must hold exclusive capability
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the caller must hold the given capability
+ * instance @x exclusively.
+ */
+# define __must_hold(x)		__requires_cap(x)
+
+/**
+ * __must_not_hold() - function attribute, caller must not hold capability
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the caller must not hold the given
+ * capability instance @x.
+ */
+# define __must_not_hold(x)	__excludes_cap(x)
+
+/**
+ * __acquires() - function attribute, function acquires capability exclusively
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the function acquires the the given
+ * capability instance @x exclusively, but does not release it.
+ */
+# define __acquires(x)		__acquires_cap(x)
+
+/**
+ * __cond_acquires() - function attribute, function conditionally
+ *                     acquires a capability exclusively
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the function conditionally acquires the
+ * given capability instance @x exclusively, but does not release it.
+ */
+# define __cond_acquires(x)	__try_acquires_cap(1, x)
+
+/**
+ * __releases() - function attribute, function releases a capability exclusively
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the function releases the given capability
+ * instance @x exclusively. The capability must be held on entry.
+ */
+# define __releases(x)		__releases_cap(x)
+
+/**
+ * __acquire() - function to acquire capability exclusively
+ * @x: capability instance pinter
+ *
+ * No-op function that acquires the given capability instance @x exclusively.
+ */
+# define __acquire(x)		__acquire_cap(x)
+
+/**
+ * __release() - function to release capability exclusively
+ * @x: capability instance pinter
+ *
+ * No-op function that releases the given capability instance @x.
+ */
+# define __release(x)		__release_cap(x)
+
+/**
+ * __cond_acquire() - function that conditionally acquires a capability
+ *                    exclusively
+ * @x: capability instance pinter
+ * @c: boolean expression
+ *
+ * Return: result of @c
+ *
+ * No-op function that conditionally acquires capability instance @x
+ * exclusively, if the boolean expression @c is true. The result of @c is the
+ * return value, to be able to create a capability-enabled interface; for
+ * example:
+ *
+ * .. code-block:: c
+ *
+ *	#define spin_trylock(l) __cond_acquire(&lock, _spin_trylock(&lock))
+ */
+# define __cond_acquire(x, c)	__try_acquire_cap(x, c)
+
+/**
+ * __must_hold_shared() - function attribute, caller must hold shared capability
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the caller must hold the given capability
+ * instance @x with shared access.
+ */
+# define __must_hold_shared(x)	__requires_shared_cap(x)
+
+/**
+ * __acquires_shared() - function attribute, function acquires capability shared
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the function acquires the the given
+ * capability instance @x with shared access, but does not release it.
+ */
+# define __acquires_shared(x)	__acquires_shared_cap(x)
+
+/**
+ * __cond_acquires_shared() - function attribute, function conditionally
+ *                            acquires a capability shared
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the function conditionally acquires the
+ * given capability instance @x with shared access, but does not release it.
+ */
+# define __cond_acquires_shared(x) __try_acquires_shared_cap(1, x)
+
+/**
+ * __releases_shared() - function attribute, function releases a
+ *                       capability shared
+ * @x: capability instance pointer
+ *
+ * Function attribute declaring that the function releases the given capability
+ * instance @x with shared access. The capability must be held on entry.
+ */
+# define __releases_shared(x)	__releases_shared_cap(x)
+
+/**
+ * __acquire_shared() - function to acquire capability shared
+ * @x: capability instance pinter
+ *
+ * No-op function that acquires the given capability instance @x with shared
+ * access.
+ */
+# define __acquire_shared(x)	__acquire_shared_cap(x)
+
+/**
+ * __release_shared() - function to release capability shared
+ * @x: capability instance pinter
+ *
+ * No-op function that releases the given capability instance @x with shared
+ * access.
+ */
+# define __release_shared(x)	__release_shared_cap(x)
+
+/**
+ * __cond_acquire_shared() - function that conditionally acquires a capability
+ *                           shared
+ * @x: capability instance pinter
+ * @c: boolean expression
+ *
+ * Return: result of @c
+ *
+ * No-op function that conditionally acquires capability instance @x with shared
+ * access, if the boolean expression @c is true. The result of @c is the return
+ * value, to be able to create a capability-enabled interface.
+ */
+# define __cond_acquire_shared(x, c) __try_acquire_shared_cap(x, c)
 
 #endif /* __CHECKER__ */
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1af972a92d06..801ad28fe6d7 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -603,6 +603,35 @@ config DEBUG_FORCE_WEAK_PER_CPU
 	  To ensure that generic code follows the above rules, this
 	  option forces all percpu variables to be defined as weak.
 
+config WARN_CAPABILITY_ANALYSIS
+	bool "Compiler capability-analysis warnings"
+	depends on CC_IS_CLANG && $(cc-option,-Wthread-safety -fexperimental-late-parse-attributes)
+	# Branch profiling re-defines "if", which messes with the compiler's
+	# ability to analyze __cond_acquire(..), resulting in false positives.
+	depends on !TRACE_BRANCH_PROFILING
+	default y
+	help
+	  Capability analysis is a C language extension, which enables
+	  statically checking that user-definable "capabilities" are acquired
+	  and released where required.
+
+	  Clang's name of the feature ("Thread Safety Analysis") refers to
+	  the original name of the feature; it was later expanded to be a
+	  generic "Capability Analysis" framework.
+
+	  Produces warnings by default. Select CONFIG_WERROR if you wish to
+	  turn these warnings into errors.
+
+config WARN_CAPABILITY_ANALYSIS_ALL
+	bool "Enable capability analysis for all source files"
+	depends on WARN_CAPABILITY_ANALYSIS
+	depends on EXPERT && !COMPILE_TEST
+	help
+	  Enable tree-wide capability analysis. This is likely to produce a
+	  large number of false positives - enable at your own risk.
+
+	  If unsure, say N.
+
 endmenu # "Compiler options"
 
 menu "Generic Kernel Debugging Instruments"
diff --git a/scripts/Makefile.capability-analysis b/scripts/Makefile.capability-analysis
new file mode 100644
index 000000000000..71383812201c
--- /dev/null
+++ b/scripts/Makefile.capability-analysis
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+export CFLAGS_CAPABILITY_ANALYSIS := -DWARN_CAPABILITY_ANALYSIS \
+	-fexperimental-late-parse-attributes -Wthread-safety	\
+	$(call cc-option,-Wthread-safety-addressof)
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index ad55ef201aac..5bf37af96cdf 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -191,6 +191,16 @@ _c_flags += $(if $(patsubst n%,, \
 	-D__KCSAN_INSTRUMENT_BARRIERS__)
 endif
 
+#
+# Enable capability analysis flags only where explicitly opted in.
+# (depends on variables CAPABILITY_ANALYSIS_obj.o, CAPABILITY_ANALYSIS)
+#
+ifeq ($(CONFIG_WARN_CAPABILITY_ANALYSIS),y)
+_c_flags += $(if $(patsubst n%,, \
+		$(CAPABILITY_ANALYSIS_$(target-stem).o)$(CAPABILITY_ANALYSIS)$(if $(is-kernel-object),$(CONFIG_WARN_CAPABILITY_ANALYSIS_ALL))), \
+		$(CFLAGS_CAPABILITY_ANALYSIS))
+endif
+
 #
 # Enable AutoFDO build flags except some files or directories we don't want to
 # enable (depends on variables AUTOFDO_PROFILE_obj.o and AUTOFDO_PROFILE).
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 04/24] compiler-capability-analysis: Add test stub

[Marco Elver]

Add a simple test stub where we will add common supported patterns that
should not generate false positive of each new supported capability.

Signed-off-by: Marco Elver <elver@google.com>
---
 lib/Kconfig.debug              | 14 ++++++++++++++
 lib/Makefile                   |  3 +++
 lib/test_capability-analysis.c | 18 ++++++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 lib/test_capability-analysis.c

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 801ad28fe6d7..b76fa3dc59ec 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2764,6 +2764,20 @@ config LINEAR_RANGES_TEST
 
 	  If unsure, say N.
 
+config CAPABILITY_ANALYSIS_TEST
+	bool "Compiler capability-analysis warnings test"
+	depends on EXPERT
+	help
+	  This builds the test for compiler-based capability analysis. The test
+	  does not add executable code to the kernel, but is meant to test that
+	  common patterns supported by the analysis do not result in false
+	  positive warnings.
+
+	  When adding support for new capabilities, it is strongly recommended
+	  to add supported patterns to this test.
+
+	  If unsure, say N.
+
 config CMDLINE_KUNIT_TEST
 	tristate "KUnit test for cmdline API" if !KUNIT_ALL_TESTS
 	depends on KUNIT
diff --git a/lib/Makefile b/lib/Makefile
index d5cfc7afbbb8..1dbb59175eb0 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -394,6 +394,9 @@ obj-$(CONFIG_CRC_KUNIT_TEST) += crc_kunit.o
 obj-$(CONFIG_SIPHASH_KUNIT_TEST) += siphash_kunit.o
 obj-$(CONFIG_USERCOPY_KUNIT_TEST) += usercopy_kunit.o
 
+CAPABILITY_ANALYSIS_test_capability-analysis.o := y
+obj-$(CONFIG_CAPABILITY_ANALYSIS_TEST) += test_capability-analysis.o
+
 obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
 
 obj-$(CONFIG_FIRMWARE_TABLE) += fw_table.o
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
new file mode 100644
index 000000000000..a0adacce30ff
--- /dev/null
+++ b/lib/test_capability-analysis.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Compile-only tests for common patterns that should not generate false
+ * positive errors when compiled with Clang's capability analysis.
+ */
+
+#include <linux/build_bug.h>
+
+/*
+ * Test that helper macros work as expected.
+ */
+static void __used test_common_helpers(void)
+{
+	BUILD_BUG_ON(capability_unsafe(3) != 3); /* plain expression */
+	BUILD_BUG_ON(capability_unsafe((void)2; 3;) != 3); /* does not swallow semi-colon */
+	BUILD_BUG_ON(capability_unsafe((void)2, 3) != 3); /* does not swallow commas */
+	capability_unsafe(do { } while (0)); /* works with void statements */
+}
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 05/24] Documentation: Add documentation for Compiler-Based Capability Analysis

[Marco Elver]

Adds documentation in Documentation/dev-tools/capability-analysis.rst,
and adds it to the index and cross-references from Sparse's document.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         | 147 ++++++++++++++++++
 Documentation/dev-tools/index.rst             |   1 +
 Documentation/dev-tools/sparse.rst            |   4 +
 3 files changed, 152 insertions(+)
 create mode 100644 Documentation/dev-tools/capability-analysis.rst

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
new file mode 100644
index 000000000000..2211af90e01b
--- /dev/null
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -0,0 +1,147 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright (C) 2025, Google LLC.
+
+.. _capability-analysis:
+
+Compiler-Based Capability Analysis
+==================================
+
+Capability analysis is a C language extension, which enables statically
+checking that user-definable "capabilities" are acquired and released where
+required. An obvious application is lock-safety checking for the kernel's
+various synchronization primitives (each of which represents a "capability"),
+and checking that locking rules are not violated.
+
+The Clang compiler currently supports the full set of capability analysis
+features. To enable for Clang, configure the kernel with::
+
+    CONFIG_WARN_CAPABILITY_ANALYSIS=y
+
+The analysis is *opt-in by default*, and requires declaring which modules and
+subsystems should be analyzed in the respective `Makefile`::
+
+    CAPABILITY_ANALYSIS_mymodule.o := y
+
+Or for all translation units in the directory::
+
+    CAPABILITY_ANALYSIS := y
+
+It is possible to enable the analysis tree-wide, however, which will result in
+numerous false positive warnings currently and is *not* generally recommended::
+
+    CONFIG_WARN_CAPABILITY_ANALYSIS_ALL=y
+
+Independent of the above Clang support, a subset of the analysis is supported
+by :ref:`Sparse <sparse>`, with weaker guarantees (fewer false positives with
+tree-wide analysis, more more false negatives). Compared to Sparse, Clang's
+analysis is more complete.
+
+Programming Model
+-----------------
+
+The below describes the programming model around using capability-enabled
+types.
+
+.. note::
+   Enabling capability analysis can be seen as enabling a dialect of Linux C with
+   a Capability System. Some valid patterns involving complex control-flow are
+   constrained (such as conditional acquisition and later conditional release
+   in the same function, or returning pointers to capabilities from functions.
+
+Capability analysis is a way to specify permissibility of operations to depend
+on capabilities being held (or not held). Typically we are interested in
+protecting data and code by requiring some capability to be held, for example a
+specific lock. The analysis ensures that the caller cannot perform the
+operation without holding the appropriate capability.
+
+Capabilities are associated with named structs, along with functions that
+operate on capability-enabled struct instances to acquire and release the
+associated capability.
+
+Capabilities can be held either exclusively or shared. This mechanism allows
+assign more precise privileges when holding a capability, typically to
+distinguish where a thread may only read (shared) or also write (exclusive) to
+guarded data.
+
+The set of capabilities that are actually held by a given thread at a given
+point in program execution is a run-time concept. The static analysis works by
+calculating an approximation of that set, called the capability environment.
+The capability environment is calculated for every program point, and describes
+the set of capabilities that are statically known to be held, or not held, at
+that particular point. This environment is a conservative approximation of the
+full set of capabilities that will actually held by a thread at run-time.
+
+More details are also documented `here
+<https://clang.llvm.org/docs/ThreadSafetyAnalysis.html>`_.
+
+.. note::
+   Unlike Sparse's context tracking analysis, Clang's analysis explicitly does
+   not infer capabilities acquired or released by inline functions. It requires
+   explicit annotations to (a) assert that it's not a bug if a capability is
+   released or acquired, and (b) to retain consistency between inline and
+   non-inline function declarations.
+
+Supported Kernel Primitives
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. Currently the following synchronization primitives are supported:
+
+For capabilities with an initialization function (e.g., `spin_lock_init()`),
+calling this function on the capability instance before initializing any
+guarded members or globals prevents the compiler from issuing warnings about
+unguarded initialization.
+
+Lockdep assertions, such as `lockdep_assert_held()`, inform the compiler's
+capability analysis that the associated synchronization primitive is held after
+the assertion. This avoids false positives in complex control-flow scenarios
+and encourages the use of Lockdep where static analysis is limited. For
+example, this is useful when a function doesn't *always* require a lock, making
+`__must_hold()` inappropriate.
+
+Keywords
+~~~~~~~~
+
+.. kernel-doc:: include/linux/compiler-capability-analysis.h
+   :identifiers: struct_with_capability
+                 token_capability token_capability_instance
+                 __var_guarded_by __ref_guarded_by
+                 __must_hold
+                 __must_not_hold
+                 __acquires
+                 __cond_acquires
+                 __releases
+                 __must_hold_shared
+                 __acquires_shared
+                 __cond_acquires_shared
+                 __releases_shared
+                 __acquire
+                 __release
+                 __cond_acquire
+                 __acquire_shared
+                 __release_shared
+                 __cond_acquire_shared
+                 capability_unsafe
+                 __no_capability_analysis
+                 disable_capability_analysis enable_capability_analysis
+
+Background
+----------
+
+Clang originally called the feature `Thread Safety Analysis
+<https://clang.llvm.org/docs/ThreadSafetyAnalysis.html>`_, with some
+terminology still using the thread-safety-analysis-only names. This was later
+changed and the feature become more flexible, gaining the ability to define
+custom "capabilities".
+
+Indeed, its foundations can be found in `capability systems
+<https://www.cs.cornell.edu/talc/papers/capabilities.pdf>`_, used to specify
+the permissibility of operations to depend on some capability being held (or
+not held).
+
+Because the feature is not just able to express capabilities related to
+synchronization primitives, the naming chosen for the kernel departs from
+Clang's initial "Thread Safety" nomenclature and refers to the feature as
+"Capability Analysis" to avoid confusion. The implementation still makes
+references to the older terminology in some places, such as `-Wthread-safety`
+being the warning enabled option that also still appears in diagnostic
+messages.
diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
index 65c54b27a60b..62ac23f797cd 100644
--- a/Documentation/dev-tools/index.rst
+++ b/Documentation/dev-tools/index.rst
@@ -18,6 +18,7 @@ Documentation/process/debugging/index.rst
    :maxdepth: 2
 
    testing-overview
+   capability-analysis
    checkpatch
    clang-format
    coccinelle
diff --git a/Documentation/dev-tools/sparse.rst b/Documentation/dev-tools/sparse.rst
index dc791c8d84d1..8c2077834b6f 100644
--- a/Documentation/dev-tools/sparse.rst
+++ b/Documentation/dev-tools/sparse.rst
@@ -2,6 +2,8 @@
 .. Copyright 2004 Pavel Machek <pavel@ucw.cz>
 .. Copyright 2006 Bob Copeland <me@bobcopeland.com>
 
+.. _sparse:
+
 Sparse
 ======
 
@@ -72,6 +74,8 @@ releasing the lock inside the function in a balanced way, no
 annotation is needed.  The three annotations above are for cases where
 sparse would otherwise report a context imbalance.
 
+Also see :ref:`Compiler-Based Capability Analysis <capability-analysis>`.
+
 Getting sparse
 --------------
 
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 06/24] checkpatch: Warn about capability_unsafe() without comment

[Marco Elver]

Warn about applications of capability_unsafe() without a comment, to
encourage documenting the reasoning behind why it was deemed safe.

Signed-off-by: Marco Elver <elver@google.com>
---
 scripts/checkpatch.pl | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7b28ad331742..c28efdb1d404 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6693,6 +6693,14 @@ sub process {
 			}
 		}
 
+# check for capability_unsafe without a comment.
+		if ($line =~ /\bcapability_unsafe\b/) {
+			if (!ctx_has_comment($first_line, $linenr)) {
+				WARN("CAPABILITY_UNSAFE",
+				     "capability_unsafe without comment\n" . $herecurr);
+			}
+		}
+
 # check of hardware specific defines
 		if ($line =~ m@^.\s*\#\s*if.*\b(__i386__|__powerpc64__|__sun__|__s390x__)\b@ && $realfile !~ m@include/asm-@) {
 			CHK("ARCH_DEFINES",
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 07/24] cleanup: Basic compatibility with capability analysis

[Marco Elver]

Due to the scoped cleanup helpers used for lock guards wrapping
acquire/release around their own constructors/destructors that store
pointers to the passed locks in a separate struct, we currently cannot
accurately annotate *destructors* which lock was released. While it's
possible to annotate the constructor to say which lock was acquired,
that alone would result in false positives claiming the lock was not
released on function return.

Instead, to avoid false positives, we can claim that the constructor
"asserts" that the taken lock is held. This will ensure we can still
benefit from the analysis where scoped guards are used to protect access
to guarded variables, while avoiding false positives. The only downside
are false negatives where we might accidentally lock the same lock
again:

	raw_spin_lock(&my_lock);
	...
	guard(raw_spinlock)(&my_lock);  // no warning

Arguably, lockdep will immediately catch issues like this.

While Clang's analysis supports scoped guards in C++ [1], there's no way
to apply this to C right now. Better support for Linux's scoped guard
design could be added in future if deemed critical.

[1] https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#scoped-capability

Signed-off-by: Marco Elver <elver@google.com>
---
 include/linux/cleanup.h | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index ec00e3f7af2b..93a166549add 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -223,7 +223,7 @@ const volatile void * __must_check_fn(const volatile void *val)
  *	@exit is an expression using '_T' -- similar to FREE above.
  *	@init is an expression in @init_args resulting in @type
  *
- * EXTEND_CLASS(name, ext, init, init_args...):
+ * EXTEND_CLASS(name, ext, ctor_attrs, init, init_args...):
  *	extends class @name to @name@ext with the new constructor
  *
  * CLASS(name, var)(args...):
@@ -243,15 +243,18 @@ const volatile void * __must_check_fn(const volatile void *val)
 #define DEFINE_CLASS(_name, _type, _exit, _init, _init_args...)		\
 typedef _type class_##_name##_t;					\
 static inline void class_##_name##_destructor(_type *p)			\
+	__no_capability_analysis					\
 { _type _T = *p; _exit; }						\
 static inline _type class_##_name##_constructor(_init_args)		\
+	__no_capability_analysis					\
 { _type t = _init; return t; }
 
-#define EXTEND_CLASS(_name, ext, _init, _init_args...)			\
+#define EXTEND_CLASS(_name, ext, ctor_attrs, _init, _init_args...)		\
 typedef class_##_name##_t class_##_name##ext##_t;			\
 static inline void class_##_name##ext##_destructor(class_##_name##_t *p)\
 { class_##_name##_destructor(p); }					\
 static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
+	__no_capability_analysis ctor_attrs					\
 { class_##_name##_t t = _init; return t; }
 
 #define CLASS(_name, var)						\
@@ -299,7 +302,7 @@ static __maybe_unused const bool class_##_name##_is_conditional = _is_cond
 
 #define DEFINE_GUARD_COND(_name, _ext, _condlock) \
 	__DEFINE_CLASS_IS_CONDITIONAL(_name##_ext, true); \
-	EXTEND_CLASS(_name, _ext, \
+	EXTEND_CLASS(_name, _ext,, \
 		     ({ void *_t = _T; if (_T && !(_condlock)) _t = NULL; _t; }), \
 		     class_##_name##_t _T) \
 	static inline void * class_##_name##_ext##_lock_ptr(class_##_name##_t *_T) \
@@ -371,6 +374,7 @@ typedef struct {							\
 } class_##_name##_t;							\
 									\
 static inline void class_##_name##_destructor(class_##_name##_t *_T)	\
+	__no_capability_analysis					\
 {									\
 	if (_T->lock) { _unlock; }					\
 }									\
@@ -383,6 +387,7 @@ static inline void *class_##_name##_lock_ptr(class_##_name##_t *_T)	\
 
 #define __DEFINE_LOCK_GUARD_1(_name, _type, _lock)			\
 static inline class_##_name##_t class_##_name##_constructor(_type *l)	\
+	__no_capability_analysis __asserts_cap(l)			\
 {									\
 	class_##_name##_t _t = { .lock = l }, *_T = &_t;		\
 	_lock;								\
@@ -391,6 +396,7 @@ static inline class_##_name##_t class_##_name##_constructor(_type *l)	\
 
 #define __DEFINE_LOCK_GUARD_0(_name, _lock)				\
 static inline class_##_name##_t class_##_name##_constructor(void)	\
+	__no_capability_analysis					\
 {									\
 	class_##_name##_t _t = { .lock = (void*)1 },			\
 			 *_T __maybe_unused = &_t;			\
@@ -410,7 +416,7 @@ __DEFINE_LOCK_GUARD_0(_name, _lock)
 
 #define DEFINE_LOCK_GUARD_1_COND(_name, _ext, _condlock)		\
 	__DEFINE_CLASS_IS_CONDITIONAL(_name##_ext, true);		\
-	EXTEND_CLASS(_name, _ext,					\
+	EXTEND_CLASS(_name, _ext, __asserts_cap(l),			\
 		     ({ class_##_name##_t _t = { .lock = l }, *_T = &_t;\
 		        if (_T->lock && !(_condlock)) _T->lock = NULL;	\
 			_t; }),						\
-- 
2.48.1.502.g6dc24dfdaf-goog

Re: [PATCH RFC 07/24] cleanup: Basic compatibility with capability analysis

[Bart Van Assche]

On 2/6/25 10:10 AM, Marco Elver wrote:
> @@ -243,15 +243,18 @@ const volatile void * __must_check_fn(const volatile void *val)
>   #define DEFINE_CLASS(_name, _type, _exit, _init, _init_args...)		\
>   typedef _type class_##_name##_t;					\
>   static inline void class_##_name##_destructor(_type *p)			\
> +	__no_capability_analysis					\
>   { _type _T = *p; _exit; }						\
>   static inline _type class_##_name##_constructor(_init_args)		\
> +	__no_capability_analysis					\
>   { _type t = _init; return t; }

guard() uses the constructor and destructor functions defined by
DEFINE_GUARD(). The DEFINE_GUARD() implementation uses DEFINE_CLASS().
Here is an example that I found in <linux/mutex.h>:

DEFINE_GUARD(mutex, struct mutex *, mutex_lock(_T), mutex_unlock(_T))

For this example, how is the compiler told that mutex _T is held around
the code protected by guard()?

Thanks,

Bart.

Re: [PATCH RFC 07/24] cleanup: Basic compatibility with capability analysis

[Marco Elver]

On Thu, 6 Feb 2025 at 22:29, Bart Van Assche <bvanassche@acm.org> wrote:
>
> On 2/6/25 10:10 AM, Marco Elver wrote:
> > @@ -243,15 +243,18 @@ const volatile void * __must_check_fn(const volatile void *val)
> >   #define DEFINE_CLASS(_name, _type, _exit, _init, _init_args...)             \
> >   typedef _type class_##_name##_t;                                    \
> >   static inline void class_##_name##_destructor(_type *p)                     \
> > +     __no_capability_analysis                                        \
> >   { _type _T = *p; _exit; }                                           \
> >   static inline _type class_##_name##_constructor(_init_args)         \
> > +     __no_capability_analysis                                        \
> >   { _type t = _init; return t; }
>
> guard() uses the constructor and destructor functions defined by
> DEFINE_GUARD(). The DEFINE_GUARD() implementation uses DEFINE_CLASS().
> Here is an example that I found in <linux/mutex.h>:
>
> DEFINE_GUARD(mutex, struct mutex *, mutex_lock(_T), mutex_unlock(_T))
>
> For this example, how is the compiler told that mutex _T is held around
> the code protected by guard()?

DEFINE_GUARD is the generic variant usable for more than just locking
primitives. DEFINE_LOCK_GUARD_X is a specialization of DEFINE_GUARD
intended for locking primitives, all of which should be
capability-enabled.

So I added automatic support for DEFINE_LOCK_GUARD_1 (keeping in mind
the limitations as described in the commit message). All later patches
that introduce support for a locking primitive that had been using
DEFINE_GUARD are switched over to DEFINE_LOCK_GUARD. There's no
additional runtime cost (_T is just a struct containing _T->lock). For
example, the change for mutex [1] switches it to use
DEFINE_LOCK_GUARD_1.

[1] https://lore.kernel.org/all/20250206181711.1902989-12-elver@google.com/

(For every primitive added I have added tests in
test_capability-analysis.c, including testing that the scoped guard()
helpers work and do not produce false positives.)

The RCU patch [15/24] also makes it work for LOCK_GUARD_0, by simply
adding an optional helper macro to declare the attributes for lock and
unlock. There's no need for additional variants of
DEFINE_LOCK_GUARD_X.

Should the need arise to add add annotations for DEFINE_GUARD, we can
introduce DECLARE_GUARD_ATTRS(), similar to
DECLARE_LOCK_GUARD_0_ATTRS() introduced in [15/24]. But it's omitted
because DEFINE_GUARD() can be replaced by DEFINE_LOCK_GUARD for
locking primitives.

In general I wanted to keep the current interface for defining guards
untouched, and keeping it simpler.

[PATCH RFC 08/24] lockdep: Annotate lockdep assertions for capability analysis

[Marco Elver]

Clang's capability analysis can be made aware of functions that assert
that capabilities/locks are held.

Presence of these annotations causes the analysis to assume the
capability is held after calls to the annotated function, and avoid
false positives with complex control-flow; for example, where not all
control-flow paths in a function require a held lock, and therefore
marking the function with __must_hold(..) is inappropriate.

Signed-off-by: Marco Elver <elver@google.com>
---
 include/linux/lockdep.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 67964dc4db95..5cea929b2219 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -282,16 +282,16 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
 	do { WARN_ON_ONCE(debug_locks && !(cond)); } while (0)
 
 #define lockdep_assert_held(l)		\
-	lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
+	do { lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD); __assert_cap(l); } while (0)
 
 #define lockdep_assert_not_held(l)	\
 	lockdep_assert(lockdep_is_held(l) != LOCK_STATE_HELD)
 
 #define lockdep_assert_held_write(l)	\
-	lockdep_assert(lockdep_is_held_type(l, 0))
+	do { lockdep_assert(lockdep_is_held_type(l, 0)); __assert_cap(l); } while (0)
 
 #define lockdep_assert_held_read(l)	\
-	lockdep_assert(lockdep_is_held_type(l, 1))
+	do { lockdep_assert(lockdep_is_held_type(l, 1)); __assert_shared_cap(l); } while (0)
 
 #define lockdep_assert_held_once(l)		\
 	lockdep_assert_once(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
@@ -389,10 +389,10 @@ extern int lockdep_is_held(const void *);
 #define lockdep_assert(c)			do { } while (0)
 #define lockdep_assert_once(c)			do { } while (0)
 
-#define lockdep_assert_held(l)			do { (void)(l); } while (0)
+#define lockdep_assert_held(l)			__assert_cap(l)
 #define lockdep_assert_not_held(l)		do { (void)(l); } while (0)
-#define lockdep_assert_held_write(l)		do { (void)(l); } while (0)
-#define lockdep_assert_held_read(l)		do { (void)(l); } while (0)
+#define lockdep_assert_held_write(l)		__assert_cap(l)
+#define lockdep_assert_held_read(l)		__assert_shared_cap(l)
 #define lockdep_assert_held_once(l)		do { (void)(l); } while (0)
 #define lockdep_assert_none_held_once()	do { } while (0)
 
-- 
2.48.1.502.g6dc24dfdaf-goog

Re: [PATCH RFC 08/24] lockdep: Annotate lockdep assertions for capability analysis

[Bart Van Assche]

On 2/6/25 10:10 AM, Marco Elver wrote:
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 67964dc4db95..5cea929b2219 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -282,16 +282,16 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
>   	do { WARN_ON_ONCE(debug_locks && !(cond)); } while (0)
>   
>   #define lockdep_assert_held(l)		\
> -	lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
> +	do { lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD); __assert_cap(l); } while (0)
>   
>   #define lockdep_assert_not_held(l)	\
>   	lockdep_assert(lockdep_is_held(l) != LOCK_STATE_HELD)
>   
>   #define lockdep_assert_held_write(l)	\
> -	lockdep_assert(lockdep_is_held_type(l, 0))
> +	do { lockdep_assert(lockdep_is_held_type(l, 0)); __assert_cap(l); } while (0)
>   
>   #define lockdep_assert_held_read(l)	\
> -	lockdep_assert(lockdep_is_held_type(l, 1))
> +	do { lockdep_assert(lockdep_is_held_type(l, 1)); __assert_shared_cap(l); } while (0)

These changes look wrong to me. The current behavior of
lockdep_assert_held(lock) is that it issues a kernel warning at
runtime if `lock` is not held when a lockdep_assert_held()
statement is executed. __assert_cap(lock) tells the compiler to
*ignore* the absence of __must_hold(lock). I think this is wrong.
The compiler should complain if a __must_hold(lock) annotation is
missing. While sparse does not support interprocedural analysis for
lock contexts, the Clang thread-safety checker supports this. If
function declarations are annotated with __must_hold(lock), Clang will
complain if the caller does not hold `lock`.

In other words, the above changes disable a useful compile-time check.
I think that useful compile-time checks should not be disabled.

Bart.

Re: [PATCH RFC 08/24] lockdep: Annotate lockdep assertions for capability analysis

[Marco Elver]

On Mon, 10 Feb 2025 at 19:10, Bart Van Assche <bvanassche@acm.org> wrote:
>
> On 2/6/25 10:10 AM, Marco Elver wrote:
> > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> > index 67964dc4db95..5cea929b2219 100644
> > --- a/include/linux/lockdep.h
> > +++ b/include/linux/lockdep.h
> > @@ -282,16 +282,16 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
> >       do { WARN_ON_ONCE(debug_locks && !(cond)); } while (0)
> >
> >   #define lockdep_assert_held(l)              \
> > -     lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
> > +     do { lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD); __assert_cap(l); } while (0)
> >
> >   #define lockdep_assert_not_held(l)  \
> >       lockdep_assert(lockdep_is_held(l) != LOCK_STATE_HELD)
> >
> >   #define lockdep_assert_held_write(l)        \
> > -     lockdep_assert(lockdep_is_held_type(l, 0))
> > +     do { lockdep_assert(lockdep_is_held_type(l, 0)); __assert_cap(l); } while (0)
> >
> >   #define lockdep_assert_held_read(l) \
> > -     lockdep_assert(lockdep_is_held_type(l, 1))
> > +     do { lockdep_assert(lockdep_is_held_type(l, 1)); __assert_shared_cap(l); } while (0)
>
> These changes look wrong to me. The current behavior of
> lockdep_assert_held(lock) is that it issues a kernel warning at
> runtime if `lock` is not held when a lockdep_assert_held()
> statement is executed. __assert_cap(lock) tells the compiler to
> *ignore* the absence of __must_hold(lock). I think this is wrong.
> The compiler should complain if a __must_hold(lock) annotation is
> missing. While sparse does not support interprocedural analysis for
> lock contexts, the Clang thread-safety checker supports this. If
> function declarations are annotated with __must_hold(lock), Clang will
> complain if the caller does not hold `lock`.
>
> In other words, the above changes disable a useful compile-time check.
> I think that useful compile-time checks should not be disabled.

The assert_capability attribute was designed precisely for assertions
that check at runtime that the lock is held, and delegate to runtime
verification where the static analysis is just not powerful enough. In
the commit description:

Presence of these annotations causes the analysis to assume the
capability is held after calls to the annotated function, and avoid
false positives with complex control-flow; for example, where not all
control-flow paths in a function require a held lock, and therefore
marking the function with __must_hold(..) is inappropriate.

If you try to write code where you access a guarded_by variable, but
the lock is held not in all paths we can write it like this:

struct bar {
  spinlock_t lock;
  bool a; // true if lock held
  int counter __var_guarded_by(&lock);
};
void foo(struct bar *d)
{
   ...
   if (d->a) {
     lockdep_assert_held(&d->lock);
     d->counter++;
   } else {
     // lock not held!
   }
  ...
}

Without lockdep_assert_held() you get false positives, and there's no
other good way to express this if you do not want to always call foo()
with the lock held.

It essentially forces addition of lockdep checks where the static
analysis can't quite prove what you've done is right. This is
desirable over adding no-analysis attributes and not checking anything
at all.

Re: [PATCH RFC 08/24] lockdep: Annotate lockdep assertions for capability analysis

[Bart Van Assche]

On 2/10/25 10:23 AM, Marco Elver wrote:
> If you try to write code where you access a guarded_by variable, but
> the lock is held not in all paths we can write it like this:
> 
> struct bar {
>    spinlock_t lock;
>    bool a; // true if lock held
>    int counter __var_guarded_by(&lock);
> };
> void foo(struct bar *d)
> {
>     ...
>     if (d->a) {
>       lockdep_assert_held(&d->lock);
>       d->counter++;
>     } else {
>       // lock not held!
>     }
>    ...
> }
> 
> Without lockdep_assert_held() you get false positives, and there's no
> other good way to express this if you do not want to always call foo()
> with the lock held.
> 
> It essentially forces addition of lockdep checks where the static
> analysis can't quite prove what you've done is right. This is
> desirable over adding no-analysis attributes and not checking anything
> at all.

In the above I see that two different options have been mentioned for
code that includes conditional lockdep_assert_held() calls:
- Either include __assert_cap() in the lockdep_assert_held() definition.
- Or annotate the entire function with __no_thread_safety_analysis.

I think there is a third possibility: add an explicit __assert_cap() 
call under the lockdep_assert_held() call. With this approach the
thread-safety analysis remains enabled for the annotated function and
the compiler will complain if neither __must_hold() nor __assert_cap()
has been used.

I prefer the third option since conditional lockdep_assert_held() calls
are relatively rare in the kernel. If I counted correctly, there are
about 40 times more unconditional lockdep_assert_held() calls than
conditional lockdep_assert_held() calls.

Bart.

Re: [PATCH RFC 08/24] lockdep: Annotate lockdep assertions for capability analysis

[Marco Elver]

On Mon, 10 Feb 2025 at 19:54, Bart Van Assche <bvanassche@acm.org> wrote:
>
>
> On 2/10/25 10:23 AM, Marco Elver wrote:
> > If you try to write code where you access a guarded_by variable, but
> > the lock is held not in all paths we can write it like this:
> >
> > struct bar {
> >    spinlock_t lock;
> >    bool a; // true if lock held
> >    int counter __var_guarded_by(&lock);
> > };
> > void foo(struct bar *d)
> > {
> >     ...
> >     if (d->a) {
> >       lockdep_assert_held(&d->lock);
> >       d->counter++;
> >     } else {
> >       // lock not held!
> >     }
> >    ...
> > }
> >
> > Without lockdep_assert_held() you get false positives, and there's no
> > other good way to express this if you do not want to always call foo()
> > with the lock held.
> >
> > It essentially forces addition of lockdep checks where the static
> > analysis can't quite prove what you've done is right. This is
> > desirable over adding no-analysis attributes and not checking anything
> > at all.
>
> In the above I see that two different options have been mentioned for
> code that includes conditional lockdep_assert_held() calls:
> - Either include __assert_cap() in the lockdep_assert_held() definition.
> - Or annotate the entire function with __no_thread_safety_analysis.
>
> I think there is a third possibility: add an explicit __assert_cap()
> call under the lockdep_assert_held() call. With this approach the
> thread-safety analysis remains enabled for the annotated function and
> the compiler will complain if neither __must_hold() nor __assert_cap()
> has been used.

That's just adding more clutter. Being able to leverage existing
lockdep_assert to avoid false positives (at potential cost of few
false negatives) is a decent trade-off. Sure, having maximum checking
guarantees would be nice, but there's a balance we have to strike vs.
ergonomics, usability, and pointless clutter.

Can we initially try to avoid clutter as much as possible? Then, if
you feel coverage is not good enough, make the analysis stricter by
e.g. removing the implicit assert from lockdep_assert in later patches
and see how it goes.

I'm basing my judgement here on experience having worked on other
analysis in the kernel, and the biggest request from maintainers has
always been to "avoid useless clutter and false positives at all
cost", often at the cost of increased potential for false negatives
but avoiding false positives and reducing annotations (I can dig out
discussions we had for KMSAN if you do not believe me...).

[PATCH RFC 09/24] locking/rwlock, spinlock: Support Clang's capability analysis

[Marco Elver]

Add support for Clang's capability analysis for raw_spinlock_t,
spinlock_t, and rwlock. This wholesale conversion is required because
all three of them are interdependent.

To avoid warnings in constructors, the initialization functions mark a
capability as acquired when initialized before guarded variables.

The test verifies that common patterns do not generate false positives.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |   3 +-
 include/linux/rwlock.h                        |  25 ++--
 include/linux/rwlock_api_smp.h                |  29 +++-
 include/linux/rwlock_rt.h                     |  35 +++--
 include/linux/rwlock_types.h                  |  10 +-
 include/linux/spinlock.h                      |  45 +++---
 include/linux/spinlock_api_smp.h              |  14 +-
 include/linux/spinlock_api_up.h               |  71 +++++-----
 include/linux/spinlock_rt.h                   |  21 +--
 include/linux/spinlock_types.h                |  10 +-
 include/linux/spinlock_types_raw.h            |   5 +-
 lib/test_capability-analysis.c                | 128 ++++++++++++++++++
 12 files changed, 299 insertions(+), 97 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index 2211af90e01b..904448605a77 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -84,7 +84,8 @@ More details are also documented `here
 Supported Kernel Primitives
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. Currently the following synchronization primitives are supported:
+Currently the following synchronization primitives are supported:
+`raw_spinlock_t`, `spinlock_t`, `rwlock_t`.
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/rwlock.h b/include/linux/rwlock.h
index 58c346947aa2..44755fd96c27 100644
--- a/include/linux/rwlock.h
+++ b/include/linux/rwlock.h
@@ -22,23 +22,24 @@ do {								\
 	static struct lock_class_key __key;			\
 								\
 	__rwlock_init((lock), #lock, &__key);			\
+	__assert_cap(lock);					\
 } while (0)
 #else
 # define rwlock_init(lock)					\
-	do { *(lock) = __RW_LOCK_UNLOCKED(lock); } while (0)
+	do { *(lock) = __RW_LOCK_UNLOCKED(lock); __assert_cap(lock); } while (0)
 #endif
 
 #ifdef CONFIG_DEBUG_SPINLOCK
- extern void do_raw_read_lock(rwlock_t *lock) __acquires(lock);
+ extern void do_raw_read_lock(rwlock_t *lock) __acquires_shared(lock);
  extern int do_raw_read_trylock(rwlock_t *lock);
- extern void do_raw_read_unlock(rwlock_t *lock) __releases(lock);
+ extern void do_raw_read_unlock(rwlock_t *lock) __releases_shared(lock);
  extern void do_raw_write_lock(rwlock_t *lock) __acquires(lock);
  extern int do_raw_write_trylock(rwlock_t *lock);
  extern void do_raw_write_unlock(rwlock_t *lock) __releases(lock);
 #else
-# define do_raw_read_lock(rwlock)	do {__acquire(lock); arch_read_lock(&(rwlock)->raw_lock); } while (0)
+# define do_raw_read_lock(rwlock)	do {__acquire_shared(lock); arch_read_lock(&(rwlock)->raw_lock); } while (0)
 # define do_raw_read_trylock(rwlock)	arch_read_trylock(&(rwlock)->raw_lock)
-# define do_raw_read_unlock(rwlock)	do {arch_read_unlock(&(rwlock)->raw_lock); __release(lock); } while (0)
+# define do_raw_read_unlock(rwlock)	do {arch_read_unlock(&(rwlock)->raw_lock); __release_shared(lock); } while (0)
 # define do_raw_write_lock(rwlock)	do {__acquire(lock); arch_write_lock(&(rwlock)->raw_lock); } while (0)
 # define do_raw_write_trylock(rwlock)	arch_write_trylock(&(rwlock)->raw_lock)
 # define do_raw_write_unlock(rwlock)	do {arch_write_unlock(&(rwlock)->raw_lock); __release(lock); } while (0)
@@ -49,7 +50,7 @@ do {								\
  * regardless of whether CONFIG_SMP or CONFIG_PREEMPT are set. The various
  * methods are defined as nops in the case they are not required.
  */
-#define read_trylock(lock)	__cond_acquire(lock, _raw_read_trylock(lock))
+#define read_trylock(lock)	__cond_acquire_shared(lock, _raw_read_trylock(lock))
 #define write_trylock(lock)	__cond_acquire(lock, _raw_write_trylock(lock))
 
 #define write_lock(lock)	_raw_write_lock(lock)
@@ -112,12 +113,12 @@ do {								\
 	} while (0)
 #define write_unlock_bh(lock)		_raw_write_unlock_bh(lock)
 
-#define write_trylock_irqsave(lock, flags) \
-({ \
-	local_irq_save(flags); \
-	write_trylock(lock) ? \
-	1 : ({ local_irq_restore(flags); 0; }); \
-})
+#define write_trylock_irqsave(lock, flags)		\
+	__cond_acquire(lock, ({				\
+		local_irq_save(flags);			\
+		_raw_write_trylock(lock) ?		\
+		1 : ({ local_irq_restore(flags); 0; });	\
+	}))
 
 #ifdef arch_rwlock_is_contended
 #define rwlock_is_contended(lock) \
diff --git a/include/linux/rwlock_api_smp.h b/include/linux/rwlock_api_smp.h
index 31d3d1116323..3e975105a606 100644
--- a/include/linux/rwlock_api_smp.h
+++ b/include/linux/rwlock_api_smp.h
@@ -15,12 +15,12 @@
  * Released under the General Public License (GPL).
  */
 
-void __lockfunc _raw_read_lock(rwlock_t *lock)		__acquires(lock);
+void __lockfunc _raw_read_lock(rwlock_t *lock)		__acquires_shared(lock);
 void __lockfunc _raw_write_lock(rwlock_t *lock)		__acquires(lock);
 void __lockfunc _raw_write_lock_nested(rwlock_t *lock, int subclass)	__acquires(lock);
-void __lockfunc _raw_read_lock_bh(rwlock_t *lock)	__acquires(lock);
+void __lockfunc _raw_read_lock_bh(rwlock_t *lock)	__acquires_shared(lock);
 void __lockfunc _raw_write_lock_bh(rwlock_t *lock)	__acquires(lock);
-void __lockfunc _raw_read_lock_irq(rwlock_t *lock)	__acquires(lock);
+void __lockfunc _raw_read_lock_irq(rwlock_t *lock)	__acquires_shared(lock);
 void __lockfunc _raw_write_lock_irq(rwlock_t *lock)	__acquires(lock);
 unsigned long __lockfunc _raw_read_lock_irqsave(rwlock_t *lock)
 							__acquires(lock);
@@ -28,11 +28,11 @@ unsigned long __lockfunc _raw_write_lock_irqsave(rwlock_t *lock)
 							__acquires(lock);
 int __lockfunc _raw_read_trylock(rwlock_t *lock);
 int __lockfunc _raw_write_trylock(rwlock_t *lock);
-void __lockfunc _raw_read_unlock(rwlock_t *lock)	__releases(lock);
+void __lockfunc _raw_read_unlock(rwlock_t *lock)	__releases_shared(lock);
 void __lockfunc _raw_write_unlock(rwlock_t *lock)	__releases(lock);
-void __lockfunc _raw_read_unlock_bh(rwlock_t *lock)	__releases(lock);
+void __lockfunc _raw_read_unlock_bh(rwlock_t *lock)	__releases_shared(lock);
 void __lockfunc _raw_write_unlock_bh(rwlock_t *lock)	__releases(lock);
-void __lockfunc _raw_read_unlock_irq(rwlock_t *lock)	__releases(lock);
+void __lockfunc _raw_read_unlock_irq(rwlock_t *lock)	__releases_shared(lock);
 void __lockfunc _raw_write_unlock_irq(rwlock_t *lock)	__releases(lock);
 void __lockfunc
 _raw_read_unlock_irqrestore(rwlock_t *lock, unsigned long flags)
@@ -145,6 +145,7 @@ static inline int __raw_write_trylock(rwlock_t *lock)
 #if !defined(CONFIG_GENERIC_LOCKBREAK) || defined(CONFIG_DEBUG_LOCK_ALLOC)
 
 static inline void __raw_read_lock(rwlock_t *lock)
+	__acquires_shared(lock) __no_capability_analysis
 {
 	preempt_disable();
 	rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
@@ -152,6 +153,7 @@ static inline void __raw_read_lock(rwlock_t *lock)
 }
 
 static inline unsigned long __raw_read_lock_irqsave(rwlock_t *lock)
+	__acquires_shared(lock) __no_capability_analysis
 {
 	unsigned long flags;
 
@@ -163,6 +165,7 @@ static inline unsigned long __raw_read_lock_irqsave(rwlock_t *lock)
 }
 
 static inline void __raw_read_lock_irq(rwlock_t *lock)
+	__acquires_shared(lock) __no_capability_analysis
 {
 	local_irq_disable();
 	preempt_disable();
@@ -171,6 +174,7 @@ static inline void __raw_read_lock_irq(rwlock_t *lock)
 }
 
 static inline void __raw_read_lock_bh(rwlock_t *lock)
+	__acquires_shared(lock) __no_capability_analysis
 {
 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET);
 	rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
@@ -178,6 +182,7 @@ static inline void __raw_read_lock_bh(rwlock_t *lock)
 }
 
 static inline unsigned long __raw_write_lock_irqsave(rwlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	unsigned long flags;
 
@@ -189,6 +194,7 @@ static inline unsigned long __raw_write_lock_irqsave(rwlock_t *lock)
 }
 
 static inline void __raw_write_lock_irq(rwlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	local_irq_disable();
 	preempt_disable();
@@ -197,6 +203,7 @@ static inline void __raw_write_lock_irq(rwlock_t *lock)
 }
 
 static inline void __raw_write_lock_bh(rwlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET);
 	rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
@@ -204,6 +211,7 @@ static inline void __raw_write_lock_bh(rwlock_t *lock)
 }
 
 static inline void __raw_write_lock(rwlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	preempt_disable();
 	rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
@@ -211,6 +219,7 @@ static inline void __raw_write_lock(rwlock_t *lock)
 }
 
 static inline void __raw_write_lock_nested(rwlock_t *lock, int subclass)
+	__acquires(lock) __no_capability_analysis
 {
 	preempt_disable();
 	rwlock_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
@@ -220,6 +229,7 @@ static inline void __raw_write_lock_nested(rwlock_t *lock, int subclass)
 #endif /* !CONFIG_GENERIC_LOCKBREAK || CONFIG_DEBUG_LOCK_ALLOC */
 
 static inline void __raw_write_unlock(rwlock_t *lock)
+	__releases(lock)
 {
 	rwlock_release(&lock->dep_map, _RET_IP_);
 	do_raw_write_unlock(lock);
@@ -227,6 +237,7 @@ static inline void __raw_write_unlock(rwlock_t *lock)
 }
 
 static inline void __raw_read_unlock(rwlock_t *lock)
+	__releases_shared(lock)
 {
 	rwlock_release(&lock->dep_map, _RET_IP_);
 	do_raw_read_unlock(lock);
@@ -235,6 +246,7 @@ static inline void __raw_read_unlock(rwlock_t *lock)
 
 static inline void
 __raw_read_unlock_irqrestore(rwlock_t *lock, unsigned long flags)
+	__releases_shared(lock)
 {
 	rwlock_release(&lock->dep_map, _RET_IP_);
 	do_raw_read_unlock(lock);
@@ -243,6 +255,7 @@ __raw_read_unlock_irqrestore(rwlock_t *lock, unsigned long flags)
 }
 
 static inline void __raw_read_unlock_irq(rwlock_t *lock)
+	__releases_shared(lock)
 {
 	rwlock_release(&lock->dep_map, _RET_IP_);
 	do_raw_read_unlock(lock);
@@ -251,6 +264,7 @@ static inline void __raw_read_unlock_irq(rwlock_t *lock)
 }
 
 static inline void __raw_read_unlock_bh(rwlock_t *lock)
+	__releases_shared(lock)
 {
 	rwlock_release(&lock->dep_map, _RET_IP_);
 	do_raw_read_unlock(lock);
@@ -259,6 +273,7 @@ static inline void __raw_read_unlock_bh(rwlock_t *lock)
 
 static inline void __raw_write_unlock_irqrestore(rwlock_t *lock,
 					     unsigned long flags)
+	__releases(lock)
 {
 	rwlock_release(&lock->dep_map, _RET_IP_);
 	do_raw_write_unlock(lock);
@@ -267,6 +282,7 @@ static inline void __raw_write_unlock_irqrestore(rwlock_t *lock,
 }
 
 static inline void __raw_write_unlock_irq(rwlock_t *lock)
+	__releases(lock)
 {
 	rwlock_release(&lock->dep_map, _RET_IP_);
 	do_raw_write_unlock(lock);
@@ -275,6 +291,7 @@ static inline void __raw_write_unlock_irq(rwlock_t *lock)
 }
 
 static inline void __raw_write_unlock_bh(rwlock_t *lock)
+	__releases(lock)
 {
 	rwlock_release(&lock->dep_map, _RET_IP_);
 	do_raw_write_unlock(lock);
diff --git a/include/linux/rwlock_rt.h b/include/linux/rwlock_rt.h
index 5320b4b66405..c6280b0e4503 100644
--- a/include/linux/rwlock_rt.h
+++ b/include/linux/rwlock_rt.h
@@ -22,28 +22,32 @@ do {							\
 							\
 	init_rwbase_rt(&(rwl)->rwbase);			\
 	__rt_rwlock_init(rwl, #rwl, &__key);		\
+	__assert_cap(rwl);				\
 } while (0)
 
-extern void rt_read_lock(rwlock_t *rwlock)	__acquires(rwlock);
+extern void rt_read_lock(rwlock_t *rwlock)	__acquires_shared(rwlock);
 extern int rt_read_trylock(rwlock_t *rwlock);
-extern void rt_read_unlock(rwlock_t *rwlock)	__releases(rwlock);
+extern void rt_read_unlock(rwlock_t *rwlock)	__releases_shared(rwlock);
 extern void rt_write_lock(rwlock_t *rwlock)	__acquires(rwlock);
 extern void rt_write_lock_nested(rwlock_t *rwlock, int subclass)	__acquires(rwlock);
 extern int rt_write_trylock(rwlock_t *rwlock);
 extern void rt_write_unlock(rwlock_t *rwlock)	__releases(rwlock);
 
 static __always_inline void read_lock(rwlock_t *rwlock)
+	__acquires_shared(rwlock)
 {
 	rt_read_lock(rwlock);
 }
 
 static __always_inline void read_lock_bh(rwlock_t *rwlock)
+	__acquires_shared(rwlock)
 {
 	local_bh_disable();
 	rt_read_lock(rwlock);
 }
 
 static __always_inline void read_lock_irq(rwlock_t *rwlock)
+	__acquires_shared(rwlock)
 {
 	rt_read_lock(rwlock);
 }
@@ -55,37 +59,43 @@ static __always_inline void read_lock_irq(rwlock_t *rwlock)
 		flags = 0;				\
 	} while (0)
 
-#define read_trylock(lock)	__cond_acquire(lock, rt_read_trylock(lock))
+#define read_trylock(lock)	__cond_acquire_shared(lock, rt_read_trylock(lock))
 
 static __always_inline void read_unlock(rwlock_t *rwlock)
+	__releases_shared(rwlock)
 {
 	rt_read_unlock(rwlock);
 }
 
 static __always_inline void read_unlock_bh(rwlock_t *rwlock)
+	__releases_shared(rwlock)
 {
 	rt_read_unlock(rwlock);
 	local_bh_enable();
 }
 
 static __always_inline void read_unlock_irq(rwlock_t *rwlock)
+	__releases_shared(rwlock)
 {
 	rt_read_unlock(rwlock);
 }
 
 static __always_inline void read_unlock_irqrestore(rwlock_t *rwlock,
 						   unsigned long flags)
+	__releases_shared(rwlock)
 {
 	rt_read_unlock(rwlock);
 }
 
 static __always_inline void write_lock(rwlock_t *rwlock)
+	__acquires(rwlock)
 {
 	rt_write_lock(rwlock);
 }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static __always_inline void write_lock_nested(rwlock_t *rwlock, int subclass)
+	__acquires(rwlock)
 {
 	rt_write_lock_nested(rwlock, subclass);
 }
@@ -94,12 +104,14 @@ static __always_inline void write_lock_nested(rwlock_t *rwlock, int subclass)
 #endif
 
 static __always_inline void write_lock_bh(rwlock_t *rwlock)
+	__acquires(rwlock)
 {
 	local_bh_disable();
 	rt_write_lock(rwlock);
 }
 
 static __always_inline void write_lock_irq(rwlock_t *rwlock)
+	__acquires(rwlock)
 {
 	rt_write_lock(rwlock);
 }
@@ -114,33 +126,34 @@ static __always_inline void write_lock_irq(rwlock_t *rwlock)
 #define write_trylock(lock)	__cond_acquire(lock, rt_write_trylock(lock))
 
 #define write_trylock_irqsave(lock, flags)		\
-({							\
-	int __locked;					\
-							\
-	typecheck(unsigned long, flags);		\
-	flags = 0;					\
-	__locked = write_trylock(lock);			\
-	__locked;					\
-})
+	__cond_acquire(lock, ({				\
+		typecheck(unsigned long, flags);	\
+		flags = 0;				\
+		rt_write_trylock(lock);			\
+	}))
 
 static __always_inline void write_unlock(rwlock_t *rwlock)
+	__releases(rwlock)
 {
 	rt_write_unlock(rwlock);
 }
 
 static __always_inline void write_unlock_bh(rwlock_t *rwlock)
+	__releases(rwlock)
 {
 	rt_write_unlock(rwlock);
 	local_bh_enable();
 }
 
 static __always_inline void write_unlock_irq(rwlock_t *rwlock)
+	__releases(rwlock)
 {
 	rt_write_unlock(rwlock);
 }
 
 static __always_inline void write_unlock_irqrestore(rwlock_t *rwlock,
 						    unsigned long flags)
+	__releases(rwlock)
 {
 	rt_write_unlock(rwlock);
 }
diff --git a/include/linux/rwlock_types.h b/include/linux/rwlock_types.h
index 1948442e7750..231489cc30f2 100644
--- a/include/linux/rwlock_types.h
+++ b/include/linux/rwlock_types.h
@@ -22,7 +22,7 @@
  * portions Copyright 2005, Red Hat, Inc., Ingo Molnar
  * Released under the General Public License (GPL).
  */
-typedef struct {
+struct_with_capability(rwlock) {
 	arch_rwlock_t raw_lock;
 #ifdef CONFIG_DEBUG_SPINLOCK
 	unsigned int magic, owner_cpu;
@@ -31,7 +31,8 @@ typedef struct {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
 #endif
-} rwlock_t;
+};
+typedef struct rwlock rwlock_t;
 
 #define RWLOCK_MAGIC		0xdeaf1eed
 
@@ -54,13 +55,14 @@ typedef struct {
 
 #include <linux/rwbase_rt.h>
 
-typedef struct {
+struct_with_capability(rwlock) {
 	struct rwbase_rt	rwbase;
 	atomic_t		readers;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
-} rwlock_t;
+};
+typedef struct rwlock rwlock_t;
 
 #define __RWLOCK_RT_INITIALIZER(name)					\
 {									\
diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 678e6f0679a1..1646a9920fd7 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -106,11 +106,12 @@ do {									\
 	static struct lock_class_key __key;				\
 									\
 	__raw_spin_lock_init((lock), #lock, &__key, LD_WAIT_SPIN);	\
+	__assert_cap(lock);						\
 } while (0)
 
 #else
 # define raw_spin_lock_init(lock)				\
-	do { *(lock) = __RAW_SPIN_LOCK_UNLOCKED(lock); } while (0)
+	do { *(lock) = __RAW_SPIN_LOCK_UNLOCKED(lock); __assert_cap(lock); } while (0)
 #endif
 
 #define raw_spin_is_locked(lock)	arch_spin_is_locked(&(lock)->raw_lock)
@@ -286,19 +287,19 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 #define raw_spin_trylock_bh(lock) \
 	__cond_acquire(lock, _raw_spin_trylock_bh(lock))
 
-#define raw_spin_trylock_irq(lock) \
-({ \
-	local_irq_disable(); \
-	raw_spin_trylock(lock) ? \
-	1 : ({ local_irq_enable(); 0;  }); \
-})
+#define raw_spin_trylock_irq(lock)			\
+	__cond_acquire(lock, ({				\
+		local_irq_disable();			\
+		_raw_spin_trylock(lock) ?		\
+		1 : ({ local_irq_enable(); 0;  });	\
+	}))
 
-#define raw_spin_trylock_irqsave(lock, flags) \
-({ \
-	local_irq_save(flags); \
-	raw_spin_trylock(lock) ? \
-	1 : ({ local_irq_restore(flags); 0; }); \
-})
+#define raw_spin_trylock_irqsave(lock, flags)		\
+	__cond_acquire(lock, ({				\
+		local_irq_save(flags);			\
+		_raw_spin_trylock(lock) ?		\
+		1 : ({ local_irq_restore(flags); 0; }); \
+	}))
 
 #ifndef CONFIG_PREEMPT_RT
 /* Include rwlock functions for !RT */
@@ -334,6 +335,7 @@ do {								\
 								\
 	__raw_spin_lock_init(spinlock_check(lock),		\
 			     #lock, &__key, LD_WAIT_CONFIG);	\
+	__assert_cap(lock);					\
 } while (0)
 
 #else
@@ -342,21 +344,25 @@ do {								\
 do {						\
 	spinlock_check(_lock);			\
 	*(_lock) = __SPIN_LOCK_UNLOCKED(_lock);	\
+	__assert_cap(_lock);			\
 } while (0)
 
 #endif
 
 static __always_inline void spin_lock(spinlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	raw_spin_lock(&lock->rlock);
 }
 
 static __always_inline void spin_lock_bh(spinlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	raw_spin_lock_bh(&lock->rlock);
 }
 
 static __always_inline int spin_trylock(spinlock_t *lock)
+	__cond_acquires(lock) __no_capability_analysis
 {
 	return raw_spin_trylock(&lock->rlock);
 }
@@ -372,6 +378,7 @@ do {									\
 } while (0)
 
 static __always_inline void spin_lock_irq(spinlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	raw_spin_lock_irq(&lock->rlock);
 }
@@ -379,47 +386,53 @@ static __always_inline void spin_lock_irq(spinlock_t *lock)
 #define spin_lock_irqsave(lock, flags)				\
 do {								\
 	raw_spin_lock_irqsave(spinlock_check(lock), flags);	\
+	__release(spinlock_check(lock)); __acquire(lock);	\
 } while (0)
 
 #define spin_lock_irqsave_nested(lock, flags, subclass)			\
 do {									\
 	raw_spin_lock_irqsave_nested(spinlock_check(lock), flags, subclass); \
+	__release(spinlock_check(lock)); __acquire(lock);		\
 } while (0)
 
 static __always_inline void spin_unlock(spinlock_t *lock)
+	__releases(lock) __no_capability_analysis
 {
 	raw_spin_unlock(&lock->rlock);
 }
 
 static __always_inline void spin_unlock_bh(spinlock_t *lock)
+	__releases(lock) __no_capability_analysis
 {
 	raw_spin_unlock_bh(&lock->rlock);
 }
 
 static __always_inline void spin_unlock_irq(spinlock_t *lock)
+	__releases(lock) __no_capability_analysis
 {
 	raw_spin_unlock_irq(&lock->rlock);
 }
 
 static __always_inline void spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
+	__releases(lock) __no_capability_analysis
 {
 	raw_spin_unlock_irqrestore(&lock->rlock, flags);
 }
 
 static __always_inline int spin_trylock_bh(spinlock_t *lock)
+	__cond_acquires(lock) __no_capability_analysis
 {
 	return raw_spin_trylock_bh(&lock->rlock);
 }
 
 static __always_inline int spin_trylock_irq(spinlock_t *lock)
+	__cond_acquires(lock) __no_capability_analysis
 {
 	return raw_spin_trylock_irq(&lock->rlock);
 }
 
 #define spin_trylock_irqsave(lock, flags)			\
-({								\
-	raw_spin_trylock_irqsave(spinlock_check(lock), flags); \
-})
+	__cond_acquire(lock, raw_spin_trylock_irqsave(spinlock_check(lock), flags))
 
 /**
  * spin_is_locked() - Check whether a spinlock is locked.
diff --git a/include/linux/spinlock_api_smp.h b/include/linux/spinlock_api_smp.h
index 9ecb0ab504e3..fab02d8bf0c9 100644
--- a/include/linux/spinlock_api_smp.h
+++ b/include/linux/spinlock_api_smp.h
@@ -34,8 +34,8 @@ unsigned long __lockfunc _raw_spin_lock_irqsave(raw_spinlock_t *lock)
 unsigned long __lockfunc
 _raw_spin_lock_irqsave_nested(raw_spinlock_t *lock, int subclass)
 								__acquires(lock);
-int __lockfunc _raw_spin_trylock(raw_spinlock_t *lock);
-int __lockfunc _raw_spin_trylock_bh(raw_spinlock_t *lock);
+int __lockfunc _raw_spin_trylock(raw_spinlock_t *lock)		__cond_acquires(lock);
+int __lockfunc _raw_spin_trylock_bh(raw_spinlock_t *lock)	__cond_acquires(lock);
 void __lockfunc _raw_spin_unlock(raw_spinlock_t *lock)		__releases(lock);
 void __lockfunc _raw_spin_unlock_bh(raw_spinlock_t *lock)	__releases(lock);
 void __lockfunc _raw_spin_unlock_irq(raw_spinlock_t *lock)	__releases(lock);
@@ -84,6 +84,7 @@ _raw_spin_unlock_irqrestore(raw_spinlock_t *lock, unsigned long flags)
 #endif
 
 static inline int __raw_spin_trylock(raw_spinlock_t *lock)
+	__cond_acquires(lock)
 {
 	preempt_disable();
 	if (do_raw_spin_trylock(lock)) {
@@ -102,6 +103,7 @@ static inline int __raw_spin_trylock(raw_spinlock_t *lock)
 #if !defined(CONFIG_GENERIC_LOCKBREAK) || defined(CONFIG_DEBUG_LOCK_ALLOC)
 
 static inline unsigned long __raw_spin_lock_irqsave(raw_spinlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	unsigned long flags;
 
@@ -113,6 +115,7 @@ static inline unsigned long __raw_spin_lock_irqsave(raw_spinlock_t *lock)
 }
 
 static inline void __raw_spin_lock_irq(raw_spinlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	local_irq_disable();
 	preempt_disable();
@@ -121,6 +124,7 @@ static inline void __raw_spin_lock_irq(raw_spinlock_t *lock)
 }
 
 static inline void __raw_spin_lock_bh(raw_spinlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET);
 	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
@@ -128,6 +132,7 @@ static inline void __raw_spin_lock_bh(raw_spinlock_t *lock)
 }
 
 static inline void __raw_spin_lock(raw_spinlock_t *lock)
+	__acquires(lock) __no_capability_analysis
 {
 	preempt_disable();
 	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
@@ -137,6 +142,7 @@ static inline void __raw_spin_lock(raw_spinlock_t *lock)
 #endif /* !CONFIG_GENERIC_LOCKBREAK || CONFIG_DEBUG_LOCK_ALLOC */
 
 static inline void __raw_spin_unlock(raw_spinlock_t *lock)
+	__releases(lock)
 {
 	spin_release(&lock->dep_map, _RET_IP_);
 	do_raw_spin_unlock(lock);
@@ -145,6 +151,7 @@ static inline void __raw_spin_unlock(raw_spinlock_t *lock)
 
 static inline void __raw_spin_unlock_irqrestore(raw_spinlock_t *lock,
 					    unsigned long flags)
+	__releases(lock)
 {
 	spin_release(&lock->dep_map, _RET_IP_);
 	do_raw_spin_unlock(lock);
@@ -153,6 +160,7 @@ static inline void __raw_spin_unlock_irqrestore(raw_spinlock_t *lock,
 }
 
 static inline void __raw_spin_unlock_irq(raw_spinlock_t *lock)
+	__releases(lock)
 {
 	spin_release(&lock->dep_map, _RET_IP_);
 	do_raw_spin_unlock(lock);
@@ -161,6 +169,7 @@ static inline void __raw_spin_unlock_irq(raw_spinlock_t *lock)
 }
 
 static inline void __raw_spin_unlock_bh(raw_spinlock_t *lock)
+	__releases(lock)
 {
 	spin_release(&lock->dep_map, _RET_IP_);
 	do_raw_spin_unlock(lock);
@@ -168,6 +177,7 @@ static inline void __raw_spin_unlock_bh(raw_spinlock_t *lock)
 }
 
 static inline int __raw_spin_trylock_bh(raw_spinlock_t *lock)
+	__cond_acquires(lock)
 {
 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET);
 	if (do_raw_spin_trylock(lock)) {
diff --git a/include/linux/spinlock_api_up.h b/include/linux/spinlock_api_up.h
index 819aeba1c87e..018f5aabc1be 100644
--- a/include/linux/spinlock_api_up.h
+++ b/include/linux/spinlock_api_up.h
@@ -24,68 +24,77 @@
  * flags straight, to suppress compiler warnings of unused lock
  * variables, and to add the proper checker annotations:
  */
-#define ___LOCK(lock) \
-  do { __acquire(lock); (void)(lock); } while (0)
+#define ___LOCK_void(lock) \
+  do { (void)(lock); } while (0)
 
-#define __LOCK(lock) \
-  do { preempt_disable(); ___LOCK(lock); } while (0)
+#define ___LOCK_(lock) \
+  do { __acquire(lock); ___LOCK_void(lock); } while (0)
 
-#define __LOCK_BH(lock) \
-  do { __local_bh_disable_ip(_THIS_IP_, SOFTIRQ_LOCK_OFFSET); ___LOCK(lock); } while (0)
+#define ___LOCK_shared(lock) \
+  do { __acquire_shared(lock); ___LOCK_void(lock); } while (0)
 
-#define __LOCK_IRQ(lock) \
-  do { local_irq_disable(); __LOCK(lock); } while (0)
+#define __LOCK(lock, ...) \
+  do { preempt_disable(); ___LOCK_##__VA_ARGS__(lock); } while (0)
 
-#define __LOCK_IRQSAVE(lock, flags) \
-  do { local_irq_save(flags); __LOCK(lock); } while (0)
+#define __LOCK_BH(lock, ...) \
+  do { __local_bh_disable_ip(_THIS_IP_, SOFTIRQ_LOCK_OFFSET); ___LOCK_##__VA_ARGS__(lock); } while (0)
 
-#define ___UNLOCK(lock) \
+#define __LOCK_IRQ(lock, ...) \
+  do { local_irq_disable(); __LOCK(lock, ##__VA_ARGS__); } while (0)
+
+#define __LOCK_IRQSAVE(lock, flags, ...) \
+  do { local_irq_save(flags); __LOCK(lock, ##__VA_ARGS__); } while (0)
+
+#define ___UNLOCK_(lock) \
   do { __release(lock); (void)(lock); } while (0)
 
-#define __UNLOCK(lock) \
-  do { preempt_enable(); ___UNLOCK(lock); } while (0)
+#define ___UNLOCK_shared(lock) \
+  do { __release_shared(lock); (void)(lock); } while (0)
 
-#define __UNLOCK_BH(lock) \
+#define __UNLOCK(lock, ...) \
+  do { preempt_enable(); ___UNLOCK_##__VA_ARGS__(lock); } while (0)
+
+#define __UNLOCK_BH(lock, ...) \
   do { __local_bh_enable_ip(_THIS_IP_, SOFTIRQ_LOCK_OFFSET); \
-       ___UNLOCK(lock); } while (0)
+       ___UNLOCK_##__VA_ARGS__(lock); } while (0)
 
-#define __UNLOCK_IRQ(lock) \
-  do { local_irq_enable(); __UNLOCK(lock); } while (0)
+#define __UNLOCK_IRQ(lock, ...) \
+  do { local_irq_enable(); __UNLOCK(lock, ##__VA_ARGS__); } while (0)
 
-#define __UNLOCK_IRQRESTORE(lock, flags) \
-  do { local_irq_restore(flags); __UNLOCK(lock); } while (0)
+#define __UNLOCK_IRQRESTORE(lock, flags, ...) \
+  do { local_irq_restore(flags); __UNLOCK(lock, ##__VA_ARGS__); } while (0)
 
 #define _raw_spin_lock(lock)			__LOCK(lock)
 #define _raw_spin_lock_nested(lock, subclass)	__LOCK(lock)
-#define _raw_read_lock(lock)			__LOCK(lock)
+#define _raw_read_lock(lock)			__LOCK(lock, shared)
 #define _raw_write_lock(lock)			__LOCK(lock)
 #define _raw_write_lock_nested(lock, subclass)	__LOCK(lock)
 #define _raw_spin_lock_bh(lock)			__LOCK_BH(lock)
-#define _raw_read_lock_bh(lock)			__LOCK_BH(lock)
+#define _raw_read_lock_bh(lock)			__LOCK_BH(lock, shared)
 #define _raw_write_lock_bh(lock)		__LOCK_BH(lock)
 #define _raw_spin_lock_irq(lock)		__LOCK_IRQ(lock)
-#define _raw_read_lock_irq(lock)		__LOCK_IRQ(lock)
+#define _raw_read_lock_irq(lock)		__LOCK_IRQ(lock, shared)
 #define _raw_write_lock_irq(lock)		__LOCK_IRQ(lock)
 #define _raw_spin_lock_irqsave(lock, flags)	__LOCK_IRQSAVE(lock, flags)
-#define _raw_read_lock_irqsave(lock, flags)	__LOCK_IRQSAVE(lock, flags)
+#define _raw_read_lock_irqsave(lock, flags)	__LOCK_IRQSAVE(lock, flags, shared)
 #define _raw_write_lock_irqsave(lock, flags)	__LOCK_IRQSAVE(lock, flags)
-#define _raw_spin_trylock(lock)			({ __LOCK(lock); 1; })
-#define _raw_read_trylock(lock)			({ __LOCK(lock); 1; })
-#define _raw_write_trylock(lock)			({ __LOCK(lock); 1; })
-#define _raw_spin_trylock_bh(lock)		({ __LOCK_BH(lock); 1; })
+#define _raw_spin_trylock(lock)			({ __LOCK(lock, void); 1; })
+#define _raw_read_trylock(lock)			({ __LOCK(lock, void); 1; })
+#define _raw_write_trylock(lock)			({ __LOCK(lock, void); 1; })
+#define _raw_spin_trylock_bh(lock)		({ __LOCK_BH(lock, void); 1; })
 #define _raw_spin_unlock(lock)			__UNLOCK(lock)
-#define _raw_read_unlock(lock)			__UNLOCK(lock)
+#define _raw_read_unlock(lock)			__UNLOCK(lock, shared)
 #define _raw_write_unlock(lock)			__UNLOCK(lock)
 #define _raw_spin_unlock_bh(lock)		__UNLOCK_BH(lock)
 #define _raw_write_unlock_bh(lock)		__UNLOCK_BH(lock)
-#define _raw_read_unlock_bh(lock)		__UNLOCK_BH(lock)
+#define _raw_read_unlock_bh(lock)		__UNLOCK_BH(lock, shared)
 #define _raw_spin_unlock_irq(lock)		__UNLOCK_IRQ(lock)
-#define _raw_read_unlock_irq(lock)		__UNLOCK_IRQ(lock)
+#define _raw_read_unlock_irq(lock)		__UNLOCK_IRQ(lock, shared)
 #define _raw_write_unlock_irq(lock)		__UNLOCK_IRQ(lock)
 #define _raw_spin_unlock_irqrestore(lock, flags) \
 					__UNLOCK_IRQRESTORE(lock, flags)
 #define _raw_read_unlock_irqrestore(lock, flags) \
-					__UNLOCK_IRQRESTORE(lock, flags)
+					__UNLOCK_IRQRESTORE(lock, flags, shared)
 #define _raw_write_unlock_irqrestore(lock, flags) \
 					__UNLOCK_IRQRESTORE(lock, flags)
 
diff --git a/include/linux/spinlock_rt.h b/include/linux/spinlock_rt.h
index eaad4dd2baac..5d9ebc3ec521 100644
--- a/include/linux/spinlock_rt.h
+++ b/include/linux/spinlock_rt.h
@@ -20,6 +20,7 @@ static inline void __rt_spin_lock_init(spinlock_t *lock, const char *name,
 do {								\
 	rt_mutex_base_init(&(slock)->lock);			\
 	__rt_spin_lock_init(slock, name, key, percpu);		\
+	__assert_cap(slock);					\
 } while (0)
 
 #define _spin_lock_init(slock, percpu)				\
@@ -40,6 +41,7 @@ extern int rt_spin_trylock_bh(spinlock_t *lock);
 extern int rt_spin_trylock(spinlock_t *lock);
 
 static __always_inline void spin_lock(spinlock_t *lock)
+	__acquires(lock)
 {
 	rt_spin_lock(lock);
 }
@@ -82,6 +84,7 @@ static __always_inline void spin_lock(spinlock_t *lock)
 	__spin_lock_irqsave_nested(lock, flags, subclass)
 
 static __always_inline void spin_lock_bh(spinlock_t *lock)
+	__acquires(lock)
 {
 	/* Investigate: Drop bh when blocking ? */
 	local_bh_disable();
@@ -89,6 +92,7 @@ static __always_inline void spin_lock_bh(spinlock_t *lock)
 }
 
 static __always_inline void spin_lock_irq(spinlock_t *lock)
+	__acquires(lock)
 {
 	rt_spin_lock(lock);
 }
@@ -101,23 +105,27 @@ static __always_inline void spin_lock_irq(spinlock_t *lock)
 	} while (0)
 
 static __always_inline void spin_unlock(spinlock_t *lock)
+	__releases(lock)
 {
 	rt_spin_unlock(lock);
 }
 
 static __always_inline void spin_unlock_bh(spinlock_t *lock)
+	__releases(lock)
 {
 	rt_spin_unlock(lock);
 	local_bh_enable();
 }
 
 static __always_inline void spin_unlock_irq(spinlock_t *lock)
+	__releases(lock)
 {
 	rt_spin_unlock(lock);
 }
 
 static __always_inline void spin_unlock_irqrestore(spinlock_t *lock,
 						   unsigned long flags)
+	__releases(lock)
 {
 	rt_spin_unlock(lock);
 }
@@ -132,14 +140,11 @@ static __always_inline void spin_unlock_irqrestore(spinlock_t *lock,
 	__cond_acquire(lock, rt_spin_trylock(lock))
 
 #define spin_trylock_irqsave(lock, flags)		\
-({							\
-	int __locked;					\
-							\
-	typecheck(unsigned long, flags);		\
-	flags = 0;					\
-	__locked = spin_trylock(lock);			\
-	__locked;					\
-})
+	__cond_acquire(lock, ({				\
+		typecheck(unsigned long, flags);	\
+		flags = 0;				\
+		rt_spin_trylock(lock);			\
+	}))
 
 #define spin_is_contended(lock)		(((void)(lock), 0))
 
diff --git a/include/linux/spinlock_types.h b/include/linux/spinlock_types.h
index 2dfa35ffec76..2c5db5b5b990 100644
--- a/include/linux/spinlock_types.h
+++ b/include/linux/spinlock_types.h
@@ -14,7 +14,7 @@
 #ifndef CONFIG_PREEMPT_RT
 
 /* Non PREEMPT_RT kernels map spinlock to raw_spinlock */
-typedef struct spinlock {
+struct_with_capability(spinlock) {
 	union {
 		struct raw_spinlock rlock;
 
@@ -26,7 +26,8 @@ typedef struct spinlock {
 		};
 #endif
 	};
-} spinlock_t;
+};
+typedef struct spinlock spinlock_t;
 
 #define ___SPIN_LOCK_INITIALIZER(lockname)	\
 	{					\
@@ -47,12 +48,13 @@ typedef struct spinlock {
 /* PREEMPT_RT kernels map spinlock to rt_mutex */
 #include <linux/rtmutex.h>
 
-typedef struct spinlock {
+struct_with_capability(spinlock) {
 	struct rt_mutex_base	lock;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
-} spinlock_t;
+};
+typedef struct spinlock spinlock_t;
 
 #define __SPIN_LOCK_UNLOCKED(name)				\
 	{							\
diff --git a/include/linux/spinlock_types_raw.h b/include/linux/spinlock_types_raw.h
index 91cb36b65a17..07792ff2c2b5 100644
--- a/include/linux/spinlock_types_raw.h
+++ b/include/linux/spinlock_types_raw.h
@@ -11,7 +11,7 @@
 
 #include <linux/lockdep_types.h>
 
-typedef struct raw_spinlock {
+struct_with_capability(raw_spinlock) {
 	arch_spinlock_t raw_lock;
 #ifdef CONFIG_DEBUG_SPINLOCK
 	unsigned int magic, owner_cpu;
@@ -20,7 +20,8 @@ typedef struct raw_spinlock {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
 #endif
-} raw_spinlock_t;
+};
+typedef struct raw_spinlock raw_spinlock_t;
 
 #define SPINLOCK_MAGIC		0xdead4ead
 
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index a0adacce30ff..f63980e134cf 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/build_bug.h>
+#include <linux/spinlock.h>
 
 /*
  * Test that helper macros work as expected.
@@ -16,3 +17,130 @@ static void __used test_common_helpers(void)
 	BUILD_BUG_ON(capability_unsafe((void)2, 3) != 3); /* does not swallow commas */
 	capability_unsafe(do { } while (0)); /* works with void statements */
 }
+
+#define TEST_SPINLOCK_COMMON(class, type, type_init, type_lock, type_unlock, type_trylock, op)	\
+	struct test_##class##_data {								\
+		type lock;									\
+		int counter __var_guarded_by(&lock);						\
+		int *pointer __ref_guarded_by(&lock);						\
+	};											\
+	static void __used test_##class##_init(struct test_##class##_data *d)			\
+	{											\
+		type_init(&d->lock);								\
+		d->counter = 0;									\
+	}											\
+	static void __used test_##class(struct test_##class##_data *d)				\
+	{											\
+		unsigned long flags;								\
+		d->pointer++;									\
+		type_lock(&d->lock);								\
+		op(d->counter);									\
+		op(*d->pointer);								\
+		type_unlock(&d->lock);								\
+		type_lock##_irq(&d->lock);							\
+		op(d->counter);									\
+		op(*d->pointer);								\
+		type_unlock##_irq(&d->lock);							\
+		type_lock##_bh(&d->lock);							\
+		op(d->counter);									\
+		op(*d->pointer);								\
+		type_unlock##_bh(&d->lock);							\
+		type_lock##_irqsave(&d->lock, flags);						\
+		op(d->counter);									\
+		op(*d->pointer);								\
+		type_unlock##_irqrestore(&d->lock, flags);					\
+	}											\
+	static void __used test_##class##_trylock(struct test_##class##_data *d)		\
+	{											\
+		if (type_trylock(&d->lock)) {							\
+			op(d->counter);								\
+			type_unlock(&d->lock);							\
+		}										\
+	}											\
+	static void __used test_##class##_assert(struct test_##class##_data *d)			\
+	{											\
+		lockdep_assert_held(&d->lock);							\
+		op(d->counter);									\
+	}											\
+	static void __used test_##class##_guard(struct test_##class##_data *d)			\
+	{											\
+		{ guard(class)(&d->lock);		op(d->counter); }			\
+		{ guard(class##_irq)(&d->lock);		op(d->counter); }			\
+		{ guard(class##_irqsave)(&d->lock);	op(d->counter); }			\
+	}
+
+#define TEST_OP_RW(x) (x)++
+#define TEST_OP_RO(x) ((void)(x))
+
+TEST_SPINLOCK_COMMON(raw_spinlock,
+		     raw_spinlock_t,
+		     raw_spin_lock_init,
+		     raw_spin_lock,
+		     raw_spin_unlock,
+		     raw_spin_trylock,
+		     TEST_OP_RW);
+static void __used test_raw_spinlock_trylock_extra(struct test_raw_spinlock_data *d)
+{
+	unsigned long flags;
+
+	if (raw_spin_trylock_irq(&d->lock)) {
+		d->counter++;
+		raw_spin_unlock_irq(&d->lock);
+	}
+	if (raw_spin_trylock_irqsave(&d->lock, flags)) {
+		d->counter++;
+		raw_spin_unlock_irqrestore(&d->lock, flags);
+	}
+	scoped_cond_guard(raw_spinlock_try, return, &d->lock) {
+		d->counter++;
+	}
+}
+
+TEST_SPINLOCK_COMMON(spinlock,
+		     spinlock_t,
+		     spin_lock_init,
+		     spin_lock,
+		     spin_unlock,
+		     spin_trylock,
+		     TEST_OP_RW);
+static void __used test_spinlock_trylock_extra(struct test_spinlock_data *d)
+{
+	unsigned long flags;
+
+	if (spin_trylock_irq(&d->lock)) {
+		d->counter++;
+		spin_unlock_irq(&d->lock);
+	}
+	if (spin_trylock_irqsave(&d->lock, flags)) {
+		d->counter++;
+		spin_unlock_irqrestore(&d->lock, flags);
+	}
+	scoped_cond_guard(spinlock_try, return, &d->lock) {
+		d->counter++;
+	}
+}
+
+TEST_SPINLOCK_COMMON(write_lock,
+		     rwlock_t,
+		     rwlock_init,
+		     write_lock,
+		     write_unlock,
+		     write_trylock,
+		     TEST_OP_RW);
+static void __used test_write_trylock_extra(struct test_write_lock_data *d)
+{
+	unsigned long flags;
+
+	if (write_trylock_irqsave(&d->lock, flags)) {
+		d->counter++;
+		write_unlock_irqrestore(&d->lock, flags);
+	}
+}
+
+TEST_SPINLOCK_COMMON(read_lock,
+		     rwlock_t,
+		     rwlock_init,
+		     read_lock,
+		     read_unlock,
+		     read_trylock,
+		     TEST_OP_RO);
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 10/24] compiler-capability-analysis: Change __cond_acquires to take return value

[Marco Elver]

While Sparse is oblivious to the return value of conditional acquire
functions, Clang's capability analysis needs to know the return value
which indicates successful acquisition.

Add the additional argument, and convert existing uses.

No functional change intended.

Signed-off-by: Marco Elver <elver@google.com>
---
 fs/dlm/lock.c                                |  2 +-
 include/linux/compiler-capability-analysis.h | 14 +++++++++-----
 include/linux/refcount.h                     |  6 +++---
 include/linux/spinlock.h                     |  6 +++---
 include/linux/spinlock_api_smp.h             |  8 ++++----
 net/ipv4/tcp_sigpool.c                       |  2 +-
 6 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/fs/dlm/lock.c b/fs/dlm/lock.c
index c8ff88f1cdcf..e39ca02b793e 100644
--- a/fs/dlm/lock.c
+++ b/fs/dlm/lock.c
@@ -343,7 +343,7 @@ void dlm_hold_rsb(struct dlm_rsb *r)
 /* TODO move this to lib/refcount.c */
 static __must_check bool
 dlm_refcount_dec_and_write_lock_bh(refcount_t *r, rwlock_t *lock)
-__cond_acquires(lock)
+      __cond_acquires(1, lock)
 {
 	if (refcount_dec_not_one(r))
 		return false;
diff --git a/include/linux/compiler-capability-analysis.h b/include/linux/compiler-capability-analysis.h
index ca63b6513dc3..10c03133ac4d 100644
--- a/include/linux/compiler-capability-analysis.h
+++ b/include/linux/compiler-capability-analysis.h
@@ -231,7 +231,7 @@
 # define __must_hold(x)		__attribute__((context(x,1,1)))
 # define __must_not_hold(x)
 # define __acquires(x)		__attribute__((context(x,0,1)))
-# define __cond_acquires(x)	__attribute__((context(x,0,-1)))
+# define __cond_acquires(ret, x) __attribute__((context(x,0,-1)))
 # define __releases(x)		__attribute__((context(x,1,0)))
 # define __acquire(x)		__context__(x,1)
 # define __release(x)		__context__(x,-1)
@@ -277,12 +277,14 @@
 /**
  * __cond_acquires() - function attribute, function conditionally
  *                     acquires a capability exclusively
+ * @ret: value returned by function if capability acquired
  * @x: capability instance pointer
  *
  * Function attribute declaring that the function conditionally acquires the
- * given capability instance @x exclusively, but does not release it.
+ * given capability instance @x exclusively, but does not release it. The
+ * function return value @ret denotes when the capability is acquired.
  */
-# define __cond_acquires(x)	__try_acquires_cap(1, x)
+# define __cond_acquires(ret, x) __try_acquires_cap(ret, x)
 
 /**
  * __releases() - function attribute, function releases a capability exclusively
@@ -349,12 +351,14 @@
 /**
  * __cond_acquires_shared() - function attribute, function conditionally
  *                            acquires a capability shared
+ * @ret: value returned by function if capability acquired
  * @x: capability instance pointer
  *
  * Function attribute declaring that the function conditionally acquires the
- * given capability instance @x with shared access, but does not release it.
+ * given capability instance @x with shared access, but does not release it. The
+ * function return value @ret denotes when the capability is acquired.
  */
-# define __cond_acquires_shared(x) __try_acquires_shared_cap(1, x)
+# define __cond_acquires_shared(ret, x) __try_acquires_shared_cap(ret, x)
 
 /**
  * __releases_shared() - function attribute, function releases a
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 35f039ecb272..f63ce3fadfa3 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -353,9 +353,9 @@ static inline void refcount_dec(refcount_t *r)
 
 extern __must_check bool refcount_dec_if_one(refcount_t *r);
 extern __must_check bool refcount_dec_not_one(refcount_t *r);
-extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock) __cond_acquires(lock);
-extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock) __cond_acquires(lock);
+extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock) __cond_acquires(1, lock);
+extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock) __cond_acquires(1, lock);
 extern __must_check bool refcount_dec_and_lock_irqsave(refcount_t *r,
 						       spinlock_t *lock,
-						       unsigned long *flags) __cond_acquires(lock);
+						       unsigned long *flags) __cond_acquires(1, lock);
 #endif /* _LINUX_REFCOUNT_H */
diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 1646a9920fd7..de5118d0e718 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -362,7 +362,7 @@ static __always_inline void spin_lock_bh(spinlock_t *lock)
 }
 
 static __always_inline int spin_trylock(spinlock_t *lock)
-	__cond_acquires(lock) __no_capability_analysis
+	__cond_acquires(1, lock) __no_capability_analysis
 {
 	return raw_spin_trylock(&lock->rlock);
 }
@@ -420,13 +420,13 @@ static __always_inline void spin_unlock_irqrestore(spinlock_t *lock, unsigned lo
 }
 
 static __always_inline int spin_trylock_bh(spinlock_t *lock)
-	__cond_acquires(lock) __no_capability_analysis
+	__cond_acquires(1, lock) __no_capability_analysis
 {
 	return raw_spin_trylock_bh(&lock->rlock);
 }
 
 static __always_inline int spin_trylock_irq(spinlock_t *lock)
-	__cond_acquires(lock) __no_capability_analysis
+	__cond_acquires(1, lock) __no_capability_analysis
 {
 	return raw_spin_trylock_irq(&lock->rlock);
 }
diff --git a/include/linux/spinlock_api_smp.h b/include/linux/spinlock_api_smp.h
index fab02d8bf0c9..9b6f7a5a0705 100644
--- a/include/linux/spinlock_api_smp.h
+++ b/include/linux/spinlock_api_smp.h
@@ -34,8 +34,8 @@ unsigned long __lockfunc _raw_spin_lock_irqsave(raw_spinlock_t *lock)
 unsigned long __lockfunc
 _raw_spin_lock_irqsave_nested(raw_spinlock_t *lock, int subclass)
 								__acquires(lock);
-int __lockfunc _raw_spin_trylock(raw_spinlock_t *lock)		__cond_acquires(lock);
-int __lockfunc _raw_spin_trylock_bh(raw_spinlock_t *lock)	__cond_acquires(lock);
+int __lockfunc _raw_spin_trylock(raw_spinlock_t *lock)		__cond_acquires(1, lock);
+int __lockfunc _raw_spin_trylock_bh(raw_spinlock_t *lock)	__cond_acquires(1, lock);
 void __lockfunc _raw_spin_unlock(raw_spinlock_t *lock)		__releases(lock);
 void __lockfunc _raw_spin_unlock_bh(raw_spinlock_t *lock)	__releases(lock);
 void __lockfunc _raw_spin_unlock_irq(raw_spinlock_t *lock)	__releases(lock);
@@ -84,7 +84,7 @@ _raw_spin_unlock_irqrestore(raw_spinlock_t *lock, unsigned long flags)
 #endif
 
 static inline int __raw_spin_trylock(raw_spinlock_t *lock)
-	__cond_acquires(lock)
+	__cond_acquires(1, lock)
 {
 	preempt_disable();
 	if (do_raw_spin_trylock(lock)) {
@@ -177,7 +177,7 @@ static inline void __raw_spin_unlock_bh(raw_spinlock_t *lock)
 }
 
 static inline int __raw_spin_trylock_bh(raw_spinlock_t *lock)
-	__cond_acquires(lock)
+	__cond_acquires(1, lock)
 {
 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_LOCK_OFFSET);
 	if (do_raw_spin_trylock(lock)) {
diff --git a/net/ipv4/tcp_sigpool.c b/net/ipv4/tcp_sigpool.c
index d8a4f192873a..10b2e5970c40 100644
--- a/net/ipv4/tcp_sigpool.c
+++ b/net/ipv4/tcp_sigpool.c
@@ -257,7 +257,7 @@ void tcp_sigpool_get(unsigned int id)
 }
 EXPORT_SYMBOL_GPL(tcp_sigpool_get);
 
-int tcp_sigpool_start(unsigned int id, struct tcp_sigpool *c) __cond_acquires(RCU_BH)
+int tcp_sigpool_start(unsigned int id, struct tcp_sigpool *c) __cond_acquires(0, RCU_BH)
 {
 	struct crypto_ahash *hash;
 
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 11/24] locking/mutex: Support Clang's capability analysis

[Marco Elver]

Add support for Clang's capability analysis for mutex.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |  2 +-
 include/linux/mutex.h                         | 29 +++++----
 include/linux/mutex_types.h                   |  4 +-
 lib/test_capability-analysis.c                | 64 +++++++++++++++++++
 4 files changed, 82 insertions(+), 17 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index 904448605a77..31f76e877be5 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -85,7 +85,7 @@ Supported Kernel Primitives
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Currently the following synchronization primitives are supported:
-`raw_spinlock_t`, `spinlock_t`, `rwlock_t`.
+`raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`.
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 2bf91b57591b..09ee3b89d342 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -62,6 +62,7 @@ do {									\
 	static struct lock_class_key __key;				\
 									\
 	__mutex_init((mutex), #mutex, &__key);				\
+	__assert_cap(mutex);						\
 } while (0)
 
 /**
@@ -154,14 +155,14 @@ static inline int __devm_mutex_init(struct device *dev, struct mutex *lock)
  * Also see Documentation/locking/mutex-design.rst.
  */
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
+extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass) __acquires(lock);
 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 
 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
-					unsigned int subclass);
+					unsigned int subclass) __cond_acquires(0, lock);
 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
-					unsigned int subclass);
-extern void mutex_lock_io_nested(struct mutex *lock, unsigned int subclass);
+					unsigned int subclass) __cond_acquires(0, lock);
+extern void mutex_lock_io_nested(struct mutex *lock, unsigned int subclass) __acquires(lock);
 
 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
@@ -175,10 +176,10 @@ do {									\
 } while (0)
 
 #else
-extern void mutex_lock(struct mutex *lock);
-extern int __must_check mutex_lock_interruptible(struct mutex *lock);
-extern int __must_check mutex_lock_killable(struct mutex *lock);
-extern void mutex_lock_io(struct mutex *lock);
+extern void mutex_lock(struct mutex *lock) __acquires(lock);
+extern int __must_check mutex_lock_interruptible(struct mutex *lock) __cond_acquires(0, lock);
+extern int __must_check mutex_lock_killable(struct mutex *lock) __cond_acquires(0, lock);
+extern void mutex_lock_io(struct mutex *lock) __acquires(lock);
 
 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
@@ -193,13 +194,13 @@ extern void mutex_lock_io(struct mutex *lock);
  *
  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
  */
-extern int mutex_trylock(struct mutex *lock);
-extern void mutex_unlock(struct mutex *lock);
+extern int mutex_trylock(struct mutex *lock) __cond_acquires(1, lock);
+extern void mutex_unlock(struct mutex *lock) __releases(lock);
 
-extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
+extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) __cond_acquires(1, lock);
 
-DEFINE_GUARD(mutex, struct mutex *, mutex_lock(_T), mutex_unlock(_T))
-DEFINE_GUARD_COND(mutex, _try, mutex_trylock(_T))
-DEFINE_GUARD_COND(mutex, _intr, mutex_lock_interruptible(_T) == 0)
+DEFINE_LOCK_GUARD_1(mutex, struct mutex, mutex_lock(_T->lock), mutex_unlock(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(mutex, _try, mutex_trylock(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(mutex, _intr, mutex_lock_interruptible(_T->lock) == 0)
 
 #endif /* __LINUX_MUTEX_H */
diff --git a/include/linux/mutex_types.h b/include/linux/mutex_types.h
index fdf7f515fde8..e1a5ea12d53c 100644
--- a/include/linux/mutex_types.h
+++ b/include/linux/mutex_types.h
@@ -38,7 +38,7 @@
  * - detects multi-task circular deadlocks and prints out all affected
  *   locks and tasks (and only those tasks)
  */
-struct mutex {
+struct_with_capability(mutex) {
 	atomic_long_t		owner;
 	raw_spinlock_t		wait_lock;
 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
@@ -59,7 +59,7 @@ struct mutex {
  */
 #include <linux/rtmutex.h>
 
-struct mutex {
+struct_with_capability(mutex) {
 	struct rt_mutex_base	rtmutex;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index f63980e134cf..3410c04c2b76 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/build_bug.h>
+#include <linux/mutex.h>
 #include <linux/spinlock.h>
 
 /*
@@ -144,3 +145,66 @@ TEST_SPINLOCK_COMMON(read_lock,
 		     read_unlock,
 		     read_trylock,
 		     TEST_OP_RO);
+
+struct test_mutex_data {
+	struct mutex mtx;
+	int counter __var_guarded_by(&mtx);
+};
+
+static void __used test_mutex_init(struct test_mutex_data *d)
+{
+	mutex_init(&d->mtx);
+	d->counter = 0;
+}
+
+static void __used test_mutex_lock(struct test_mutex_data *d)
+{
+	mutex_lock(&d->mtx);
+	d->counter++;
+	mutex_unlock(&d->mtx);
+	mutex_lock_io(&d->mtx);
+	d->counter++;
+	mutex_unlock(&d->mtx);
+}
+
+static void __used test_mutex_trylock(struct test_mutex_data *d, atomic_t *a)
+{
+	if (!mutex_lock_interruptible(&d->mtx)) {
+		d->counter++;
+		mutex_unlock(&d->mtx);
+	}
+	if (!mutex_lock_killable(&d->mtx)) {
+		d->counter++;
+		mutex_unlock(&d->mtx);
+	}
+	if (mutex_trylock(&d->mtx)) {
+		d->counter++;
+		mutex_unlock(&d->mtx);
+	}
+	if (atomic_dec_and_mutex_lock(a, &d->mtx)) {
+		d->counter++;
+		mutex_unlock(&d->mtx);
+	}
+}
+
+static void __used test_mutex_assert(struct test_mutex_data *d)
+{
+	lockdep_assert_held(&d->mtx);
+	d->counter++;
+}
+
+static void __used test_mutex_guard(struct test_mutex_data *d)
+{
+	guard(mutex)(&d->mtx);
+	d->counter++;
+}
+
+static void __used test_mutex_cond_guard(struct test_mutex_data *d)
+{
+	scoped_cond_guard(mutex_try, return, &d->mtx) {
+		d->counter++;
+	}
+	scoped_cond_guard(mutex_intr, return, &d->mtx) {
+		d->counter++;
+	}
+}
-- 
2.48.1.502.g6dc24dfdaf-goog

Re: [PATCH RFC 11/24] locking/mutex: Support Clang's capability analysis

[Peter Zijlstra]

On Thu, Feb 06, 2025 at 07:10:05PM +0100, Marco Elver wrote:

>  extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
> +					unsigned int subclass) __cond_acquires(0, lock);
>  extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
> +					unsigned int subclass) __cond_acquires(0, lock);

> +extern int __must_check mutex_lock_interruptible(struct mutex *lock) __cond_acquires(0, lock);
> +extern int __must_check mutex_lock_killable(struct mutex *lock) __cond_acquires(0, lock);

> +extern int mutex_trylock(struct mutex *lock) __cond_acquires(1, lock);

> +extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) __cond_acquires(1, lock);

So this form is *MUCH* saner than what we currently have.

Can we please fix up all the existing __cond_lock() code too?

Re: [PATCH RFC 11/24] locking/mutex: Support Clang's capability analysis

[Bart Van Assche]

On 2/7/25 12:31 AM, Peter Zijlstra wrote:
> Can we please fix up all the existing __cond_lock() code too?

It would be great to get rid of __cond_lock().

In the description of commit 4a557a5d1a61 ("sparse: introduce
conditional lock acquire function attribute") I found the following
URL: 
https://lore.kernel.org/all/CAHk-=wjZfO9hGqJ2_hGQG3U_XzSh9_XaXze=HgPdvJbgrvASfA@mail.gmail.com/

That URL points at an e-mail from Linus Torvalds with a patch for sparse
that implements support for __cond_acquires(). It seems to me that the
sparse patch has never been applied to the sparse code base (the git URL
for sparse is available at https://sparse.docs.kernel.org/en/latest/).
Additionally, the most recent commit to the sparse code base is from
more than a year ago (see also 
https://git.kernel.org/pub/scm/devel/sparse/sparse.git/).

In other words, switching from __cond_lock() to __cond_acquires()
probably will make sparse report more "context imbalance" warnings.

If this is a concern to anyone, please speak up.

Thanks,

Bart.

[PATCH RFC 12/24] locking/seqlock: Support Clang's capability analysis

[Marco Elver]

Add support for Clang's capability analysis for seqlock_t.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |  2 +-
 include/linux/seqlock.h                       | 24 +++++++++++
 include/linux/seqlock_types.h                 |  5 ++-
 lib/test_capability-analysis.c                | 43 +++++++++++++++++++
 4 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index 31f76e877be5..8d9336e91ce2 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -85,7 +85,7 @@ Supported Kernel Primitives
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Currently the following synchronization primitives are supported:
-`raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`.
+`raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`.
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 5ce48eab7a2a..c914eb9714e9 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -816,6 +816,7 @@ static __always_inline void write_seqcount_latch_end(seqcount_latch_t *s)
 	do {								\
 		spin_lock_init(&(sl)->lock);				\
 		seqcount_spinlock_init(&(sl)->seqcount, &(sl)->lock);	\
+		__assert_cap(sl);					\
 	} while (0)
 
 /**
@@ -832,6 +833,7 @@ static __always_inline void write_seqcount_latch_end(seqcount_latch_t *s)
  * Return: count, to be passed to read_seqretry()
  */
 static inline unsigned read_seqbegin(const seqlock_t *sl)
+	__acquires_shared(sl) __no_capability_analysis
 {
 	return read_seqcount_begin(&sl->seqcount);
 }
@@ -848,6 +850,7 @@ static inline unsigned read_seqbegin(const seqlock_t *sl)
  * Return: true if a read section retry is required, else false
  */
 static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
+	__releases_shared(sl) __no_capability_analysis
 {
 	return read_seqcount_retry(&sl->seqcount, start);
 }
@@ -872,6 +875,7 @@ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
  * _irqsave or _bh variants of this function instead.
  */
 static inline void write_seqlock(seqlock_t *sl)
+	__acquires(sl) __no_capability_analysis
 {
 	spin_lock(&sl->lock);
 	do_write_seqcount_begin(&sl->seqcount.seqcount);
@@ -885,6 +889,7 @@ static inline void write_seqlock(seqlock_t *sl)
  * critical section of given seqlock_t.
  */
 static inline void write_sequnlock(seqlock_t *sl)
+	__releases(sl) __no_capability_analysis
 {
 	do_write_seqcount_end(&sl->seqcount.seqcount);
 	spin_unlock(&sl->lock);
@@ -898,6 +903,7 @@ static inline void write_sequnlock(seqlock_t *sl)
  * other write side sections, can be invoked from softirq contexts.
  */
 static inline void write_seqlock_bh(seqlock_t *sl)
+	__acquires(sl) __no_capability_analysis
 {
 	spin_lock_bh(&sl->lock);
 	do_write_seqcount_begin(&sl->seqcount.seqcount);
@@ -912,6 +918,7 @@ static inline void write_seqlock_bh(seqlock_t *sl)
  * write_seqlock_bh().
  */
 static inline void write_sequnlock_bh(seqlock_t *sl)
+	__releases(sl) __no_capability_analysis
 {
 	do_write_seqcount_end(&sl->seqcount.seqcount);
 	spin_unlock_bh(&sl->lock);
@@ -925,6 +932,7 @@ static inline void write_sequnlock_bh(seqlock_t *sl)
  * other write sections, can be invoked from hardirq contexts.
  */
 static inline void write_seqlock_irq(seqlock_t *sl)
+	__acquires(sl) __no_capability_analysis
 {
 	spin_lock_irq(&sl->lock);
 	do_write_seqcount_begin(&sl->seqcount.seqcount);
@@ -938,12 +946,14 @@ static inline void write_seqlock_irq(seqlock_t *sl)
  * seqlock_t write side section opened with write_seqlock_irq().
  */
 static inline void write_sequnlock_irq(seqlock_t *sl)
+	__releases(sl) __no_capability_analysis
 {
 	do_write_seqcount_end(&sl->seqcount.seqcount);
 	spin_unlock_irq(&sl->lock);
 }
 
 static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
+	__acquires(sl) __no_capability_analysis
 {
 	unsigned long flags;
 
@@ -976,6 +986,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
  */
 static inline void
 write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
+	__releases(sl) __no_capability_analysis
 {
 	do_write_seqcount_end(&sl->seqcount.seqcount);
 	spin_unlock_irqrestore(&sl->lock, flags);
@@ -998,6 +1009,7 @@ write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
  * The opened read section must be closed with read_sequnlock_excl().
  */
 static inline void read_seqlock_excl(seqlock_t *sl)
+	__acquires_shared(sl) __no_capability_analysis
 {
 	spin_lock(&sl->lock);
 }
@@ -1007,6 +1019,7 @@ static inline void read_seqlock_excl(seqlock_t *sl)
  * @sl: Pointer to seqlock_t
  */
 static inline void read_sequnlock_excl(seqlock_t *sl)
+	__releases_shared(sl) __no_capability_analysis
 {
 	spin_unlock(&sl->lock);
 }
@@ -1021,6 +1034,7 @@ static inline void read_sequnlock_excl(seqlock_t *sl)
  * from softirq contexts.
  */
 static inline void read_seqlock_excl_bh(seqlock_t *sl)
+	__acquires_shared(sl) __no_capability_analysis
 {
 	spin_lock_bh(&sl->lock);
 }
@@ -1031,6 +1045,7 @@ static inline void read_seqlock_excl_bh(seqlock_t *sl)
  * @sl: Pointer to seqlock_t
  */
 static inline void read_sequnlock_excl_bh(seqlock_t *sl)
+	__releases_shared(sl) __no_capability_analysis
 {
 	spin_unlock_bh(&sl->lock);
 }
@@ -1045,6 +1060,7 @@ static inline void read_sequnlock_excl_bh(seqlock_t *sl)
  * hardirq context.
  */
 static inline void read_seqlock_excl_irq(seqlock_t *sl)
+	__acquires_shared(sl) __no_capability_analysis
 {
 	spin_lock_irq(&sl->lock);
 }
@@ -1055,11 +1071,13 @@ static inline void read_seqlock_excl_irq(seqlock_t *sl)
  * @sl: Pointer to seqlock_t
  */
 static inline void read_sequnlock_excl_irq(seqlock_t *sl)
+	__releases_shared(sl) __no_capability_analysis
 {
 	spin_unlock_irq(&sl->lock);
 }
 
 static inline unsigned long __read_seqlock_excl_irqsave(seqlock_t *sl)
+	__acquires_shared(sl) __no_capability_analysis
 {
 	unsigned long flags;
 
@@ -1089,6 +1107,7 @@ static inline unsigned long __read_seqlock_excl_irqsave(seqlock_t *sl)
  */
 static inline void
 read_sequnlock_excl_irqrestore(seqlock_t *sl, unsigned long flags)
+	__releases_shared(sl) __no_capability_analysis
 {
 	spin_unlock_irqrestore(&sl->lock, flags);
 }
@@ -1125,6 +1144,7 @@ read_sequnlock_excl_irqrestore(seqlock_t *sl, unsigned long flags)
  * parameter of the next read_seqbegin_or_lock() iteration.
  */
 static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
+	__acquires_shared(lock) __no_capability_analysis
 {
 	if (!(*seq & 1))	/* Even */
 		*seq = read_seqbegin(lock);
@@ -1140,6 +1160,7 @@ static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
  * Return: true if a read section retry is required, false otherwise
  */
 static inline int need_seqretry(seqlock_t *lock, int seq)
+	__releases_shared(lock) __no_capability_analysis
 {
 	return !(seq & 1) && read_seqretry(lock, seq);
 }
@@ -1153,6 +1174,7 @@ static inline int need_seqretry(seqlock_t *lock, int seq)
  * with read_seqbegin_or_lock() and validated by need_seqretry().
  */
 static inline void done_seqretry(seqlock_t *lock, int seq)
+	__no_capability_analysis
 {
 	if (seq & 1)
 		read_sequnlock_excl(lock);
@@ -1180,6 +1202,7 @@ static inline void done_seqretry(seqlock_t *lock, int seq)
  */
 static inline unsigned long
 read_seqbegin_or_lock_irqsave(seqlock_t *lock, int *seq)
+	__acquires_shared(lock) __no_capability_analysis
 {
 	unsigned long flags = 0;
 
@@ -1205,6 +1228,7 @@ read_seqbegin_or_lock_irqsave(seqlock_t *lock, int *seq)
  */
 static inline void
 done_seqretry_irqrestore(seqlock_t *lock, int seq, unsigned long flags)
+	__no_capability_analysis
 {
 	if (seq & 1)
 		read_sequnlock_excl_irqrestore(lock, flags);
diff --git a/include/linux/seqlock_types.h b/include/linux/seqlock_types.h
index dfdf43e3fa3d..9775d6f1a234 100644
--- a/include/linux/seqlock_types.h
+++ b/include/linux/seqlock_types.h
@@ -81,13 +81,14 @@ SEQCOUNT_LOCKNAME(mutex,        struct mutex,    true,     mutex)
  *    - Comments on top of seqcount_t
  *    - Documentation/locking/seqlock.rst
  */
-typedef struct {
+struct_with_capability(seqlock) {
 	/*
 	 * Make sure that readers don't starve writers on PREEMPT_RT: use
 	 * seqcount_spinlock_t instead of seqcount_t. Check __SEQ_LOCK().
 	 */
 	seqcount_spinlock_t seqcount;
 	spinlock_t lock;
-} seqlock_t;
+};
+typedef struct seqlock seqlock_t;
 
 #endif /* __LINUX_SEQLOCK_TYPES_H */
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index 3410c04c2b76..1e4b90f76420 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -6,6 +6,7 @@
 
 #include <linux/build_bug.h>
 #include <linux/mutex.h>
+#include <linux/seqlock.h>
 #include <linux/spinlock.h>
 
 /*
@@ -208,3 +209,45 @@ static void __used test_mutex_cond_guard(struct test_mutex_data *d)
 		d->counter++;
 	}
 }
+
+struct test_seqlock_data {
+	seqlock_t sl;
+	int counter __var_guarded_by(&sl);
+};
+
+static void __used test_seqlock_init(struct test_seqlock_data *d)
+{
+	seqlock_init(&d->sl);
+	d->counter = 0;
+}
+
+static void __used test_seqlock_reader(struct test_seqlock_data *d)
+{
+	unsigned int seq;
+
+	do {
+		seq = read_seqbegin(&d->sl);
+		(void)d->counter;
+	} while (read_seqretry(&d->sl, seq));
+}
+
+static void __used test_seqlock_writer(struct test_seqlock_data *d)
+{
+	unsigned long flags;
+
+	write_seqlock(&d->sl);
+	d->counter++;
+	write_sequnlock(&d->sl);
+
+	write_seqlock_irq(&d->sl);
+	d->counter++;
+	write_sequnlock_irq(&d->sl);
+
+	write_seqlock_bh(&d->sl);
+	d->counter++;
+	write_sequnlock_bh(&d->sl);
+
+	write_seqlock_irqsave(&d->sl, flags);
+	d->counter++;
+	write_sequnlock_irqrestore(&d->sl, flags);
+}
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 13/24] bit_spinlock: Include missing <asm/processor.h>

[Marco Elver]

Including <linux/bit_spinlock.h> into an empty TU will result in the
compiler complaining:

./include/linux/bit_spinlock.h:34:4: error: call to undeclared function 'cpu_relax'; <...>
   34 |                         cpu_relax();
      |                         ^
1 error generated.

Include <asm/processor.h> to allow including bit_spinlock.h where
<asm/processor.h> is not otherwise included.

Signed-off-by: Marco Elver <elver@google.com>
---
 include/linux/bit_spinlock.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
index bbc4730a6505..f1174a2fcc4d 100644
--- a/include/linux/bit_spinlock.h
+++ b/include/linux/bit_spinlock.h
@@ -7,6 +7,8 @@
 #include <linux/atomic.h>
 #include <linux/bug.h>
 
+#include <asm/processor.h>  /* for cpu_relax() */
+
 /*
  *  bit-based spin_lock()
  *
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 14/24] bit_spinlock: Support Clang's capability analysis

[Marco Elver]

The annotations for bit_spinlock.h have simply been using "bitlock" as
the token. For Sparse, that was likely sufficient in most cases. But
Clang's capability analysis is more precise, and we need to ensure we
can distinguish different bitlocks.

To do so, add a token capability, and a macro __bitlock(bitnum, addr)
that is used to construct unique per-bitlock tokens.

Add the appropriate test.

<linux/list_bl.h> is implicitly included through other includes, and
requires 2 annotations to indicate that acquisition (without release)
and release (without prior acquisition) of its bitlock is intended.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |  3 ++-
 include/linux/bit_spinlock.h                  | 22 +++++++++++++---
 include/linux/list_bl.h                       |  2 ++
 lib/test_capability-analysis.c                | 26 +++++++++++++++++++
 4 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index 8d9336e91ce2..a34dfe7b0b09 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -85,7 +85,8 @@ Supported Kernel Primitives
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Currently the following synchronization primitives are supported:
-`raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`.
+`raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`,
+`bit_spinlock`.
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
index f1174a2fcc4d..57114b44ce5d 100644
--- a/include/linux/bit_spinlock.h
+++ b/include/linux/bit_spinlock.h
@@ -9,6 +9,16 @@
 
 #include <asm/processor.h>  /* for cpu_relax() */
 
+/*
+ * For static capability analysis, we need a unique token for each possible bit
+ * that can be used as a bit_spinlock. The easiest way to do that is to create a
+ * fake capability that we can cast to with the __bitlock(bitnum, addr) macro
+ * below, which will give us unique instances for each (bit, addr) pair that the
+ * static analysis can use.
+ */
+struct_with_capability(__capability_bitlock) { };
+#define __bitlock(bitnum, addr) (struct __capability_bitlock *)(bitnum + (addr))
+
 /*
  *  bit-based spin_lock()
  *
@@ -16,6 +26,7 @@
  * are significantly faster.
  */
 static inline void bit_spin_lock(int bitnum, unsigned long *addr)
+	__acquires(__bitlock(bitnum, addr))
 {
 	/*
 	 * Assuming the lock is uncontended, this never enters
@@ -34,13 +45,14 @@ static inline void bit_spin_lock(int bitnum, unsigned long *addr)
 		preempt_disable();
 	}
 #endif
-	__acquire(bitlock);
+	__acquire(__bitlock(bitnum, addr));
 }
 
 /*
  * Return true if it was acquired
  */
 static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
+	__cond_acquires(1, __bitlock(bitnum, addr))
 {
 	preempt_disable();
 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
@@ -49,7 +61,7 @@ static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
 		return 0;
 	}
 #endif
-	__acquire(bitlock);
+	__acquire(__bitlock(bitnum, addr));
 	return 1;
 }
 
@@ -57,6 +69,7 @@ static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
  *  bit-based spin_unlock()
  */
 static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
+	__releases(__bitlock(bitnum, addr))
 {
 #ifdef CONFIG_DEBUG_SPINLOCK
 	BUG_ON(!test_bit(bitnum, addr));
@@ -65,7 +78,7 @@ static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
 	clear_bit_unlock(bitnum, addr);
 #endif
 	preempt_enable();
-	__release(bitlock);
+	__release(__bitlock(bitnum, addr));
 }
 
 /*
@@ -74,6 +87,7 @@ static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
  *  protecting the rest of the flags in the word.
  */
 static inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
+	__releases(__bitlock(bitnum, addr))
 {
 #ifdef CONFIG_DEBUG_SPINLOCK
 	BUG_ON(!test_bit(bitnum, addr));
@@ -82,7 +96,7 @@ static inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
 	__clear_bit_unlock(bitnum, addr);
 #endif
 	preempt_enable();
-	__release(bitlock);
+	__release(__bitlock(bitnum, addr));
 }
 
 /*
diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index ae1b541446c9..df9eebe6afca 100644
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -144,11 +144,13 @@ static inline void hlist_bl_del_init(struct hlist_bl_node *n)
 }
 
 static inline void hlist_bl_lock(struct hlist_bl_head *b)
+	__acquires(__bitlock(0, b))
 {
 	bit_spin_lock(0, (unsigned long *)b);
 }
 
 static inline void hlist_bl_unlock(struct hlist_bl_head *b)
+	__releases(__bitlock(0, b))
 {
 	__bit_spin_unlock(0, (unsigned long *)b);
 }
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index 1e4b90f76420..fc8dcad2a994 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -4,6 +4,7 @@
  * positive errors when compiled with Clang's capability analysis.
  */
 
+#include <linux/bit_spinlock.h>
 #include <linux/build_bug.h>
 #include <linux/mutex.h>
 #include <linux/seqlock.h>
@@ -251,3 +252,28 @@ static void __used test_seqlock_writer(struct test_seqlock_data *d)
 	d->counter++;
 	write_sequnlock_irqrestore(&d->sl, flags);
 }
+
+struct test_bit_spinlock_data {
+	unsigned long bits;
+	int counter __var_guarded_by(__bitlock(3, &bits));
+};
+
+static void __used test_bit_spin_lock(struct test_bit_spinlock_data *d)
+{
+	/*
+	 * Note, the analysis seems to have false negatives, because it won't
+	 * precisely recognize the bit of the fake __bitlock() token.
+	 */
+	bit_spin_lock(3, &d->bits);
+	d->counter++;
+	bit_spin_unlock(3, &d->bits);
+
+	bit_spin_lock(3, &d->bits);
+	d->counter++;
+	__bit_spin_unlock(3, &d->bits);
+
+	if (bit_spin_trylock(3, &d->bits)) {
+		d->counter++;
+		bit_spin_unlock(3, &d->bits);
+	}
+}
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Marco Elver]

Improve the existing annotations to properly support Clang's capability
analysis.

The old annotations distinguished between RCU, RCU_BH, and RCU_SCHED.
However, it does not make sense to acquire rcu_read_lock_bh() after
rcu_read_lock() - annotate the _bh() and _sched() variants to also
acquire 'RCU', so that Clang (and also Sparse) can warn about it.

The above change also simplified introducing annotations, where it would
not matter if RCU, RCU_BH, or RCU_SCHED is acquired: through the
introduction of __rcu_guarded, we can use Clang's capability analysis to
warn if a pointer is dereferenced without any of the RCU locks held, or
updated without the appropriate helpers.

The primitives rcu_assign_pointer() and friends are wrapped with
capability_unsafe(), which enforces using them to update RCU-protected
pointers marked with __rcu_guarded.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |  2 +-
 include/linux/cleanup.h                       |  4 +
 include/linux/rcupdate.h                      | 73 +++++++++++++------
 lib/test_capability-analysis.c                | 68 +++++++++++++++++
 4 files changed, 123 insertions(+), 24 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index a34dfe7b0b09..73dd28a23b11 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -86,7 +86,7 @@ Supported Kernel Primitives
 
 Currently the following synchronization primitives are supported:
 `raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`,
-`bit_spinlock`.
+`bit_spinlock`, RCU.
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index 93a166549add..7d70d308357a 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -404,6 +404,10 @@ static inline class_##_name##_t class_##_name##_constructor(void)	\
 	return _t;							\
 }
 
+#define DECLARE_LOCK_GUARD_0_ATTRS(_name, _lock, _unlock)		\
+static inline class_##_name##_t class_##_name##_constructor(void) _lock;\
+static inline void class_##_name##_destructor(class_##_name##_t *_T) _unlock
+
 #define DEFINE_LOCK_GUARD_1(_name, _type, _lock, _unlock, ...)		\
 __DEFINE_CLASS_IS_CONDITIONAL(_name, false);				\
 __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, __VA_ARGS__)		\
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 48e5c03df1dd..ee68095ba9f0 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -31,6 +31,16 @@
 #include <asm/processor.h>
 #include <linux/context_tracking_irq.h>
 
+token_capability(RCU);
+token_capability_instance(RCU, RCU_SCHED);
+token_capability_instance(RCU, RCU_BH);
+
+/*
+ * A convenience macro that can be used for RCU-protected globals or struct
+ * members; adds type qualifier __rcu, and also enforces __var_guarded_by(RCU).
+ */
+#define __rcu_guarded __rcu __var_guarded_by(RCU)
+
 #define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
 #define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
 
@@ -431,7 +441,8 @@ static inline void rcu_preempt_sleep_check(void) { }
 
 // See RCU_LOCKDEP_WARN() for an explanation of the double call to
 // debug_lockdep_rcu_enabled().
-static inline bool lockdep_assert_rcu_helper(bool c)
+static inline bool lockdep_assert_rcu_helper(bool c, const struct __capability_RCU *cap)
+	__asserts_shared_cap(RCU) __asserts_shared_cap(cap)
 {
 	return debug_lockdep_rcu_enabled() &&
 	       (c || !rcu_is_watching() || !rcu_lockdep_current_cpu_online()) &&
@@ -444,7 +455,7 @@ static inline bool lockdep_assert_rcu_helper(bool c)
  * Splats if lockdep is enabled and there is no rcu_read_lock() in effect.
  */
 #define lockdep_assert_in_rcu_read_lock() \
-	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map)))
+	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map), RCU))
 
 /**
  * lockdep_assert_in_rcu_read_lock_bh - WARN if not protected by rcu_read_lock_bh()
@@ -454,7 +465,7 @@ static inline bool lockdep_assert_rcu_helper(bool c)
  * actual rcu_read_lock_bh() is required.
  */
 #define lockdep_assert_in_rcu_read_lock_bh() \
-	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map)))
+	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map), RCU_BH))
 
 /**
  * lockdep_assert_in_rcu_read_lock_sched - WARN if not protected by rcu_read_lock_sched()
@@ -464,7 +475,7 @@ static inline bool lockdep_assert_rcu_helper(bool c)
  * instead an actual rcu_read_lock_sched() is required.
  */
 #define lockdep_assert_in_rcu_read_lock_sched() \
-	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map)))
+	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map), RCU_SCHED))
 
 /**
  * lockdep_assert_in_rcu_reader - WARN if not within some type of RCU reader
@@ -482,17 +493,17 @@ static inline bool lockdep_assert_rcu_helper(bool c)
 	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map) &&			\
 					       !lock_is_held(&rcu_bh_lock_map) &&		\
 					       !lock_is_held(&rcu_sched_lock_map) &&		\
-					       preemptible()))
+					       preemptible(), RCU))
 
 #else /* #ifdef CONFIG_PROVE_RCU */
 
 #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
 #define rcu_sleep_check() do { } while (0)
 
-#define lockdep_assert_in_rcu_read_lock() do { } while (0)
-#define lockdep_assert_in_rcu_read_lock_bh() do { } while (0)
-#define lockdep_assert_in_rcu_read_lock_sched() do { } while (0)
-#define lockdep_assert_in_rcu_reader() do { } while (0)
+#define lockdep_assert_in_rcu_read_lock() __assert_shared_cap(RCU)
+#define lockdep_assert_in_rcu_read_lock_bh() __assert_shared_cap(RCU_BH)
+#define lockdep_assert_in_rcu_read_lock_sched() __assert_shared_cap(RCU_SCHED)
+#define lockdep_assert_in_rcu_reader() __assert_shared_cap(RCU)
 
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 
@@ -512,11 +523,11 @@ static inline bool lockdep_assert_rcu_helper(bool c)
 #endif /* #else #ifdef __CHECKER__ */
 
 #define __unrcu_pointer(p, local)					\
-({									\
+capability_unsafe(							\
 	typeof(*p) *local = (typeof(*p) *__force)(p);			\
 	rcu_check_sparse(p, __rcu);					\
 	((typeof(*p) __force __kernel *)(local)); 			\
-})
+)
 /**
  * unrcu_pointer - mark a pointer as not being RCU protected
  * @p: pointer needing to lose its __rcu property
@@ -592,7 +603,7 @@ static inline bool lockdep_assert_rcu_helper(bool c)
  * other macros that it invokes.
  */
 #define rcu_assign_pointer(p, v)					      \
-do {									      \
+capability_unsafe(							      \
 	uintptr_t _r_a_p__v = (uintptr_t)(v);				      \
 	rcu_check_sparse(p, __rcu);					      \
 									      \
@@ -600,7 +611,7 @@ do {									      \
 		WRITE_ONCE((p), (typeof(p))(_r_a_p__v));		      \
 	else								      \
 		smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
-} while (0)
+)
 
 /**
  * rcu_replace_pointer() - replace an RCU pointer, returning its old value
@@ -843,9 +854,10 @@ do {									      \
  * only when acquiring spinlocks that are subject to priority inheritance.
  */
 static __always_inline void rcu_read_lock(void)
+	__acquires_shared(RCU)
 {
 	__rcu_read_lock();
-	__acquire(RCU);
+	__acquire_shared(RCU);
 	rcu_lock_acquire(&rcu_lock_map);
 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
 			 "rcu_read_lock() used illegally while idle");
@@ -874,11 +886,12 @@ static __always_inline void rcu_read_lock(void)
  * See rcu_read_lock() for more information.
  */
 static inline void rcu_read_unlock(void)
+	__releases_shared(RCU)
 {
 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
 			 "rcu_read_unlock() used illegally while idle");
 	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
-	__release(RCU);
+	__release_shared(RCU);
 	__rcu_read_unlock();
 }
 
@@ -897,9 +910,11 @@ static inline void rcu_read_unlock(void)
  * was invoked from some other task.
  */
 static inline void rcu_read_lock_bh(void)
+	__acquires_shared(RCU) __acquires_shared(RCU_BH)
 {
 	local_bh_disable();
-	__acquire(RCU_BH);
+	__acquire_shared(RCU);
+	__acquire_shared(RCU_BH);
 	rcu_lock_acquire(&rcu_bh_lock_map);
 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
 			 "rcu_read_lock_bh() used illegally while idle");
@@ -911,11 +926,13 @@ static inline void rcu_read_lock_bh(void)
  * See rcu_read_lock_bh() for more information.
  */
 static inline void rcu_read_unlock_bh(void)
+	__releases_shared(RCU) __releases_shared(RCU_BH)
 {
 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
 			 "rcu_read_unlock_bh() used illegally while idle");
 	rcu_lock_release(&rcu_bh_lock_map);
-	__release(RCU_BH);
+	__release_shared(RCU_BH);
+	__release_shared(RCU);
 	local_bh_enable();
 }
 
@@ -935,9 +952,11 @@ static inline void rcu_read_unlock_bh(void)
  * rcu_read_lock_sched() was invoked from an NMI handler.
  */
 static inline void rcu_read_lock_sched(void)
+	__acquires_shared(RCU) __acquires_shared(RCU_SCHED)
 {
 	preempt_disable();
-	__acquire(RCU_SCHED);
+	__acquire_shared(RCU);
+	__acquire_shared(RCU_SCHED);
 	rcu_lock_acquire(&rcu_sched_lock_map);
 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
 			 "rcu_read_lock_sched() used illegally while idle");
@@ -945,9 +964,11 @@ static inline void rcu_read_lock_sched(void)
 
 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 static inline notrace void rcu_read_lock_sched_notrace(void)
+	__acquires_shared(RCU) __acquires_shared(RCU_SCHED)
 {
 	preempt_disable_notrace();
-	__acquire(RCU_SCHED);
+	__acquire_shared(RCU);
+	__acquire_shared(RCU_SCHED);
 }
 
 /**
@@ -956,18 +977,22 @@ static inline notrace void rcu_read_lock_sched_notrace(void)
  * See rcu_read_lock_sched() for more information.
  */
 static inline void rcu_read_unlock_sched(void)
+	__releases_shared(RCU) __releases_shared(RCU_SCHED)
 {
 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
 			 "rcu_read_unlock_sched() used illegally while idle");
 	rcu_lock_release(&rcu_sched_lock_map);
-	__release(RCU_SCHED);
+	__release_shared(RCU_SCHED);
+	__release_shared(RCU);
 	preempt_enable();
 }
 
 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 static inline notrace void rcu_read_unlock_sched_notrace(void)
+	__releases_shared(RCU) __releases_shared(RCU_SCHED)
 {
-	__release(RCU_SCHED);
+	__release_shared(RCU_SCHED);
+	__release_shared(RCU);
 	preempt_enable_notrace();
 }
 
@@ -1010,10 +1035,10 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * ordering guarantees for either the CPU or the compiler.
  */
 #define RCU_INIT_POINTER(p, v) \
-	do { \
+	capability_unsafe( \
 		rcu_check_sparse(p, __rcu); \
 		WRITE_ONCE(p, RCU_INITIALIZER(v)); \
-	} while (0)
+	)
 
 /**
  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
@@ -1172,4 +1197,6 @@ DEFINE_LOCK_GUARD_0(rcu,
 	} while (0),
 	rcu_read_unlock())
 
+DECLARE_LOCK_GUARD_0_ATTRS(rcu, __acquires_shared(RCU), __releases_shared(RCU));
+
 #endif /* __LINUX_RCUPDATE_H */
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index fc8dcad2a994..f5a1dda6ca38 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -7,6 +7,7 @@
 #include <linux/bit_spinlock.h>
 #include <linux/build_bug.h>
 #include <linux/mutex.h>
+#include <linux/rcupdate.h>
 #include <linux/seqlock.h>
 #include <linux/spinlock.h>
 
@@ -277,3 +278,70 @@ static void __used test_bit_spin_lock(struct test_bit_spinlock_data *d)
 		bit_spin_unlock(3, &d->bits);
 	}
 }
+
+/*
+ * Test that we can mark a variable guarded by RCU, and we can dereference and
+ * write to the pointer with RCU's primitives.
+ */
+struct test_rcu_data {
+	long __rcu_guarded *data;
+};
+
+static void __used test_rcu_guarded_reader(struct test_rcu_data *d)
+{
+	rcu_read_lock();
+	(void)rcu_dereference(d->data);
+	rcu_read_unlock();
+
+	rcu_read_lock_bh();
+	(void)rcu_dereference(d->data);
+	rcu_read_unlock_bh();
+
+	rcu_read_lock_sched();
+	(void)rcu_dereference(d->data);
+	rcu_read_unlock_sched();
+}
+
+static void __used test_rcu_guard(struct test_rcu_data *d)
+{
+	guard(rcu)();
+	(void)rcu_dereference(d->data);
+}
+
+static void __used test_rcu_guarded_updater(struct test_rcu_data *d)
+{
+	rcu_assign_pointer(d->data, NULL);
+	RCU_INIT_POINTER(d->data, NULL);
+	(void)unrcu_pointer(d->data);
+}
+
+static void wants_rcu_held(void)	__must_hold_shared(RCU)       { }
+static void wants_rcu_held_bh(void)	__must_hold_shared(RCU_BH)    { }
+static void wants_rcu_held_sched(void)	__must_hold_shared(RCU_SCHED) { }
+
+static void __used test_rcu_lock_variants(void)
+{
+	rcu_read_lock();
+	wants_rcu_held();
+	rcu_read_unlock();
+
+	rcu_read_lock_bh();
+	wants_rcu_held_bh();
+	rcu_read_unlock_bh();
+
+	rcu_read_lock_sched();
+	wants_rcu_held_sched();
+	rcu_read_unlock_sched();
+}
+
+static void __used test_rcu_assert_variants(void)
+{
+	lockdep_assert_in_rcu_read_lock();
+	wants_rcu_held();
+
+	lockdep_assert_in_rcu_read_lock_bh();
+	wants_rcu_held_bh();
+
+	lockdep_assert_in_rcu_read_lock_sched();
+	wants_rcu_held_sched();
+}
-- 
2.48.1.502.g6dc24dfdaf-goog

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Paul E. McKenney]

On Thu, Feb 06, 2025 at 07:10:09PM +0100, Marco Elver wrote:
> Improve the existing annotations to properly support Clang's capability
> analysis.
> 
> The old annotations distinguished between RCU, RCU_BH, and RCU_SCHED.
> However, it does not make sense to acquire rcu_read_lock_bh() after
> rcu_read_lock() - annotate the _bh() and _sched() variants to also
> acquire 'RCU', so that Clang (and also Sparse) can warn about it.

You lost me on this one.  What breaks if rcu_read_lock_bh() is invoked
while rcu_read_lock() is in effect?

							Thanx, Paul

> The above change also simplified introducing annotations, where it would
> not matter if RCU, RCU_BH, or RCU_SCHED is acquired: through the
> introduction of __rcu_guarded, we can use Clang's capability analysis to
> warn if a pointer is dereferenced without any of the RCU locks held, or
> updated without the appropriate helpers.
> 
> The primitives rcu_assign_pointer() and friends are wrapped with
> capability_unsafe(), which enforces using them to update RCU-protected
> pointers marked with __rcu_guarded.
> 
> Signed-off-by: Marco Elver <elver@google.com>
> ---
>  .../dev-tools/capability-analysis.rst         |  2 +-
>  include/linux/cleanup.h                       |  4 +
>  include/linux/rcupdate.h                      | 73 +++++++++++++------
>  lib/test_capability-analysis.c                | 68 +++++++++++++++++
>  4 files changed, 123 insertions(+), 24 deletions(-)
> 
> diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
> index a34dfe7b0b09..73dd28a23b11 100644
> --- a/Documentation/dev-tools/capability-analysis.rst
> +++ b/Documentation/dev-tools/capability-analysis.rst
> @@ -86,7 +86,7 @@ Supported Kernel Primitives
>  
>  Currently the following synchronization primitives are supported:
>  `raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`,
> -`bit_spinlock`.
> +`bit_spinlock`, RCU.
>  
>  For capabilities with an initialization function (e.g., `spin_lock_init()`),
>  calling this function on the capability instance before initializing any
> diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
> index 93a166549add..7d70d308357a 100644
> --- a/include/linux/cleanup.h
> +++ b/include/linux/cleanup.h
> @@ -404,6 +404,10 @@ static inline class_##_name##_t class_##_name##_constructor(void)	\
>  	return _t;							\
>  }
>  
> +#define DECLARE_LOCK_GUARD_0_ATTRS(_name, _lock, _unlock)		\
> +static inline class_##_name##_t class_##_name##_constructor(void) _lock;\
> +static inline void class_##_name##_destructor(class_##_name##_t *_T) _unlock
> +
>  #define DEFINE_LOCK_GUARD_1(_name, _type, _lock, _unlock, ...)		\
>  __DEFINE_CLASS_IS_CONDITIONAL(_name, false);				\
>  __DEFINE_UNLOCK_GUARD(_name, _type, _unlock, __VA_ARGS__)		\
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 48e5c03df1dd..ee68095ba9f0 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -31,6 +31,16 @@
>  #include <asm/processor.h>
>  #include <linux/context_tracking_irq.h>
>  
> +token_capability(RCU);
> +token_capability_instance(RCU, RCU_SCHED);
> +token_capability_instance(RCU, RCU_BH);
> +
> +/*
> + * A convenience macro that can be used for RCU-protected globals or struct
> + * members; adds type qualifier __rcu, and also enforces __var_guarded_by(RCU).
> + */
> +#define __rcu_guarded __rcu __var_guarded_by(RCU)
> +
>  #define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
>  #define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
>  
> @@ -431,7 +441,8 @@ static inline void rcu_preempt_sleep_check(void) { }
>  
>  // See RCU_LOCKDEP_WARN() for an explanation of the double call to
>  // debug_lockdep_rcu_enabled().
> -static inline bool lockdep_assert_rcu_helper(bool c)
> +static inline bool lockdep_assert_rcu_helper(bool c, const struct __capability_RCU *cap)
> +	__asserts_shared_cap(RCU) __asserts_shared_cap(cap)
>  {
>  	return debug_lockdep_rcu_enabled() &&
>  	       (c || !rcu_is_watching() || !rcu_lockdep_current_cpu_online()) &&
> @@ -444,7 +455,7 @@ static inline bool lockdep_assert_rcu_helper(bool c)
>   * Splats if lockdep is enabled and there is no rcu_read_lock() in effect.
>   */
>  #define lockdep_assert_in_rcu_read_lock() \
> -	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map)))
> +	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map), RCU))
>  
>  /**
>   * lockdep_assert_in_rcu_read_lock_bh - WARN if not protected by rcu_read_lock_bh()
> @@ -454,7 +465,7 @@ static inline bool lockdep_assert_rcu_helper(bool c)
>   * actual rcu_read_lock_bh() is required.
>   */
>  #define lockdep_assert_in_rcu_read_lock_bh() \
> -	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map)))
> +	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map), RCU_BH))
>  
>  /**
>   * lockdep_assert_in_rcu_read_lock_sched - WARN if not protected by rcu_read_lock_sched()
> @@ -464,7 +475,7 @@ static inline bool lockdep_assert_rcu_helper(bool c)
>   * instead an actual rcu_read_lock_sched() is required.
>   */
>  #define lockdep_assert_in_rcu_read_lock_sched() \
> -	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map)))
> +	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map), RCU_SCHED))
>  
>  /**
>   * lockdep_assert_in_rcu_reader - WARN if not within some type of RCU reader
> @@ -482,17 +493,17 @@ static inline bool lockdep_assert_rcu_helper(bool c)
>  	WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map) &&			\
>  					       !lock_is_held(&rcu_bh_lock_map) &&		\
>  					       !lock_is_held(&rcu_sched_lock_map) &&		\
> -					       preemptible()))
> +					       preemptible(), RCU))
>  
>  #else /* #ifdef CONFIG_PROVE_RCU */
>  
>  #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
>  #define rcu_sleep_check() do { } while (0)
>  
> -#define lockdep_assert_in_rcu_read_lock() do { } while (0)
> -#define lockdep_assert_in_rcu_read_lock_bh() do { } while (0)
> -#define lockdep_assert_in_rcu_read_lock_sched() do { } while (0)
> -#define lockdep_assert_in_rcu_reader() do { } while (0)
> +#define lockdep_assert_in_rcu_read_lock() __assert_shared_cap(RCU)
> +#define lockdep_assert_in_rcu_read_lock_bh() __assert_shared_cap(RCU_BH)
> +#define lockdep_assert_in_rcu_read_lock_sched() __assert_shared_cap(RCU_SCHED)
> +#define lockdep_assert_in_rcu_reader() __assert_shared_cap(RCU)
>  
>  #endif /* #else #ifdef CONFIG_PROVE_RCU */
>  
> @@ -512,11 +523,11 @@ static inline bool lockdep_assert_rcu_helper(bool c)
>  #endif /* #else #ifdef __CHECKER__ */
>  
>  #define __unrcu_pointer(p, local)					\
> -({									\
> +capability_unsafe(							\
>  	typeof(*p) *local = (typeof(*p) *__force)(p);			\
>  	rcu_check_sparse(p, __rcu);					\
>  	((typeof(*p) __force __kernel *)(local)); 			\
> -})
> +)
>  /**
>   * unrcu_pointer - mark a pointer as not being RCU protected
>   * @p: pointer needing to lose its __rcu property
> @@ -592,7 +603,7 @@ static inline bool lockdep_assert_rcu_helper(bool c)
>   * other macros that it invokes.
>   */
>  #define rcu_assign_pointer(p, v)					      \
> -do {									      \
> +capability_unsafe(							      \
>  	uintptr_t _r_a_p__v = (uintptr_t)(v);				      \
>  	rcu_check_sparse(p, __rcu);					      \
>  									      \
> @@ -600,7 +611,7 @@ do {									      \
>  		WRITE_ONCE((p), (typeof(p))(_r_a_p__v));		      \
>  	else								      \
>  		smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
> -} while (0)
> +)
>  
>  /**
>   * rcu_replace_pointer() - replace an RCU pointer, returning its old value
> @@ -843,9 +854,10 @@ do {									      \
>   * only when acquiring spinlocks that are subject to priority inheritance.
>   */
>  static __always_inline void rcu_read_lock(void)
> +	__acquires_shared(RCU)
>  {
>  	__rcu_read_lock();
> -	__acquire(RCU);
> +	__acquire_shared(RCU);
>  	rcu_lock_acquire(&rcu_lock_map);
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(),
>  			 "rcu_read_lock() used illegally while idle");
> @@ -874,11 +886,12 @@ static __always_inline void rcu_read_lock(void)
>   * See rcu_read_lock() for more information.
>   */
>  static inline void rcu_read_unlock(void)
> +	__releases_shared(RCU)
>  {
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(),
>  			 "rcu_read_unlock() used illegally while idle");
>  	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
> -	__release(RCU);
> +	__release_shared(RCU);
>  	__rcu_read_unlock();
>  }
>  
> @@ -897,9 +910,11 @@ static inline void rcu_read_unlock(void)
>   * was invoked from some other task.
>   */
>  static inline void rcu_read_lock_bh(void)
> +	__acquires_shared(RCU) __acquires_shared(RCU_BH)
>  {
>  	local_bh_disable();
> -	__acquire(RCU_BH);
> +	__acquire_shared(RCU);
> +	__acquire_shared(RCU_BH);
>  	rcu_lock_acquire(&rcu_bh_lock_map);
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(),
>  			 "rcu_read_lock_bh() used illegally while idle");
> @@ -911,11 +926,13 @@ static inline void rcu_read_lock_bh(void)
>   * See rcu_read_lock_bh() for more information.
>   */
>  static inline void rcu_read_unlock_bh(void)
> +	__releases_shared(RCU) __releases_shared(RCU_BH)
>  {
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(),
>  			 "rcu_read_unlock_bh() used illegally while idle");
>  	rcu_lock_release(&rcu_bh_lock_map);
> -	__release(RCU_BH);
> +	__release_shared(RCU_BH);
> +	__release_shared(RCU);
>  	local_bh_enable();
>  }
>  
> @@ -935,9 +952,11 @@ static inline void rcu_read_unlock_bh(void)
>   * rcu_read_lock_sched() was invoked from an NMI handler.
>   */
>  static inline void rcu_read_lock_sched(void)
> +	__acquires_shared(RCU) __acquires_shared(RCU_SCHED)
>  {
>  	preempt_disable();
> -	__acquire(RCU_SCHED);
> +	__acquire_shared(RCU);
> +	__acquire_shared(RCU_SCHED);
>  	rcu_lock_acquire(&rcu_sched_lock_map);
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(),
>  			 "rcu_read_lock_sched() used illegally while idle");
> @@ -945,9 +964,11 @@ static inline void rcu_read_lock_sched(void)
>  
>  /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
>  static inline notrace void rcu_read_lock_sched_notrace(void)
> +	__acquires_shared(RCU) __acquires_shared(RCU_SCHED)
>  {
>  	preempt_disable_notrace();
> -	__acquire(RCU_SCHED);
> +	__acquire_shared(RCU);
> +	__acquire_shared(RCU_SCHED);
>  }
>  
>  /**
> @@ -956,18 +977,22 @@ static inline notrace void rcu_read_lock_sched_notrace(void)
>   * See rcu_read_lock_sched() for more information.
>   */
>  static inline void rcu_read_unlock_sched(void)
> +	__releases_shared(RCU) __releases_shared(RCU_SCHED)
>  {
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(),
>  			 "rcu_read_unlock_sched() used illegally while idle");
>  	rcu_lock_release(&rcu_sched_lock_map);
> -	__release(RCU_SCHED);
> +	__release_shared(RCU_SCHED);
> +	__release_shared(RCU);
>  	preempt_enable();
>  }
>  
>  /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
>  static inline notrace void rcu_read_unlock_sched_notrace(void)
> +	__releases_shared(RCU) __releases_shared(RCU_SCHED)
>  {
> -	__release(RCU_SCHED);
> +	__release_shared(RCU_SCHED);
> +	__release_shared(RCU);
>  	preempt_enable_notrace();
>  }
>  
> @@ -1010,10 +1035,10 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
>   * ordering guarantees for either the CPU or the compiler.
>   */
>  #define RCU_INIT_POINTER(p, v) \
> -	do { \
> +	capability_unsafe( \
>  		rcu_check_sparse(p, __rcu); \
>  		WRITE_ONCE(p, RCU_INITIALIZER(v)); \
> -	} while (0)
> +	)
>  
>  /**
>   * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
> @@ -1172,4 +1197,6 @@ DEFINE_LOCK_GUARD_0(rcu,
>  	} while (0),
>  	rcu_read_unlock())
>  
> +DECLARE_LOCK_GUARD_0_ATTRS(rcu, __acquires_shared(RCU), __releases_shared(RCU));
> +
>  #endif /* __LINUX_RCUPDATE_H */
> diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
> index fc8dcad2a994..f5a1dda6ca38 100644
> --- a/lib/test_capability-analysis.c
> +++ b/lib/test_capability-analysis.c
> @@ -7,6 +7,7 @@
>  #include <linux/bit_spinlock.h>
>  #include <linux/build_bug.h>
>  #include <linux/mutex.h>
> +#include <linux/rcupdate.h>
>  #include <linux/seqlock.h>
>  #include <linux/spinlock.h>
>  
> @@ -277,3 +278,70 @@ static void __used test_bit_spin_lock(struct test_bit_spinlock_data *d)
>  		bit_spin_unlock(3, &d->bits);
>  	}
>  }
> +
> +/*
> + * Test that we can mark a variable guarded by RCU, and we can dereference and
> + * write to the pointer with RCU's primitives.
> + */
> +struct test_rcu_data {
> +	long __rcu_guarded *data;
> +};
> +
> +static void __used test_rcu_guarded_reader(struct test_rcu_data *d)
> +{
> +	rcu_read_lock();
> +	(void)rcu_dereference(d->data);
> +	rcu_read_unlock();
> +
> +	rcu_read_lock_bh();
> +	(void)rcu_dereference(d->data);
> +	rcu_read_unlock_bh();
> +
> +	rcu_read_lock_sched();
> +	(void)rcu_dereference(d->data);
> +	rcu_read_unlock_sched();
> +}
> +
> +static void __used test_rcu_guard(struct test_rcu_data *d)
> +{
> +	guard(rcu)();
> +	(void)rcu_dereference(d->data);
> +}
> +
> +static void __used test_rcu_guarded_updater(struct test_rcu_data *d)
> +{
> +	rcu_assign_pointer(d->data, NULL);
> +	RCU_INIT_POINTER(d->data, NULL);
> +	(void)unrcu_pointer(d->data);
> +}
> +
> +static void wants_rcu_held(void)	__must_hold_shared(RCU)       { }
> +static void wants_rcu_held_bh(void)	__must_hold_shared(RCU_BH)    { }
> +static void wants_rcu_held_sched(void)	__must_hold_shared(RCU_SCHED) { }
> +
> +static void __used test_rcu_lock_variants(void)
> +{
> +	rcu_read_lock();
> +	wants_rcu_held();
> +	rcu_read_unlock();
> +
> +	rcu_read_lock_bh();
> +	wants_rcu_held_bh();
> +	rcu_read_unlock_bh();
> +
> +	rcu_read_lock_sched();
> +	wants_rcu_held_sched();
> +	rcu_read_unlock_sched();
> +}
> +
> +static void __used test_rcu_assert_variants(void)
> +{
> +	lockdep_assert_in_rcu_read_lock();
> +	wants_rcu_held();
> +
> +	lockdep_assert_in_rcu_read_lock_bh();
> +	wants_rcu_held_bh();
> +
> +	lockdep_assert_in_rcu_read_lock_sched();
> +	wants_rcu_held_sched();
> +}
> -- 
> 2.48.1.502.g6dc24dfdaf-goog
> 

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Marco Elver]

On Thu, 20 Feb 2025 at 23:00, Paul E. McKenney <paulmck@kernel.org> wrote:
>
> On Thu, Feb 06, 2025 at 07:10:09PM +0100, Marco Elver wrote:
> > Improve the existing annotations to properly support Clang's capability
> > analysis.
> >
> > The old annotations distinguished between RCU, RCU_BH, and RCU_SCHED.
> > However, it does not make sense to acquire rcu_read_lock_bh() after
> > rcu_read_lock() - annotate the _bh() and _sched() variants to also
> > acquire 'RCU', so that Clang (and also Sparse) can warn about it.
>
> You lost me on this one.  What breaks if rcu_read_lock_bh() is invoked
> while rcu_read_lock() is in effect?

I thought something like this does not make sense:

  rcu_read_lock_bh();
  ..
  rcu_read_lock();
  ..
  rcu_read_unlock();
  ..
  rcu_read_unlock_bh();

However, the inverse may well be something we might find somewhere in
the kernel?
Another problem was that if we want to indicate that "RCU" read lock
is held, then we should just be able to write
"__must_hold_shared(RCU)", and it shouldn't matter if rcu_read_lock()
or rcu_read_lock_bh() was used. Previously each of them acquired their
own capability "RCU" and "RCU_BH" respectively. But rather, we're
dealing with one acquiring a superset of the other, and expressing
that is also what I attempted to solve.
Let me rethink this...

Thanks,
-- Marco

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Paul E. McKenney]

On Thu, Feb 20, 2025 at 11:11:04PM +0100, Marco Elver wrote:
> On Thu, 20 Feb 2025 at 23:00, Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > On Thu, Feb 06, 2025 at 07:10:09PM +0100, Marco Elver wrote:
> > > Improve the existing annotations to properly support Clang's capability
> > > analysis.
> > >
> > > The old annotations distinguished between RCU, RCU_BH, and RCU_SCHED.
> > > However, it does not make sense to acquire rcu_read_lock_bh() after
> > > rcu_read_lock() - annotate the _bh() and _sched() variants to also
> > > acquire 'RCU', so that Clang (and also Sparse) can warn about it.
> >
> > You lost me on this one.  What breaks if rcu_read_lock_bh() is invoked
> > while rcu_read_lock() is in effect?
> 
> I thought something like this does not make sense:
> 
>   rcu_read_lock_bh();
>   ..
>   rcu_read_lock();
>   ..
>   rcu_read_unlock();
>   ..
>   rcu_read_unlock_bh();

If you have the choice, it is often better to do the rcu_read_lock()
first and the rcu_read_lock_bh() second.

> However, the inverse may well be something we might find somewhere in
> the kernel?

Suppose that one function walks an RCU-protected list, calling some
function from some other subsystem on each element.  Suppose that each
element has another RCU protected list.

It would be good if the two subsystems could just choose their desired
flavor of RCU reader, without having to know about each other.

> Another problem was that if we want to indicate that "RCU" read lock
> is held, then we should just be able to write
> "__must_hold_shared(RCU)", and it shouldn't matter if rcu_read_lock()
> or rcu_read_lock_bh() was used. Previously each of them acquired their
> own capability "RCU" and "RCU_BH" respectively. But rather, we're
> dealing with one acquiring a superset of the other, and expressing
> that is also what I attempted to solve.
> Let me rethink this...

Would it work to have just one sort of RCU reader, relying on a separate
BH-disable capability for the additional semantics of rcu_read_lock_bh()?

							Thanx, Paul

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Marco Elver]

On Thu, 20 Feb 2025 at 23:36, Paul E. McKenney <paulmck@kernel.org> wrote:
[...]
> Suppose that one function walks an RCU-protected list, calling some
> function from some other subsystem on each element.  Suppose that each
> element has another RCU protected list.
>
> It would be good if the two subsystems could just choose their desired
> flavor of RCU reader, without having to know about each other.

That's what I figured might be the case - thanks for clarifying.

> > Another problem was that if we want to indicate that "RCU" read lock
> > is held, then we should just be able to write
> > "__must_hold_shared(RCU)", and it shouldn't matter if rcu_read_lock()
> > or rcu_read_lock_bh() was used. Previously each of them acquired their
> > own capability "RCU" and "RCU_BH" respectively. But rather, we're
> > dealing with one acquiring a superset of the other, and expressing
> > that is also what I attempted to solve.
> > Let me rethink this...
>
> Would it work to have just one sort of RCU reader, relying on a separate
> BH-disable capability for the additional semantics of rcu_read_lock_bh()?

That's what I've tried with this patch (rcu_read_lock_bh() also
acquires "RCU", on top of "RCU_BH"). I need to add a re-entrancy test,
and make sure it doesn't complain about that. At a later stage we
might also want to add more general "BH" and "IRQ" capabilities to
denote they're disabled when held, but that'd overcomplicate the first
version of this series.

Thanks,
-- Marco

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Paul E. McKenney]

On Fri, Feb 21, 2025 at 01:16:00AM +0100, Marco Elver wrote:
> On Thu, 20 Feb 2025 at 23:36, Paul E. McKenney <paulmck@kernel.org> wrote:
> [...]
> > Suppose that one function walks an RCU-protected list, calling some
> > function from some other subsystem on each element.  Suppose that each
> > element has another RCU protected list.
> >
> > It would be good if the two subsystems could just choose their desired
> > flavor of RCU reader, without having to know about each other.
> 
> That's what I figured might be the case - thanks for clarifying.
> 
> > > Another problem was that if we want to indicate that "RCU" read lock
> > > is held, then we should just be able to write
> > > "__must_hold_shared(RCU)", and it shouldn't matter if rcu_read_lock()
> > > or rcu_read_lock_bh() was used. Previously each of them acquired their
> > > own capability "RCU" and "RCU_BH" respectively. But rather, we're
> > > dealing with one acquiring a superset of the other, and expressing
> > > that is also what I attempted to solve.
> > > Let me rethink this...
> >
> > Would it work to have just one sort of RCU reader, relying on a separate
> > BH-disable capability for the additional semantics of rcu_read_lock_bh()?
> 
> That's what I've tried with this patch (rcu_read_lock_bh() also
> acquires "RCU", on top of "RCU_BH"). I need to add a re-entrancy test,
> and make sure it doesn't complain about that. At a later stage we
> might also want to add more general "BH" and "IRQ" capabilities to
> denote they're disabled when held, but that'd overcomplicate the first
> version of this series.

Fair enough!  Then would it work to just do "RCU" now, and ad the "BH"
and "IRQ" when those capabilities are added?

							Thanx, Paul

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Marco Elver]

On Thu, Feb 20, 2025 at 05:26PM -0800, Paul E. McKenney wrote:
[...]
> > That's what I've tried with this patch (rcu_read_lock_bh() also
> > acquires "RCU", on top of "RCU_BH"). I need to add a re-entrancy test,
> > and make sure it doesn't complain about that. At a later stage we
> > might also want to add more general "BH" and "IRQ" capabilities to
> > denote they're disabled when held, but that'd overcomplicate the first
> > version of this series.
> 
> Fair enough!  Then would it work to just do "RCU" now, and ad the "BH"
> and "IRQ" when those capabilities are added?

I tried if this kind of re-entrant locking works - a test like this:

 | --- a/lib/test_capability-analysis.c
 | +++ b/lib/test_capability-analysis.c
 | @@ -370,6 +370,15 @@ static void __used test_rcu_guarded_reader(struct test_rcu_data *d)
 |  	rcu_read_unlock_sched();
 |  }
 |  
 | +static void __used test_rcu_reentrancy(struct test_rcu_data *d)
 | +{
 | +	rcu_read_lock();
 | +	rcu_read_lock_bh();
 | +	(void)rcu_dereference(d->data);
 | +	rcu_read_unlock_bh();
 | +	rcu_read_unlock();
 | +}


 | $ make lib/test_capability-analysis.o
 |   DESCEND objtool
 |   CC      arch/x86/kernel/asm-offsets.s
 |   INSTALL libsubcmd_headers
 |   CALL    scripts/checksyscalls.sh
 |   CC      lib/test_capability-analysis.o
 | lib/test_capability-analysis.c:376:2: error: acquiring __capability_RCU 'RCU' that is already held [-Werror,-Wthread-safety-analysis]
 |   376 |         rcu_read_lock_bh();
 |       |         ^
 | lib/test_capability-analysis.c:375:2: note: __capability_RCU acquired here
 |   375 |         rcu_read_lock();
 |       |         ^
 | lib/test_capability-analysis.c:379:2: error: releasing __capability_RCU 'RCU' that was not held [-Werror,-Wthread-safety-analysis]
 |   379 |         rcu_read_unlock();
 |       |         ^
 | lib/test_capability-analysis.c:378:2: note: __capability_RCU released here
 |   378 |         rcu_read_unlock_bh();
 |       |         ^
 | 2 errors generated.
 | make[3]: *** [scripts/Makefile.build:207: lib/test_capability-analysis.o] Error 1
 | make[2]: *** [scripts/Makefile.build:465: lib] Error 2


... unfortunately even for shared locks, the compiler does not like
re-entrancy yet. It's not yet supported, and to fix that I'd have to go
and implement that in Clang first before coming back to this.

I see 2 options for now:

  a. Accepting the limitation that doing a rcu_read_lock() (and
     variants) while the RCU read lock is already held in the same function
     will result in a false positive warning (like above). Cases like that
     will need to disable the analysis for that piece of code.

  b. Make the compiler not warn about unbalanced rcu_read_lock/unlock(),
     but instead just help enforce a rcu_read_lock() was issued somewhere
     in the function before an RCU-guarded access.

Option (b) is obviously weaker than (a), but avoids the false positives
while accepting more false negatives.

For all the code that I have already tested this on I observed no false
positives, so I'd go with (a), but I'm also fine with the weaker
checking for now until the compiler gains re-entrancy support.

Preferences?

Thanks,
-- Marco

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Paul E. McKenney]

On Fri, Feb 21, 2025 at 06:10:02PM +0100, Marco Elver wrote:
> On Thu, Feb 20, 2025 at 05:26PM -0800, Paul E. McKenney wrote:
> [...]
> > > That's what I've tried with this patch (rcu_read_lock_bh() also
> > > acquires "RCU", on top of "RCU_BH"). I need to add a re-entrancy test,
> > > and make sure it doesn't complain about that. At a later stage we
> > > might also want to add more general "BH" and "IRQ" capabilities to
> > > denote they're disabled when held, but that'd overcomplicate the first
> > > version of this series.
> > 
> > Fair enough!  Then would it work to just do "RCU" now, and ad the "BH"
> > and "IRQ" when those capabilities are added?
> 
> I tried if this kind of re-entrant locking works - a test like this:
> 
>  | --- a/lib/test_capability-analysis.c
>  | +++ b/lib/test_capability-analysis.c
>  | @@ -370,6 +370,15 @@ static void __used test_rcu_guarded_reader(struct test_rcu_data *d)
>  |  	rcu_read_unlock_sched();
>  |  }
>  |  
>  | +static void __used test_rcu_reentrancy(struct test_rcu_data *d)
>  | +{
>  | +	rcu_read_lock();
>  | +	rcu_read_lock_bh();
>  | +	(void)rcu_dereference(d->data);
>  | +	rcu_read_unlock_bh();
>  | +	rcu_read_unlock();
>  | +}
> 
> 
>  | $ make lib/test_capability-analysis.o
>  |   DESCEND objtool
>  |   CC      arch/x86/kernel/asm-offsets.s
>  |   INSTALL libsubcmd_headers
>  |   CALL    scripts/checksyscalls.sh
>  |   CC      lib/test_capability-analysis.o
>  | lib/test_capability-analysis.c:376:2: error: acquiring __capability_RCU 'RCU' that is already held [-Werror,-Wthread-safety-analysis]
>  |   376 |         rcu_read_lock_bh();
>  |       |         ^
>  | lib/test_capability-analysis.c:375:2: note: __capability_RCU acquired here
>  |   375 |         rcu_read_lock();
>  |       |         ^
>  | lib/test_capability-analysis.c:379:2: error: releasing __capability_RCU 'RCU' that was not held [-Werror,-Wthread-safety-analysis]
>  |   379 |         rcu_read_unlock();
>  |       |         ^
>  | lib/test_capability-analysis.c:378:2: note: __capability_RCU released here
>  |   378 |         rcu_read_unlock_bh();
>  |       |         ^
>  | 2 errors generated.
>  | make[3]: *** [scripts/Makefile.build:207: lib/test_capability-analysis.o] Error 1
>  | make[2]: *** [scripts/Makefile.build:465: lib] Error 2

I was hoping!  Ah well...  ;-)

> ... unfortunately even for shared locks, the compiler does not like
> re-entrancy yet. It's not yet supported, and to fix that I'd have to go
> and implement that in Clang first before coming back to this.

This would be needed for some types of reader-writer locks, and also for
reference counting, so here is hoping that such support is forthcoming
sooner rather than later.

> I see 2 options for now:
> 
>   a. Accepting the limitation that doing a rcu_read_lock() (and
>      variants) while the RCU read lock is already held in the same function
>      will result in a false positive warning (like above). Cases like that
>      will need to disable the analysis for that piece of code.
> 
>   b. Make the compiler not warn about unbalanced rcu_read_lock/unlock(),
>      but instead just help enforce a rcu_read_lock() was issued somewhere
>      in the function before an RCU-guarded access.
> 
> Option (b) is obviously weaker than (a), but avoids the false positives
> while accepting more false negatives.
> 
> For all the code that I have already tested this on I observed no false
> positives, so I'd go with (a), but I'm also fine with the weaker
> checking for now until the compiler gains re-entrancy support.
> 
> Preferences?

Whichever one provides the best checking without false positives.
Which sounds to me like (a) unless and until false positives crop up,
in which case (b).  Which looks to be where you were going anyway.  ;-)

							Thanx, Paul

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Peter Zijlstra]

On Fri, Feb 21, 2025 at 10:08:06AM -0800, Paul E. McKenney wrote:

> > ... unfortunately even for shared locks, the compiler does not like
> > re-entrancy yet. It's not yet supported, and to fix that I'd have to go
> > and implement that in Clang first before coming back to this.
> 
> This would be needed for some types of reader-writer locks, and also for
> reference counting, so here is hoping that such support is forthcoming
> sooner rather than later.

Right, so I read the clang documentation for this feature the other day,
and my take away was that this was all really primitive and lots of work
will need to go into making this more capable before we can cover much
of the more interesting things we do in the kernel.

Notably the whole guarded_by member annotations, which are very cool in
concept, are very primitive in practise and will need much extensions.

To that effect, and because this is basically a static analysis pass
with no codegen implications, I would suggest that we keep the whole
feature limited to the very latest clang version for now and don't
bother supporting older versions at all.

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Marco Elver]

On Fri, 21 Feb 2025 at 19:52, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Feb 21, 2025 at 10:08:06AM -0800, Paul E. McKenney wrote:
>
> > > ... unfortunately even for shared locks, the compiler does not like
> > > re-entrancy yet. It's not yet supported, and to fix that I'd have to go
> > > and implement that in Clang first before coming back to this.
> >
> > This would be needed for some types of reader-writer locks, and also for
> > reference counting, so here is hoping that such support is forthcoming
> > sooner rather than later.
>
> Right, so I read the clang documentation for this feature the other day,
> and my take away was that this was all really primitive and lots of work
> will need to go into making this more capable before we can cover much
> of the more interesting things we do in the kernel.
>
> Notably the whole guarded_by member annotations, which are very cool in
> concept, are very primitive in practise and will need much extensions.

I have one extension in flight:
https://github.com/llvm/llvm-project/pull/127396 - it'll improve
coverage for pointer passing of guarded_by members.

Anything else you see as urgent? Re-entrant locks support a deal breaker?

But yes, a lot of complex locking patterns will not easily be
expressible right away.

> To that effect, and because this is basically a static analysis pass
> with no codegen implications, I would suggest that we keep the whole
> feature limited to the very latest clang version for now and don't
> bother supporting older versions at all.

Along those lines, in an upcoming v2, I'm planning to bump it up to
Clang 20+ because that version introduced a reasonable way to ignore
warnings in not-yet-annotated headers:
https://git.kernel.org/pub/scm/linux/kernel/git/melver/linux.git/commit/?h=cap-analysis/dev&id=2432a39eae8197f5058c578430bd1906c18480c3

Re: [PATCH RFC 15/24] rcu: Support Clang's capability analysis

[Peter Zijlstra]

On Fri, Feb 21, 2025 at 08:46:45PM +0100, Marco Elver wrote:

> Anything else you see as urgent? Re-entrant locks support a deal breaker?

Most actual locks are not recursive -- RCU being the big exception here.

As to this being deal breakers, I don't think so. We should just start
with the bits we can do and chip away at stuff. Raise the LLVM version
requirement every time new stuff gets added.

[PATCH RFC 16/24] srcu: Support Clang's capability analysis

[Marco Elver]

Add support for Clang's capability analysis for SRCU.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |  2 +-
 include/linux/srcu.h                          | 61 +++++++++++++------
 lib/test_capability-analysis.c                | 24 ++++++++
 3 files changed, 66 insertions(+), 21 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index 73dd28a23b11..3766ac466470 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -86,7 +86,7 @@ Supported Kernel Primitives
 
 Currently the following synchronization primitives are supported:
 `raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`,
-`bit_spinlock`, RCU.
+`bit_spinlock`, RCU, SRCU (`srcu_struct`).
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index d7ba46e74f58..560310643c54 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -21,7 +21,7 @@
 #include <linux/workqueue.h>
 #include <linux/rcu_segcblist.h>
 
-struct srcu_struct;
+struct_with_capability(srcu_struct);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
@@ -60,14 +60,14 @@ int init_srcu_struct(struct srcu_struct *ssp);
 void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
 		void (*func)(struct rcu_head *head));
 void cleanup_srcu_struct(struct srcu_struct *ssp);
-int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
-void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
+int __srcu_read_lock(struct srcu_struct *ssp) __acquires_shared(ssp);
+void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases_shared(ssp);
 #ifdef CONFIG_TINY_SRCU
 #define __srcu_read_lock_lite __srcu_read_lock
 #define __srcu_read_unlock_lite __srcu_read_unlock
 #else // #ifdef CONFIG_TINY_SRCU
-int __srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp);
-void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) __releases(ssp);
+int __srcu_read_lock_lite(struct srcu_struct *ssp) __acquires_shared(ssp);
+void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) __releases_shared(ssp);
 #endif // #else // #ifdef CONFIG_TINY_SRCU
 void synchronize_srcu(struct srcu_struct *ssp);
 
@@ -110,14 +110,16 @@ static inline bool same_state_synchronize_srcu(unsigned long oldstate1, unsigned
 }
 
 #ifdef CONFIG_NEED_SRCU_NMI_SAFE
-int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
-void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);
+int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires_shared(ssp);
+void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases_shared(ssp);
 #else
 static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	return __srcu_read_lock(ssp);
 }
 static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
+	__releases_shared(ssp)
 {
 	__srcu_read_unlock(ssp, idx);
 }
@@ -189,6 +191,14 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
+/*
+ * No-op helper to denote that ssp must be held. Because SRCU-protected pointers
+ * should still be marked with __rcu_guarded, and we do not want to mark them
+ * with __var_guarded_by(ssp) as it would complicate annotations for writers, we
+ * choose the following strategy: srcu_dereference_check() calls this helper
+ * that checks that the passed ssp is held, and then fake-acquires 'RCU'.
+ */
+static inline void __srcu_read_lock_must_hold(const struct srcu_struct *ssp) __must_hold_shared(ssp) { }
 
 /**
  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
@@ -202,9 +212,15 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
  * to 1.  The @c argument will normally be a logical expression containing
  * lockdep_is_held() calls.
  */
-#define srcu_dereference_check(p, ssp, c) \
-	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
-				(c) || srcu_read_lock_held(ssp), __rcu)
+#define srcu_dereference_check(p, ssp, c)					\
+({										\
+	__srcu_read_lock_must_hold(ssp);					\
+	__acquire_shared_cap(RCU);						\
+	__auto_type __v = __rcu_dereference_check((p), __UNIQUE_ID(rcu),	\
+				(c) || srcu_read_lock_held(ssp), __rcu);	\
+	__release_shared_cap(RCU);						\
+	__v;									\
+})
 
 /**
  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
@@ -247,7 +263,8 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
  * invoke srcu_read_unlock() from one task and the matching srcu_read_lock()
  * from another.
  */
-static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
+static inline int srcu_read_lock(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int retval;
 
@@ -274,7 +291,8 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
  * where RCU is watching, that is, from contexts where it would be legal
  * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
  */
-static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
+static inline int srcu_read_lock_lite(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int retval;
 
@@ -295,7 +313,8 @@ static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
  * then none of the other flavors may be used, whether before, during,
  * or after.
  */
-static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
+static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int retval;
 
@@ -307,7 +326,8 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp
 
 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
 static inline notrace int
-srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
+srcu_read_lock_notrace(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int retval;
 
@@ -337,7 +357,8 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
  * Calls to srcu_down_read() may be nested, similar to the manner in
  * which calls to down_read() may be nested.
  */
-static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
+static inline int srcu_down_read(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	WARN_ON_ONCE(in_nmi());
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
@@ -352,7 +373,7 @@ static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
  * Exit an SRCU read-side critical section.
  */
 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
@@ -368,7 +389,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
  * Exit a light-weight SRCU read-side critical section.
  */
 static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
@@ -384,7 +405,7 @@ static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
  * Exit an SRCU read-side critical section, but in an NMI-safe manner.
  */
 static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
@@ -394,7 +415,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 
 /* Used by tracing, cannot be traced and cannot call lockdep. */
 static inline notrace void
-srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
+srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases_shared(ssp)
 {
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	__srcu_read_unlock(ssp, idx);
@@ -409,7 +430,7 @@ srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
  * the same context as the maching srcu_down_read().
  */
 static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	WARN_ON_ONCE(in_nmi());
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index f5a1dda6ca38..8bc8c3e6cb5c 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -10,6 +10,7 @@
 #include <linux/rcupdate.h>
 #include <linux/seqlock.h>
 #include <linux/spinlock.h>
+#include <linux/srcu.h>
 
 /*
  * Test that helper macros work as expected.
@@ -345,3 +346,26 @@ static void __used test_rcu_assert_variants(void)
 	lockdep_assert_in_rcu_read_lock_sched();
 	wants_rcu_held_sched();
 }
+
+struct test_srcu_data {
+	struct srcu_struct srcu;
+	long __rcu_guarded *data;
+};
+
+static void __used test_srcu(struct test_srcu_data *d)
+{
+	init_srcu_struct(&d->srcu);
+
+	int idx = srcu_read_lock(&d->srcu);
+	long *data = srcu_dereference(d->data, &d->srcu);
+	(void)data;
+	srcu_read_unlock(&d->srcu, idx);
+
+	rcu_assign_pointer(d->data, NULL);
+}
+
+static void __used test_srcu_guard(struct test_srcu_data *d)
+{
+	guard(srcu)(&d->srcu);
+	(void)srcu_dereference(d->data, &d->srcu);
+}
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 17/24] kref: Add capability-analysis annotations

[Marco Elver]

Mark functions that conditionally acquire the passed lock.

Signed-off-by: Marco Elver <elver@google.com>
---
 include/linux/kref.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/kref.h b/include/linux/kref.h
index 88e82ab1367c..c1bd26936f41 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -81,6 +81,7 @@ static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)
 static inline int kref_put_mutex(struct kref *kref,
 				 void (*release)(struct kref *kref),
 				 struct mutex *mutex)
+	__cond_acquires(1, mutex)
 {
 	if (refcount_dec_and_mutex_lock(&kref->refcount, mutex)) {
 		release(kref);
@@ -102,6 +103,7 @@ static inline int kref_put_mutex(struct kref *kref,
 static inline int kref_put_lock(struct kref *kref,
 				void (*release)(struct kref *kref),
 				spinlock_t *lock)
+	__cond_acquires(1, lock)
 {
 	if (refcount_dec_and_lock(&kref->refcount, lock)) {
 		release(kref);
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 18/24] locking/rwsem: Support Clang's capability analysis

[Marco Elver]

Add support for Clang's capability analysis for rw_semaphore.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |  2 +-
 include/linux/rwsem.h                         | 56 +++++++++-------
 lib/test_capability-analysis.c                | 64 +++++++++++++++++++
 3 files changed, 97 insertions(+), 25 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index 3766ac466470..719986739b0e 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -86,7 +86,7 @@ Supported Kernel Primitives
 
 Currently the following synchronization primitives are supported:
 `raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`,
-`bit_spinlock`, RCU, SRCU (`srcu_struct`).
+`bit_spinlock`, RCU, SRCU (`srcu_struct`), `rw_semaphore`.
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index c8b543d428b0..0c84e3072370 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -45,7 +45,7 @@
  * reduce the chance that they will share the same cacheline causing
  * cacheline bouncing problem.
  */
-struct rw_semaphore {
+struct_with_capability(rw_semaphore) {
 	atomic_long_t count;
 	/*
 	 * Write owner or one of the read owners as well flags regarding
@@ -76,11 +76,13 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
 }
 
 static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
+	__asserts_cap(sem)
 {
 	WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE);
 }
 
 static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
+	__asserts_cap(sem)
 {
 	WARN_ON(!(atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED));
 }
@@ -119,6 +121,7 @@ do {								\
 	static struct lock_class_key __key;			\
 								\
 	__init_rwsem((sem), #sem, &__key);			\
+	__assert_cap(sem);					\
 } while (0)
 
 /*
@@ -136,7 +139,7 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem)
 
 #include <linux/rwbase_rt.h>
 
-struct rw_semaphore {
+struct_with_capability(rw_semaphore) {
 	struct rwbase_rt	rwbase;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
@@ -160,6 +163,7 @@ do {								\
 	static struct lock_class_key __key;			\
 								\
 	__init_rwsem((sem), #sem, &__key);			\
+	__assert_cap(sem);					\
 } while (0)
 
 static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem)
@@ -168,11 +172,13 @@ static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem)
 }
 
 static __always_inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
+	__asserts_cap(sem)
 {
 	WARN_ON(!rwsem_is_locked(sem));
 }
 
 static __always_inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
+	__asserts_cap(sem)
 {
 	WARN_ON(!rw_base_is_write_locked(&sem->rwbase));
 }
@@ -190,6 +196,7 @@ static __always_inline int rwsem_is_contended(struct rw_semaphore *sem)
  */
 
 static inline void rwsem_assert_held(const struct rw_semaphore *sem)
+	__asserts_cap(sem)
 {
 	if (IS_ENABLED(CONFIG_LOCKDEP))
 		lockdep_assert_held(sem);
@@ -198,6 +205,7 @@ static inline void rwsem_assert_held(const struct rw_semaphore *sem)
 }
 
 static inline void rwsem_assert_held_write(const struct rw_semaphore *sem)
+	__asserts_cap(sem)
 {
 	if (IS_ENABLED(CONFIG_LOCKDEP))
 		lockdep_assert_held_write(sem);
@@ -208,47 +216,47 @@ static inline void rwsem_assert_held_write(const struct rw_semaphore *sem)
 /*
  * lock for reading
  */
-extern void down_read(struct rw_semaphore *sem);
-extern int __must_check down_read_interruptible(struct rw_semaphore *sem);
-extern int __must_check down_read_killable(struct rw_semaphore *sem);
+extern void down_read(struct rw_semaphore *sem) __acquires_shared(sem);
+extern int __must_check down_read_interruptible(struct rw_semaphore *sem) __cond_acquires_shared(0, sem);
+extern int __must_check down_read_killable(struct rw_semaphore *sem) __cond_acquires_shared(0, sem);
 
 /*
  * trylock for reading -- returns 1 if successful, 0 if contention
  */
-extern int down_read_trylock(struct rw_semaphore *sem);
+extern int down_read_trylock(struct rw_semaphore *sem) __cond_acquires_shared(1, sem);
 
 /*
  * lock for writing
  */
-extern void down_write(struct rw_semaphore *sem);
-extern int __must_check down_write_killable(struct rw_semaphore *sem);
+extern void down_write(struct rw_semaphore *sem) __acquires(sem);
+extern int __must_check down_write_killable(struct rw_semaphore *sem) __cond_acquires(0, sem);
 
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
-extern int down_write_trylock(struct rw_semaphore *sem);
+extern int down_write_trylock(struct rw_semaphore *sem) __cond_acquires(1, sem);
 
 /*
  * release a read lock
  */
-extern void up_read(struct rw_semaphore *sem);
+extern void up_read(struct rw_semaphore *sem) __releases_shared(sem);
 
 /*
  * release a write lock
  */
-extern void up_write(struct rw_semaphore *sem);
+extern void up_write(struct rw_semaphore *sem) __releases(sem);
 
-DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T))
-DEFINE_GUARD_COND(rwsem_read, _try, down_read_trylock(_T))
-DEFINE_GUARD_COND(rwsem_read, _intr, down_read_interruptible(_T) == 0)
+DEFINE_LOCK_GUARD_1(rwsem_read, struct rw_semaphore, down_read(_T->lock), up_read(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(rwsem_read, _try, down_read_trylock(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(rwsem_read, _intr, down_read_interruptible(_T->lock) == 0)
 
-DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T))
-DEFINE_GUARD_COND(rwsem_write, _try, down_write_trylock(_T))
+DEFINE_LOCK_GUARD_1(rwsem_write, struct rw_semaphore, down_write(_T->lock), up_write(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(rwsem_write, _try, down_write_trylock(_T->lock))
 
 /*
  * downgrade write lock to read lock
  */
-extern void downgrade_write(struct rw_semaphore *sem);
+extern void downgrade_write(struct rw_semaphore *sem) __releases(sem) __acquires_shared(sem);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 /*
@@ -264,11 +272,11 @@ extern void downgrade_write(struct rw_semaphore *sem);
  * lockdep_set_class() at lock initialization time.
  * See Documentation/locking/lockdep-design.rst for more details.)
  */
-extern void down_read_nested(struct rw_semaphore *sem, int subclass);
-extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass);
-extern void down_write_nested(struct rw_semaphore *sem, int subclass);
-extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
-extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
+extern void down_read_nested(struct rw_semaphore *sem, int subclass) __acquires_shared(sem);
+extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass) __cond_acquires_shared(0, sem);
+extern void down_write_nested(struct rw_semaphore *sem, int subclass) __acquires(sem);
+extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass) __cond_acquires(0, sem);
+extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock) __acquires(sem);
 
 # define down_write_nest_lock(sem, nest_lock)			\
 do {								\
@@ -282,8 +290,8 @@ do {								\
  * [ This API should be avoided as much as possible - the
  *   proper abstraction for this case is completions. ]
  */
-extern void down_read_non_owner(struct rw_semaphore *sem);
-extern void up_read_non_owner(struct rw_semaphore *sem);
+extern void down_read_non_owner(struct rw_semaphore *sem) __acquires_shared(sem);
+extern void up_read_non_owner(struct rw_semaphore *sem) __releases_shared(sem);
 #else
 # define down_read_nested(sem, subclass)		down_read(sem)
 # define down_read_killable_nested(sem, subclass)	down_read_killable(sem)
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index 8bc8c3e6cb5c..4638d220f474 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -8,6 +8,7 @@
 #include <linux/build_bug.h>
 #include <linux/mutex.h>
 #include <linux/rcupdate.h>
+#include <linux/rwsem.h>
 #include <linux/seqlock.h>
 #include <linux/spinlock.h>
 #include <linux/srcu.h>
@@ -255,6 +256,69 @@ static void __used test_seqlock_writer(struct test_seqlock_data *d)
 	write_sequnlock_irqrestore(&d->sl, flags);
 }
 
+struct test_rwsem_data {
+	struct rw_semaphore sem;
+	int counter __var_guarded_by(&sem);
+};
+
+static void __used test_rwsem_init(struct test_rwsem_data *d)
+{
+	init_rwsem(&d->sem);
+	d->counter = 0;
+}
+
+static void __used test_rwsem_reader(struct test_rwsem_data *d)
+{
+	down_read(&d->sem);
+	(void)d->counter;
+	up_read(&d->sem);
+
+	if (down_read_trylock(&d->sem)) {
+		(void)d->counter;
+		up_read(&d->sem);
+	}
+}
+
+static void __used test_rwsem_writer(struct test_rwsem_data *d)
+{
+	down_write(&d->sem);
+	d->counter++;
+	up_write(&d->sem);
+
+	down_write(&d->sem);
+	d->counter++;
+	downgrade_write(&d->sem);
+	(void)d->counter;
+	up_read(&d->sem);
+
+	if (down_write_trylock(&d->sem)) {
+		d->counter++;
+		up_write(&d->sem);
+	}
+}
+
+static void __used test_rwsem_assert(struct test_rwsem_data *d)
+{
+	rwsem_assert_held_nolockdep(&d->sem);
+	d->counter++;
+}
+
+static void __used test_rwsem_guard(struct test_rwsem_data *d)
+{
+	{ guard(rwsem_read)(&d->sem); (void)d->counter; }
+	{ guard(rwsem_write)(&d->sem); d->counter++; }
+}
+
+static void __used test_rwsem_cond_guard(struct test_rwsem_data *d)
+{
+	scoped_cond_guard(rwsem_read_try, return, &d->sem) {
+		(void)d->counter;
+	}
+	scoped_cond_guard(rwsem_write_try, return, &d->sem) {
+		d->counter++;
+	}
+}
+
 struct test_bit_spinlock_data {
 	unsigned long bits;
 	int counter __var_guarded_by(__bitlock(3, &bits));
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 19/24] locking/local_lock: Support Clang's capability analysis

[Marco Elver]

Add support for Clang's capability analysis for local_lock_t.

Signed-off-by: Marco Elver <elver@google.com>
---
 .../dev-tools/capability-analysis.rst         |  2 +-
 include/linux/local_lock.h                    | 18 ++++----
 include/linux/local_lock_internal.h           | 41 ++++++++++++++---
 lib/test_capability-analysis.c                | 46 +++++++++++++++++++
 4 files changed, 90 insertions(+), 17 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index 719986739b0e..1e9ce018e30e 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -86,7 +86,7 @@ Supported Kernel Primitives
 
 Currently the following synchronization primitives are supported:
 `raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`,
-`bit_spinlock`, RCU, SRCU (`srcu_struct`), `rw_semaphore`.
+`bit_spinlock`, RCU, SRCU (`srcu_struct`), `rw_semaphore`, `local_lock_t`.
 
 For capabilities with an initialization function (e.g., `spin_lock_init()`),
 calling this function on the capability instance before initializing any
diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
index 091dc0b6bdfb..63fadcf66216 100644
--- a/include/linux/local_lock.h
+++ b/include/linux/local_lock.h
@@ -51,12 +51,12 @@
 #define local_unlock_irqrestore(lock, flags)			\
 	__local_unlock_irqrestore(lock, flags)
 
-DEFINE_GUARD(local_lock, local_lock_t __percpu*,
-	     local_lock(_T),
-	     local_unlock(_T))
-DEFINE_GUARD(local_lock_irq, local_lock_t __percpu*,
-	     local_lock_irq(_T),
-	     local_unlock_irq(_T))
+DEFINE_LOCK_GUARD_1(local_lock, local_lock_t __percpu,
+		    local_lock(_T->lock),
+		    local_unlock(_T->lock))
+DEFINE_LOCK_GUARD_1(local_lock_irq, local_lock_t __percpu,
+		    local_lock_irq(_T->lock),
+		    local_unlock_irq(_T->lock))
 DEFINE_LOCK_GUARD_1(local_lock_irqsave, local_lock_t __percpu,
 		    local_lock_irqsave(_T->lock, _T->flags),
 		    local_unlock_irqrestore(_T->lock, _T->flags),
@@ -68,8 +68,8 @@ DEFINE_LOCK_GUARD_1(local_lock_irqsave, local_lock_t __percpu,
 #define local_unlock_nested_bh(_lock)				\
 	__local_unlock_nested_bh(_lock)
 
-DEFINE_GUARD(local_lock_nested_bh, local_lock_t __percpu*,
-	     local_lock_nested_bh(_T),
-	     local_unlock_nested_bh(_T))
+DEFINE_LOCK_GUARD_1(local_lock_nested_bh, local_lock_t __percpu,
+		    local_lock_nested_bh(_T->lock),
+		    local_unlock_nested_bh(_T->lock))
 
 #endif
diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
index 8dd71fbbb6d2..031de28d8ffb 100644
--- a/include/linux/local_lock_internal.h
+++ b/include/linux/local_lock_internal.h
@@ -8,12 +8,13 @@
 
 #ifndef CONFIG_PREEMPT_RT
 
-typedef struct {
+struct_with_capability(local_lock) {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 	struct task_struct	*owner;
 #endif
-} local_lock_t;
+};
+typedef struct local_lock local_lock_t;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define LOCAL_LOCK_DEBUG_INIT(lockname)		\
@@ -60,6 +61,7 @@ do {								\
 			      0, LD_WAIT_CONFIG, LD_WAIT_INV,	\
 			      LD_LOCK_PERCPU);			\
 	local_lock_debug_init(lock);				\
+	__assert_cap(lock);					\
 } while (0)
 
 #define __spinlock_nested_bh_init(lock)				\
@@ -71,40 +73,47 @@ do {								\
 			      0, LD_WAIT_CONFIG, LD_WAIT_INV,	\
 			      LD_LOCK_NORMAL);			\
 	local_lock_debug_init(lock);				\
+	__assert_cap(lock);					\
 } while (0)
 
 #define __local_lock(lock)					\
 	do {							\
 		preempt_disable();				\
 		local_lock_acquire(this_cpu_ptr(lock));		\
+		__acquire(lock);				\
 	} while (0)
 
 #define __local_lock_irq(lock)					\
 	do {							\
 		local_irq_disable();				\
 		local_lock_acquire(this_cpu_ptr(lock));		\
+		__acquire(lock);				\
 	} while (0)
 
 #define __local_lock_irqsave(lock, flags)			\
 	do {							\
 		local_irq_save(flags);				\
 		local_lock_acquire(this_cpu_ptr(lock));		\
+		__acquire(lock);				\
 	} while (0)
 
 #define __local_unlock(lock)					\
 	do {							\
+		__release(lock);				\
 		local_lock_release(this_cpu_ptr(lock));		\
 		preempt_enable();				\
 	} while (0)
 
 #define __local_unlock_irq(lock)				\
 	do {							\
+		__release(lock);				\
 		local_lock_release(this_cpu_ptr(lock));		\
 		local_irq_enable();				\
 	} while (0)
 
 #define __local_unlock_irqrestore(lock, flags)			\
 	do {							\
+		__release(lock);				\
 		local_lock_release(this_cpu_ptr(lock));		\
 		local_irq_restore(flags);			\
 	} while (0)
@@ -113,19 +122,37 @@ do {								\
 	do {							\
 		lockdep_assert_in_softirq();			\
 		local_lock_acquire(this_cpu_ptr(lock));	\
+		__acquire(lock);				\
 	} while (0)
 
 #define __local_unlock_nested_bh(lock)				\
-	local_lock_release(this_cpu_ptr(lock))
+	do {							\
+		__release(lock);				\
+		local_lock_release(this_cpu_ptr(lock));		\
+	} while (0)
 
 #else /* !CONFIG_PREEMPT_RT */
 
+#include <linux/spinlock.h>
+
 /*
  * On PREEMPT_RT local_lock maps to a per CPU spinlock, which protects the
  * critical section while staying preemptible.
  */
 typedef spinlock_t local_lock_t;
 
+/*
+ * Because the compiler only knows about the base per-CPU variable, use this
+ * helper function to make the compiler think we lock/unlock the @base variable,
+ * and hide the fact we actually pass the per-CPU instance @pcpu to lock/unlock
+ * functions.
+ */
+static inline local_lock_t *__local_lock_alias(local_lock_t __percpu *base, local_lock_t *pcpu)
+	__returns_cap(base)
+{
+	return pcpu;
+}
+
 #define INIT_LOCAL_LOCK(lockname) __LOCAL_SPIN_LOCK_UNLOCKED((lockname))
 
 #define __local_lock_init(l)					\
@@ -136,7 +163,7 @@ typedef spinlock_t local_lock_t;
 #define __local_lock(__lock)					\
 	do {							\
 		migrate_disable();				\
-		spin_lock(this_cpu_ptr((__lock)));		\
+		spin_lock(__local_lock_alias(__lock, this_cpu_ptr((__lock)))); \
 	} while (0)
 
 #define __local_lock_irq(lock)			__local_lock(lock)
@@ -150,7 +177,7 @@ typedef spinlock_t local_lock_t;
 
 #define __local_unlock(__lock)					\
 	do {							\
-		spin_unlock(this_cpu_ptr((__lock)));		\
+		spin_unlock(__local_lock_alias(__lock, this_cpu_ptr((__lock)))); \
 		migrate_enable();				\
 	} while (0)
 
@@ -161,12 +188,12 @@ typedef spinlock_t local_lock_t;
 #define __local_lock_nested_bh(lock)				\
 do {								\
 	lockdep_assert_in_softirq_func();			\
-	spin_lock(this_cpu_ptr(lock));				\
+	spin_lock(__local_lock_alias(lock, this_cpu_ptr(lock))); \
 } while (0)
 
 #define __local_unlock_nested_bh(lock)				\
 do {								\
-	spin_unlock(this_cpu_ptr((lock)));			\
+	spin_unlock(__local_lock_alias(lock, this_cpu_ptr((lock)))); \
 } while (0)
 
 #endif /* CONFIG_PREEMPT_RT */
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index 4638d220f474..dd3fccff2352 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -6,7 +6,9 @@
 
 #include <linux/bit_spinlock.h>
 #include <linux/build_bug.h>
+#include <linux/local_lock.h>
 #include <linux/mutex.h>
+#include <linux/percpu.h>
 #include <linux/rcupdate.h>
 #include <linux/rwsem.h>
 #include <linux/seqlock.h>
@@ -433,3 +435,47 @@ static void __used test_srcu_guard(struct test_srcu_data *d)
 	guard(srcu)(&d->srcu);
 	(void)srcu_dereference(d->data, &d->srcu);
 }
+
+struct test_local_lock_data {
+	local_lock_t lock;
+	int counter __var_guarded_by(&lock);
+};
+
+static DEFINE_PER_CPU(struct test_local_lock_data, test_local_lock_data) = {
+	.lock = INIT_LOCAL_LOCK(lock),
+};
+
+static void __used test_local_lock_init(struct test_local_lock_data *d)
+{
+	local_lock_init(&d->lock);
+	d->counter = 0;
+}
+
+static void __used test_local_lock(void)
+{
+	unsigned long flags;
+
+	local_lock(&test_local_lock_data.lock);
+	this_cpu_add(test_local_lock_data.counter, 1);
+	local_unlock(&test_local_lock_data.lock);
+
+	local_lock_irq(&test_local_lock_data.lock);
+	this_cpu_add(test_local_lock_data.counter, 1);
+	local_unlock_irq(&test_local_lock_data.lock);
+
+	local_lock_irqsave(&test_local_lock_data.lock, flags);
+	this_cpu_add(test_local_lock_data.counter, 1);
+	local_unlock_irqrestore(&test_local_lock_data.lock, flags);
+
+	local_lock_nested_bh(&test_local_lock_data.lock);
+	this_cpu_add(test_local_lock_data.counter, 1);
+	local_unlock_nested_bh(&test_local_lock_data.lock);
+}
+
+static void __used test_local_lock_guard(void)
+{
+	{ guard(local_lock)(&test_local_lock_data.lock); this_cpu_add(test_local_lock_data.counter, 1); }
+	{ guard(local_lock_irq)(&test_local_lock_data.lock); this_cpu_add(test_local_lock_data.counter, 1); }
+	{ guard(local_lock_irqsave)(&test_local_lock_data.lock); this_cpu_add(test_local_lock_data.counter, 1); }
+	{ guard(local_lock_nested_bh)(&test_local_lock_data.lock); this_cpu_add(test_local_lock_data.counter, 1); }
+}
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 20/24] debugfs: Make debugfs_cancellation a capability struct

[Marco Elver]

When compiling include/linux/debugfs.h with CAPABILITY_ANALYSIS enabled,
we can see this error:

./include/linux/debugfs.h:239:17: error: use of undeclared identifier 'cancellation'
  239 | void __acquires(cancellation)

Move the __acquires(..) attribute after the declaration, so that the
compiler can see the cancellation function argument, as well as making
struct debugfs_cancellation a real capability to benefit from Clang's
capability analysis.

Signed-off-by: Marco Elver <elver@google.com>
---
 include/linux/debugfs.h | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index fa2568b4380d..c6a429381887 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -240,18 +240,16 @@ ssize_t debugfs_read_file_str(struct file *file, char __user *user_buf,
  * @cancel: callback to call
  * @cancel_data: extra data for the callback to call
  */
-struct debugfs_cancellation {
+struct_with_capability(debugfs_cancellation) {
 	struct list_head list;
 	void (*cancel)(struct dentry *, void *);
 	void *cancel_data;
 };
 
-void __acquires(cancellation)
-debugfs_enter_cancellation(struct file *file,
-			   struct debugfs_cancellation *cancellation);
-void __releases(cancellation)
-debugfs_leave_cancellation(struct file *file,
-			   struct debugfs_cancellation *cancellation);
+void debugfs_enter_cancellation(struct file *file,
+				struct debugfs_cancellation *cancellation) __acquires(cancellation);
+void debugfs_leave_cancellation(struct file *file,
+				struct debugfs_cancellation *cancellation) __releases(cancellation);
 
 #else
 
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 21/24] kfence: Enable capability analysis

[Marco Elver]

Enable capability analysis for the KFENCE subsystem.

Notable, kfence_handle_page_fault() required minor restructure, which
also fixed a subtle race; arguably that function is more readable now.

Signed-off-by: Marco Elver <elver@google.com>
---
 mm/kfence/Makefile      |  2 ++
 mm/kfence/core.c        | 24 +++++++++++++++++-------
 mm/kfence/kfence.h      | 18 ++++++++++++------
 mm/kfence/kfence_test.c |  4 ++++
 mm/kfence/report.c      |  8 ++++++--
 5 files changed, 41 insertions(+), 15 deletions(-)

diff --git a/mm/kfence/Makefile b/mm/kfence/Makefile
index 2de2a58d11a1..b3640bdc3c69 100644
--- a/mm/kfence/Makefile
+++ b/mm/kfence/Makefile
@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
+CAPABILITY_ANALYSIS := y
+
 obj-y := core.o report.o
 
 CFLAGS_kfence_test.o := -fno-omit-frame-pointer -fno-optimize-sibling-calls
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 102048821c22..c2d1ffd20a1f 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -7,6 +7,8 @@
 
 #define pr_fmt(fmt) "kfence: " fmt
 
+disable_capability_analysis();
+
 #include <linux/atomic.h>
 #include <linux/bug.h>
 #include <linux/debugfs.h>
@@ -34,6 +36,8 @@
 
 #include <asm/kfence.h>
 
+enable_capability_analysis();
+
 #include "kfence.h"
 
 /* Disables KFENCE on the first warning assuming an irrecoverable error. */
@@ -132,8 +136,8 @@ struct kfence_metadata *kfence_metadata __read_mostly;
 static struct kfence_metadata *kfence_metadata_init __read_mostly;
 
 /* Freelist with available objects. */
-static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist);
-static DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */
+DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */
+static struct list_head kfence_freelist __var_guarded_by(&kfence_freelist_lock) = LIST_HEAD_INIT(kfence_freelist);
 
 /*
  * The static key to set up a KFENCE allocation; or if static keys are not used
@@ -253,6 +257,7 @@ static bool kfence_unprotect(unsigned long addr)
 }
 
 static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta)
+	__must_hold(&meta->lock)
 {
 	unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2;
 	unsigned long pageaddr = (unsigned long)&__kfence_pool[offset];
@@ -288,6 +293,7 @@ static inline bool kfence_obj_allocated(const struct kfence_metadata *meta)
 static noinline void
 metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state next,
 		      unsigned long *stack_entries, size_t num_stack_entries)
+	__must_hold(&meta->lock)
 {
 	struct kfence_track *track =
 		next == KFENCE_OBJECT_ALLOCATED ? &meta->alloc_track : &meta->free_track;
@@ -485,7 +491,7 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g
 	alloc_covered_add(alloc_stack_hash, 1);
 
 	/* Set required slab fields. */
-	slab = virt_to_slab((void *)meta->addr);
+	slab = virt_to_slab(addr);
 	slab->slab_cache = cache;
 	slab->objects = 1;
 
@@ -514,6 +520,7 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g
 static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool zombie)
 {
 	struct kcsan_scoped_access assert_page_exclusive;
+	u32 alloc_stack_hash;
 	unsigned long flags;
 	bool init;
 
@@ -546,9 +553,10 @@ static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool z
 	/* Mark the object as freed. */
 	metadata_update_state(meta, KFENCE_OBJECT_FREED, NULL, 0);
 	init = slab_want_init_on_free(meta->cache);
+	alloc_stack_hash = meta->alloc_stack_hash;
 	raw_spin_unlock_irqrestore(&meta->lock, flags);
 
-	alloc_covered_add(meta->alloc_stack_hash, -1);
+	alloc_covered_add(alloc_stack_hash, -1);
 
 	/* Check canary bytes for memory corruption. */
 	check_canary(meta);
@@ -593,6 +601,7 @@ static void rcu_guarded_free(struct rcu_head *h)
  * which partial initialization succeeded.
  */
 static unsigned long kfence_init_pool(void)
+	__no_capability_analysis
 {
 	unsigned long addr;
 	struct page *pages;
@@ -1192,6 +1201,7 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
 {
 	const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE;
 	struct kfence_metadata *to_report = NULL;
+	unsigned long unprotected_page = 0;
 	enum kfence_error_type error_type;
 	unsigned long flags;
 
@@ -1225,9 +1235,8 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
 		if (!to_report)
 			goto out;
 
-		raw_spin_lock_irqsave(&to_report->lock, flags);
-		to_report->unprotected_page = addr;
 		error_type = KFENCE_ERROR_OOB;
+		unprotected_page = addr;
 
 		/*
 		 * If the object was freed before we took the look we can still
@@ -1239,7 +1248,6 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
 		if (!to_report)
 			goto out;
 
-		raw_spin_lock_irqsave(&to_report->lock, flags);
 		error_type = KFENCE_ERROR_UAF;
 		/*
 		 * We may race with __kfence_alloc(), and it is possible that a
@@ -1251,6 +1259,8 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
 
 out:
 	if (to_report) {
+		raw_spin_lock_irqsave(&to_report->lock, flags);
+		to_report->unprotected_page = unprotected_page;
 		kfence_report_error(addr, is_write, regs, to_report, error_type);
 		raw_spin_unlock_irqrestore(&to_report->lock, flags);
 	} else {
diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h
index dfba5ea06b01..27829d70baf6 100644
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -9,6 +9,8 @@
 #ifndef MM_KFENCE_KFENCE_H
 #define MM_KFENCE_KFENCE_H
 
+disable_capability_analysis();
+
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
@@ -16,6 +18,8 @@
 
 #include "../slab.h" /* for struct kmem_cache */
 
+enable_capability_analysis();
+
 /*
  * Get the canary byte pattern for @addr. Use a pattern that varies based on the
  * lower 3 bits of the address, to detect memory corruptions with higher
@@ -34,6 +38,8 @@
 /* Maximum stack depth for reports. */
 #define KFENCE_STACK_DEPTH 64
 
+extern raw_spinlock_t kfence_freelist_lock;
+
 /* KFENCE object states. */
 enum kfence_object_state {
 	KFENCE_OBJECT_UNUSED,		/* Object is unused. */
@@ -53,7 +59,7 @@ struct kfence_track {
 
 /* KFENCE metadata per guarded allocation. */
 struct kfence_metadata {
-	struct list_head list;		/* Freelist node; access under kfence_freelist_lock. */
+	struct list_head list __var_guarded_by(&kfence_freelist_lock);	/* Freelist node. */
 	struct rcu_head rcu_head;	/* For delayed freeing. */
 
 	/*
@@ -91,13 +97,13 @@ struct kfence_metadata {
 	 * In case of an invalid access, the page that was unprotected; we
 	 * optimistically only store one address.
 	 */
-	unsigned long unprotected_page;
+	unsigned long unprotected_page __var_guarded_by(&lock);
 
 	/* Allocation and free stack information. */
-	struct kfence_track alloc_track;
-	struct kfence_track free_track;
+	struct kfence_track alloc_track __var_guarded_by(&lock);
+	struct kfence_track free_track __var_guarded_by(&lock);
 	/* For updating alloc_covered on frees. */
-	u32 alloc_stack_hash;
+	u32 alloc_stack_hash __var_guarded_by(&lock);
 #ifdef CONFIG_MEMCG
 	struct slabobj_ext obj_exts;
 #endif
@@ -141,6 +147,6 @@ enum kfence_error_type {
 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
 			 const struct kfence_metadata *meta, enum kfence_error_type type);
 
-void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);
+void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta) __must_hold(&meta->lock);
 
 #endif /* MM_KFENCE_KFENCE_H */
diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
index 00034e37bc9f..67eca6e9a8de 100644
--- a/mm/kfence/kfence_test.c
+++ b/mm/kfence/kfence_test.c
@@ -11,6 +11,8 @@
  *         Marco Elver <elver@google.com>
  */
 
+disable_capability_analysis();
+
 #include <kunit/test.h>
 #include <linux/jiffies.h>
 #include <linux/kernel.h>
@@ -26,6 +28,8 @@
 
 #include <asm/kfence.h>
 
+enable_capability_analysis();
+
 #include "kfence.h"
 
 /* May be overridden by <asm/kfence.h>. */
diff --git a/mm/kfence/report.c b/mm/kfence/report.c
index 10e6802a2edf..bbee90d0034d 100644
--- a/mm/kfence/report.c
+++ b/mm/kfence/report.c
@@ -5,6 +5,8 @@
  * Copyright (C) 2020, Google LLC.
  */
 
+disable_capability_analysis();
+
 #include <linux/stdarg.h>
 
 #include <linux/kernel.h>
@@ -22,6 +24,8 @@
 
 #include <asm/kfence.h>
 
+enable_capability_analysis();
+
 #include "kfence.h"
 
 /* May be overridden by <asm/kfence.h>. */
@@ -106,6 +110,7 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries
 
 static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadata *meta,
 			       bool show_alloc)
+	__must_hold(&meta->lock)
 {
 	const struct kfence_track *track = show_alloc ? &meta->alloc_track : &meta->free_track;
 	u64 ts_sec = track->ts_nsec;
@@ -207,8 +212,6 @@ void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *r
 	if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
 		return;
 
-	if (meta)
-		lockdep_assert_held(&meta->lock);
 	/*
 	 * Because we may generate reports in printk-unfriendly parts of the
 	 * kernel, such as scheduler code, the use of printk() could deadlock.
@@ -263,6 +266,7 @@ void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *r
 	stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0);
 
 	if (meta) {
+		lockdep_assert_held(&meta->lock);
 		pr_err("\n");
 		kfence_print_object(NULL, meta);
 	}
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 22/24] kcov: Enable capability analysis

[Marco Elver]

Enable capability analysis for the KCOV subsystem.

Signed-off-by: Marco Elver <elver@google.com>
---
 kernel/Makefile |  2 ++
 kernel/kcov.c   | 40 +++++++++++++++++++++++++++++-----------
 2 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/kernel/Makefile b/kernel/Makefile
index 87866b037fbe..7e399998532d 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -39,6 +39,8 @@ KASAN_SANITIZE_kcov.o := n
 KCSAN_SANITIZE_kcov.o := n
 UBSAN_SANITIZE_kcov.o := n
 KMSAN_SANITIZE_kcov.o := n
+
+CAPABILITY_ANALYSIS_kcov.o := y
 CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack) -fno-stack-protector
 
 obj-y += sched/
diff --git a/kernel/kcov.c b/kernel/kcov.c
index 187ba1b80bda..d89c933fe682 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -1,6 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0
 #define pr_fmt(fmt) "kcov: " fmt
 
+disable_capability_analysis();
+
 #define DISABLE_BRANCH_PROFILING
 #include <linux/atomic.h>
 #include <linux/compiler.h>
@@ -27,6 +29,8 @@
 #include <linux/log2.h>
 #include <asm/setup.h>
 
+enable_capability_analysis();
+
 #define kcov_debug(fmt, ...) pr_debug("%s: " fmt, __func__, ##__VA_ARGS__)
 
 /* Number of 64-bit words written per one comparison: */
@@ -55,13 +59,13 @@ struct kcov {
 	refcount_t		refcount;
 	/* The lock protects mode, size, area and t. */
 	spinlock_t		lock;
-	enum kcov_mode		mode;
+	enum kcov_mode		mode __var_guarded_by(&lock);
 	/* Size of arena (in long's). */
-	unsigned int		size;
+	unsigned int		size __var_guarded_by(&lock);
 	/* Coverage buffer shared with user space. */
-	void			*area;
+	void			*area __var_guarded_by(&lock);
 	/* Task for which we collect coverage, or NULL. */
-	struct task_struct	*t;
+	struct task_struct	*t __var_guarded_by(&lock);
 	/* Collecting coverage from remote (background) threads. */
 	bool			remote;
 	/* Size of remote area (in long's). */
@@ -391,6 +395,7 @@ void kcov_task_init(struct task_struct *t)
 }
 
 static void kcov_reset(struct kcov *kcov)
+	__must_hold(&kcov->lock)
 {
 	kcov->t = NULL;
 	kcov->mode = KCOV_MODE_INIT;
@@ -400,6 +405,7 @@ static void kcov_reset(struct kcov *kcov)
 }
 
 static void kcov_remote_reset(struct kcov *kcov)
+	__must_hold(&kcov->lock)
 {
 	int bkt;
 	struct kcov_remote *remote;
@@ -419,6 +425,7 @@ static void kcov_remote_reset(struct kcov *kcov)
 }
 
 static void kcov_disable(struct task_struct *t, struct kcov *kcov)
+	__must_hold(&kcov->lock)
 {
 	kcov_task_reset(t);
 	if (kcov->remote)
@@ -435,8 +442,11 @@ static void kcov_get(struct kcov *kcov)
 static void kcov_put(struct kcov *kcov)
 {
 	if (refcount_dec_and_test(&kcov->refcount)) {
-		kcov_remote_reset(kcov);
-		vfree(kcov->area);
+		/* Capability-safety: no references left, object being destroyed. */
+		capability_unsafe(
+			kcov_remote_reset(kcov);
+			vfree(kcov->area);
+		);
 		kfree(kcov);
 	}
 }
@@ -491,6 +501,7 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
 	unsigned long size, off;
 	struct page *page;
 	unsigned long flags;
+	unsigned long *area;
 
 	spin_lock_irqsave(&kcov->lock, flags);
 	size = kcov->size * sizeof(unsigned long);
@@ -499,10 +510,11 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
 		res = -EINVAL;
 		goto exit;
 	}
+	area = kcov->area;
 	spin_unlock_irqrestore(&kcov->lock, flags);
 	vm_flags_set(vma, VM_DONTEXPAND);
 	for (off = 0; off < size; off += PAGE_SIZE) {
-		page = vmalloc_to_page(kcov->area + off);
+		page = vmalloc_to_page(area + off);
 		res = vm_insert_page(vma, vma->vm_start + off, page);
 		if (res) {
 			pr_warn_once("kcov: vm_insert_page() failed\n");
@@ -522,10 +534,10 @@ static int kcov_open(struct inode *inode, struct file *filep)
 	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
 	if (!kcov)
 		return -ENOMEM;
+	spin_lock_init(&kcov->lock);
 	kcov->mode = KCOV_MODE_DISABLED;
 	kcov->sequence = 1;
 	refcount_set(&kcov->refcount, 1);
-	spin_lock_init(&kcov->lock);
 	filep->private_data = kcov;
 	return nonseekable_open(inode, filep);
 }
@@ -556,6 +568,7 @@ static int kcov_get_mode(unsigned long arg)
  * vmalloc fault handling path is instrumented.
  */
 static void kcov_fault_in_area(struct kcov *kcov)
+	__must_hold(&kcov->lock)
 {
 	unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
 	unsigned long *area = kcov->area;
@@ -584,6 +597,7 @@ static inline bool kcov_check_handle(u64 handle, bool common_valid,
 
 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 			     unsigned long arg)
+	__must_hold(&kcov->lock)
 {
 	struct task_struct *t;
 	unsigned long flags, unused;
@@ -814,6 +828,7 @@ static inline bool kcov_mode_enabled(unsigned int mode)
 }
 
 static void kcov_remote_softirq_start(struct task_struct *t)
+	__must_hold(&kcov_percpu_data.lock)
 {
 	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
 	unsigned int mode;
@@ -831,6 +846,7 @@ static void kcov_remote_softirq_start(struct task_struct *t)
 }
 
 static void kcov_remote_softirq_stop(struct task_struct *t)
+	__must_hold(&kcov_percpu_data.lock)
 {
 	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
 
@@ -896,10 +912,12 @@ void kcov_remote_start(u64 handle)
 	/* Put in kcov_remote_stop(). */
 	kcov_get(kcov);
 	/*
-	 * Read kcov fields before unlock to prevent races with
-	 * KCOV_DISABLE / kcov_remote_reset().
+	 * Read kcov fields before unlocking kcov_remote_lock to prevent races
+	 * with KCOV_DISABLE and kcov_remote_reset(); cannot acquire kcov->lock
+	 * here, because it might lead to deadlock given kcov_remote_lock is
+	 * acquired _after_ kcov->lock elsewhere.
 	 */
-	mode = kcov->mode;
+	mode = capability_unsafe(kcov->mode);
 	sequence = kcov->sequence;
 	if (in_task()) {
 		size = kcov->remote_size;
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 23/24] stackdepot: Enable capability analysis

[Marco Elver]

Enable capability analysis for stackdepot.

Signed-off-by: Marco Elver <elver@google.com>
---
 lib/Makefile     |  1 +
 lib/stackdepot.c | 24 ++++++++++++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/lib/Makefile b/lib/Makefile
index 1dbb59175eb0..f40ba93c9a94 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -270,6 +270,7 @@ obj-$(CONFIG_POLYNOMIAL) += polynomial.o
 # Prevent the compiler from calling builtins like memcmp() or bcmp() from this
 # file.
 CFLAGS_stackdepot.o += -fno-builtin
+CAPABILITY_ANALYSIS_stackdepot.o := y
 obj-$(CONFIG_STACKDEPOT) += stackdepot.o
 KASAN_SANITIZE_stackdepot.o := n
 # In particular, instrumenting stackdepot.c with KMSAN will result in infinite
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 245d5b416699..6664146d1f31 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -14,6 +14,8 @@
 
 #define pr_fmt(fmt) "stackdepot: " fmt
 
+disable_capability_analysis();
+
 #include <linux/debugfs.h>
 #include <linux/gfp.h>
 #include <linux/jhash.h>
@@ -36,6 +38,8 @@
 #include <linux/memblock.h>
 #include <linux/kasan-enabled.h>
 
+enable_capability_analysis();
+
 #define DEPOT_POOLS_CAP 8192
 /* The pool_index is offset by 1 so the first record does not have a 0 handle. */
 #define DEPOT_MAX_POOLS \
@@ -61,18 +65,18 @@ static unsigned int stack_bucket_number_order;
 /* Hash mask for indexing the table. */
 static unsigned int stack_hash_mask;
 
+/* The lock must be held when performing pool or freelist modifications. */
+static DEFINE_RAW_SPINLOCK(pool_lock);
 /* Array of memory regions that store stack records. */
-static void *stack_pools[DEPOT_MAX_POOLS];
+static void *stack_pools[DEPOT_MAX_POOLS] __var_guarded_by(&pool_lock);
 /* Newly allocated pool that is not yet added to stack_pools. */
 static void *new_pool;
 /* Number of pools in stack_pools. */
 static int pools_num;
 /* Offset to the unused space in the currently used pool. */
-static size_t pool_offset = DEPOT_POOL_SIZE;
+static size_t pool_offset __var_guarded_by(&pool_lock) = DEPOT_POOL_SIZE;
 /* Freelist of stack records within stack_pools. */
-static LIST_HEAD(free_stacks);
-/* The lock must be held when performing pool or freelist modifications. */
-static DEFINE_RAW_SPINLOCK(pool_lock);
+static __var_guarded_by(&pool_lock) LIST_HEAD(free_stacks);
 
 /* Statistics counters for debugfs. */
 enum depot_counter_id {
@@ -242,6 +246,7 @@ EXPORT_SYMBOL_GPL(stack_depot_init);
  * Initializes new stack pool, and updates the list of pools.
  */
 static bool depot_init_pool(void **prealloc)
+	__must_hold(&pool_lock)
 {
 	lockdep_assert_held(&pool_lock);
 
@@ -289,6 +294,7 @@ static bool depot_init_pool(void **prealloc)
 
 /* Keeps the preallocated memory to be used for a new stack depot pool. */
 static void depot_keep_new_pool(void **prealloc)
+	__must_hold(&pool_lock)
 {
 	lockdep_assert_held(&pool_lock);
 
@@ -308,6 +314,7 @@ static void depot_keep_new_pool(void **prealloc)
  * the current pre-allocation.
  */
 static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size)
+	__must_hold(&pool_lock)
 {
 	struct stack_record *stack;
 	void *current_pool;
@@ -342,6 +349,7 @@ static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size)
 
 /* Try to find next free usable entry from the freelist. */
 static struct stack_record *depot_pop_free(void)
+	__must_hold(&pool_lock)
 {
 	struct stack_record *stack;
 
@@ -379,6 +387,7 @@ static inline size_t depot_stack_record_size(struct stack_record *s, unsigned in
 /* Allocates a new stack in a stack depot pool. */
 static struct stack_record *
 depot_alloc_stack(unsigned long *entries, unsigned int nr_entries, u32 hash, depot_flags_t flags, void **prealloc)
+	__must_hold(&pool_lock)
 {
 	struct stack_record *stack = NULL;
 	size_t record_size;
@@ -437,6 +446,7 @@ depot_alloc_stack(unsigned long *entries, unsigned int nr_entries, u32 hash, dep
 }
 
 static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
+	__must_not_hold(&pool_lock)
 {
 	const int pools_num_cached = READ_ONCE(pools_num);
 	union handle_parts parts = { .handle = handle };
@@ -453,7 +463,8 @@ static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
 		return NULL;
 	}
 
-	pool = stack_pools[pool_index];
+	/* @pool_index either valid, or user passed in corrupted value. */
+	pool = capability_unsafe(stack_pools[pool_index]);
 	if (WARN_ON(!pool))
 		return NULL;
 
@@ -466,6 +477,7 @@ static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
 
 /* Links stack into the freelist. */
 static void depot_free_stack(struct stack_record *stack)
+	__must_not_hold(&pool_lock)
 {
 	unsigned long flags;
 
-- 
2.48.1.502.g6dc24dfdaf-goog

[PATCH RFC 24/24] rhashtable: Enable capability analysis

[Marco Elver]

Enable capability analysis for rhashtable, which was used as an initial
test as it contains a combination of RCU, mutex, and bit_spinlock usage.

Users of rhashtable now also benefit from annotations on the API, which
will now warn if the RCU read lock is not held where required.

Signed-off-by: Marco Elver <elver@google.com>
---
 include/linux/rhashtable.h | 14 +++++++++++---
 lib/Makefile               |  2 ++
 lib/rhashtable.c           | 12 +++++++++---
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 8463a128e2f4..c6374691ccc7 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -245,16 +245,17 @@ void *rhashtable_insert_slow(struct rhashtable *ht, const void *key,
 void rhashtable_walk_enter(struct rhashtable *ht,
 			   struct rhashtable_iter *iter);
 void rhashtable_walk_exit(struct rhashtable_iter *iter);
-int rhashtable_walk_start_check(struct rhashtable_iter *iter) __acquires(RCU);
+int rhashtable_walk_start_check(struct rhashtable_iter *iter) __acquires_shared(RCU);
 
 static inline void rhashtable_walk_start(struct rhashtable_iter *iter)
+	__acquires_shared(RCU)
 {
 	(void)rhashtable_walk_start_check(iter);
 }
 
 void *rhashtable_walk_next(struct rhashtable_iter *iter);
 void *rhashtable_walk_peek(struct rhashtable_iter *iter);
-void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases(RCU);
+void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases_shared(RCU);
 
 void rhashtable_free_and_destroy(struct rhashtable *ht,
 				 void (*free_fn)(void *ptr, void *arg),
@@ -325,6 +326,7 @@ static inline struct rhash_lock_head __rcu **rht_bucket_insert(
 
 static inline unsigned long rht_lock(struct bucket_table *tbl,
 				     struct rhash_lock_head __rcu **bkt)
+	__acquires(__bitlock(0, bkt))
 {
 	unsigned long flags;
 
@@ -337,6 +339,7 @@ static inline unsigned long rht_lock(struct bucket_table *tbl,
 static inline unsigned long rht_lock_nested(struct bucket_table *tbl,
 					struct rhash_lock_head __rcu **bucket,
 					unsigned int subclass)
+	__acquires(__bitlock(0, bucket))
 {
 	unsigned long flags;
 
@@ -349,6 +352,7 @@ static inline unsigned long rht_lock_nested(struct bucket_table *tbl,
 static inline void rht_unlock(struct bucket_table *tbl,
 			      struct rhash_lock_head __rcu **bkt,
 			      unsigned long flags)
+	__releases(__bitlock(0, bkt))
 {
 	lock_map_release(&tbl->dep_map);
 	bit_spin_unlock(0, (unsigned long *)bkt);
@@ -402,13 +406,14 @@ static inline void rht_assign_unlock(struct bucket_table *tbl,
 				     struct rhash_lock_head __rcu **bkt,
 				     struct rhash_head *obj,
 				     unsigned long flags)
+	__releases(__bitlock(0, bkt))
 {
 	if (rht_is_a_nulls(obj))
 		obj = NULL;
 	lock_map_release(&tbl->dep_map);
 	rcu_assign_pointer(*bkt, (void *)obj);
 	preempt_enable();
-	__release(bitlock);
+	__release(__bitlock(0, bkt));
 	local_irq_restore(flags);
 }
 
@@ -589,6 +594,7 @@ static inline int rhashtable_compare(struct rhashtable_compare_arg *arg,
 static inline struct rhash_head *__rhashtable_lookup(
 	struct rhashtable *ht, const void *key,
 	const struct rhashtable_params params)
+	__must_hold_shared(RCU)
 {
 	struct rhashtable_compare_arg arg = {
 		.ht = ht,
@@ -642,6 +648,7 @@ static inline struct rhash_head *__rhashtable_lookup(
 static inline void *rhashtable_lookup(
 	struct rhashtable *ht, const void *key,
 	const struct rhashtable_params params)
+	__must_hold_shared(RCU)
 {
 	struct rhash_head *he = __rhashtable_lookup(ht, key, params);
 
@@ -692,6 +699,7 @@ static inline void *rhashtable_lookup_fast(
 static inline struct rhlist_head *rhltable_lookup(
 	struct rhltable *hlt, const void *key,
 	const struct rhashtable_params params)
+	__must_hold_shared(RCU)
 {
 	struct rhash_head *he = __rhashtable_lookup(&hlt->ht, key, params);
 
diff --git a/lib/Makefile b/lib/Makefile
index f40ba93c9a94..c7004270ad5f 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -45,6 +45,8 @@ lib-$(CONFIG_MIN_HEAP) += min_heap.o
 lib-y	+= kobject.o klist.o
 obj-y	+= lockref.o
 
+CAPABILITY_ANALYSIS_rhashtable.o := y
+
 obj-y += bcd.o sort.o parser.o debug_locks.o random32.o \
 	 bust_spinlocks.o kasprintf.o bitmap.o scatterlist.o \
 	 list_sort.o uuid.o iov_iter.o clz_ctz.o \
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 3e555d012ed6..47a61e214621 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -11,6 +11,10 @@
  * pointer as suggested by Josh Triplett
  */
 
+#include <linux/rhashtable.h>
+
+disable_capability_analysis();
+
 #include <linux/atomic.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
@@ -22,10 +26,11 @@
 #include <linux/mm.h>
 #include <linux/jhash.h>
 #include <linux/random.h>
-#include <linux/rhashtable.h>
 #include <linux/err.h>
 #include <linux/export.h>
 
+enable_capability_analysis();
+
 #define HASH_DEFAULT_SIZE	64UL
 #define HASH_MIN_SIZE		4U
 
@@ -358,6 +363,7 @@ static int rhashtable_rehash_table(struct rhashtable *ht)
 static int rhashtable_rehash_alloc(struct rhashtable *ht,
 				   struct bucket_table *old_tbl,
 				   unsigned int size)
+	__must_hold(&ht->mutex)
 {
 	struct bucket_table *new_tbl;
 	int err;
@@ -392,6 +398,7 @@ static int rhashtable_rehash_alloc(struct rhashtable *ht,
  * bucket locks or concurrent RCU protected lookups and traversals.
  */
 static int rhashtable_shrink(struct rhashtable *ht)
+	__must_hold(&ht->mutex)
 {
 	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 	unsigned int nelems = atomic_read(&ht->nelems);
@@ -724,7 +731,7 @@ EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
  * resize events and always continue.
  */
 int rhashtable_walk_start_check(struct rhashtable_iter *iter)
-	__acquires(RCU)
+	__acquires_shared(RCU)
 {
 	struct rhashtable *ht = iter->ht;
 	bool rhlist = ht->rhlist;
@@ -940,7 +947,6 @@ EXPORT_SYMBOL_GPL(rhashtable_walk_peek);
  * hash table.
  */
 void rhashtable_walk_stop(struct rhashtable_iter *iter)
-	__releases(RCU)
 {
 	struct rhashtable *ht;
 	struct bucket_table *tbl = iter->walker.tbl;
-- 
2.48.1.502.g6dc24dfdaf-goog

Re: [PATCH RFC 00/24] Compiler-Based Capability- and Locking-Analysis

[Marco Elver]

On Thu, 6 Feb 2025 at 19:17, Marco Elver <elver@google.com> wrote:
[...]
> Capability analysis is a C language extension, which enables statically
> checking that user-definable "capabilities" are acquired and released where
> required. An obvious application is lock-safety checking for the kernel's
> various synchronization primitives (each of which represents a "capability"),
> and checking that locking rules are not violated.
[...]
> This series is also available at this Git tree:

   https://web.git.kernel.org/pub/scm/linux/kernel/git/melver/linux.git/log/?h=cap-analysis/dev

I'm planning to send a v2 soon (Clang just gained
-Wthread-safety-pointer which I wanted to have committed before).
Preview at the above tree.

Thanks,
-- Marco