[PATCH v4 15/35] srcu: Support Clang's context analysis

[Marco Elver <elver@google.com>]

Add support for Clang's context analysis for SRCU.

Signed-off-by: Marco Elver <elver@google.com>
---
v4:
* Rename capability -> context analysis.

v3:
* Switch to DECLARE_LOCK_GUARD_1_ATTRS() (suggested by Peter)
* Support SRCU being reentrant.
---
 Documentation/dev-tools/context-analysis.rst |  2 +-
 include/linux/srcu.h                         | 64 +++++++++++++-------
 include/linux/srcutiny.h                     |  4 ++
 include/linux/srcutree.h                     |  6 +-
 lib/test_context-analysis.c                  | 24 ++++++++
 5 files changed, 77 insertions(+), 23 deletions(-)

diff --git a/Documentation/dev-tools/context-analysis.rst b/Documentation/dev-tools/context-analysis.rst
index 05164804a92a..59fc8e4cc203 100644
--- a/Documentation/dev-tools/context-analysis.rst
+++ b/Documentation/dev-tools/context-analysis.rst
@@ -81,7 +81,7 @@ 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 context guards with an initialization function (e.g., `spin_lock_init()`),
 calling this function before initializing any guarded members or globals
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index ada65b58bc4c..a0e2b8187100 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;
+context_guard_struct(srcu_struct, __reentrant_ctx_guard);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
@@ -53,7 +53,7 @@ int init_srcu_struct(struct srcu_struct *ssp);
 #define SRCU_READ_FLAVOR_SLOWGP	SRCU_READ_FLAVOR_FAST
 						// Flavors requiring synchronize_rcu()
 						// instead of smp_mb().
-void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
+void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases_shared(ssp);
 
 #ifdef CONFIG_TINY_SRCU
 #include <linux/srcutiny.h>
@@ -107,14 +107,16 @@ 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);
 }
@@ -186,6 +188,14 @@ 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 __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
@@ -199,9 +209,15 @@ 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_ctx_guard(RCU);					\
+	__auto_type __v = __rcu_dereference_check((p), __UNIQUE_ID(rcu),	\
+				(c) || srcu_read_lock_held(ssp), __rcu);	\
+	__release_shared_ctx_guard(RCU);					\
+	__v;									\
+})
 
 /**
  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
@@ -244,7 +260,8 @@ 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;
 
@@ -271,7 +288,8 @@ 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 struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires(ssp)
+static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires_shared(ssp)
+	__acquires_shared(ssp)
 {
 	struct srcu_ctr __percpu *retval;
 
@@ -287,7 +305,7 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *
  * See srcu_read_lock_fast() for more information.
  */
 static inline struct srcu_ctr __percpu *srcu_read_lock_fast_notrace(struct srcu_struct *ssp)
-	__acquires(ssp)
+	__acquires_shared(ssp)
 {
 	struct srcu_ctr __percpu *retval;
 
@@ -307,7 +325,7 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast_notrace(struct srcu_
  * The same srcu_struct may be used concurrently by srcu_down_read_fast()
  * and srcu_read_lock_fast().
  */
-static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *ssp) __acquires(ssp)
+static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *ssp) __acquires_shared(ssp)
 {
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi());
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_down_read_fast().");
@@ -326,7 +344,8 @@ static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *
  * 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;
 
@@ -338,7 +357,8 @@ 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;
 
@@ -369,7 +389,8 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
  * which calls to down_read() may be nested.  The same srcu_struct may be
  * used concurrently by srcu_down_read() and srcu_read_lock().
  */
-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);
@@ -384,7 +405,7 @@ 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);
@@ -400,7 +421,7 @@ 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_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
 	srcu_lock_release(&ssp->dep_map);
@@ -413,7 +434,7 @@ static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ct
  * See srcu_read_unlock_fast() for more information.
  */
 static inline void srcu_read_unlock_fast_notrace(struct srcu_struct *ssp,
-						 struct srcu_ctr __percpu *scp) __releases(ssp)
+						 struct srcu_ctr __percpu *scp) __releases_shared(ssp)
 {
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
 	__srcu_read_unlock_fast(ssp, scp);
@@ -428,7 +449,7 @@ static inline void srcu_read_unlock_fast_notrace(struct srcu_struct *ssp,
  * the same context as the maching srcu_down_read_fast().
  */
 static inline void srcu_up_read_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
-	__releases(ssp)
+	__releases_shared(ssp)
 {
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi());
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
@@ -444,7 +465,7 @@ static inline void srcu_up_read_fast(struct srcu_struct *ssp, struct srcu_ctr __
  * 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);
@@ -454,7 +475,7 @@ 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);
@@ -469,7 +490,7 @@ 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());
@@ -509,6 +530,7 @@ DEFINE_LOCK_GUARD_1(srcu, struct srcu_struct,
 		    _T->idx = srcu_read_lock(_T->lock),
 		    srcu_read_unlock(_T->lock, _T->idx),
 		    int idx)
+DECLARE_LOCK_GUARD_1_ATTRS(srcu, __assumes_ctx_guard(_T), /* */)
 
 DEFINE_LOCK_GUARD_1(srcu_fast, struct srcu_struct,
 		    _T->scp = srcu_read_lock_fast(_T->lock),
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 51ce25f07930..c194b3c7c43b 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -61,6 +61,7 @@ void synchronize_srcu(struct srcu_struct *ssp);
  * index that must be passed to the matching srcu_read_unlock().
  */
 static inline int __srcu_read_lock(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	int idx;
 
@@ -68,6 +69,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
 	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
 	WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
 	preempt_enable();
+	__acquire_shared(ssp);
 	return idx;
 }
 
@@ -84,11 +86,13 @@ static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ss
 }
 
 static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	return __srcu_ctr_to_ptr(ssp, __srcu_read_lock(ssp));
 }
 
 static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
+	__releases_shared(ssp)
 {
 	__srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp));
 }
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 42098e0fa0b7..4bfd80f55043 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -207,7 +207,7 @@ struct srcu_struct {
 #define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
 #define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
 
-int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
+int __srcu_read_lock(struct srcu_struct *ssp) __acquires_shared(ssp);
 void synchronize_srcu_expedited(struct srcu_struct *ssp);
 void srcu_barrier(struct srcu_struct *ssp);
 void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf);
@@ -259,6 +259,7 @@ static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ss
  * implementations of this_cpu_inc().
  */
 static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct srcu_struct *ssp)
+	__acquires_shared(ssp)
 {
 	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
 
@@ -267,6 +268,7 @@ static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct src
 	else
 		atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks));  // Y, and implicit RCU reader.
 	barrier(); /* Avoid leaking the critical section. */
+	__acquire_shared(ssp);
 	return scp;
 }
 
@@ -281,7 +283,9 @@ static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct src
  */
 static inline void notrace
 __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
+	__releases_shared(ssp)
 {
+	__release_shared(ssp);
 	barrier();  /* Avoid leaking the critical section. */
 	if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))
 		this_cpu_inc(scp->srcu_unlocks.counter);  // Z, and implicit RCU reader.
diff --git a/lib/test_context-analysis.c b/lib/test_context-analysis.c
index f18b7252646d..bd75b5ade8ff 100644
--- a/lib/test_context-analysis.c
+++ b/lib/test_context-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.
@@ -362,3 +363,26 @@ 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);
+}
-- 
2.52.0.rc1.455.g30608eb744-goog