[PATCH v3 15/35] srcu: Support Clang's capability analysis

Marco Elver
2025-09-18T14:06:09Z

Add support for Clang's capability analysis for SRCU.

Signed-off-by: Marco Elver <elver@google.com>
---
v3:
* Switch to DECLARE_LOCK_GUARD_1_ATTRS() (suggested by Peter)
* Support SRCU being reentrant.
---
.../dev-tools/capability-analysis.rst | 2 +-
include/linux/srcu.h | 60 +++++++++++++------
include/linux/srcutiny.h | 4 ++
include/linux/srcutree.h | 6 +-
lib/test_capability-analysis.c | 24 ++++++++
5 files changed, 75 insertions(+), 21 deletions(-)

diff --git a/Documentation/dev-tools/capability-analysis.rst b/Documentation/dev-tools/capability-analysis.rst
index fdacc7f73da8..779ecb5ec17a 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -82,7 +82,7 @@ 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 f179700fecaf..6cafaf6dde71 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, __reentrant_cap);

#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_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
@@ -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;

@@ -292,7 +310,7 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *
* 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());
srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
@@ -310,7 +328,8 @@ 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;

@@ -322,7 +341,8 @@ 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;

@@ -353,7 +373,8 @@ 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);
@@ -368,7 +389,7 @@ 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);
@@ -384,7 +405,7 @@ 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);
@@ -400,7 +421,7 @@ static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ct
* 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);
@@ -415,7 +436,7 @@ 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);
@@ -425,7 +446,7 @@ 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);
@@ -440,7 +461,7 @@ 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());
@@ -480,6 +501,7 @@ 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_cap(_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 bf44d8d1e69e..43754472e07a 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);
@@ -241,6 +241,7 @@ 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 *__srcu_read_lock_fast(struct srcu_struct *ssp)
+ __acquires_shared(ssp)
{
struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);

@@ -250,6 +251,7 @@ static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct
else
atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks)); /* Z */
barrier(); /* Avoid leaking the critical section. */
+ __acquire_shared(ssp);
return scp;
}

@@ -269,7 +271,9 @@ static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct
* implementations of this_cpu_inc().
*/
static inline void __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 */
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index 31c9bc1e2405..5b17fd94f31e 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.
@@ -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);
+}
--
2.51.0.384.g4c02a37b29-goog