[PATCH v2 15/34] srcu: Support Clang's capability analysis

Marco Elver
2025-03-04T09:25:51Z

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 a14d796bcd0e..918e35d110df 100644
--- a/Documentation/dev-tools/capability-analysis.rst
+++ b/Documentation/dev-tools/capability-analysis.rst
@@ -80,7 +80,7 @@ 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..fde8bba191a5 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 __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 050fa7c9fcba..63d81ad1562f 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);
+}