locking/rwsem: Support Clang's context analysis

Add support for Clang's context analysis for rw_semaphore.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-18-elver@google.com

Documentation/dev-tools/context-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, SRCU (`srcu_struct`).
+`bit_spinlock`, RCU, SRCU (`srcu_struct`), `rw_semaphore`.
 
 For context locks with an initialization function (e.g., `spin_lock_init()`),
 calling this function before initializing any guarded members or globals

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 {
+context_lock_struct(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)
+	__assumes_ctx_lock(sem)
 {
 	WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE);
 }
 
 static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
+	__assumes_ctx_lock(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);			\
+	__assume_ctx_lock(sem);					\
 } while (0)
 
 /*
@@ -148,7 +151,7 @@ extern bool is_rwsem_reader_owned(struct rw_semaphore *sem);
 
 #include <linux/rwbase_rt.h>
 
-struct rw_semaphore {
+context_lock_struct(rw_semaphore) {
 	struct rwbase_rt	rwbase;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
@@ -172,6 +175,7 @@ do {								\
 	static struct lock_class_key __key;			\
 								\
 	__init_rwsem((sem), #sem, &__key);			\
+	__assume_ctx_lock(sem);					\
 } while (0)
 
 static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem)
@@ -180,11 +184,13 @@ 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)
+	__assumes_ctx_lock(sem)
 {
 	WARN_ON(!rwsem_is_locked(sem));
 }
 
 static __always_inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
+	__assumes_ctx_lock(sem)
 {
 	WARN_ON(!rw_base_is_write_locked(&sem->rwbase));
 }
@@ -202,6 +208,7 @@ static __always_inline int rwsem_is_contended(struct rw_semaphore *sem)
  */
 
 static inline void rwsem_assert_held(const struct rw_semaphore *sem)
+	__assumes_ctx_lock(sem)
 {
 	if (IS_ENABLED(CONFIG_LOCKDEP))
 		lockdep_assert_held(sem);
@@ -210,6 +217,7 @@ static inline void rwsem_assert_held(const struct rw_semaphore *sem)
 }
 
 static inline void rwsem_assert_held_write(const struct rw_semaphore *sem)
+	__assumes_ctx_lock(sem)
 {
 	if (IS_ENABLED(CONFIG_LOCKDEP))
 		lockdep_assert_held_write(sem);
@@ -220,48 +228,62 @@ 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(true, 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(true, 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), _RET == 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), _RET == 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_GUARD_COND(rwsem_write, _kill, down_write_killable(_T), _RET == 0)
+DECLARE_LOCK_GUARD_1_ATTRS(rwsem_read, __acquires_shared(_T), __releases_shared(*(struct rw_semaphore **)_T))
+#define class_rwsem_read_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(rwsem_read, _T)
+DECLARE_LOCK_GUARD_1_ATTRS(rwsem_read_try, __acquires_shared(_T), __releases_shared(*(struct rw_semaphore **)_T))
+#define class_rwsem_read_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(rwsem_read_try, _T)
+DECLARE_LOCK_GUARD_1_ATTRS(rwsem_read_intr, __acquires_shared(_T), __releases_shared(*(struct rw_semaphore **)_T))
+#define class_rwsem_read_intr_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(rwsem_read_intr, _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))
+DEFINE_LOCK_GUARD_1_COND(rwsem_write, _kill, down_write_killable(_T->lock), _RET == 0)
+
+DECLARE_LOCK_GUARD_1_ATTRS(rwsem_write, __acquires(_T), __releases(*(struct rw_semaphore **)_T))
+#define class_rwsem_write_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(rwsem_write, _T)
+DECLARE_LOCK_GUARD_1_ATTRS(rwsem_write_try, __acquires(_T), __releases(*(struct rw_semaphore **)_T))
+#define class_rwsem_write_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(rwsem_write_try, _T)
+DECLARE_LOCK_GUARD_1_ATTRS(rwsem_write_kill, __acquires(_T), __releases(*(struct rw_semaphore **)_T))
+#define class_rwsem_write_kill_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(rwsem_write_kill, _T)
 
 /*
  * 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
 /*
@@ -277,11 +299,11 @@ 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 {								\
@@ -295,8 +317,8 @@ 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)

lib/test_context-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>
@@ -262,6 +263,69 @@ static void __used test_seqlock_scoped(struct test_seqlock_data *d)
 	}
 }
 
+struct test_rwsem_data {
+	struct rw_semaphore sem;
+	int counter __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 __guarded_by(__bitlock(3, &bits));