Commit e4fd3be8 authored by Marco Elver's avatar Marco Elver Committed by Peter Zijlstra
Browse files

locking/rwsem: Support Clang's context analysis 



Add support for Clang's context analysis for rw_semaphore.

Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-18-elver@google.com
parent 5e256db9

Documentation/dev-tools/context-analysis.rst

+1 −1
Original line number Diff line number Diff line
@@ -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

+49 −27
Original line number Diff line number Diff line
@@ -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);



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_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)

extern void up_write(struct rw_semaphore *sem) __releases(sem);



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)



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

+64 −0
Original line number Diff line number Diff line
@@ -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));