Commit 285c61ae authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

locking/rwsem: Introduce rwsem_write_trylock() 



One copy of this logic is better than three.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201207090243.GE3040@hirez.programming.kicks-ass.net
parent 3379116a

kernel/locking/rwsem.c

+16 −22
Original line number Diff line number Diff line
@@ -285,6 +285,18 @@ static inline bool rwsem_read_trylock(struct rw_semaphore *sem) 
	return false;

}



static inline bool rwsem_write_trylock(struct rw_semaphore *sem)

{

	long tmp = RWSEM_UNLOCKED_VALUE;



	if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {

		rwsem_set_owner(sem);

		return true;

	}



	return false;

}



/*

 * Return just the real task structure pointer of the owner

 */
@@ -1395,42 +1407,24 @@ static inline int __down_read_trylock(struct rw_semaphore *sem) 
 */

static inline void __down_write(struct rw_semaphore *sem)

{

	long tmp = RWSEM_UNLOCKED_VALUE;



	if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,

						      RWSEM_WRITER_LOCKED)))

	if (unlikely(!rwsem_write_trylock(sem)))

		rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);

	else

		rwsem_set_owner(sem);

}



static inline int __down_write_killable(struct rw_semaphore *sem)

{

	long tmp = RWSEM_UNLOCKED_VALUE;



	if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,

						      RWSEM_WRITER_LOCKED))) {

	if (unlikely(!rwsem_write_trylock(sem))) {

		if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))

			return -EINTR;

	} else {

		rwsem_set_owner(sem);

	}



	return 0;

}



static inline int __down_write_trylock(struct rw_semaphore *sem)

{

	long tmp;



	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);



	tmp  = RWSEM_UNLOCKED_VALUE;

	if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,

					    RWSEM_WRITER_LOCKED)) {

		rwsem_set_owner(sem);

		return true;

	}

	return false;

	return rwsem_write_trylock(sem);

}



/*