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Commit a7d2c573 authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Linus Torvalds
Browse files

rwsem: avoid taking wait_lock in rwsem_down_write_failed 



In rwsem_down_write_failed(), if there are active locks after we wake up
(i.e.  the lock got stolen from us), skip taking the wait_lock and go
back to sleep immediately.

Signed-off-by: default avatarMichel Lespinasse <walken@google.com>
Reviewed-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Acked-by: default avatarDavidlohr Bueso <davidlohr.bueso@hp.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5ede972d

lib/rwsem.c

+8 −2
Original line number Diff line number Diff line
@@ -214,8 +214,8 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) 
		sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED);



	/* wait until we successfully acquire the lock */

	while (true) {

	set_task_state(tsk, TASK_UNINTERRUPTIBLE);

	while (true) {



		/* Try acquiring the write lock. */

		count = RWSEM_ACTIVE_WRITE_BIAS;
@@ -226,7 +226,13 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) 
			break;



		raw_spin_unlock_irq(&sem->wait_lock);



		/* Block until there are no active lockers. */

		do {

			schedule();

			set_task_state(tsk, TASK_UNINTERRUPTIBLE);

		} while (sem->count & RWSEM_ACTIVE_MASK);



		raw_spin_lock_irq(&sem->wait_lock);

	}