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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: Michel Lespinasse <walken@google.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michel Lespinasse 2013-05-07 06:45:56 -07:00 committed by Linus Torvalds
parent 5ede972df1
commit a7d2c573ae
1 changed files with 8 additions and 2 deletions
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10
lib/rwsem.c
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@ -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 */
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
while (true) {
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
/* 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);
schedule();
/* 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);
}