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>
diff --git a/lib/rwsem.c b/lib/rwsem.c
index 64c2dc0..edf3d9c 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -214,8 +214,8 @@
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 @@
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);
}