From: Michel Lespinasse <walken@google.com>
Date: Tue, 7 May 2013 13:45:56 +0000 (-0700)
Subject: rwsem: avoid taking wait_lock in rwsem_down_write_failed
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=a7d2c573ae7fad1b2c877d1a1342fa5bb0d6478c;p=openwrt%2Fstaging%2Fblogic.git

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 64c2dc007be2..edf3d9ca670e 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -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);
 	}