[tip:locking/core] locking/pv-qspinlock: Use cmpxchg_release() in __pv_queued_spin_unlock()

[tip-bot for Pan Xinhui]

Commit-ID:  b193049375b04df3ada8c3347b7083db95918bc3
Gitweb:     http://git.kernel.org/tip/b193049375b04df3ada8c3347b7083db95918bc3
Author:     Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 19 Sep 2016 05:23:52 -0400
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 22 Sep 2016 15:25:51 +0200

locking/pv-qspinlock: Use cmpxchg_release() in __pv_queued_spin_unlock()

cmpxchg_release() is more lighweight than cmpxchg() on some archs(e.g.
PPC), moreover, in __pv_queued_spin_unlock() we only needs a RELEASE in
the fast path(pairing with *_try_lock() or *_lock()). And the slow path
has smp_store_release too. So it's safe to use cmpxchg_release here.

Suggested-by:  Boqun Feng <boqun.feng@xxxxxxxxx>
Signed-off-by: Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: benh@xxxxxxxxxxxxxxxxxxx
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: mpe@xxxxxxxxxxxxxx
Cc: paulmck@xxxxxxxxxxxxxxxxxx
Cc: paulus@xxxxxxxxx
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: waiman.long@xxxxxxx
Link: http://lkml.kernel.org/r/1474277037-15200-2-git-send-email-xinhui.pan@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/locking/qspinlock_paravirt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 3acf16d..e3b5520 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -540,7 +540,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
 	 * unhash. Otherwise it would be possible to have multiple @lock
 	 * entries, which would be BAD.
 	 */
-	locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
+	locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0);
 	if (likely(locked == _Q_LOCKED_VAL))
 		return;