[PATCH v7 1/6] pv-qspinlock: use cmpxchg_release in __pv_queued_spin_unlock

[Pan Xinhui]

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.f...@gmail.com>
Signed-off-by: Pan Xinhui <xinhui....@linux.vnet.ibm.com>
---
 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 8a99abf..ce655aa 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -544,7 +544,7 @@ __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;
 
-- 
2.4.11