linux-kernel - [tip:locking/core] locking/pv-qspinlock: Use cmpxchg_release() in __pv_queued_spin

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Date:   Thu, 22 Sep 2016 07:02:46 -0700
From:   tip-bot for Pan Xinhui <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, xinhui.pan@...ux.vnet.ibm.com,
        tglx@...utronix.de, mingo@...nel.org, hpa@...or.com,
        boqun.feng@...il.com, linux-kernel@...r.kernel.org,
        peterz@...radead.org
Subject: [tip:locking/core] locking/pv-qspinlock: Use cmpxchg_release() in
 __pv_queued_spin_unlock()

Commit-ID:  b193049375b04df3ada8c3347b7083db95918bc3
Gitweb:     http://git.kernel.org/tip/b193049375b04df3ada8c3347b7083db95918bc3
Author:     Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
AuthorDate: Mon, 19 Sep 2016 05:23:52 -0400
Committer:  Ingo Molnar <mingo@...nel.org>
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@...il.com>
Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: benh@...nel.crashing.org
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: mpe@...erman.id.au
Cc: paulmck@...ux.vnet.ibm.com
Cc: paulus@...ba.org
Cc: virtualization@...ts.linux-foundation.org
Cc: waiman.long@....com
Link: http://lkml.kernel.org/r/1474277037-15200-2-git-send-email-xinhui.pan@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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;