From: Waiman Long <Waiman.Long@hp.com>
Date: Mon, 11 May 2015 01:17:10 +0000 (-0400)
Subject: locking/pvqspinlock: Replace xchg() by the more descriptive set_mb()
X-Git-Tag: firefly_0821_release~176^2~1635^2~10
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=52c9d2badd1ae4d11c29de57d4e964e48afd3cb4;p=firefly-linux-kernel-4.4.55.git

locking/pvqspinlock: Replace xchg() by the more descriptive set_mb()

The xchg() function was used in pv_wait_node() to set a certain
value and provide a memory barrier which is what the set_mb()
function is for.  This patch replaces the xchg() call by
set_mb().

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index b5758a95a8d3..27ab96dca68c 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -175,7 +175,7 @@ static void pv_wait_node(struct mcs_spinlock *node)
 		 *
 		 * Matches the xchg() from pv_kick_node().
 		 */
-		(void)xchg(&pn->state, vcpu_halted);
+		set_mb(pn->state, vcpu_halted);
 
 		if (!READ_ONCE(node->locked))
 			pv_wait(&pn->state, vcpu_halted);