[PATCH -tip] locking/pvqspinlock: replace xchg() by the more descriptive set_mb()

[Waiman Long]

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@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
---
 kernel/locking/qspinlock_paravirt.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index b5758a9..27ab96d 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);
-- 
1.7.1
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