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

From: Waiman Long
Date: Sun May 10 2015 - 21:18:15 EST

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);
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