linux-kernel - [PATCH 5/5] locking/mcs: Use acquire/release semantics

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Message-Id: <1442866676-10359-6-git-send-email-dave@stgolabs.net>
Date:	Mon, 21 Sep 2015 13:17:56 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 5/5] locking/mcs: Use acquire/release semantics

As such, weakly ordered archs can benefit from more relaxed use
of barriers when locking/unlocking.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 kernel/locking/mcs_spinlock.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
index fd91aaa..5b9102a 100644
--- a/kernel/locking/mcs_spinlock.h
+++ b/kernel/locking/mcs_spinlock.h
@@ -67,7 +67,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
 	node->locked = 0;
 	node->next   = NULL;
 
-	prev = xchg(lock, node);
+	prev = xchg_acquire(lock, node);
 	if (likely(prev == NULL)) {
 		/*
 		 * Lock acquired, don't need to set node->locked to 1. Threads
@@ -98,7 +98,7 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
 		/*
 		 * Release the lock by setting it to NULL
 		 */
-		if (likely(cmpxchg(lock, node, NULL) == node))
+		if (likely(cmpxchg_release(lock, node, NULL) == node))
 			return;
 		/* Wait until the next pointer is set */
 		while (!(next = READ_ONCE(node->next)))
-- 
2.1.4

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