linux-kernel - [PATCH 2/4] locking/rtmutex: Use cmp-cmpxchg

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Message-Id: <1432056298-18738-3-git-send-email-dave@stgolabs.net>
Date:	Tue, 19 May 2015 10:24:56 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Davidlohr Bueso <dave@...olabs.net>,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 2/4] locking/rtmutex: Use cmp-cmpxchg

Avoid unnecessary cmpxchg calls, all of our other locks
use it as well.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 kernel/locking/rtmutex.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 74188d8..1d5cc9d 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -74,7 +74,9 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  * set up.
  */
 #ifndef CONFIG_DEBUG_RT_MUTEXES
-# define rt_mutex_cmpxchg(l,c,n)	(cmpxchg(&l->owner, c, n) == c)
+# define rt_mutex_cmpxchg(l,c,n) \
+	(l->owner == c && cmpxchg(&l->owner, c, n) == c)
+
 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 {
 	unsigned long owner, *p = (unsigned long *) &lock->owner;
-- 
2.1.4

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