From: Waiman Long <Waiman.Long@hp.com>
Date: Tue, 21 Jan 2014 23:35:53 +0000 (-0800)
Subject: locking/mutexes/mcs: Correct barrier usage
X-Git-Tag: v3.15-rc1~184^2~22
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=aff7385b5a16bca6b8d9243f01a9ea5a5b411e1d;p=pandora-kernel.git

locking/mutexes/mcs: Correct barrier usage

This patch corrects the way memory barriers are used in the MCS lock
with smp_load_acquire and smp_store_release fucnctions.  The previous
barriers could leak critical sections if mcs lock is used by itself.
It is not a problem when mcs lock is embedded in mutex but will be an
issue when the mcs_lock is used elsewhere.

The patch removes the incorrect barriers and put in correct
barriers with the pair of functions smp_load_acquire and smp_store_release.

Suggested-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1390347353.3138.62.camel@schen9-DESK
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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