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locking/mutexes/mcs: Correct barrier usage

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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>
This commit is contained in:
Waiman Long 2014-01-21 15:35:53 -08:00 committed by Ingo Molnar
parent 270750dbc1
commit aff7385b5a
1 changed files with 13 additions and 5 deletions
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18
kernel/locking/mutex.c
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@ -136,9 +136,12 @@ void mspin_lock(struct mspin_node **lock, struct mspin_node *node)
return;
}
ACCESS_ONCE(prev->next) = node;
smp_wmb();
/* Wait until the lock holder passes the lock down */
while (!ACCESS_ONCE(node->locked))
/*
* Wait until the lock holder passes the lock down.
* Using smp_load_acquire() provides a memory barrier that
* ensures subsequent operations happen after the lock is acquired.
*/
while (!(smp_load_acquire(&node->locked)))
arch_mutex_cpu_relax();
}
@ -156,8 +159,13 @@ static void mspin_unlock(struct mspin_node **lock, struct mspin_node *node)
while (!(next = ACCESS_ONCE(node->next)))
arch_mutex_cpu_relax();
}
ACCESS_ONCE(next->locked) = 1;
smp_wmb();
/*
* Pass lock to next waiter.
* smp_store_release() provides a memory barrier to ensure
* all operations in the critical section has been completed
* before unlocking.
*/
smp_store_release(&next->locked, 1);
}
/*