diff options
| author | Waiman Long <Waiman.Long@hp.com> | 2014-01-22 03:35:53 +0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2014-01-28 16:13:26 +0400 |
| commit | aff7385b5a16bca6b8d9243f01a9ea5a5b411e1d (patch) | |
| tree | ca8b03e4e6aa1d0fcd8ae971e98b0719fdb08666 /kernel/locking | |
| parent | 270750dbc18a71b23d660df110e433ff9616a2d4 (diff) | |
| download | linux-aff7385b5a16bca6b8d9243f01a9ea5a5b411e1d.tar.xz | |
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>
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/mutex.c | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 4dd6e4c219de..fbbd2eda867e 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -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); } /* |