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authorDavidlohr Bueso <dave@stgolabs.net>2015-09-14 00:37:24 -0700
committerIngo Molnar <mingo@kernel.org>2015-09-18 09:27:29 +0200
commitc55a6ffa6285e29f874ed403979472631ec70bff (patch)
tree122677e6f6cb995ba2bf53591c9b24e8322e1ff0
parent6e1e5196975fb7ecc501b3fe1075b77aea2b7839 (diff)
locking/osq: Relax atomic semantics
... by using acquire/release for ops around the lock->tail. As such, weakly ordered archs can benefit from more relaxed use of barriers when issuing atomics. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <Waiman.Long@hpe.com> Link: http://lkml.kernel.org/r/1442216244-4409-3-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/locking/osq_lock.c11
1 files changed, 8 insertions, 3 deletions
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index dc85ee23a26f..d092a0c9c2d4 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -50,7 +50,7 @@ osq_wait_next(struct optimistic_spin_queue *lock,
for (;;) {
if (atomic_read(&lock->tail) == curr &&
- atomic_cmpxchg(&lock->tail, curr, old) == curr) {
+ atomic_cmpxchg_acquire(&lock->tail, curr, old) == curr) {
/*
* We were the last queued, we moved @lock back. @prev
* will now observe @lock and will complete its
@@ -92,7 +92,11 @@ bool osq_lock(struct optimistic_spin_queue *lock)
node->next = NULL;
node->cpu = curr;
- old = atomic_xchg(&lock->tail, curr);
+ /*
+ * ACQUIRE semantics, pairs with corresponding RELEASE
+ * in unlock() uncontended, or fastpath.
+ */
+ old = atomic_xchg_acquire(&lock->tail, curr);
if (old == OSQ_UNLOCKED_VAL)
return true;
@@ -184,7 +188,8 @@ void osq_unlock(struct optimistic_spin_queue *lock)
/*
* Fast path for the uncontended case.
*/
- if (likely(atomic_cmpxchg(&lock->tail, curr, OSQ_UNLOCKED_VAL) == curr))
+ if (likely(atomic_cmpxchg_release(&lock->tail, curr,
+ OSQ_UNLOCKED_VAL) == curr))
return;
/*