diff options
| author | Davidlohr Bueso <dave@stgolabs.net> | 2015-09-14 00:37:24 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-09-18 09:27:29 +0200 |
| commit | c55a6ffa6285e29f874ed403979472631ec70bff (patch) | |
| tree | 122677e6f6cb995ba2bf53591c9b24e8322e1ff0 | |
| parent | 6e1e5196975fb7ecc501b3fe1075b77aea2b7839 (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.c | 11 |
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; /* |