linux-kernel - [PATCH -tip 3/3] locking/osq: Relax atomic semantics

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 14 Sep 2015 00:37:24 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH -tip 3/3] 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@...e.de>
---
 kernel/locking/osq_lock.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index dc85ee2..d092a0c 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;
 
 	/*
-- 
2.1.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/