From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f41.google.com (mail-pb0-f41.google.com [209.85.160.41]) by kanga.kvack.org (Postfix) with ESMTP id 3F58D6B0036 for ; Mon, 20 Jan 2014 20:24:32 -0500 (EST) Received: by mail-pb0-f41.google.com with SMTP id up15so7203455pbc.0 for ; Mon, 20 Jan 2014 17:24:31 -0800 (PST) Received: from mga02.intel.com (mga02.intel.com. [134.134.136.20]) by mx.google.com with ESMTP id eb3si3121399pbd.137.2014.01.20.17.24.27 for ; Mon, 20 Jan 2014 17:24:28 -0800 (PST) Subject: [PATCH v8 1/6] MCS Lock: Barrier corrections From: Tim Chen In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Date: Mon, 20 Jan 2014 17:24:20 -0800 Message-ID: <1390267460.3138.35.camel@schen9-DESK> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar , Andrew Morton , Thomas Gleixner , "Paul E.McKenney" , Will Deacon Cc: linux-kernel@vger.kernel.org, linux-mm , linux-arch@vger.kernel.org, Linus Torvalds , Waiman Long , Andrea Arcangeli , Alex Shi , Andi Kleen , Michel Lespinasse , Davidlohr Bueso , Matthew R Wilcox , Dave Hansen , Peter Zijlstra , Rik van Riel , Peter Hurley , Tim Chen , Raghavendra K T , George Spelvin , "H. Peter Anvin" , Arnd Bergmann , Aswin Chandramouleeswaran , Scott J Norton , "Figo.zhang" From: Waiman Long This patch corrects the way memory barriers are used in the MCS lock with smp_load_acquire and smp_store_release fucnction. It removes ones that are not needed. Suggested-by: Michel Lespinasse Signed-off-by: Waiman Long Signed-off-by: Jason Low Signed-off-by: Tim Chen --- kernel/locking/mutex.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 4dd6e4c..fbbd2ed 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); } /* -- 1.7.11.7 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org