Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751694AbaAOHop (ORCPT ); Wed, 15 Jan 2014 02:44:45 -0500 Received: from merlin.infradead.org ([205.233.59.134]:56855 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750724AbaAOHoo (ORCPT ); Wed, 15 Jan 2014 02:44:44 -0500 Date: Wed, 15 Jan 2014 08:44:20 +0100 From: Peter Zijlstra To: Jason Low Cc: mingo@redhat.com, paulmck@linux.vnet.ibm.com, Waiman.Long@hp.com, torvalds@linux-foundation.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, riel@redhat.com, akpm@linux-foundation.org, davidlohr@hp.com, hpa@zytor.com, aswin@hp.com, scott.norton@hp.com Subject: Re: [RFC 1/3] mutex: In mutex_can_spin_on_owner(), return false if task need_resched() Message-ID: <20140115074420.GV31570@twins.programming.kicks-ass.net> References: <1389745990-7069-1-git-send-email-jason.low2@hp.com> <1389745990-7069-2-git-send-email-jason.low2@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1389745990-7069-2-git-send-email-jason.low2@hp.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 14, 2014 at 04:33:08PM -0800, Jason Low wrote: > The mutex_can_spin_on_owner() function should also return false if the > task needs to be rescheduled. > While I was staring at mutex_can_spin_on_owner(); don't we need this? kernel/locking/mutex.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 4dd6e4c219de..480d2f437964 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -214,8 +214,10 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock) rcu_read_lock(); owner = ACCESS_ONCE(lock->owner); - if (owner) + if (owner) { + smp_read_barrier_depends(); retval = owner->on_cpu; + } rcu_read_unlock(); /* * if lock->owner is not set, the mutex owner may have just acquired -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/