From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755237Ab1FGNr1 (ORCPT ); Tue, 7 Jun 2011 09:47:27 -0400 Received: from casper.infradead.org ([85.118.1.10]:37750 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753350Ab1FGNr0 convert rfc822-to-8bit (ORCPT ); Tue, 7 Jun 2011 09:47:26 -0400 Subject: Re: [PATCH] sched: correct testing need_resched in mutex_spin_on_owner() From: Peter Zijlstra To: Hillf Danton Cc: LKML , Ingo Molnar In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Tue, 07 Jun 2011 15:47:19 +0200 Message-ID: <1307454439.2322.260.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2011-06-07 at 21:41 +0800, Hillf Danton wrote: > It is suppose to check the owner task that is not absolutly running on the > local CPU, Oh, why do you think so? > and if NEED_RESCHED is happenly set on the current task of local > CPU, we get incorrect result. Only if your above assumption holds, which it doesn't. It explicitly checks to see if _this_ cpu needs a resched while spinning, if so it bails the spinning and calls schedule in the lock slow path. If the owner cpu reschedules, owner will leave the rq and owner_running() will return false, also breaking the loop. > > Signed-off-by: Hillf Danton > --- > kernel/sched.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/sched.c b/kernel/sched.c > index fd18f39..3ea64fe 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -4326,7 +4326,7 @@ int mutex_spin_on_owner(struct mutex *lock, > struct task_struct *owner) > return 0; > > while (owner_running(lock, owner)) { > - if (need_resched()) > + if (test_tsk_need_resched(owner)) > return 0; > > arch_mutex_cpu_relax();