From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752881AbZGTL5r (ORCPT ); Mon, 20 Jul 2009 07:57:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752472AbZGTL5o (ORCPT ); Mon, 20 Jul 2009 07:57:44 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:42154 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751829AbZGTL5n (ORCPT ); Mon, 20 Jul 2009 07:57:43 -0400 Date: Mon, 20 Jul 2009 13:56:38 +0200 From: Ingo Molnar To: Peter Zijlstra Cc: Frederic Weisbecker , Li Zefan , hpa@zytor.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:sched/core] sched: Pull up the might_sleep() check into cond_resched() Message-ID: <20090720115638.GC29811@elte.hu> References: <1247725694-6082-6-git-send-email-fweisbec@gmail.com> <4A6413AB.2050807@cn.fujitsu.com> <20090720081210.GA5309@nowhere> <1248079747.15751.8202.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1248079747.15751.8202.camel@twins> User-Agent: Mutt/1.5.19 (2009-01-05) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra wrote: > On Mon, 2009-07-20 at 04:12 -0400, Frederic Weisbecker wrote: > > > From: Frederic Weisbecker > > Subject: [PATCH] sched: Check if the spinlock is locked in cond_resched_lock() > > > > Some uses of cond_resched_lock() might involve an > > unlocked spinlock, resulting in spurious sleep in > > atomic warnings. > > Check whether the spinlock is actually locked and > > take that into account in the might_sleep() check. > > > > Reported-by: Li Zefan > > Signed-off-by: Frederic Weisbecker > > --- > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index cb070dc..2789658 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -2294,9 +2294,10 @@ extern int _cond_resched(void); > > > > extern int __cond_resched_lock(spinlock_t *lock); > > > > -#define cond_resched_lock(lock) ({ \ > > - __might_sleep(__FILE__, __LINE__, PREEMPT_OFFSET); \ > > - __cond_resched_lock(lock); \ > > +#define cond_resched_lock(lock) ({ \ > > + __might_sleep(__FILE__, __LINE__, spin_is_locked(lock) ? \ > > + PREEMPT_OFFSET : 0); \ > > + __cond_resched_lock(lock); \ > > }) > > > > extern int __cond_resched_softirq(void); > > > No, this looks utterly broken.. who is to say it doesn't get unlocked > right after that spin_is_locked() check? > > cond_resched_lock() callers must hold the lock they use it on, not doing > so is broken. > > So I would suggest something like the below instead: > > (utterly untested) FYI, i've undone the tip:sched/core bits from tip:master for now - please send a delta patch against tip:sched/core once this is fixed. Thanks, Ingo