Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753129Ab0AZKn6 (ORCPT ); Tue, 26 Jan 2010 05:43:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752890Ab0AZKn5 (ORCPT ); Tue, 26 Jan 2010 05:43:57 -0500 Received: from www.tglx.de ([62.245.132.106]:56757 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752733Ab0AZKn4 (ORCPT ); Tue, 26 Jan 2010 05:43:56 -0500 Date: Tue, 26 Jan 2010 11:43:21 +0100 (CET) From: Thomas Gleixner To: Jason Wessel cc: linux-kernel@vger.kernel.org, kgdb-bugreport@lists.sourceforge.net, mingo@elte.hu, Martin Schwidefsky , John Stultz , Andrew Morton , Magnus Damm Subject: Re: [PATCH 3/4] kgdb,clocksource: Prevent kernel hang in kernel debugger In-Reply-To: <1264480000-6997-4-git-send-email-jason.wessel@windriver.com> Message-ID: References: <1264480000-6997-1-git-send-email-jason.wessel@windriver.com> <1264480000-6997-4-git-send-email-jason.wessel@windriver.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1988 Lines: 52 On Mon, 25 Jan 2010, Jason Wessel wrote: > This is a regression fix against: 0f8e8ef7c204988246da5a42d576b7fa5277a8e4 > > Spin locks were added to the clocksource_resume_watchdog() which cause > the kernel debugger to deadlock on an SMP system frequently. > > The kernel debugger can try for the lock, but if it fails it should > continue to touch the clocksource watchdog anyway, else it will trip > if the general kernel execution has been paused for too long. > > This introduces an possible race condition where the kernel debugger > might not process the list correctly if a clocksource is being added > or removed at the time of this call. This race is sufficiently rare vs > having the kernel debugger hang the kernel > > CC: Thomas Gleixner > CC: Martin Schwidefsky > CC: John Stultz > CC: Andrew Morton > CC: Magnus Damm > Signed-off-by: Jason Wessel > --- > kernel/time/clocksource.c | 7 ++++++- > 1 files changed, 6 insertions(+), 1 deletions(-) > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > index e85c234..74f9ba6 100644 > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -463,7 +463,12 @@ void clocksource_resume(void) > */ > void clocksource_touch_watchdog(void) > { > - clocksource_resume_watchdog(); > + unsigned long flags; > + > + int got_lock = spin_trylock_irqsave(&watchdog_lock, flags); > + clocksource_reset_watchdog(); > + if (got_lock) > + spin_unlock_irqrestore(&watchdog_lock, flags); Just for the record. This patch would not compile on any platform which has CONFIG_CLOCKSOURCE_WATCHDOG=n Thanks, tglx -- 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/