From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755532Ab0KJSHe (ORCPT ); Wed, 10 Nov 2010 13:07:34 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:39894 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755372Ab0KJSHc (ORCPT ); Wed, 10 Nov 2010 13:07:32 -0500 Date: Wed, 10 Nov 2010 19:07:11 +0100 From: Ingo Molnar To: Don Zickus Cc: fweisbec@gmail.com, Peter Zijlstra , LKML , akpm@linux-foundation.org, sergey.senozhatsky@gmail.com Subject: Re: [PATCH v3] watchdog: touch_nmi_watchdog should only touch local cpu not every one Message-ID: <20101110180711.GB22410@elte.hu> References: <1289240913-16677-1-git-send-email-dzickus@redhat.com> <20101110074941.GD29493@elte.hu> <20101110160516.GZ4823@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101110160516.GZ4823@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -2.0 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 * Don Zickus wrote: > > Hm, the flip side is that if a CPU is stuck spewing backtraces, we will now make > > all the other CPUs a lot more noisy - which might only 'lock up' because this > > CPU is stuck spewing oopses, right? > > When you say the other CPUs will be a lot more noisy, is that because they are > busy processing backtraces for the first cpu to spew? I guess I don't understand > how the other CPUs could have their interrupts off the whole time while the first > cpu is spewing a backtrace (just trying to educate myself). Say the kernel crashes on a CPU and keeps spewing new oopses, while write-holding tasklist_lock. Any other CPU that delivers a signal from IRQ context, trying to take the tasklist_lock, will loop indefinitely until that crashing CPU releases the lock. In that case the 'secondary' NMI warnings from all other CPUs (eventually every CPU gets stuck in such a scenario) will start spewing NMI lockup messages. Dunno. Maybe we should do your change - but also have an option to 'shut up' the kernel after the first hard oops [not warning]. That would silence the secondary NMI watchdog messages as well. Thanks, Ingo