From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756844Ab0KJQGK (ORCPT ); Wed, 10 Nov 2010 11:06:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40659 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756346Ab0KJQGI (ORCPT ); Wed, 10 Nov 2010 11:06:08 -0500 Date: Wed, 10 Nov 2010 11:05:16 -0500 From: Don Zickus To: Ingo Molnar 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: <20101110160516.GZ4823@redhat.com> References: <1289240913-16677-1-git-send-email-dzickus@redhat.com> <20101110074941.GD29493@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101110074941.GD29493@elte.hu> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 10, 2010 at 08:49:41AM +0100, Ingo Molnar wrote: > > * Don Zickus wrote: > > > I ran into a scenario where while one cpu was stuck and should have panic'd > > because of the NMI watchdog, it didn't. The reason was another cpu was spewing > > stack dumps on to the console. Upon investigation, I noticed that when writing to > > the console and also when dumping the stack, the watchdog is touched. > > > > This causes all the cpus to reset their NMI watchdog flags and the 'stuck' cpu > > just spins forever. > > 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). Cheers, Don