From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756562Ab0KJTEx (ORCPT ); Wed, 10 Nov 2010 14:04:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:14614 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756039Ab0KJTEt (ORCPT ); Wed, 10 Nov 2010 14:04:49 -0500 Date: Wed, 10 Nov 2010 14:03:52 -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: <20101110190352.GA31794@redhat.com> References: <1289240913-16677-1-git-send-email-dzickus@redhat.com> <20101110074941.GD29493@elte.hu> <20101110160516.GZ4823@redhat.com> <20101110180711.GB22410@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101110180711.GB22410@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 07:07:11PM +0100, Ingo Molnar wrote: > > * 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. You mean inside the panic() routine? like a ratelimit? Cheers, Don