From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753538Ab3DRSJo (ORCPT ); Thu, 18 Apr 2013 14:09:44 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:36073 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752099Ab3DRSJm (ORCPT ); Thu, 18 Apr 2013 14:09:42 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Don Zickus Cc: linux-watchdog@vger.kernel.org, kexec@lists.infradead.org, wim@iguana.be, LKML , vgoyal@redhat.com, dyoung@redhat.com, Guenter Roeck References: <1366233596-34681-1-git-send-email-dzickus@redhat.com> <87ip3j94qu.fsf@xmission.com> <20130418174432.GN79013@redhat.com> Date: Thu, 18 Apr 2013 11:09:29 -0700 In-Reply-To: <20130418174432.GN79013@redhat.com> (Don Zickus's message of "Thu, 18 Apr 2013 13:44:32 -0400") Message-ID: <87ehe77lt2.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX1/lRHycJ7vyjnmIwossMACOhvMvAAlAMrI= X-SA-Exim-Connect-IP: 98.207.154.105 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -3.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa05 1397; Body=1 Fuz1=1 Fuz2=1] X-Spam-DCC: XMission; sa05 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Don Zickus X-Spam-Relay-Country: Subject: Re: [PATCH v3] watchdog: Add hook for kicking in kdump path X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Wed, 14 Nov 2012 14:26:46 -0700) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Don Zickus writes: > On Thu, Apr 18, 2013 at 09:35:05AM -0700, Eric W. Biederman wrote: >> Don Zickus writes: >> >> > A common problem with kdump is that during the boot up of the >> > second kernel, the hardware watchdog times out and reboots the >> > machine before a vmcore can be captured. >> > >> > Instead of tellling customers to disable their hardware watchdog >> > timers, I hacked up a hook to put in the kdump path that provides >> > one last kick before jumping into the second kernel. >> >> Having thought about this a little more this patch is actively wrong. >> >> The problem is you can easily be petting the watchdog in violation of >> whatever policy is normally in place. Which means that this extra >> petting can result in a system that is unavailable for an unacceptably >> long period of time. > > Not really, just an extra period which isn't that much. This would only > be noticable if kdump is setup and enabled and then _hung_, otherwise it > just quickly reboots and noone notices. :-) For the folks who care the definition of acceptable unavailability would look like: watchdog timeout + max boot time + margin of error. So it is possible for an extra watchdog pet to eat up or exceed your margin of error. You are more likely to cause a how in the world did that happen than something more extreme, but even playing invalidating peoples mental model can be a problem sometimes. >> I expect most watchdog policies are not that strict, but this patch >> would preclude using those that are. > > I would assume most of those users would not enable kdump and would not be > affected. I have seen it be the case that the goal is to record what went wrong if there is time, but to get back into service in a timely manner regardless. >> And like is being discussed in another subthread it does look like >> changing the timeout and the interval should be enough all on it's own. > > Probably and I will pursue that. Thanks for the suggestion. Eric