From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756209AbbJALGH (ORCPT ); Thu, 1 Oct 2015 07:06:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54611 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755189AbbJALGF (ORCPT ); Thu, 1 Oct 2015 07:06:05 -0400 Date: Thu, 1 Oct 2015 12:05:57 +0100 From: Aaron Tomlin To: Jiri Kosina Cc: Andrew Morton , Ulrich Obergfell , Don Zickus , linux-kernel@vger.kernel.org Subject: Re: [PATCH] watchdog: perform all-CPU backtrace in case of hard lockup Message-ID: <20151001110557.GS25024@atomlin.usersys.redhat.com> References: <20151001073703.GR25024@atomlin.usersys.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-PGP-Key: http://pgp.mit.edu/pks/lookup?search=atomlin%40redhat.com X-PGP-Fingerprint: 7906 84EB FA8A 9638 8D1E 6E9B E2DE 9658 19CC 77D6 User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2015-10-01 09:45 +0200, Jiri Kosina wrote: > That should be fine. Worst case scenario is hardlockup and softlockup > trigerring 'in parallel' on different CPUs, and all-cpu backtrace being > triggered twice. > > Frankly, I've never seen this happen in practice (hardlockup and > softlockup triggering at different CPUs at the very same time). > > We could possibly make a global 'all_cpus_dump_in_progress' flag so that > we guarantee only one stream of dumps, but we'd need to convert everybody > using this facility (e.g. RCU stall detector, and whoever else) to be > aware of it as well, otherwise it wouldn't make too much sense. > > Something to add to TODO I guess. This could indeed be worth further investigation. -- Aaron Tomlin