Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753920AbbERPq0 (ORCPT ); Mon, 18 May 2015 11:46:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45577 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751435AbbERPqQ (ORCPT ); Mon, 18 May 2015 11:46:16 -0400 Date: Mon, 18 May 2015 11:45:31 -0400 From: Don Zickus To: Michal Hocko Cc: Ulrich Obergfell , Peter Zijlstra , Linus Torvalds , Stephane Eranian , Ingo Molnar , Andrew Morton , "Rafael J. Wysocki" , Kevin Hilman , Ulf Hansson , linux-pm@vger.kernel.org, LKML Subject: Re: suspend regression in 4.1-rc1 Message-ID: <20150518154531.GQ184517@redhat.com> References: <20150517185041.GA5897@dhcp22.suse.cz> <20150518073046.GO17717@twins.programming.kicks-ass.net> <20150518090336.GA6393@dhcp22.suse.cz> <20150518093150.GC21418@twins.programming.kicks-ass.net> <309071648.615900.1431946606778.JavaMail.zimbra@redhat.com> <20150518142607.GL184517@redhat.com> <20150518144136.GB5726@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150518144136.GB5726@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1924 Lines: 41 On Mon, May 18, 2015 at 04:41:37PM +0200, Michal Hocko wrote: > On Mon 18-05-15 10:26:07, Don Zickus wrote: > > On Mon, May 18, 2015 at 06:56:46AM -0400, Ulrich Obergfell wrote: > > > > > > > There further appears to be a distinct lack of serialization between > > > > setting and using watchdog_enabled, so perhaps we should wrap the > > > > {en,dis}able_all() things in watchdog_proc_mutex. > > > > > > As I understand it, the {en,dis}able_all() functions are only called early > > > at kernel startup, so I do not see how they could be racing with watchdog > > > code that is executed in the context of write() system calls to parameters > > > in /proc/sys/kernel. Please see also my earlier reply to Michal for further > > > details: http://marc.info/?l=linux-pm&m=143194387208250&w=2 > > > > > > Do we really need synchronization here? > > > > As Peter said we have to focus on doing things correctly and not based on > > what is currently. > > > > During s2ram, I believe all the threads get parked and then unparked during > > resume. I am wondering if the race happens there, threads get unparked and > > stomp on each other when watchdog_nmi_enable_all() is called. > > Wouldn't that cause an issue during freezer mode of pm_test? I can see > it much later in the processors mode. I am not familiar with the freeze mode of pm_test. But I believe the race only happens with cpu0. I would have thought cpu0 is slower to stop in freezer mode than in s2ram. Again, this was just my initial guess at the race problem. :-( Peter seems to have a patch (and Uli too) that addresses this problem, so not sure how much time to focus on figuring this out. Cheers, Don -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/