From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934350AbcAZLOp (ORCPT ); Tue, 26 Jan 2016 06:14:45 -0500 Received: from mx2.suse.de ([195.135.220.15]:40046 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932109AbcAZLOl (ORCPT ); Tue, 26 Jan 2016 06:14:41 -0500 Date: Tue, 26 Jan 2016 12:14:38 +0100 From: Petr Mladek To: Jan Kara Cc: Thomas Gleixner , Ben Hutchings , Tejun Heo , Sasha Levin , Shaohua Li , LKML , stable@vger.kernel.org, Daniel Bilik Subject: Re: Crashes with 874bbfe600a6 in 3.18.25 Message-ID: <20160126111438.GA731@pathway.suse.cz> References: <20160120211926.GJ10810@quack.suse.cz> <20160120213901.GA755895@devbig084.prn1.facebook.com> <20160121095234.GN10810@quack.suse.cz> <56A1817C.10300@oracle.com> <20160122160903.GH32380@htj.duckdns.org> <1453515623.3734.156.camel@decadent.org.uk> <20160126093400.GV24938@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20160126093400.GV24938@quack.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 On Tue 2016-01-26 10:34:00, Jan Kara wrote: > On Sat 23-01-16 17:11:54, Thomas Gleixner wrote: > > On Sat, 23 Jan 2016, Ben Hutchings wrote: > > > On Fri, 2016-01-22 at 11:09 -0500, Tejun Heo wrote: > > > > > Looks like it requires more than trivial backport (I think). Tejun? > > > > > > > > The timer migration has changed quite a bit.  Given that we've never > > > > seen vmstat work crashing in 3.18 era, I wonder whether the right > > > > thing to do here is reverting 874bbfe600a6 from 3.18 stable? > > > > > > It's not just 3.18 that has this; 874bbfe600a6 was backported to all > > > stable branches from 3.10 onward.  Only the 4.2-ckt branch has > > > 22b886dd10180939. > > > > 22b886dd10180939 fixes a bug which was introduced with the timer wheel > > overhaul in 4.2. So only 4.2/3 should have it backported. > > Thanks for explanation. So do I understand right that timers are always run > on the calling CPU in kernels prior to 4.2 and thus commit 874bbfe600a6 (to > run timer for delayed work on the calling CPU) doesn't make sense there? If > that is true than reverting the commit from older stable kernels is > probably the easiest way to resolve the crashes. The commit 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu") forces the timer to run on the local CPU. It might be correct for vmstat. But I wonder if it might break some other delayed work user that depends on running on different CPU. Best Regards, Petr