From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752130AbdHHJGE (ORCPT ); Tue, 8 Aug 2017 05:06:04 -0400 Received: from isilmar-4.linta.de ([136.243.71.142]:33454 "EHLO isilmar-4.linta.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752043AbdHHJGC (ORCPT ); Tue, 8 Aug 2017 05:06:02 -0400 Date: Tue, 8 Aug 2017 11:06:01 +0200 From: Dominik Brodowski To: NeilBrown Cc: Shaohua Li , David R , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, tj@kernel.org Subject: Re: [MD] Crash with 4.12+ kernel and high disk load -- bisected to 4ad23a976413: MD: use per-cpu counter for writes_pending Message-ID: <20170808090600.GA28583@isilmar-4.linta.de> References: <20170807112025.GA3094@light.dominikbrodowski.net> <87k22esfuf.fsf@notabene.neil.brown.name> <20170808073614.GA21316@light.dominikbrodowski.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170808073614.GA21316@light.dominikbrodowski.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 08, 2017 at 09:36:14AM +0200, Dominik Brodowski wrote: > On Tue, Aug 08, 2017 at 05:01:28PM +1000, NeilBrown wrote: > > On Mon, Aug 07 2017, Dominik Brodowski wrote: > > > > > Neil, Shaohua, > > > > > > following up on David R's bug message: I have observed something similar > > > on v4.12.[345] and v4.13-rc4, but not on v4.11. This is a RAID1 (on bare > > > metal partitions, /dev/sdaX and /dev/sdbY linked together). In case it > > > matters: Further upwards are cryptsetup, a DM volume group, then logical > > > volumes, and then filesystems (ext4, but also happened with xfs). > > > > > > In a tedious bisect (the bug wasn't as quickly reproducible as I would like, > > > but happened when I repeatedly created large lvs and filled them with some > > > content, while compiling kernels in parallel), I was able to track this > > > down to: > > > > > > > > > commit 4ad23a976413aa57fe5ba7a25953dc35ccca5b71 > > > Author: NeilBrown > > > Date: Wed Mar 15 14:05:14 2017 +1100 > > > > > > MD: use per-cpu counter for writes_pending > > > > > > The 'writes_pending' counter is used to determine when the > > > array is stable so that it can be marked in the superblock > > > as "Clean". Consequently it needs to be updated frequently > > > but only checked for zero occasionally. Recent changes to > > > raid5 cause the count to be updated even more often - once > > > per 4K rather than once per bio. This provided > > > justification for making the updates more efficient. > > > > > > ... > > > > Thanks for the report... and for bisecting and for re-sending... > > > > I believe I have found the problem, and have sent a patch separately. > > > > If mddev->safemode == 1 and mddev->in_sync != 0, md_check_recovery() > > causes the thread that calls it to spin. > > Prior to the patch you found, that couldn't happen. Now it can, > > so it needs to be handled more carefully. > > > > While I was examining the code, I found another bug - so that is a win! > > > > Thanks, > > NeilBrown > > > Nice catch. Thanks! Will give it (both patches at once) a try on the test > system immediately. More than 2 hours of stress-testing shows no issues any more. Very nice. Thanks! Dominik