From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751989AbdFTQpe (ORCPT ); Tue, 20 Jun 2017 12:45:34 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:53745 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751052AbdFTQpb (ORCPT ); Tue, 20 Jun 2017 12:45:31 -0400 Date: Tue, 20 Jun 2017 09:45:23 -0700 From: "Paul E. McKenney" To: Tejun Heo Cc: jiangshanlai@gmail.com, linux-kernel@vger.kernel.org Subject: Re: WARN_ON_ONCE() in process_one_work()? Reply-To: paulmck@linux.vnet.ibm.com References: <20170501185819.GJ3956@linux.vnet.ibm.com> <20170505171159.GA10296@linux.vnet.ibm.com> <20170613205837.GB7359@htj.duckdns.org> <20170613223103.GX3721@linux.vnet.ibm.com> <20170614151548.GA14462@linux.vnet.ibm.com> <20170615153857.GA27788@linux.vnet.ibm.com> <20170616173658.GA451@linux.vnet.ibm.com> <20170617115314.GA20758@htj.duckdns.org> <20170617173105.GI3721@linux.vnet.ibm.com> <20170618104000.GC28042@htj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170618104000.GC28042@htj.duckdns.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17062016-0052-0000-0000-00000228A868 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007262; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00877519; UDB=6.00437147; IPR=6.00657658; BA=6.00005432; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015900; XFM=3.00000015; UTC=2017-06-20 16:45:24 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17062016-0053-0000-0000-00005108CE74 Message-Id: <20170620164523.GI3721@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-06-20_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1706200288 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jun 18, 2017 at 06:40:00AM -0400, Tejun Heo wrote: > Hello, > > On Sat, Jun 17, 2017 at 10:31:05AM -0700, Paul E. McKenney wrote: > > On Sat, Jun 17, 2017 at 07:53:14AM -0400, Tejun Heo wrote: > > > Hello, > > > > > > On Fri, Jun 16, 2017 at 10:36:58AM -0700, Paul E. McKenney wrote: > > > > And no test failures from yesterday evening. So it looks like we get > > > > somewhere on the order of one failure per 138 hours of TREE07 rcutorture > > > > runtime with your printk() in the mix. > > > > > > > > Was the above output from your printk() output of any help? > > > > > > Yeah, if my suspicion is correct, it'd require new kworker creation > > > racing against CPU offline, which would explain why it's so difficult > > > to repro. Can you please see whether the following patch resolves the > > > issue? > > > > That could explain why only Steve Rostedt and I saw the issue. As far > > as I know, we are the only ones who regularly run CPU-hotplug stress > > tests. ;-) > > I was a bit confused. It has to be racing against either new kworker > being created on the wrong CPU or rescuer trying to migrate to the > CPU, and it looks like we're mostly seeing the rescuer condition, but, > yeah, this would only get triggered rarely. Another contributing > factor could be the vmstat work putting on a workqueue w/ rescuer > recently. It runs quite often, so probably has increased the chance > of hitting the right condition. Sounds like too much fun! ;-) But more constructively... If I understand correctly, it is now possible to take a CPU partially offline and put it back online again. This should allow much more intense testing of this sort of interaction. And no, I haven't yet tried this with RCU because I would probably need to do some mix of just-RCU online/offline and full-up online-offline. Plus RCU requires pretty much a full online/offline cycle to fully exercise it. :-/ > > I have a weekend-long run going, but will give this a shot overnight on > > Monday, Pacific Time. Thank you for putting it together, looking forward > > to seeing what it does! > > Thanks a lot for the testing and patience. Sorry that it took so > long. I'm not completely sure the patch is correct. It might have to > be more specifc about which type of migration or require further > synchronization around migration, but hopefully it'll at least be able > to show that this was the cause of the problem. And last night's tests had no failures. Which might actually mean something, will get more info when I run without your patch this evening. ;-) Thanx, Paul