From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752085AbbKBTsn (ORCPT ); Mon, 2 Nov 2015 14:48:43 -0500 Received: from mail-io0-f173.google.com ([209.85.223.173]:34541 "EHLO mail-io0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752025AbbKBTsm (ORCPT ); Mon, 2 Nov 2015 14:48:42 -0500 MIME-Version: 1.0 In-Reply-To: <20151031175404.3c57a17a@tlielax.poochiereds.net> References: <20151029103113.2f893924@tlielax.poochiereds.net> <20151029135836.02ad9000@synchrony.poochiereds.net> <20151031020012.GH3582@mtj.duckdns.org> <20151031073400.2cf05d77@tlielax.poochiereds.net> <20151031213107.GA23841@mtj.duckdns.org> <20151031175404.3c57a17a@tlielax.poochiereds.net> Date: Mon, 2 Nov 2015 09:48:41 -1000 Message-ID: Subject: Re: timer code oops when calling mod_delayed_work From: Chris Worley To: Jeff Layton Cc: Tejun Heo , linux-kernel@vger.kernel.org, bfields@fieldses.org, Michael Skralivetsky , Trond Myklebust , Lai Jiangshan Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 31, 2015 at 11:54 AM, Jeff Layton wrote: > On Sat, 31 Oct 2015 17:31:07 -0400 > Tejun Heo wrote: ... >> >> > I have asked Chris and Michael to see if they can bisect it down, but >> > it may be a bit before they can get that done. Any insight you might >> > have in the meantime would helpful. >> >> Yeah, I'd love to find out how reproducible the issue is. If the >> problem is rarely reproducible, it might make sense to try >> instrumentation before trying bisection as it *could* be a latent bug >> which has been there all along and bisecting to the commit introducing >> the code wouldn't help us too much. >> > > It seems fairly reproducible, at least on v4.3-rc7 kernels: > > This came about when I asked them to perf test some nfsd patches that I > have queued up. I patched a Fedora 4.3-rc7 kernel and wanted to see > what the perf delta was (with NFSv3, fwiw): > > Patched kernels here: http://koji.fedoraproject.org/koji/taskinfo?taskID=11598089 > > Unpatched kernels here: http://koji.fedoraproject.org/koji/buildinfo?buildID=694377 > > Michael was using the SPEC SFS VDI workload to test, and was able to > get the same panic on both kernels. So it does seem to be reproducible. > It might even be possible to tune the VM to make the shrinker fire more > often, which may help tickle this more. > > In any case, I've asked them to try something v4.2-ish and see if it's > reproducible there, and then try v4.1 if it is. I figure anything > earlier is probably not worth testing if it still fails on v4.1. If it > turns out not to be reproducible on those earlier kernels then we can > bisect from there to track it down. The trick seems to be the NFS thread count: I initially though this was SFS/VDI specific, but when I ratcheted up the thread count to what Michael was using, 256 threads oopses on fio (throughput) benchmarks too. In bisecting kernels, it appeared between 4.2.3-200 and 4.2.5-200 (all the 4.2.4 kernels were bad). Jeff has a lead on this... Chris