From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 41834C2D0A3 for ; Tue, 3 Nov 2020 10:15:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DCE742074B for ; Tue, 3 Nov 2020 10:15:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728055AbgKCKPp (ORCPT ); Tue, 3 Nov 2020 05:15:45 -0500 Received: from mx2.suse.de ([195.135.220.15]:32784 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726109AbgKCKPp (ORCPT ); Tue, 3 Nov 2020 05:15:45 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 93DCAAC1F; Tue, 3 Nov 2020 10:15:43 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 3B33D1E12FB; Tue, 3 Nov 2020 11:15:43 +0100 (CET) Date: Tue, 3 Nov 2020 11:15:43 +0100 From: Jan Kara To: Filipe Manana Cc: Peter Zijlstra , LKML , Jan Kara , David Sterba , matorola@gmail.com, mingo@kernel.org Subject: Re: possible lockdep regression introduced by 4d004099a668 ("lockdep: Fix lockdep recursion") Message-ID: <20201103101543.GC3440@quack2.suse.cz> References: <20201026114009.GN2594@hirez.programming.kicks-ass.net> <0c0d815c-bd5a-ff2d-1417-28a41173f2b4@suse.com> <20201026125524.GP2594@hirez.programming.kicks-ass.net> <20201026152256.GB2651@hirez.programming.kicks-ass.net> <968c6023-612c-342b-aa69-ec9e1e428eb0@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <968c6023-612c-342b-aa69-ec9e1e428eb0@suse.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 02-11-20 17:58:54, Filipe Manana wrote: > > > On 26/10/20 15:22, Peter Zijlstra wrote: > > On Mon, Oct 26, 2020 at 01:55:24PM +0100, Peter Zijlstra wrote: > >> On Mon, Oct 26, 2020 at 11:56:03AM +0000, Filipe Manana wrote: > >>>> That smells like the same issue reported here: > >>>> > >>>> https://lkml.kernel.org/r/20201022111700.GZ2651@hirez.programming.kicks-ass.net > >>>> > >>>> Make sure you have commit: > >>>> > >>>> f8e48a3dca06 ("lockdep: Fix preemption WARN for spurious IRQ-enable") > >>>> > >>>> (in Linus' tree by now) and do you have CONFIG_DEBUG_PREEMPT enabled? > >>> > >>> Yes, CONFIG_DEBUG_PREEMPT is enabled. > >> > >> Bummer :/ > >> > >>> I'll try with that commit and let you know, however it's gonna take a > >>> few hours to build a kernel and run all fstests (on that test box it > >>> takes over 3 hours) to confirm that fixes the issue. > >> > >> *ouch*, 3 hours is painful. How long to make it sick with the current > >> kernel? quicker I would hope? > >> > >>> Thanks for the quick reply! > >> > >> Anyway, I don't think that commit can actually explain the issue :/ > >> > >> The false positive on lockdep_assert_held() happens when the recursion > >> count is !0, however we _should_ be having IRQs disabled when > >> lockdep_recursion > 0, so that should never be observable. > >> > >> My hope was that DEBUG_PREEMPT would trigger on one of the > >> __this_cpu_{inc,dec}(lockdep_recursion) instance, because that would > >> then be a clear violation. > >> > >> And you're seeing this on x86, right? > >> > >> Let me puzzle moar.. > > > > So I might have an explanation for the Sparc64 fail, but that can't > > explain x86 :/ > > > > I initially thought raw_cpu_read() was OK, since if it is !0 we have > > IRQs disabled and can't get migrated, so if we get migrated both CPUs > > must have 0 and it doesn't matter which 0 we read. > > > > And while that is true; it isn't the whole store, on pretty much all > > architectures (except x86) this can result in computing the address for > > one CPU, getting migrated, the old CPU continuing execution with another > > task (possibly setting recursion) and then the new CPU reading the value > > of the old CPU, which is no longer 0. > > > > I already fixed a bunch of that in: > > > > baffd723e44d ("lockdep: Revert "lockdep: Use raw_cpu_*() for per-cpu variables"") > > > > but clearly this one got crossed. > > > > Still, that leaves me puzzled over you seeing this on x86 :/ > > Hi Peter, > > I still get the same issue with 5.10-rc2. > Is there any non-merged patch I should try, or anything I can help with? BTW, I've just hit the same deadlock issue with ext4 on generic/390 so I confirm this isn't btrfs specific issue (as we already knew from the analysis but still it's good to have that confirmed). Honza -- Jan Kara SUSE Labs, CR