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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 EEE27C2D0A3 for ; Mon, 26 Oct 2020 20:36:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF5272080A for ; Mon, 26 Oct 2020 20:36:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388555AbgJZUgh (ORCPT ); Mon, 26 Oct 2020 16:36:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:43850 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388529AbgJZUgh (ORCPT ); Mon, 26 Oct 2020 16:36:37 -0400 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 7C04CAC7D; Mon, 26 Oct 2020 20:36:35 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 0055ADA6E2; Mon, 26 Oct 2020 21:35:01 +0100 (CET) Date: Mon, 26 Oct 2020 21:35:01 +0100 From: David Sterba To: Peter Zijlstra Cc: Filipe Manana , LKML , Jan Kara , David Sterba Subject: Re: possible lockdep regression introduced by 4d004099a668 ("lockdep: Fix lockdep recursion") Message-ID: <20201026203501.GU6756@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Peter Zijlstra , Filipe Manana , LKML , Jan Kara , David Sterba References: <20201026114009.GN2594@hirez.programming.kicks-ass.net> <0c0d815c-bd5a-ff2d-1417-28a41173f2b4@suse.com> <20201026125524.GP2594@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201026125524.GP2594@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 :/ My builds don't have that enabled (CONFIG_PREEMPT_NONE=y) but I still see the warning (same scenario as for Filipe). That is with today's master branch + your fix from locking/urgent. > > 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. I can start another round (in my case it's more than 4 hours to reproduce it) with DEBUG_PREEMPT, unless you have something else to test.