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=-11.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 C8F6FC432BE for ; Wed, 4 Aug 2021 22:34:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9FA0861078 for ; Wed, 4 Aug 2021 22:34:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230085AbhHDWeV (ORCPT ); Wed, 4 Aug 2021 18:34:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:59084 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229674AbhHDWeR (ORCPT ); Wed, 4 Aug 2021 18:34:17 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 934E66104F; Wed, 4 Aug 2021 22:33:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1628116438; bh=0dsbEmAguaSfHlozxbO03jG4cUL4rS7RbChy6uYIzB4=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=Z+kQZHeg13krHlaBS4u37wzE0TuHStij2oh+bIs7ldGzauoqqf2YKFN5fvitdEX/V nqKax6KBKKUiepCqjGpdPgluxwscIC6VyNJ5wskwLDn/S3JcbiwyfWo3MwocEwGR4g YXe1SKF/yc/e8zLJUYya70ZrRNhnumxRIwUOTtevSyAZIm6/HgxLvqBW+c0JDsP3b9 FhZMOJtHL/w2VezQnUZeJwK9B/Cj0qSTlMXgB4Zr/g6cebW9NhpuWJl2PpU7BsaGFw gCp2qMhi5fXDxDioV0+1lBRD2b9HDL8z2kHKdAkLT0FbBWnWK0YgVFPL89jqGmS1H8 tvoQBghUxM58g== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 5944E5C22D9; Wed, 4 Aug 2021 15:33:58 -0700 (PDT) Date: Wed, 4 Aug 2021 15:33:58 -0700 From: "Paul E. McKenney" To: Qais Yousef Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, Yanfei Xu Subject: Re: [PATCH rcu 02/18] rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock Message-ID: <20210804223358.GZ4397@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20210721202042.GA1472052@paulmck-ThinkPad-P17-Gen-1> <20210721202127.2129660-2-paulmck@kernel.org> <20210803142458.teveyn6t2gwifdcp@e107158-lin.cambridge.arm.com> <20210803155226.GQ4397@paulmck-ThinkPad-P17-Gen-1> <20210803161221.igae6y6xa6mlzltn@e107158-lin.cambridge.arm.com> <20210803162855.GT4397@paulmck-ThinkPad-P17-Gen-1> <20210804135017.g6tfaubvygki2osk@e107158-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210804135017.g6tfaubvygki2osk@e107158-lin.cambridge.arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 04, 2021 at 02:50:17PM +0100, Qais Yousef wrote: > On 08/03/21 09:28, Paul E. McKenney wrote: > > On Tue, Aug 03, 2021 at 05:12:21PM +0100, Qais Yousef wrote: > > > On 08/03/21 08:52, Paul E. McKenney wrote: > > > > On Tue, Aug 03, 2021 at 03:24:58PM +0100, Qais Yousef wrote: > > > > > Hi > > > > > > > > > > On 07/21/21 13:21, Paul E. McKenney wrote: > > > > > > From: Yanfei Xu > > > > > > > > > > > > If rcu_print_task_stall() is invoked on an rcu_node structure that does > > > > > > not contain any tasks blocking the current grace period, it takes an > > > > > > early exit that fails to release that rcu_node structure's lock. This > > > > > > results in a self-deadlock, which is detected by lockdep. > > > > > > > > > > > > To reproduce this bug: > > > > > > > > > > > > tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 3 --trust-make --configs "TREE03" --kconfig "CONFIG_PROVE_LOCKING=y" --bootargs "rcutorture.stall_cpu=30 rcutorture.stall_cpu_block=1 rcutorture.fwd_progress=0 rcutorture.test_boost=0" > > > > > > > > > > > > This will also result in other complaints, including RCU's scheduler > > > > > > hook complaining about blocking rather than preemption and an rcutorture > > > > > > writer stall. > > > > > > > > > > > > Only a partial RCU CPU stall warning message will be printed because of > > > > > > the self-deadlock. > > > > > > > > > > > > This commit therefore releases the lock on the rcu_print_task_stall() > > > > > > function's early exit path. > > > > > > > > > > > > Fixes: c583bcb8f5ed ("rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled") > > > > > > Signed-off-by: Yanfei Xu > > > > > > Signed-off-by: Paul E. McKenney > > > > > > --- > > > > > > > > > > We are seeing similar stall/deadlock issue on android 5.10 kernel, is the fix > > > > > relevant here? Trying to apply the patches and test, but the problem is tricky > > > > > to reproduce so thought worth asking first. > > > > > > > > Looks like the relevant symptoms to me, so I suggest trying this series > > > > from -rcu: > > > > > > > > 8baded711edc ("rcu: Fix to include first blocked task in stall warning") > > > > f6b3995a8b56 ("rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock") > > > > > > Great thanks. These are the ones we picked as the rest was a bit tricky to > > > apply on 5.10. > > > > > > While at it, we see these errors too though they look harmless. They happen > > > all the time > > > > > > [ 595.292685] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #02!!!"} > > > [ 595.301467] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"} > > > [ 595.389353] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"} > > > [ 595.397454] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"} > > > [ 595.417112] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"} > > > [ 595.425215] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"} > > > [ 595.438807] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"} > > > > > > I used to see them on mainline a while back but seem to have been fixed. > > > Something didn't get backported to 5.10 perhaps? > > > > I believe that you need at least this one: > > > > 47c218dcae65 ("tick/sched: Prevent false positive softirq pending warnings on RT") > > After looking at the content of the patch, it's not related. We don't run with > PREEMPT_RT. > > I think we're hitting a genuine issue, most likely due to out-of-tree changes > done by Android to fix RT latency problems against softirq (surprise surprise). > > Thanks for your help and sorry for the noise. No problem! But I used to see this very frequently in non-PREEMPT_RT rcutorture runs, and there was a patch from Thomas that made them go away. So it might be worth looking at has patches in this area since 5.10. Maybe I just got confused and picked the wrong one. Thanx, Paul