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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 0390CC4320A for ; Fri, 6 Aug 2021 12:33:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D80FE61164 for ; Fri, 6 Aug 2021 12:33:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343730AbhHFMeJ (ORCPT ); Fri, 6 Aug 2021 08:34:09 -0400 Received: from foss.arm.com ([217.140.110.172]:60020 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238794AbhHFMeH (ORCPT ); Fri, 6 Aug 2021 08:34:07 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4617E31B; Fri, 6 Aug 2021 05:33:51 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (unknown [10.1.195.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 13C7A3F40C; Fri, 6 Aug 2021 05:33:48 -0700 (PDT) Date: Fri, 6 Aug 2021 13:33:46 +0100 From: Qais Yousef To: "Paul E. McKenney" 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: <20210806123346.qkddi4kqi4z4666e@e107158-lin.cambridge.arm.com> References: <20210721202042.GA1472052@paulmck-ThinkPad-P17-Gen-1> <20210721202127.2129660-2-paulmck@kernel.org> <20210806095730.tw3bgnjtsytrqqfq@e107158-lin.cambridge.arm.com> <20210806114327.GP4397@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210806114327.GP4397@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/06/21 04:43, Paul E. McKenney wrote: > On Fri, Aug 06, 2021 at 10:57:30AM +0100, Qais Yousef wrote: > > 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 were seeing similar issue on Android 5.10. Applying patches 1 and 2 did fix > > the deadlock problem and we get proper RCU stall splat now. > > > > For patches 1 and 2: > > > > Tested-by: Qais Yousef > > Thank you, and I will apply this on the next rebase. > > > They have Fixes tags, so should end up in 5.10 stable I presume. > > Here is hoping! ;-) Leave it with me, I've got a todo to make sure this happens ;-) Thanks! -- Qais Yousef