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 15DCEC4338F for ; Fri, 6 Aug 2021 09:57:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EC5366115C for ; Fri, 6 Aug 2021 09:57:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244731AbhHFJ5y (ORCPT ); Fri, 6 Aug 2021 05:57:54 -0400 Received: from foss.arm.com ([217.140.110.172]:57228 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229725AbhHFJ5v (ORCPT ); Fri, 6 Aug 2021 05:57:51 -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 4C5F41042; Fri, 6 Aug 2021 02:57:35 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.195.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1A7963F719; Fri, 6 Aug 2021 02:57:32 -0700 (PDT) Date: Fri, 6 Aug 2021 10:57:30 +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: <20210806095730.tw3bgnjtsytrqqfq@e107158-lin.cambridge.arm.com> References: <20210721202042.GA1472052@paulmck-ThinkPad-P17-Gen-1> <20210721202127.2129660-2-paulmck@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210721202127.2129660-2-paulmck@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 They have Fixes tags, so should end up in 5.10 stable I presume. Thanks! -- Qais Yousef