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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 68C2EC433EF for ; Mon, 13 Sep 2021 14:26:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4AE8D60F26 for ; Mon, 13 Sep 2021 14:26:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345986AbhIMO1g (ORCPT ); Mon, 13 Sep 2021 10:27:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:41880 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345254AbhIMOW2 (ORCPT ); Mon, 13 Sep 2021 10:22:28 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 53FD861B39; Mon, 13 Sep 2021 13:47:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631540843; bh=nD1nGfIPISEgG+0FeIZQbH3JTWsPv+IA/1iKH8ecKIA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JzwyPIYG0RGKNUpuEzH0La3QiSEvE8C07kxqfxJ3W5oAWmntdpDrxLz6yfymYuvsV BMrB0Q/WTqwjeQYp4HIb5PbsOTwdWyHPGpz+4BkhzBD3Yb8F5EZZu4qKeKemSzH9ZP Hvnpcq5rOW8oLZdzued4+gDg87ex7DfdqUvA+Z2o= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Qais Yousef , Yanfei Xu , "Paul E. McKenney" , Sasha Levin Subject: [PATCH 5.14 056/334] rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock Date: Mon, 13 Sep 2021 15:11:50 +0200 Message-Id: <20210913131115.312077932@linuxfoundation.org> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210913131113.390368911@linuxfoundation.org> References: <20210913131113.390368911@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yanfei Xu [ Upstream commit dc87740c8a6806bd2162bfb441770e4e53be5601 ] 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") Tested-by: Qais Yousef Signed-off-by: Yanfei Xu Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin --- kernel/rcu/tree_stall.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index d56b4ede1db3..0e7a60706d1c 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -269,8 +269,10 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) struct task_struct *ts[8]; lockdep_assert_irqs_disabled(); - if (!rcu_preempt_blocked_readers_cgp(rnp)) + if (!rcu_preempt_blocked_readers_cgp(rnp)) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return 0; + } pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", rnp->level, rnp->grplo, rnp->grphi); t = list_entry(rnp->gp_tasks->prev, -- 2.30.2