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=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 95AE4C2D0DB for ; Sat, 25 Jan 2020 10:46:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6DAFF22522 for ; Sat, 25 Jan 2020 10:46:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730469AbgAYKqR (ORCPT ); Sat, 25 Jan 2020 05:46:17 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:44173 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729240AbgAYKmz (ORCPT ); Sat, 25 Jan 2020 05:42:55 -0500 Received: from [5.158.153.53] (helo=tip-bot2.lab.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1ivIts-0008MB-Ad; Sat, 25 Jan 2020 11:42:48 +0100 Received: from [127.0.1.1] (localhost [IPv6:::1]) by tip-bot2.lab.linutronix.de (Postfix) with ESMTP id 001001C1A75; Sat, 25 Jan 2020 11:42:43 +0100 (CET) Date: Sat, 25 Jan 2020 10:42:42 -0000 From: "tip-bot2 for Paul E. McKenney" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: core/rcu] rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special() Cc: syzbot+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com, "Paul E. McKenney" , Marco Elver , x86 , LKML MIME-Version: 1.0 Message-ID: <157994896281.396.13421941439896300344.tip-bot2@tip-bot2> X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the core/rcu branch of tip: Commit-ID: c51f83c315c392d9776c33eb16a2fe1349d65c7f Gitweb: https://git.kernel.org/tip/c51f83c315c392d9776c33eb16a2fe1349d65c7f Author: Paul E. McKenney AuthorDate: Mon, 04 Nov 2019 08:22:45 -08:00 Committer: Paul E. McKenney CommitterDate: Fri, 24 Jan 2020 10:27:33 -08:00 rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special() The rcu_node structure's ->expmask field is updated only when holding the ->lock, but is also accessed locklessly. This means that all ->expmask updates must use WRITE_ONCE() and all reads carried out without holding ->lock must use READ_ONCE(). This commit therefore changes the lockless ->expmask read in rcu_read_unlock_special() to use READ_ONCE(). Reported-by: syzbot+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com Signed-off-by: Paul E. McKenney Acked-by: Marco Elver --- kernel/rcu/tree_plugin.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c3a3271..698a7f1 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -599,7 +599,7 @@ static void rcu_read_unlock_special(struct task_struct *t) struct rcu_node *rnp = rdp->mynode; exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) || - (rdp->grpmask & rnp->expmask) || + (rdp->grpmask & READ_ONCE(rnp->expmask)) || tick_nohz_full_cpu(rdp->cpu); // Need to defer quiescent state until everything is enabled. if (irqs_were_disabled && use_softirq &&