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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 6EFD9C3F68F for ; Fri, 14 Feb 2020 23:57:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3FB562072D for ; Fri, 14 Feb 2020 23:57:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724628; bh=D6j1tXPphXZ5GajKLJ8/Pzq/9LkCUdeqMQ58e6TV40g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=UC4CAgvyYObYteKB5cki7gsFhaie6ackeTJlIJ2uyd5MDkbFcB+HZGg+nBkIItcfz mXG3LGz/r2Dl7d9ETZlp7AVMV5Lp54S8IQNqEVasXeJJjnPljCkQrGGb52+BIqKaVG +lCouwjtKSq6dstfy631KjG3rFu3a9MgugvBWYt4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728596AbgBNX5H (ORCPT ); Fri, 14 Feb 2020 18:57:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:36934 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726164AbgBNX5G (ORCPT ); Fri, 14 Feb 2020 18:57:06 -0500 Received: from paulmck-ThinkPad-P72.c.hoisthospitality.com (unknown [62.84.152.189]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2B6F724650; Fri, 14 Feb 2020 23:57:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724625; bh=D6j1tXPphXZ5GajKLJ8/Pzq/9LkCUdeqMQ58e6TV40g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=geXbzF697MOrynFf1hxiWhU7GgEASH7kMrhakr3COK+Lw2TmEDfNZ5CBgCtQncZAR REglkGnJx4DMD17AmoY1JgqmDlkdaFD3pd8ZU14jPfichFkL1WBrJZUG3lCdC705MF E7MGX9ABi+10NHkX/30wlb62hFZuC6C6xAdLn+OQ= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.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, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 15/30] rcu: Add *_ONCE() to rcu_data ->rcu_forced_tick Date: Fri, 14 Feb 2020 15:55:52 -0800 Message-Id: <20200214235607.13749-15-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200214235536.GA13364@paulmck-ThinkPad-P72> References: <20200214235536.GA13364@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" The rcu_data structure's ->rcu_forced_tick field is read locklessly, so this commit adds WRITE_ONCE() to all updates and READ_ONCE() to all lockless reads. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e851a12..be59a5d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -818,11 +818,12 @@ static __always_inline void rcu_nmi_enter_common(bool irq) incby = 1; } else if (tick_nohz_full_cpu(rdp->cpu) && rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE && - READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) { + READ_ONCE(rdp->rcu_urgent_qs) && + !READ_ONCE(rdp->rcu_forced_tick)) { raw_spin_lock_rcu_node(rdp->mynode); // Recheck under lock. if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { - rdp->rcu_forced_tick = true; + WRITE_ONCE(rdp->rcu_forced_tick, true); tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU); } raw_spin_unlock_rcu_node(rdp->mynode); @@ -899,7 +900,7 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp) WRITE_ONCE(rdp->rcu_need_heavy_qs, false); if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) { tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU); - rdp->rcu_forced_tick = false; + WRITE_ONCE(rdp->rcu_forced_tick, false); } } -- 2.9.5