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=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 85E43C35242 for ; Fri, 14 Feb 2020 23:56:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5BD3A2072D for ; Fri, 14 Feb 2020 23:56:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724601; bh=a+d+yGszZsRkYNysaO47CtnEwZ3j2on+f+XowZQtC7s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=yP6BtlHjCo88+sjKWQdeL1jmnCmVUADzvr1BnISOtDdZyj9XNI/HJY9nI2dgvNx8E lXRd9f0BAFFpDX8IhI6BVeUnsf+2609yPjZGbmQfKRuMkX37/3B/qE9pWniYkJ/K1f D5tLafRxBQV97UZYIg56csH5WuwH2iXQjqtFmsnY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727815AbgBNX4k (ORCPT ); Fri, 14 Feb 2020 18:56:40 -0500 Received: from mail.kernel.org ([198.145.29.99]:36458 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727959AbgBNX4k (ORCPT ); Fri, 14 Feb 2020 18:56:40 -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 50B63206B6; Fri, 14 Feb 2020 23:56:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724599; bh=a+d+yGszZsRkYNysaO47CtnEwZ3j2on+f+XowZQtC7s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FQqawMAAwEqaaXlRoqPYLxsAUbOIJKFVWL/L93ytctxYttL2YhwHCzPJbU2hg9JDS GMmNMXbYOyp3ga6yS9AgIatkJJimfqq9TqzuN02p63g7liLiAU5uOhf+8DpSYhJpkl QS1zhNHp9hqqHVjoBEXdanxFPKzZ+yBmPQHUlvjA= 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 08/30] rcu: Add WRITE_ONCE() to rcu_state ->gp_req_activity Date: Fri, 14 Feb 2020 15:55:45 -0800 Message-Id: <20200214235607.13749-8-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: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Paul E. McKenney" The rcu_state structure's ->gp_req_activity field is read locklessly, so this commit adds the WRITE_ONCE() to an update in order to provide proper documentation and READ_ONCE()/WRITE_ONCE() pairing. 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 | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 236692d..9443909 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1200,7 +1200,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp, } trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot")); WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT); - rcu_state.gp_req_activity = jiffies; + WRITE_ONCE(rcu_state.gp_req_activity, jiffies); if (!rcu_state.gp_kthread) { trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread")); goto unlock_out; @@ -1775,7 +1775,7 @@ static void rcu_gp_cleanup(void) rcu_segcblist_is_offloaded(&rdp->cblist); if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) { WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT); - rcu_state.gp_req_activity = jiffies; + WRITE_ONCE(rcu_state.gp_req_activity, jiffies); trace_rcu_grace_period(rcu_state.name, READ_ONCE(rcu_state.gp_seq), TPS("newreq")); -- 2.9.5