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 C2AB6C35242 for ; Fri, 14 Feb 2020 23:56:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 990FE2072D for ; 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=1581724596; bh=z/2snwWYS6lPAT5kl+oy5uQQY78M2650jQPM28iMAsc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=N6gavCVYDXokKJpA5C1Y6O+flMNHQyJ5xnUUZMq8IQgCWDeFspLfB0MukOiGytGig Uozf2DWSBDJmL0AAhBhUauHEsZTS6/GqXYhsqtP3ik5OLa8C8VT38dVgUbK5ktUqUx PqUF2ipWVCuGlSU0BYrm4BcasFRTEK9hWxiOcqFY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728475AbgBNX4c (ORCPT ); Fri, 14 Feb 2020 18:56:32 -0500 Received: from mail.kernel.org ([198.145.29.99]:36320 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727959AbgBNX4c (ORCPT ); Fri, 14 Feb 2020 18:56:32 -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 D0EDB24673; Fri, 14 Feb 2020 23:56:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724592; bh=z/2snwWYS6lPAT5kl+oy5uQQY78M2650jQPM28iMAsc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jVoVpijKzfWJfwVgLZ8uIEDZqcU/TeOsXZoqJxAVbY57RwRl8kABYpwhMF+l3KBMq zkTOFUs/dety0SyWSluV6bBkT3zsQgYt9Pvla0gEaB0aPDSMJOhKXHyxheUtmm9Q9d olGr3by9qSgbyp3TzcgMNUcJPnW8nn1XW8CE5W18= 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 06/30] rcu: Add WRITE_ONCE to rcu_node ->exp_seq_rq store Date: Fri, 14 Feb 2020 15:55:43 -0800 Message-Id: <20200214235607.13749-6-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_node structure's ->exp_seq_rq field is read locklessly, so this commit adds the WRITE_ONCE() to a load 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_exp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index d7e0484..85b009e 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -314,7 +314,7 @@ static bool exp_funnel_lock(unsigned long s) sync_exp_work_done(s)); return true; } - rnp->exp_seq_rq = s; /* Followers can wait on us. */ + WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */ spin_unlock(&rnp->exp_lock); trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level, rnp->grplo, rnp->grphi, TPS("nxtlvl")); -- 2.9.5