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 3B9A3C35242 for ; Fri, 14 Feb 2020 23:56:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0C4722072D for ; Fri, 14 Feb 2020 23:56:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724599; bh=f3Tn3xPjKHcw7qbEA4Ah425M6HfJtwTb8IVSi9j9KuY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=hb2J3SmfzRHP6prDYDkGTVNyLlzMG0VXCuueDojZwHcN4nVz+KDUTW2fBg6rCUTra bEOh5BYphxKme5+Baatohgsj+ZEUEmk6n0LR018XXUCvs4V2JofAjsr21zJCzJztyc Y1q4TbgrV6VYGJZqzMcIAWzl4iN5PVPksOZamsnY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728506AbgBNX4i (ORCPT ); Fri, 14 Feb 2020 18:56:38 -0500 Received: from mail.kernel.org ([198.145.29.99]:36398 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727959AbgBNX4g (ORCPT ); Fri, 14 Feb 2020 18:56:36 -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 9D6C624670; Fri, 14 Feb 2020 23:56:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724595; bh=f3Tn3xPjKHcw7qbEA4Ah425M6HfJtwTb8IVSi9j9KuY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=X9AQ5i6Vj/Hoc3YL0ouEhaeYdxxh56QEAcMCPZlqAoZClhGkKRQ/so/c7q77oEyqq OCbj7K14X3r1HOwJXYb5K5eITa4lWt+Gh3WVUIyIUqKu5W7t/WGHex0WZ6kJguFh5j fGB/iw4AVKtyLNrsiqlu59hWtAQaCnzIge0Y0xgc= 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 07/30] rcu: Add READ_ONCE() to rcu_node ->gp_seq Date: Fri, 14 Feb 2020 15:55:44 -0800 Message-Id: <20200214235607.13749-7-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_node structure's ->gp_seq field is read locklessly, so this commit adds the READ_ONCE() to several loads in order to avoid destructive compiler optimizations. This data race was reported by KCSAN. Not appropriate for backporting because this affects only tracing and warnings. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index bb57c24..236692d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1126,8 +1126,9 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, unsigned long gp_seq_req, const char *s) { - trace_rcu_future_grace_period(rcu_state.name, rnp->gp_seq, gp_seq_req, - rnp->level, rnp->grplo, rnp->grphi, s); + trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), + gp_seq_req, rnp->level, + rnp->grplo, rnp->grphi, s); } /* @@ -1904,7 +1905,7 @@ static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp, rnp_c = rnp; rnp = rnp->parent; raw_spin_lock_irqsave_rcu_node(rnp, flags); - oldmask = rnp_c->qsmask; + oldmask = READ_ONCE(rnp_c->qsmask); } /* @@ -2052,7 +2053,7 @@ int rcutree_dying_cpu(unsigned int cpu) return 0; blkd = !!(rnp->qsmask & rdp->grpmask); - trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, + trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), blkd ? TPS("cpuofl") : TPS("cpuofl-bgp")); return 0; } -- 2.9.5