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 7D062C35242 for ; Fri, 14 Feb 2020 23:56:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4DA412072D for ; Fri, 14 Feb 2020 23:56:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724604; bh=HwUNCGUdfre5UmNq9Q+iEz2ZVX6Edk3KkkIAZWEfhV8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=NB1+OoU+Ka/koqyTWdAJz+eBqIuZ3kHSf9LNYT6P2SNBl0FB5EDKqhMJlaYQfi3r8 S9r6jcQAy5rlQkMOiH8ITmNL738IG73Gkbsx8ERxAhf+8K9almRZUex9Da2cYQkkd2 sRgePQZ4j4MKNt2nfcYi2VMjkHuYp6TsPQVV+pKY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728529AbgBNX4o (ORCPT ); Fri, 14 Feb 2020 18:56:44 -0500 Received: from mail.kernel.org ([198.145.29.99]:36510 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727959AbgBNX4n (ORCPT ); Fri, 14 Feb 2020 18:56:43 -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 EABFA2467D; 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=1581724603; bh=HwUNCGUdfre5UmNq9Q+iEz2ZVX6Edk3KkkIAZWEfhV8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tCcJzu++A/qHESXdUUEcN90k9g7/Ms3GSjJUKfmW535E9iUj2LTPUlG/5Q8ANcVye Yk+MkuEl8hZMNZeZdcSZCC6dXGN94jFb4jVrCbPhchZPohJxOXRpX8Byq/+4TgamjC FNXPdKT7qxwOqJblpm6hk41EfLEsUGbKfd3t/3MU= 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 09/30] rcu: Add WRITE_ONCE() to rcu_node ->qsmaskinitnext Date: Fri, 14 Feb 2020 15:55:46 -0800 Message-Id: <20200214235607.13749-9-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 ->qsmaskinitnext 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 for systems not doing incessant CPU-hotplug operations. 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 9443909..346321a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3379,7 +3379,7 @@ void rcu_cpu_starting(unsigned int cpu) rnp = rdp->mynode; mask = rdp->grpmask; raw_spin_lock_irqsave_rcu_node(rnp, flags); - rnp->qsmaskinitnext |= mask; + WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); oldmask = rnp->expmaskinitnext; rnp->expmaskinitnext |= mask; oldmask ^= rnp->expmaskinitnext; @@ -3432,7 +3432,7 @@ void rcu_report_dead(unsigned int cpu) rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); raw_spin_lock_irqsave_rcu_node(rnp, flags); } - rnp->qsmaskinitnext &= ~mask; + WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); raw_spin_unlock(&rcu_state.ofl_lock); -- 2.9.5