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 076C2C35242 for ; Sat, 15 Feb 2020 00:25:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D13442081E for ; Sat, 15 Feb 2020 00:25:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581726328; bh=oRIAumjNHqmn10LWc9qa0Ieb2wE58818JG+Ees1xFYk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=L9YzwgMWQXOo/CH6FmOuzTaGLD+NznLQLrY7fwsJMCteMOTGMYgbZbgeSC+EtBu5V mmZIkXlHHAdZBr8EdBNvEcFwXxGD4nn5QfSgzbxgM1SCJWgZQeDQGHjm5zyF7VGdP4 gdzTSmJ+9IV4Tn6FOlyLeAtyPmtlg0LVnEXhQJd4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727529AbgBOAZ2 (ORCPT ); Fri, 14 Feb 2020 19:25:28 -0500 Received: from mail.kernel.org ([198.145.29.99]:44490 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726079AbgBOAZ2 (ORCPT ); Fri, 14 Feb 2020 19:25:28 -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 551EB206D7; Sat, 15 Feb 2020 00:25:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581726327; bh=oRIAumjNHqmn10LWc9qa0Ieb2wE58818JG+Ees1xFYk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=S5a2cI0RoFbXLbi3BUcg7ch60zm/r2BbVzRxLKpoftdCAFFJUS4cwMaphe6DVh28x T79Q1sNM18K/A7Rp+zF2ulJXSi3yWP6joesu0MO3xfCrPslsYDNnaCdOjhxzpGBJ1K hcinhyVJDUKl09nLvxOPtryfHCQ7OpXRjP1qJnGE= 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 1/3] rcu-tasks: *_ONCE() for rcu_tasks_cbs_head Date: Fri, 14 Feb 2020 16:25:18 -0800 Message-Id: <20200215002520.15746-1-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200215002446.GA15663@paulmck-ThinkPad-P72> References: <20200215002446.GA15663@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 tasks list of callbacks, rcu_tasks_cbs_head, is sampled locklessly by rcu_tasks_kthread() when waiting for work to do. This commit therefore applies READ_ONCE() to that lockless sampling and WRITE_ONCE() to the single potential store outside of rcu_tasks_kthread. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely. Signed-off-by: Paul E. McKenney --- kernel/rcu/update.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 6c4b862..a27df76 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -528,7 +528,7 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) rhp->func = func; raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); needwake = !rcu_tasks_cbs_head; - *rcu_tasks_cbs_tail = rhp; + WRITE_ONCE(*rcu_tasks_cbs_tail, rhp); rcu_tasks_cbs_tail = &rhp->next; raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); /* We can't create the thread unless interrupts are enabled. */ @@ -658,7 +658,7 @@ static int __noreturn rcu_tasks_kthread(void *arg) /* If there were none, wait a bit and start over. */ if (!list) { wait_event_interruptible(rcu_tasks_cbs_wq, - rcu_tasks_cbs_head); + READ_ONCE(rcu_tasks_cbs_head)); if (!rcu_tasks_cbs_head) { WARN_ON(signal_pending(current)); schedule_timeout_interruptible(HZ/10); -- 2.9.5