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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB5B8C54EE9 for ; Fri, 16 Sep 2022 11:04:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232192AbiIPLEi (ORCPT ); Fri, 16 Sep 2022 07:04:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45522 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232339AbiIPLD6 (ORCPT ); Fri, 16 Sep 2022 07:03:58 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8C6508F95E; Fri, 16 Sep 2022 03:55:28 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9C0DC62ADE; Fri, 16 Sep 2022 10:55:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7FAB8C433C1; Fri, 16 Sep 2022 10:55:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1663325727; bh=d7++6KU0EYcQnNvGqmzIiNTKAGfjD93jm1cap1+0pPE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ZXYYnDGwLn70nlBjLtd/c66NwpHeLZEzfwnC3alj08Y2cj6e8xajqmmrhC+MLeIdW N4upEfDRxvgJ+HUNadVTM6ctcTY+T4tjg3ZYFVvtcrVAyvGJr6lcROYyaXjoM+z/mn F2AACSFZyR37QxvmshO8jmMuDmAn80jjgLmM8RDDF1SICIe7qJw1ldI07VsfVbytfo 8m3Q6LytrD9wgBt/LChZ1axAZ0AxkiUvKmZHcJ9lKnEIoua6t7govZs6YsxQQod5Hf PnRCtYlxatHeuRCtClvvt3sHRpwZwPh+kSaYhJrsSsMinJG9FHxbhcCKpKZkPg9A48 yENH/1TgT8log== Date: Fri, 16 Sep 2022 12:55:23 +0200 From: Frederic Weisbecker To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , Neeraj Upadhyay , "Paul E. McKenney" , rcu@vger.kernel.org, Steven Rostedt Subject: Re: [PATCH rcu/next 1/3] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask Message-ID: <20220916105523.GA25456@lothringen> References: <20220915001419.55617-1-joel@joelfernandes.org> <20220915001419.55617-2-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220915001419.55617-2-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 15, 2022 at 12:14:17AM +0000, Joel Fernandes (Google) wrote: > The rnp->qsmask is locklessly accessed from rcutree_dying_cpu(). This > may help avoid load tearing due to concurrent access, KCSAN > issues, and preserve sanity of people reading the mask in tracing. > > Signed-off-by: Joel Fernandes (Google) > --- > kernel/rcu/tree.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 0ca21ac0f064..5ec97e3f7468 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2106,7 +2106,7 @@ int rcutree_dying_cpu(unsigned int cpu) > if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) > return 0; > > - blkd = !!(rnp->qsmask & rdp->grpmask); > + blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask); > trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), > blkd ? TPS("cpuofl-bgp") : TPS("cpuofl")); > return 0; Reviewed-by: Frederic Weisbecker