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 9A6AEECAAD3 for ; Thu, 1 Sep 2022 22:18:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234747AbiIAWSQ (ORCPT ); Thu, 1 Sep 2022 18:18:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45762 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234381AbiIAWSB (ORCPT ); Thu, 1 Sep 2022 18:18:01 -0400 Received: from mail-qv1-xf2c.google.com (mail-qv1-xf2c.google.com [IPv6:2607:f8b0:4864:20::f2c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59AF8543C2 for ; Thu, 1 Sep 2022 15:18:00 -0700 (PDT) Received: by mail-qv1-xf2c.google.com with SMTP id q8so157347qvr.9 for ; Thu, 01 Sep 2022 15:18:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc; bh=wacV+wNWevSZZedckm8hHMeO8v0HhmKZhpXkr12CWiU=; b=e7rfmVttSIAE2dX9U/UrdKI2/QNY3ZP3fKeyJGley56wIpwe2qS6saz3KZesypfmqe hM1riUNN/4tHj4mrt7IXt6dpL2LLv2du/nCXvZZI8MdoBiSD0/AnUB8528he0Bh8pZQV vrMkt1S957E51Pelj+JfGSpSAlfQVDY8utxxc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc; bh=wacV+wNWevSZZedckm8hHMeO8v0HhmKZhpXkr12CWiU=; b=QHryVwDuDQby4iBBA1Jg0/KHBxd/gRq++7UpJVZaN3xibzy0LJPBId0md/p//8kPbi ZMIR7ebkh1IsmshbVVawQetj/xvm45BJr/B927W/hYWyufWzohjpkmJ3eQp6b9Yn0JE4 cmWlj0RL8NJEYDTaE8yIn2aGJjTqqZp4+L+H4CozKI2kRxIxZ5NjUXDfdSTZWzfKjkc9 AYBZuW4LIhNyDg/aLf/x+A3N2vnOkW1iPnOZAL46t9S2nnbnz98q47POu58lB42bNeeC fM3IzB3AQnm8tz8T1X6XpVdI+NLPxIPRqx8bPeysw3C8paChf0I7spGBiHhDy1MMVg6E l+Zg== X-Gm-Message-State: ACgBeo2olqCcaizUI+k8VYeDCnoVgPefncMtwRG+9IILON1pu9bVpMkv lRidM825PRA9jJ9yIy6LOp+vww== X-Google-Smtp-Source: AA6agR7ebVdicXTu0lYFUslN4hqrp3yrx/UXs4hw278sz5joSWluao70f6a70ft5FQ57ZlDUz+4CoA== X-Received: by 2002:a05:6214:27c1:b0:473:85c9:3eeb with SMTP id ge1-20020a05621427c100b0047385c93eebmr26877303qvb.53.1662070679524; Thu, 01 Sep 2022 15:17:59 -0700 (PDT) Received: from joelboxx.c.googlers.com.com (228.221.150.34.bc.googleusercontent.com. [34.150.221.228]) by smtp.gmail.com with ESMTPSA id s16-20020ac85290000000b0034305a91aaesm11060794qtn.83.2022.09.01.15.17.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Sep 2022 15:17:59 -0700 (PDT) From: "Joel Fernandes (Google)" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, rushikesh.s.kadam@intel.com, urezki@gmail.com, neeraj.iitr10@gmail.com, frederic@kernel.org, paulmck@kernel.org, rostedt@goodmis.org, vineeth@bitbyteword.org, boqun.feng@gmail.com, "Joel Fernandes (Google)" Subject: [PATCH v5 03/18] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask Date: Thu, 1 Sep 2022 22:17:05 +0000 Message-Id: <20220901221720.1105021-4-joel@joelfernandes.org> X-Mailer: git-send-email 2.37.2.789.g6183377224-goog In-Reply-To: <20220901221720.1105021-1-joel@joelfernandes.org> References: <20220901221720.1105021-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The rnp->qsmask is locklessly accessed from rcutree_dying_cpu(). This may help avoid load/store 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; -- 2.37.2.789.g6183377224-goog