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,URIBL_BLOCKED,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 F0916C433DF for ; Tue, 23 Jun 2020 00:44:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C141420706 for ; Tue, 23 Jun 2020 00:44:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592873045; bh=GR6ogSxmcukOgF4mhlKqOxxYURZEZlC7F/ht+xRgJQA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=weQB5V4yYWEQ9Qg9+KpxPk7UzAYGNvOgED2uAoWC6bvi7/TGcCo7rEGGmLNNhRAbd R5PkELH0CalPqR1B4jQnFu47XGINpYC8O+uD65ooWSXmy3t7+q3nrE59lmZuPETKmp fyIrhfursf0ATV8Z93JHnzHqs7BYqNdtTcgfa6vo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732330AbgFWAoE (ORCPT ); Mon, 22 Jun 2020 20:44:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:40730 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732163AbgFWAng (ORCPT ); Mon, 22 Jun 2020 20:43:36 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 252CC20874; Tue, 23 Jun 2020 00:43:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592873016; bh=GR6ogSxmcukOgF4mhlKqOxxYURZEZlC7F/ht+xRgJQA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=O63hfk33Uc841mQwyHC0jVGfE+PsV/oqXYkheo6LyuglgqOb+vlT0cN35aMhSBQXB RZgN/dHyveMlR9C9ZDSFS9jtQDjti0kin9/1sd8/gfnTx6VUNhFFRRIv8DvCUcU8cT Kxbhf+2crGK0MNUHXZdtQI1d4ic1OLTYp6uwWn8c= From: paulmck@kernel.org To: linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, kernel-team@fb.com, mingo@kernel.org Cc: elver@google.com, andreyknvl@google.com, glider@google.com, dvyukov@google.com, cai@lca.pw, boqun.feng@gmail.com, "Paul E . McKenney" Subject: [PATCH tip/core/rcu 05/10] locking/osq_lock: Annotate a data race in osq_lock Date: Mon, 22 Jun 2020 17:43:28 -0700 Message-Id: <20200623004333.27227-5-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200623003731.GA26717@paulmck-ThinkPad-P72> References: <20200623003731.GA26717@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Qian Cai The prev->next pointer can be accessed concurrently as noticed by KCSAN: write (marked) to 0xffff9d3370dbbe40 of 8 bytes by task 3294 on cpu 107: osq_lock+0x25f/0x350 osq_wait_next at kernel/locking/osq_lock.c:79 (inlined by) osq_lock at kernel/locking/osq_lock.c:185 rwsem_optimistic_spin read to 0xffff9d3370dbbe40 of 8 bytes by task 3398 on cpu 100: osq_lock+0x196/0x350 osq_lock at kernel/locking/osq_lock.c:157 rwsem_optimistic_spin Since the write only stores NULL to prev->next and the read tests if prev->next equals to this_cpu_ptr(&osq_node). Even if the value is shattered, the code is still working correctly. Thus, mark it as an intentional data race using the data_race() macro. Signed-off-by: Qian Cai Signed-off-by: Paul E. McKenney --- kernel/locking/osq_lock.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 1f77349..1de006e 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -154,7 +154,11 @@ bool osq_lock(struct optimistic_spin_queue *lock) */ for (;;) { - if (prev->next == node && + /* + * cpu_relax() below implies a compiler barrier which would + * prevent this comparison being optimized away. + */ + if (data_race(prev->next) == node && cmpxchg(&prev->next, node, NULL) == node) break; -- 2.9.5