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 75B4CC3B1BF for ; Fri, 14 Feb 2020 23:57:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 407062187F for ; Fri, 14 Feb 2020 23:57:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724623; bh=kgbOOD/LyyezKap7GowhfcJfIGGyH0kHTlo/T6LzXEg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=KIvLvRmkh8l71QdWFRzIZ2wIDaMPZHX/jV7IYkhSdGgvwMxDWI2qp7GOUMcEij6Wr Cg6U8fjSy6WTEhIHvd2NfIArbEzv/nkiMrqJPwWDfZ3pGDp0dEqMH9JUUvlSdr8IPh /JqFW6uQWcx0yRRh2BqS3CLDVRhl6Cnuqrxzuw+s= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728282AbgBNX5C (ORCPT ); Fri, 14 Feb 2020 18:57:02 -0500 Received: from mail.kernel.org ([198.145.29.99]:36864 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726164AbgBNX5C (ORCPT ); Fri, 14 Feb 2020 18:57:02 -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 93CD22468C; Fri, 14 Feb 2020 23:56:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724621; bh=kgbOOD/LyyezKap7GowhfcJfIGGyH0kHTlo/T6LzXEg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mKgZvMn3/JjuIDIEWAuzQoURmDcjTpaGy6/nr3kU6t/w2MmfkA0FqXISruuoFzy/U 7kP/QWtg5gefmNhZznCrMhg+pd1fou+qdfZYtGyIjYVupDxJ/K5aV50AlcV86XNShw qPCsMb9DJgNfVbrEaYN+D4TzWqctz1ankDrDDzKk= 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 14/30] rcu: Add READ_ONCE() to rcu_data ->gpwrap Date: Fri, 14 Feb 2020 15:55:51 -0800 Message-Id: <20200214235607.13749-14-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_data structure's ->gpwrap field is read locklessly, and so this commit adds the required READ_ONCE() to a pair of laods in order to avoid destructive compiler optimizations. This data race was reported by KCSAN. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 +- kernel/rcu/tree_stall.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index a70f56b..e851a12 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1322,7 +1322,7 @@ static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp, rcu_lockdep_assert_cblist_protected(rdp); c = rcu_seq_snap(&rcu_state.gp_seq); - if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) { + if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) { /* Old request still live, so mark recent callbacks. */ (void)rcu_segcblist_accelerate(&rdp->cblist, c); return; diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 3dcbecf..3275f27 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -602,7 +602,7 @@ void show_rcu_gp_kthreads(void) continue; for_each_leaf_node_possible_cpu(rnp, cpu) { rdp = per_cpu_ptr(&rcu_data, cpu); - if (rdp->gpwrap || + if (READ_ONCE(rdp->gpwrap) || ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), READ_ONCE(rdp->gp_seq_needed))) continue; -- 2.9.5