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=unavailable 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 C4DB4C2D0B1 for ; Tue, 10 Dec 2019 04:26:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8CB0920652 for ; Tue, 10 Dec 2019 04:26:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575952011; bh=sPFgIz3fLu8Ou+YZ5Q//dR6+97jnvTVPTDEC6o0YHQY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ooNwkBZQy3V0F+GzBumWCg5tuBr5An4llAg8ruTMTTjzW5PhkpSjU81cl0C4ARdDz 49JU2Fxq2xH2bbh35QGFjj0WIZOkVj/s6T3wAMvfXMnzLvzo880KCtcBRBLEQTNnVp Eq/PuRKGGzLVBz6bmP7NLkzy7F3Pfm1D4v0fO0pQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727145AbfLJE0i (ORCPT ); Mon, 9 Dec 2019 23:26:38 -0500 Received: from mail.kernel.org ([198.145.29.99]:48710 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727118AbfLJE0i (ORCPT ); Mon, 9 Dec 2019 23:26:38 -0500 Received: from paulmck-ThinkPad-P72.home (199-192-87-166.static.wiline.com [199.192.87.166]) (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 39EE524654; Tue, 10 Dec 2019 04:26:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575951997; bh=sPFgIz3fLu8Ou+YZ5Q//dR6+97jnvTVPTDEC6o0YHQY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=khulCWv/XHdMBEmTiqls1MVCEpH8yG8UPD7Oc0hG0wLNJ0ZF543WNbLYat9e1KZ/m 60V+/6lE1I+He1ivHK5i+gaS+WANhCyVGzpWcV89KPZzAcRcaDbm2YEKUj1xjK7Un+ QPkntoO5kbaMNNpoQBE5e8EfFEqb1ELRb/zbIzgo= 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 09/11] rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special() Date: Mon, 9 Dec 2019 20:26:27 -0800 Message-Id: <20191210042629.3808-9-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20191210042606.GA3624@paulmck-ThinkPad-P72> References: <20191210042606.GA3624@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_node structure's ->expmask field is updated only when holding the ->lock, but is also accessed locklessly. This means that all ->expmask updates must use WRITE_ONCE() and all reads carried out without holding ->lock must use READ_ONCE(). This commit therefore changes the lockless ->expmask read in rcu_read_unlock_special() to use READ_ONCE(). Reported-by: syzbot+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com Signed-off-by: Paul E. McKenney Acked-by: Marco Elver --- kernel/rcu/tree_plugin.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c3a3271..698a7f1 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -599,7 +599,7 @@ static void rcu_read_unlock_special(struct task_struct *t) struct rcu_node *rnp = rdp->mynode; exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) || - (rdp->grpmask & rnp->expmask) || + (rdp->grpmask & READ_ONCE(rnp->expmask)) || tick_nohz_full_cpu(rdp->cpu); // Need to defer quiescent state until everything is enabled. if (irqs_were_disabled && use_softirq && -- 2.9.5