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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=no 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 25F11C352A4 for ; Sat, 15 Feb 2020 03:53:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0551220873 for ; Sat, 15 Feb 2020 03:53:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727778AbgBODxJ (ORCPT ); Fri, 14 Feb 2020 22:53:09 -0500 Received: from mail.kernel.org ([198.145.29.99]:52892 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727642AbgBODxI (ORCPT ); Fri, 14 Feb 2020 22:53:08 -0500 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A404220718; Sat, 15 Feb 2020 03:53:06 +0000 (UTC) Date: Fri, 14 Feb 2020 22:53:05 -0500 From: Steven Rostedt To: paulmck@kernel.org Cc: rcu@vger.kernel.org, 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, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, Linus Torvalds Subject: Re: [PATCH tip/core/rcu 22/30] rcu: Don't flag non-starting GPs before GP kthread is running Message-ID: <20200214225305.48550d6a@oasis.local.home> In-Reply-To: <20200214235607.13749-22-paulmck@kernel.org> References: <20200214235536.GA13364@paulmck-ThinkPad-P72> <20200214235607.13749-22-paulmck@kernel.org> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 14 Feb 2020 15:55:59 -0800 paulmck@kernel.org wrote: > @@ -1252,10 +1252,10 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp) > */ > static void rcu_gp_kthread_wake(void) > { > - if ((current == rcu_state.gp_kthread && > + if ((current == READ_ONCE(rcu_state.gp_kthread) && > !in_irq() && !in_serving_softirq()) || > !READ_ONCE(rcu_state.gp_flags) || > - !rcu_state.gp_kthread) > + !READ_ONCE(rcu_state.gp_kthread)) > return; This looks buggy. You have two instances of READ_ONCE(rcu_state.gp_thread), which means they can be different. Is that intentional? -- Steve