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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A946BC433DF for ; Fri, 12 Jun 2020 19:25:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9544920835 for ; Fri, 12 Jun 2020 19:25:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726499AbgFLTZg (ORCPT ); Fri, 12 Jun 2020 15:25:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45142 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726478AbgFLTZe (ORCPT ); Fri, 12 Jun 2020 15:25:34 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0B1ADC03E96F; Fri, 12 Jun 2020 12:25:34 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jjpIn-00030f-Le; Fri, 12 Jun 2020 21:25:21 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id E09E0100F5A; Fri, 12 Jun 2020 21:25:20 +0200 (CEST) From: Thomas Gleixner To: paulmck@kernel.org Cc: LKML , rcu@vger.kernel.org, Andrew Lutomirski , X86 ML , Frederic Weisbecker , Steven Rostedt , Joel Fernandes , Mathieu Desnoyers , Will Deacon , Peter Zijlstra Subject: Re: [PATCH x86/entry: Force rcu_irq_enter() when in idle task In-Reply-To: <20200612191921.GA18255@paulmck-ThinkPad-P72> References: <20200611235305.GA32342@paulmck-ThinkPad-P72> <871rmkzcc8.fsf@nanos.tec.linutronix.de> <87wo4cxubv.fsf@nanos.tec.linutronix.de> <20200612174953.GA19188@paulmck-ThinkPad-P72> <20200612191921.GA18255@paulmck-ThinkPad-P72> Date: Fri, 12 Jun 2020 21:25:20 +0200 Message-ID: <87r1ukxf1b.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Paul E. McKenney" writes: > On Fri, Jun 12, 2020 at 10:49:53AM -0700, Paul E. McKenney wrote: >> I will therefore address this issue in a follow-on patch. > > I should add that -your- patch from yesterday did -not- cause this > problem, in case that is of interest. So I still can add it back and amend the changelog and comment: Change the condition from !rcu_is_watching() to is_idle_task(current) || rcu_is_watching() which enforces that interrupts in the idle task unconditionally invoke rcu_irq_enter() independent of the RCU state. For most scenarios is_idle_task() would be sufficient but Task RCU needs it according to Paul. Thanks, tglx