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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 1D6ECC7618B for ; Mon, 29 Jul 2019 10:38:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2F1D206BA for ; Mon, 29 Jul 2019 10:38:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728300AbfG2Kik (ORCPT ); Mon, 29 Jul 2019 06:38:40 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:53187 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728151AbfG2Kik (ORCPT ); Mon, 29 Jul 2019 06:38:40 -0400 Received: from pd9ef1cb8.dip0.t-ipconnect.de ([217.239.28.184] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hs331-0007e8-9y; Mon, 29 Jul 2019 12:38:31 +0200 Date: Mon, 29 Jul 2019 12:38:30 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: Guenter Roeck , x86@kernel.org, Ingo Molnar , linux-kernel@vger.kernel.org, Borislav Petkov Subject: Re: sched: Unexpected reschedule of offline CPU#2! In-Reply-To: <20190729101349.GX31381@hirez.programming.kicks-ass.net> Message-ID: References: <20190727164450.GA11726@roeck-us.net> <20190729093545.GV31381@hirez.programming.kicks-ass.net> <20190729101349.GX31381@hirez.programming.kicks-ass.net> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 On Mon, 29 Jul 2019, Peter Zijlstra wrote: > On Mon, Jul 29, 2019 at 11:58:24AM +0200, Thomas Gleixner wrote: > > On Mon, 29 Jul 2019, Peter Zijlstra wrote: > > > On Sat, Jul 27, 2019 at 09:44:50AM -0700, Guenter Roeck wrote: > > > > [ 61.348866] Call Trace: > > > > [ 61.349392] kick_ilb+0x90/0xa0 > > > > [ 61.349629] trigger_load_balance+0xf0/0x5c0 > > > > [ 61.349859] ? check_preempt_wakeup+0x1b0/0x1b0 > > > > [ 61.350057] scheduler_tick+0xa7/0xd0 > > > > > > kick_ilb() iterates nohz.idle_cpus_mask to find itself an idle_cpu(). > > > > > > idle_cpus_mask() is set from nohz_balance_enter_idle() and cleared from > > > nohz_balance_exit_idle(). nohz_balance_enter_idle() is called from > > > __tick_nohz_idle_stop_tick() when entering nohz idle, this includes the > > > cpu_is_offline() clause of the idle loop. > > > > > > However, when offline, cpu_active() should also be false, and this > > > function should no-op. > > > > Ha. That reboot mess is not clearing cpu active as it's not going through > > the regular cpu hotplug path. It's using reboot IPI which 'stops' the cpus > > dead in their tracks after clearing cpu online.... > > $string-of-cock-compliant-curses > > What a trainwreck... > > So if it doesn't play by the normal rules; how does it expect to work? > > So what do we do? 'Fix' reboot or extend the rules? Reboot has two modes: - Regular reboot initiated from user space - Panic reboot For the regular reboot we can make it go through proper hotplug, for the panic case not so much. thanks, tglx