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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 84ADDC433FF for ; Mon, 29 Jul 2019 10:47:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4DCE920C01 for ; Mon, 29 Jul 2019 10:47:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="fd191qBh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387457AbfG2Kr4 (ORCPT ); Mon, 29 Jul 2019 06:47:56 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:37922 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387413AbfG2Krz (ORCPT ); Mon, 29 Jul 2019 06:47:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Qklqaof7VmayvCqgxyeqIWUp4Ufy7CHaJ+JorFTqnjo=; b=fd191qBh6TvzNYMqEfFj14xXA 3jqXNl+CPUzSl1/hKQ25x7zxZzyigWTbBuIq+gO8T8MmJ6CiQa2rtihR1Fvt8+7rHXuF2JISiq4nb j+g7GxArrR8cGnQ2LjL4t1jzY130nyGkvw5nuZtdz9a3kDGlE2IbPcQlhClC22vzcCKRu2e/2wqLb p98xy3O+gd4+NNtEQSpdnNr0cXt7wOGu7kGi+pEWnkM0D9MA/8tE4PI5el32QrLXfzJRJMSxo+Pxb rp9oberKn5txgAkW/Z/A7ztlmDkr74/Gb96/luYif3jgYEWD6IC/tOYfllP6h/DyXnd28irB64zfw F/FQN+hZw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hs3Bz-0006PN-FN; Mon, 29 Jul 2019 10:47:47 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BA5B320227078; Mon, 29 Jul 2019 12:47:45 +0200 (CEST) Date: Mon, 29 Jul 2019 12:47:45 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: Guenter Roeck , x86@kernel.org, Ingo Molnar , linux-kernel@vger.kernel.org, Borislav Petkov Subject: Re: sched: Unexpected reschedule of offline CPU#2! Message-ID: <20190729104745.GA31398@hirez.programming.kicks-ass.net> References: <20190727164450.GA11726@roeck-us.net> <20190729093545.GV31381@hirez.programming.kicks-ass.net> <20190729101349.GX31381@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 29, 2019 at 12:38:30PM +0200, Thomas Gleixner wrote: > 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, That seems sensible. > for the panic case not so much. It's panic, shit has already hit fan, one or two more pieces shouldn't something anybody cares about.