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_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 061BBC432C3 for ; Tue, 3 Dec 2019 15:08:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CF32520803 for ; Tue, 3 Dec 2019 15:08:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726755AbfLCPIi (ORCPT ); Tue, 3 Dec 2019 10:08:38 -0500 Received: from foss.arm.com ([217.140.110.172]:44090 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726138AbfLCPIi (ORCPT ); Tue, 3 Dec 2019 10:08:38 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D5FC031B; Tue, 3 Dec 2019 07:08:37 -0800 (PST) Received: from [192.168.0.9] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0B6683F52E; Tue, 3 Dec 2019 07:08:36 -0800 (PST) Subject: Re: Crash in fair scheduler To: Valentin Schneider , "Schmid, Carsten" , "mingo@redhat.com" , "peterz@infradead.org" , "linux-kernel@vger.kernel.org" References: <1575364273836.74450@mentor.com> <564e45cb-8230-9c3d-24a8-b58e6e88349f@arm.com> <944927a7-b578-c6f9-a73d-25c5b0a39adb@arm.com> From: Dietmar Eggemann Message-ID: Date: Tue, 3 Dec 2019 16:08:35 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/12/2019 12:09, Valentin Schneider wrote: > On 03/12/2019 10:40, Dietmar Eggemann wrote: >> On 03/12/2019 11:30, Valentin Schneider wrote: >>> On 03/12/2019 09:11, Schmid, Carsten wrote: >> >> [...] >> >>> That looks a lot like a recent issue we've had, see >>> >>> https://lore.kernel.org/lkml/20191108131909.428842459@infradead.org/ >>> >>> The issue is caused by >>> >>> 67692435c411 ("sched: Rework pick_next_task() slow-path") >>> >>> which 5.4-rc2 has (without the fix which landed in -rc7) but 4.14 really >>> shouldn't, unless the kernel you're using has had core scheduling somehow >>> backported to it? >>> >>> I've only scraped the surface but I'd like to first ask: can you reproduce >>> the issue on v5.4 final ? >> >> Can't be. 4.14.86 does not have ("sched: Rework pick_next_task() >> slow-path"). >> > > Right, which is why I wondered if the kernel under test had had that > backported to it for some reason (e.g. core scheduling). Peter pointed out > that this is a slightly different issue (nr_running matches the rbt), so > this is probably unrelated. I can't reproduce it on Arm64 Juno running 4.14.86. I suppose that there is no extra reproducer testcase since the issue happened with prev->sched_class eq. &idle_sched_class [prev eq. swapper/X 0] in the simple path of pick_next_task_fair(). I'm running with CONFIG_SCHED_AUTOGROUP=y and CONFIG_FAIR_GROUP_SCHED=y some taskgroup related tests for hours now. So the sched_entity (se) can be a task, an autogroup or a taskgroup in the simple path. pref is either swapper/X or migration/X.