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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 E55E2C4363D for ; Fri, 25 Sep 2020 10:10:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F58E21741 for ; Fri, 25 Sep 2020 10:10:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ZSx8LeXo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727922AbgIYKKr (ORCPT ); Fri, 25 Sep 2020 06:10:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42110 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727132AbgIYKKq (ORCPT ); Fri, 25 Sep 2020 06:10:46 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 942FAC0613CE for ; Fri, 25 Sep 2020 03:10:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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; bh=JEzIhAQZ21VR1+sPN/DteO9JU9EP8zZM8KBBLet+0vE=; b=ZSx8LeXoR83faG3ndMPl6Eg5uR jH+VLah5hfsLcrfoMzzfsT++zvquPOIsN/w7wanYpTR6jsEi+BiqBkOHdUMOXNk+tUfhngTEFL+RY lEOHC4vvZI5egUuK1XnYtm96eQP0siXV5hrcUHhcfaKKGw9iFjcMRy7PZZ3iX0odLVUr08i+miua8 NCuAfxTQNzM8v9MEdns/fI8ZDXR4mpL3y0tdkTQi/K2wn5vpEsci/KIGfV421YpgIVtQSfrA5nahV t51LYopaow7ULNroQSedKQZ/Jl3mal9U+ZnZ0KPcDovGVxZavAjth7b7wZhmiTdkBuCPb9y6vmTGC x9g/I7Sg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLkgS-0003yR-LR; Fri, 25 Sep 2020 10:10:32 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id DD59E301A27; Fri, 25 Sep 2020 12:10:30 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CA5E720839A45; Fri, 25 Sep 2020 12:10:30 +0200 (CEST) Date: Fri, 25 Sep 2020 12:10:30 +0200 From: Peter Zijlstra To: Dietmar Eggemann Cc: tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, bigeasy@linutronix.de, qais.yousef@arm.com, swood@redhat.com, valentin.schneider@arm.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vincent.donnefort@arm.com Subject: Re: [PATCH 0/9] sched: Migrate disable support Message-ID: <20200925101030.GA2594@hirez.programming.kicks-ass.net> References: <20200921163557.234036895@infradead.org> <6f55a303-0e5c-8e84-65d3-798b589a5d75@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6f55a303-0e5c-8e84-65d3-798b589a5d75@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 25, 2020 at 11:12:09AM +0200, Dietmar Eggemann wrote: > I get this when running 6 (periodic) RT50 tasks with CPU hp stress on my > 6 CPU JUNO board (!CONFIG_PREEMPT_RT). > > [ 55.490263] ------------[ cut here ]------------ > [ 55.505261] Modules linked in: > [ 55.508322] CPU: 3 PID: 24 Comm: migration/3 Not tainted > 5.9.0-rc1-00132-gc096e6406c50-dirty #90 > [ 55.517119] Hardware name: ARM Juno development board (r0) (DT) > [ 55.523058] Stopper: multi_cpu_stop+0x0/0x170 <- 0x0 > [ 55.528029] pstate: 20000085 (nzCv daIf -PAN -UAO BTYPE=--) > [ 55.533612] pc : sched_cpu_dying+0x124/0x130 > [ 55.537887] lr : sched_cpu_dying+0xd8/0x130 > [ 55.542071] sp : ffff800011f0bca0 > [ 55.545385] x29: ffff800011f0bca0 x28: 0000000000000002 > [ 55.550703] x27: 0000000000000000 x26: 0000000000000060 > [ 55.556022] x25: 0000000000000000 x24: 0000000000000001 > [ 55.561340] x23: 0000000000000000 x22: 0000000000000003 > [ 55.566659] x21: 0000000000000080 x20: 0000000000000003 > [ 55.571977] x19: ffff00097ef9e1c0 x18: 0000000000000010 > [ 55.577295] x17: 0000000000000000 x16: 0000000000000000 > [ 55.582613] x15: 0000000000000000 x14: 000000000000015c > [ 55.587932] x13: 0000000000000000 x12: 00000000000006f1 > [ 55.593250] x11: 0000000000000080 x10: 0000000000000000 > [ 55.598567] x9 : 0000000000000003 x8 : ffff0009743f5900 > [ 55.603886] x7 : 0000000000000003 x6 : 0000000000000000 > [ 55.609204] x5 : 0000000000000001 x4 : 0000000000000002 > [ 55.614521] x3 : 0000000000000000 x2 : 0000000000000013 > [ 55.619839] x1 : 0000000000000008 x0 : 0000000000000003 > [ 55.625158] Call trace: > [ 55.627607] sched_cpu_dying+0x124/0x130 > [ 55.631535] cpuhp_invoke_callback+0x88/0x210 > [ 55.635897] take_cpu_down+0x7c/0xd8 > [ 55.639475] multi_cpu_stop+0xac/0x170 > [ 55.643227] cpu_stopper_thread+0x98/0x130 > [ 55.647327] smpboot_thread_fn+0x1c4/0x280 > [ 55.651427] kthread+0x140/0x160 > [ 55.654658] ret_from_fork+0x10/0x34 > [ 55.658239] Code: f000e1c1 913fc021 1400034a 17ffffde (d4210000) > [ 55.664342] ---[ end trace c5b8988b7b701e56 ]--- > [ 55.668963] note: migration/3[24] exited with preempt_count 3 > > 7309 int sched_cpu_dying(unsigned int cpu) > ... > BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq)); > ... > > rq->nr_running is always 2 here in this cases. > > balance_hotplug_wait and sched_cpu_wait_empty run in cpuhp/X (CFS) > whereas sched_cpu_dying in migration/X ? takedown_cpu() has: kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread); before calling: err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu)); So when we get to sched_cpu_dying(), the only task that _should_ still be there is migration/X. Do you have any idea what thread, other than migration/X, is still active on that CPU? per sched_cpu_wait_empty() we should've pushed out all userspace tasks, and the cpu hotplug machinery should've put all the per-cpu kthreads to sleep at this point.