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=-8.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_NEOMUTT autolearn=ham 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 645A6C43613 for ; Mon, 24 Jun 2019 10:57:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 446C020820 for ; Mon, 24 Jun 2019 10:57:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729147AbfFXK5k (ORCPT ); Mon, 24 Jun 2019 06:57:40 -0400 Received: from foss.arm.com ([217.140.110.172]:46956 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728477AbfFXK5k (ORCPT ); Mon, 24 Jun 2019 06:57:40 -0400 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 5CCEB2B; Mon, 24 Jun 2019 03:57:39 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.195.51]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8F3063F718; Mon, 24 Jun 2019 03:57:38 -0700 (PDT) Date: Mon, 24 Jun 2019 11:57:36 +0100 From: Qais Yousef To: Nicholas Piggin Cc: linux-kernel@vger.kernel.org, Frederic Weisbecker , Ingo Molnar , Peter Zijlstra Subject: Re: [PATCH] kernel/isolation: Asset that a housekeeping CPU comes up at boot time Message-ID: <20190624105729.3isejrp4455suxaz@e107158-lin.cambridge.arm.com> References: <20190601113919.2678-1-npiggin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190601113919.2678-1-npiggin@gmail.com> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/01/19 21:39, Nicholas Piggin wrote: > With the change to allow the boot CPU0 to be isolated, it is possible > to specify command line options that result in no housekeeping CPU > online at boot. > > An 8 CPU system booted with "nohz_full=0-6 maxcpus=4", for example. > > It is not easily possible at housekeeping init time to know all the > various SMP options that will result in an invalid configuration, so > this patch adds a sanity check after SMP init, to ensure that a > housekeeping CPU has been onlined. > > The panic is undesirable, but it's better than the alternative of an > obscure non deterministic failure. The panic will reliably happen > when advanced parameters are used incorrectly. > > Signed-off-by: Nicholas Piggin > --- > kernel/sched/isolation.c | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c > index 123ea07a3f3b..7b9e1e0d4ec3 100644 > --- a/kernel/sched/isolation.c > +++ b/kernel/sched/isolation.c > @@ -63,6 +63,29 @@ void __init housekeeping_init(void) > WARN_ON_ONCE(cpumask_empty(housekeeping_mask)); > } > > +static int __init housekeeping_verify_smp(void) > +{ > + int cpu; > + > + /* > + * Early housekeeping setup is done before CPUs come up, and there are > + * a range of options scattered around that can restrict which CPUs > + * come up. It is possible to pass in a combination of housekeeping > + * and SMP arguments that result in housekeeping assigned to an > + * offline CPU. > + * > + * Check that condition here after SMP comes up, and give a useful > + * error message rather than an obscure non deterministic crash or > + * hang later. > + */ > + for_each_online_cpu(cpu) { > + if (cpumask_test_cpu(cpu, housekeeping_mask)) > + return 0; > + } > + panic("Housekeeping: nohz_full= or isolcpus= resulted in no online CPUs for housekeeping.\n"); I am hitting this panic when I boot my juno board. I have CONFIG_CPU_ISOLATION=y but I don't pass nohuz_full nor isolcpus in the commandline. I think what's going on is that housekeeping_setup() doesn't get called and hence housekeeping_mask isn't initialized in my case, causing this check to fail and trigger the panic. The below seems to 'fix' it though not sure if it's the right way forward. A revert obviously fixes it too but I doubt we want that :-) diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 7b9e1e0d4ec3..a9ca8628c1a2 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -67,6 +67,9 @@ static int __init housekeeping_verify_smp(void) { int cpu; + if (!housekeeping_flags) + return 0; + /* * Early housekeeping setup is done before CPUs come up, and there are * a range of options scattered around that can restrict which CPUs Cheers -- Qais Yousef > +} > +core_initcall(housekeeping_verify_smp); > + > static int __init housekeeping_setup(char *str, enum hk_flags flags) > { > cpumask_var_t non_housekeeping_mask; > -- > 2.20.1 >