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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 77D17C433E0 for ; Wed, 17 Jun 2020 14:15:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 55EB020734 for ; Wed, 17 Jun 2020 14:15:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726900AbgFQOPj (ORCPT ); Wed, 17 Jun 2020 10:15:39 -0400 Received: from foss.arm.com ([217.140.110.172]:58646 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbgFQOPi (ORCPT ); Wed, 17 Jun 2020 10:15:38 -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 3239B31B; Wed, 17 Jun 2020 07:15:38 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A08603F73C; Wed, 17 Jun 2020 07:15:36 -0700 (PDT) References: <20200617121742.cpxppyi7twxmpin7@linutronix.de> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Sebastian Andrzej Siewior Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Thomas Gleixner , Scott Wood Subject: Re: [PATCH] sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr In-reply-to: <20200617121742.cpxppyi7twxmpin7@linutronix.de> Date: Wed, 17 Jun 2020 15:15:31 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/06/20 13:17, Sebastian Andrzej Siewior wrote: > From: Scott Wood > > This function is concerned with the long-term cpu mask, not the > transitory mask the task might have while migrate disabled. Before > this patch, if a task was migrate disabled at the time > __set_cpus_allowed_ptr() was called, and the new mask happened to be > equal to the cpu that the task was running on, then the mask update > would be lost. > > Signed-off-by: Scott Wood > Signed-off-by: Sebastian Andrzej Siewior > --- > kernel/sched/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1637,7 +1637,7 @@ static int __set_cpus_allowed_ptr(struct > goto out; > } > > - if (cpumask_equal(p->cpus_ptr, new_mask)) > + if (cpumask_equal(&p->cpus_mask, new_mask)) > goto out; > > /* Makes sense, but what about the rest of the checks? Further down there is /* Can the task run on the task's current CPU? If so, we're done */ if (cpumask_test_cpu(task_cpu(p), new_mask)) goto out; If the task is currently migrate disabled and for some stupid reason it gets affined elsewhere, we could try to move it out - which AFAICT we don't want to do because migrate disabled. So I suppose you'd want an extra bailout condition here when the task is migrate disabled. ISTR in RT you do re-check the affinity and potentially move the task away when re-enabling migration, so that should work out all fine.