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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 48EDCC4743D for ; Fri, 4 Jun 2021 17:12:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 30C9E61359 for ; Fri, 4 Jun 2021 17:12:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230311AbhFDRNp (ORCPT ); Fri, 4 Jun 2021 13:13:45 -0400 Received: from foss.arm.com ([217.140.110.172]:43838 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230106AbhFDRNo (ORCPT ); Fri, 4 Jun 2021 13:13:44 -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 853941063; Fri, 4 Jun 2021 10:11:57 -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 D58693F73D; Fri, 4 Jun 2021 10:11:54 -0700 (PDT) From: Valentin Schneider To: Will Deacon , linux-arm-kernel@lists.infradead.org Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Will Deacon , Catalin Marinas , Marc Zyngier , Greg Kroah-Hartman , Peter Zijlstra , Morten Rasmussen , Qais Yousef , Suren Baghdasaryan , Quentin Perret , Tejun Heo , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , "Rafael J. Wysocki" , Dietmar Eggemann , Daniel Bristot de Oliveira , kernel-team@android.com Subject: Re: [PATCH v8 08/19] sched: Reject CPU affinity changes based on task_cpu_possible_mask() In-Reply-To: <20210602164719.31777-9-will@kernel.org> References: <20210602164719.31777-1-will@kernel.org> <20210602164719.31777-9-will@kernel.org> Date: Fri, 04 Jun 2021 18:11:52 +0100 Message-ID: <874kedeeqv.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/06/21 17:47, Will Deacon wrote: > Reject explicit requests to change the affinity mask of a task via > set_cpus_allowed_ptr() if the requested mask is not a subset of the > mask returned by task_cpu_possible_mask(). This ensures that the > 'cpus_mask' for a given task cannot contain CPUs which are incapable of > executing it, except in cases where the affinity is forced. > > Reviewed-by: Quentin Perret > Signed-off-by: Will Deacon One comment/observation below, but regardless: Reviewed-by: Valentin Schneider > --- > kernel/sched/core.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 0c1b6f1a6c91..b23c7f0ab31a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2347,15 +2347,17 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, > u32 flags) > { > const struct cpumask *cpu_valid_mask = cpu_active_mask; > + const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p); > unsigned int dest_cpu; > struct rq_flags rf; > struct rq *rq; > int ret = 0; > + bool kthread = p->flags & PF_KTHREAD; > > rq = task_rq_lock(p, &rf); > update_rq_clock(rq); > > - if (p->flags & PF_KTHREAD || is_migration_disabled(p)) { > + if (kthread || is_migration_disabled(p)) { > /* > * Kernel threads are allowed on online && !active CPUs, > * however, during cpu-hot-unplug, even these might get pushed > @@ -2369,6 +2371,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, > cpu_valid_mask = cpu_online_mask; > } > > + if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) { > + ret = -EINVAL; > + goto out; > + } > + IIUC this wouldn't be required if guarantee_online_cpus() couldn't build a mask that extends beyond task_cpu_possible_mask(p): if the new mask doesn't intersect with that possible mask, it means we're carrying an empty cpumask and the cpumask_any_and_distribute() below would return nr_cpu_ids, so we'd bail with -EINVAL. I don't really see a way around it though due to the expectations behind guarantee_online_cpus() :/ > /* > * Must re-check here, to close a race against __kthread_bind(), > * sched_setaffinity() is not guaranteed to observe the flag. > -- > 2.32.0.rc0.204.g9fa02ecfa5-goog