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=-13.7 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=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 2D8DAC2BB40 for ; Thu, 17 Dec 2020 12:16:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D7B46238EC for ; Thu, 17 Dec 2020 12:16:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727793AbgLQMQo (ORCPT ); Thu, 17 Dec 2020 07:16:44 -0500 Received: from foss.arm.com ([217.140.110.172]:60956 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726291AbgLQMQn (ORCPT ); Thu, 17 Dec 2020 07:16:43 -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 B49E831B; Thu, 17 Dec 2020 04:15:57 -0800 (PST) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.194.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 458A53F66B; Thu, 17 Dec 2020 04:15:55 -0800 (PST) Date: Thu, 17 Dec 2020 12:15:52 +0000 From: Qais Yousef To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Catalin Marinas , Marc Zyngier , Greg Kroah-Hartman , Peter Zijlstra , Morten Rasmussen , Suren Baghdasaryan , Quentin Perret , Tejun Heo , Li Zefan , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , kernel-team@android.com Subject: Re: [PATCH v5 07/15] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Message-ID: <20201217121552.ds7g2icvqp5nvtha@e107158-lin.cambridge.arm.com> References: <20201208132835.6151-1-will@kernel.org> <20201208132835.6151-8-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201208132835.6151-8-will@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 12/08/20 13:28, Will Deacon wrote: > If the scheduler cannot find an allowed CPU for a task, > cpuset_cpus_allowed_fallback() will widen the affinity to cpu_possible_mask > if cgroup v1 is in use. > > In preparation for allowing architectures to provide their own fallback > mask, just return early if we're not using cgroup v2 and allow > select_fallback_rq() to figure out the mask by itself. > > Cc: Li Zefan > Cc: Tejun Heo > Cc: Johannes Weiner > Reviewed-by: Quentin Perret > Signed-off-by: Will Deacon > --- > kernel/cgroup/cpuset.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 57b5b5d0a5fd..e970737c3ed2 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -3299,9 +3299,11 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) > > void cpuset_cpus_allowed_fallback(struct task_struct *tsk) > { > + if (!is_in_v2_mode()) > + return; /* select_fallback_rq will try harder */ > + > rcu_read_lock(); > - do_set_cpus_allowed(tsk, is_in_v2_mode() ? > - task_cs(tsk)->cpus_allowed : cpu_possible_mask); > + do_set_cpus_allowed(tsk, task_cs(tsk)->cpus_allowed); Why is it safe to return that for cpuset v2? task_cs(tsk)->cpus_allowed is the original user configured settings of the cpuset.cpus; which could have empty intersection with task_cpu_possible_mask(), no? do_set_cpus_allowed() will call set_cpus_allowed_common() which will end up copying the mask as-is. So unless I missed something there's a risk a 32bit task ends up having a 64bit only cpu_mask when using cpuset v2. Thanks -- Qais Yousef > rcu_read_unlock(); > > /* > -- > 2.29.2.576.ga3fc446d84-goog >