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, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS 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 2919FC00449 for ; Wed, 3 Oct 2018 19:42:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D6A5C21470 for ; Wed, 3 Oct 2018 19:42:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D6A5C21470 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727488AbeJDCcU (ORCPT ); Wed, 3 Oct 2018 22:32:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:53994 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726964AbeJDCcU (ORCPT ); Wed, 3 Oct 2018 22:32:20 -0400 Received: from gandalf.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EC06E20652; Wed, 3 Oct 2018 19:42:31 +0000 (UTC) Date: Wed, 3 Oct 2018 15:42:30 -0400 From: Steven Rostedt To: Juri Lelli Cc: peterz@infradead.org, mingo@redhat.com, linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it, claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it, bristot@redhat.com, mathieu.poirier@linaro.org, lizefan@huawei.com, cgroups@vger.kernel.org Subject: Re: [PATCH v5 4/5] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Message-ID: <20181003154230.4b8792fb@gandalf.local.home> In-Reply-To: <20180903142801.20046-5-juri.lelli@redhat.com> References: <20180903142801.20046-1-juri.lelli@redhat.com> <20180903142801.20046-5-juri.lelli@redhat.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 3 Sep 2018 16:28:00 +0200 Juri Lelli wrote: > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 5b43f482fa0f..8dc26005bb1e 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -2410,6 +2410,24 @@ void __init cpuset_init_smp(void) > BUG_ON(!cpuset_migrate_mm_wq); > } > > +/** > + * cpuset_read_only_lock - Grab the callback_lock from another subsysytem > + * > + * Description: Gives the holder read-only access to cpusets. > + */ > +void cpuset_read_only_lock(void) > +{ > + raw_spin_lock(&callback_lock); This was confusing to figure out why grabbing a spinlock gives read only access. So I read the long comment above the definition of callback_lock. A couple of notes. 1) The above description needs to go into more detail as to why grabbing a spinlock is "read only". 2) The comment above the callback_lock needs to incorporate this, as reading that comment alone will not give anyone an idea that this exists. Other than that, I don't see any issue with this patch. -- Steve > +} > + > +/** > + * cpuset_read_only_unlock - Release the callback_lock from another subsysytem > + */ > +void cpuset_read_only_unlock(void) > +{ > + raw_spin_unlock(&callback_lock); > +} > + > /** > * cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset. > * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed. > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 22f5622cba69..ac11ee599968 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4228,6 +4228,13 @@ static int __sched_setscheduler(struct task_struct *p, > rq = task_rq_lock(p, &rf); > update_rq_clock(rq); > > + /* > + * Make sure we don't race with the cpuset subsystem where root > + * domains can be rebuilt or modified while operations like DL > + * admission checks are carried out. > + */ > + cpuset_read_only_lock(); > + > /* > * Changing the policy of the stop threads its a very bad idea: > */ > @@ -4289,6 +4296,7 @@ static int __sched_setscheduler(struct task_struct *p, > /* Re-check policy now with rq lock held: */ > if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) { > policy = oldpolicy = -1; > + cpuset_read_only_unlock(); > task_rq_unlock(rq, p, &rf); > goto recheck; > } > @@ -4346,6 +4354,7 @@ static int __sched_setscheduler(struct task_struct *p, > > /* Avoid rq from going away on us: */ > preempt_disable(); > + cpuset_read_only_unlock(); > task_rq_unlock(rq, p, &rf); > > if (pi) > @@ -4358,6 +4367,7 @@ static int __sched_setscheduler(struct task_struct *p, > return 0; > > unlock: > + cpuset_read_only_unlock(); > task_rq_unlock(rq, p, &rf); > return retval; > }