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=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 15DDCC282C4 for ; Mon, 4 Feb 2019 12:10:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CF50E2081B for ; Mon, 4 Feb 2019 12:10:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="AS0IB77f" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729991AbfBDMKw (ORCPT ); Mon, 4 Feb 2019 07:10:52 -0500 Received: from merlin.infradead.org ([205.233.59.134]:35706 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728216AbfBDMKw (ORCPT ); Mon, 4 Feb 2019 07:10:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=xk9BHV1P6GGtyJFkFlG3uN5UNNhnFsyEyojuYFBV8Gk=; b=AS0IB77f9Q/HJxUDddKqss52Q kEhNhxX+q435sNibLuRCzg/UQDeEqovzLKwLMQdyTQEF/0MdSGh8GfbBMYALyXPyYyH2xuu2TIgUK n15cwhQVWdjVs09ohs5nE3DdETPoCdgJW3gEKhB+s49gIaA9FI5Ti1dwxi4wu+I/vqbM+gneGfBzz +dHiDvkolZefcFCZh6X/QEFC2uux6lXS9iuQ5m7yhPMDFQriLLC8d6cDBAC7B1KfieZVgaf2SIpIn WRfbeOnEAQkyRKETWoD9hcL3eNh+iwRyMvhgIeA/ox6z6oOhBPwBiDe2j4N72WHcJ1Ug4kkZ6DRUi 3vz8s2Taw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gqd59-0002ON-Hb; Mon, 04 Feb 2019 12:10:36 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 432702029FA06; Mon, 4 Feb 2019 13:10:29 +0100 (CET) Date: Mon, 4 Feb 2019 13:10:29 +0100 From: Peter Zijlstra To: Juri Lelli Cc: mingo@redhat.com, rostedt@goodmis.org, tj@kernel.org, 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 v6 4/5] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Message-ID: <20190204121029.GD17550@hirez.programming.kicks-ass.net> References: <20190117084739.17078-1-juri.lelli@redhat.com> <20190117084739.17078-5-juri.lelli@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190117084739.17078-5-juri.lelli@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 17, 2019 at 09:47:38AM +0100, Juri Lelli wrote: > No synchronisation mechanism exists between the cpuset subsystem and calls > to function __sched_setscheduler(). As such, it is possible that new root > domains are created on the cpuset side while a deadline acceptance test > is carried out in __sched_setscheduler(), leading to a potential oversell > of CPU bandwidth. > > Grab callback_lock from core scheduler, so to prevent situations such as > the one described above from happening. > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index f5263383170e..d928a42b8852 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4224,6 +4224,13 @@ 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: > */ > @@ -4285,6 +4292,7 @@ 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; > } > @@ -4342,6 +4350,7 @@ 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) > @@ -4354,6 +4363,7 @@ static int __sched_setscheduler(struct task_struct *p, > return 0; > > unlock: > + cpuset_read_only_unlock(); > task_rq_unlock(rq, p, &rf); > return retval; > } Why take callback_lock inside rq->lock and not the other way around? AFAICT there is no pre-existing order so we can pick one here.