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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by aws-us-west-2-korg-lkml-1.web.codeaurora.org (Postfix) with ESMTP id 98211C07D5C for ; Thu, 14 Jun 2018 20:11:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4E33F208DD for ; Thu, 14 Jun 2018 20:11:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E33F208DD 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 S1755452AbeFNULr (ORCPT ); Thu, 14 Jun 2018 16:11:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:41264 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754806AbeFNULp (ORCPT ); Thu, 14 Jun 2018 16:11:45 -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 E716B208CB; Thu, 14 Jun 2018 20:11:43 +0000 (UTC) Date: Thu, 14 Jun 2018 16:11:42 -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 v4 4/5] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Message-ID: <20180614161142.69f186a6@gandalf.local.home> In-Reply-To: <20180613121711.5018-5-juri.lelli@redhat.com> References: <20180613121711.5018-1-juri.lelli@redhat.com> <20180613121711.5018-5-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 Wed, 13 Jun 2018 14:17:10 +0200 Juri Lelli wrote: > +/** > + * cpuset_lock - Grab the cpuset_mutex from another subsysytem > + */ > +int cpuset_lock(void) > +{ > + return mutex_trylock(&cpuset_mutex); > +} > + > +/** > + * cpuset_unlock - Release the cpuset_mutex from another subsysytem > + */ > +void cpuset_unlock(void) > +{ > + mutex_unlock(&cpuset_mutex); > +} > + > /** > * 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 ca788f74259d..a5b0c6c25b44 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4218,6 +4218,14 @@ static int __sched_setscheduler(struct task_struct *p, > if (attr->sched_flags & SCHED_FLAG_SUGOV) > return -EINVAL; > > + /* > + * 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. > + */ > + if (!cpuset_lock()) > + return -EBUSY; > + How important is this for being a trylock? Reason I am asking is that it is making my deadline test fail to get the resources. What my test does is to create a bunch of threads, and they try to get the deadline resources as they are created. This happens in parallel. Thus, when one gets the cpuset_lock, the others are hitting this and returning -EBUSY. At first I thought I was over committing somehow but after adding a trace_printk() in cpuset_lock(), and this fail case it became obvious to what was happening: deadline_test-1376 [004] 107.179693: sys_enter_sched_setattr: pid: 0x00000000, uattr: 0x7f017fceeed0, flags: 0x00000000 deadline_test-1376 [004] 107.179697: bputs: cpuset_lock: cpuset_mutex trylock deadline_test-1377 [003] 107.179763: sys_exit_futex: 0x0 deadline_test-1377 [003] 107.179767: sys_enter_sched_setattr: pid: 0x00000000, uattr: 0x7f017f4eded0, flags: 0x00000000 deadline_test-1377 [003] 107.179771: bputs: cpuset_lock: cpuset_mutex trylock deadline_test-1377 [003] 107.179771: bputs: __sched_setscheduler: cpuset_lock deadline_test-1377 [003] 107.179773: sys_exit_sched_setattr: 0xfffffffffffffff0 -- Steve > retval = security_task_setscheduler(p); > if (retval) > return retval;