From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756917Ab3LTRhN (ORCPT ); Fri, 20 Dec 2013 12:37:13 -0500 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.225]:36066 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753107Ab3LTRhK (ORCPT ); Fri, 20 Dec 2013 12:37:10 -0500 Date: Fri, 20 Dec 2013 12:37:07 -0500 From: Steven Rostedt To: Peter Zijlstra Cc: tglx@linutronix.de, mingo@redhat.com, oleg@redhat.com, fweisbec@gmail.com, darren@dvhart.com, johan.eker@ericsson.com, p.faure@akatech.ch, linux-kernel@vger.kernel.org, claudio@evidence.eu.com, michael@amarulasolutions.com, fchecconi@gmail.com, tommaso.cucinotta@sssup.it, juri.lelli@gmail.com, nicola.manica@disi.unitn.it, luca.abeni@unitn.it, dhaval.giani@gmail.com, hgu1972@gmail.com, paulmck@linux.vnet.ibm.com, raistlin@linux.it, insop.song@gmail.com, liming.wang@windriver.com, jkacur@redhat.com Subject: Re: [PATCH 09/13] sched: Add bandwidth management for sched_dl Message-ID: <20131220123707.44fb7192@gandalf.local.home> In-Reply-To: <20131220171343.GL2480@laptop.programming.kicks-ass.net> References: <20131217122720.950475833@infradead.org> <20131217123353.180539582@infradead.org> <20131218165508.GB30183@twins.programming.kicks-ass.net> <20131220171343.GL2480@laptop.programming.kicks-ass.net> X-Mailer: Claws Mail 3.9.2 (GTK+ 2.24.22; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.130:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 20 Dec 2013 18:13:43 +0100 Peter Zijlstra wrote: > @@ -4985,6 +4942,23 @@ migration_call(struct notifier_block *nf > unsigned long flags; > struct rq *rq = cpu_rq(cpu); > > + switch (action) { > + case CPU_DOWN_PREPARE: /* explicitly allow suspend */ > + { > + struct dl_bw *dl_b = dl_bw_of(cpu); > + int cpus = dl_bw_cpus(cpu); > + bool overflow; > + > + raw_spin_lock_irqsave(&dl_b->lock, flags); > + overflow = __dl_overflow(dl_b, cpus-1, 0, 0); > + raw_spin_unlock_irqrestore(&dl_b->lock, flags); > + > + if (overflow) > + return notifier_from_errno(-EBUSY); Is it possible to have a race here to create a new deadline task that may work with cpus but not cpus-1? That is, if a new deadline task is currently being created as a CPU is going offline, this check happens first while the creation is spinning on the dl_b->lock, and it sets overflow to false, then once the lock is released, the new deadline task makes the condition true. Should the system call have a get_online_cpus() somewhere? -- Steve > + } > + break; > + } > + > switch (action & ~CPU_TASKS_FROZEN) { > > case CPU_UP_PREPARE: