From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932107Ab3JOJze (ORCPT ); Tue, 15 Oct 2013 05:55:34 -0400 Received: from cantor2.suse.de ([195.135.220.15]:38373 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757872Ab3JOJzd (ORCPT ); Tue, 15 Oct 2013 05:55:33 -0400 Date: Tue, 15 Oct 2013 10:55:27 +0100 From: Mel Gorman To: Peter Zijlstra Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, hannes@cmpxchg.org, riel@redhat.com, aarcange@redhat.com, srikar@linux.vnet.ibm.com, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:sched/core] sched/numa: Introduce migrate_swap() Message-ID: <20131015095527.GH11028@suse.de> References: <1381141781-10992-39-git-send-email-mgorman@suse.de> <20131010181722.GO13848@laptop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20131010181722.GO13848@laptop.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 10, 2013 at 08:17:22PM +0200, Peter Zijlstra wrote: > On Wed, Oct 09, 2013 at 10:30:13AM -0700, tip-bot for Peter Zijlstra wrote: > > sched/numa: Introduce migrate_swap() > > Thanks to Rik for writing the Changelog! > > --- > From: Peter Zijlstra > Subject: sched: Fix race in migrate_swap_stop > > There is a subtle race in migrate_swap, when task P, on CPU A, decides to swap > places with task T, on CPU B. > > Task P: > - call migrate_swap > Task T: > - go to sleep, removing itself from the runqueue > Task P: > - double lock the runqueues on CPU A & B > Task T: > - get woken up, place itself on the runqueue of CPU C > Task P: > - see that task T is on a runqueue, and pretend to remove it > from the runqueue on CPU B > > Now CPUs B & C both have corrupted scheduler data structures. > > This patch fixes it, by holding the pi_lock for both of the tasks > involved in the migrate swap. This prevents task T from waking up, > and placing itself onto another runqueue, until after migrate_swap > has released all locks. > > This means that, when migrate_swap checks, task T will be either > on the runqueue where it was originally seen, or not on any > runqueue at all. Migrate_swap deals correctly with of those cases. > > Signed-off-by: Peter Zijlstra > Tested-by: Joe Mario Acked-by: Mel Gorman -- Mel Gorman SUSE Labs