From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753844AbcAVPXQ (ORCPT ); Fri, 22 Jan 2016 10:23:16 -0500 Received: from mail-qg0-f67.google.com ([209.85.192.67]:36385 "EHLO mail-qg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751190AbcAVPXM (ORCPT ); Fri, 22 Jan 2016 10:23:12 -0500 Date: Fri, 22 Jan 2016 10:23:09 -0500 From: Tejun Heo To: Li Zefan , Johannes Weiner Cc: Linux Kernel Mailing List , Christian Borntraeger , linux-s390 , KVM list , Oleg Nesterov , Peter Zijlstra , "Paul E. McKenney" , cgroups@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH cgroup/for-4.5-fixes] cpuset: make mm migration asynchronous Message-ID: <20160122152309.GC32380@htj.duckdns.org> References: <56978452.6010606@de.ibm.com> <20160114195630.GA3520@mtj.duckdns.org> <5698A023.9070703@de.ibm.com> <20160115164023.GH3520@mtj.duckdns.org> <20160119171841.GP3520@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160119171841.GP3520@mtj.duckdns.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 19, 2016 at 12:18:41PM -0500, Tejun Heo wrote: > If "cpuset.memory_migrate" is set, when a process is moved from one > cpuset to another with a different memory node mask, pages in used by > the process are migrated to the new set of nodes. This was performed > synchronously in the ->attach() callback, which is synchronized > against process management. Recently, the synchronization was changed > from per-process rwsem to global percpu rwsem for simplicity and > optimization. > > Combined with the synchronous mm migration, this led to deadlocks > because mm migration could schedule a work item which may in turn try > to create a new worker blocking on the process management lock held > from cgroup process migration path. > > This heavy an operation shouldn't be performed synchronously from that > deep inside cgroup migration in the first place. This patch punts the > actual migration to an ordered workqueue and updates cgroup process > migration and cpuset config update paths to flush the workqueue after > all locks are released. This way, the operations still seem > synchronous to userland without entangling mm migration with process > management synchronization. CPU hotplug can also invoke mm migration > but there's no reason for it to wait for mm migrations and thus > doesn't synchronize against their completions. > > Signed-off-by: Tejun Heo > Reported-and-tested-by: Christian Borntraeger > Cc: stable@vger.kernel.org # v4.4+ Applied to cgroup/for-4.5-fixes. Thanks. -- tejun