From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753246AbcGUPeo (ORCPT <rfc822;w@1wt.eu>);
	Thu, 21 Jul 2016 11:34:44 -0400
Received: from bedivere.hansenpartnership.com ([66.63.167.143]:45348 "EHLO
	bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1753100AbcGUPel (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 21 Jul 2016 11:34:41 -0400
Message-ID: <1469115276.2331.23.camel@HansenPartnership.com>
Subject: Re: [PATCH v1 3/3] cgroup: relax common ancestor restriction for
 direct descendants
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Tejun Heo <tj@kernel.org>
Cc: Aleksa Sarai <asarai@suse.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Li Zefan <lizefan@huawei.com>, Johannes Weiner <hannes@cmpxchg.org>,
        "Serge E. Hallyn" <serge.hallyn@ubuntu.com>,
        Aditya Kali <adityakali@google.com>,
        Chris Wilson <chris@chris-wilson.co.uk>, linux-kernel@vger.kernel.org,
        cgroups@vger.kernel.org, Christian Brauner <cbrauner@suse.de>,
        dev@opencontainers.org
Date: Thu, 21 Jul 2016 08:34:36 -0700
In-Reply-To: <20160721152648.GA23759@htj.duckdns.org>
References: <20160720155147.GG4574@htj.duckdns.org>
	 <6e975d80-4077-fb8b-ec84-708e37c8e149@suse.de>
	 <20160720230228.GA19588@mtj.duckdns.org>
	 <982fcf3a-3685-9bd7-dd95-7bff255c9421@suse.de>
	 <20160720231949.GB19588@mtj.duckdns.org>
	 <379e5b13-29d4-ca75-1935-0a64f3db8d27@suse.de>
	 <20160721145242.GB22680@htj.duckdns.org>
	 <1469113456.2331.16.camel@HansenPartnership.com>
	 <20160721150740.GF22680@htj.duckdns.org>
	 <1469114194.2331.20.camel@HansenPartnership.com>
	 <20160721152648.GA23759@htj.duckdns.org>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.16.5 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, 2016-07-21 at 11:26 -0400, Tejun Heo wrote:
> Hello, James.
> 
> On Thu, Jul 21, 2016 at 08:16:34AM -0700, James Bottomley wrote:
> > > That'd be one side.  The other side is the one moving.  Let's say 
> > > the system admin thing wants to move all processe from A proper 
> > > to B.   It would do that by draining processes from A's procs 
> > > file into B's and even that is multistep and can race.
> > 
> > So the second part is that once we allow the creation of
> > subdirectories, there's no unified tasks file, so there's no way of
> > draining A proper without enumerating and descending into the 
> > cgroupns created subtrees in A?
> 
> Not that.  If it races, it will end up moving processes which are no
> longer in A proper.

So if I as the cgroup ns owner am moving a task from A to A_subdir, the
admin scanning tasks in all of A may miss this task in motion because
all the tasks files can't be scanned atomically?

James