linux-kernel - Re: [PATCH 8/9] cgroup_freezer: add ->post_create() and ->pre

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Message-ID: <20121108171742.GJ12973@htj.dyndns.org>
Date:	Thu, 8 Nov 2012 09:17:42 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	lizefan@...wei.com, rjw@...k.pl,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	fweisbec@...il.com
Subject: Re: [PATCH 8/9] cgroup_freezer: add ->post_create() and
 ->pre_destroy() and track online state

Hello,

On Thu, Nov 08, 2012 at 02:23:06PM +0100, Michal Hocko wrote:
> On Sat 03-11-12 01:38:34, Tejun Heo wrote:
> > A cgroup is online and visible to iteration between ->post_create()
> > and ->pre_destroy().  This patch introduces CGROUP_FREEZER_ONLINE and
> > toggles it from the newly added freezer_post_create() and
> > freezer_pre_destroy() while holding freezer->lock such that a
> > cgroup_freezer can be reilably distinguished to be online.  This will
> > be used by full hierarchy support.
> 
> I am thinking whether freezer_pre_destroy is really needed. Once we
> reach pre_destroy then there are no tasks nor any children in the group
> so there is nobody to wake up if the group was frozen and the destroy
> callback is called after synchronize_rcu so the traversing should be
> safe.

Yeah, it might be true, but I'd still like to keep the offlining in
->pre_destroy() so that it's symmetrical w/ ->post_create().  I'll
rename and document the ops so that the roles of each are clearer.

Thanks.

-- 
tejun
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