From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v2 1/2] cgroups: allow a cgroup subsystem to reject a fork
Date: Wed, 11 Mar 2015 07:46:46 -0400
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To: Aleksa Sarai <cyphar@cyphar.com>
Cc: lizefan@huawei.com, mingo@redhat.com, peterz@infradead.org, richard@nod.at, =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org

On Wed, Mar 11, 2015 at 04:16:30PM +1100, Aleksa Sarai wrote:
> We know that the task will have its css_set set to task_css_set(current), and
> we could just use that in cgroup_can_fork(). The only question is, can
> task_css_set(current) change between cgroup_can_fork() and cgroup_post_fork()?

Yes, that's what I've been writing in the previous messages.  It can change.

> If it can change between the two calls, then we're in trouble -- there'd be no
> reliable way of checking that the future css_set allows for the fork without
> going through the registration of the css_set *proper* in cgroup_post_fork()
> unless we hold css_set_rwsem for the entirety of the can_fork() to post_fork()
> segment (which I can't imagine is a good idea).

Please re-read my previous messages.

Thanks.

-- 
tejun