linux-kernel - Re: [PATCH v2 1/2] cgroups: allow a cgroup subsystem to reject a fork

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Message-ID: <20150311114646.GC25944@htj.duckdns.org>
Date:	Wed, 11 Mar 2015 07:46:46 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Aleksa Sarai <cyphar@...har.com>
Cc:	lizefan@...wei.com, mingo@...hat.com, peterz@...radead.org,
	richard@....at,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH v2 1/2] cgroups: allow a cgroup subsystem to reject a fork

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
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