linux-kernel - Re: [RFC PATCH 1/4] cgroups: Allow a cgroup subsys to reject a fork

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Date:	Thu, 23 Jun 2011 15:38:58 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Paul Menage <menage@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 1/4] cgroups: Allow a cgroup subsys to reject a fork

On Tue, Jun 21, 2011 at 10:39:04AM -0700, Paul Menage wrote:
> On Sun, Jun 19, 2011 at 4:51 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > Make the cgroup subsystem fork callback return a value
> > so that subsystems are able to accept or reject a fork
> > completion with a custom error value.
> 
> This is unnecessary complexity in the cgroup subsystem (and seems to
> miss cleanup for subsystems that have previously had their fork()
> method return success).

No it seems only the freezer subsystem had this fork callback implemented.
But indeed it adds complexity because if a subsystem can cancel a fork,
then previous subsystems that called ->fork() would need to have a
kind cancel_fork() callback to call.

I haven't looked very deep but the freezer doesn't seem to need any
rollback. Future subsystems using the fork() callback may need it
though.

> If you want a subsystem to be able to reject a fork, I think it's
> better to have that subsystem be called explicitly from do_fork(), and
> keep that logic out of cgroups.

Ok I can do that.
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