linux-kernel - Re: [PATCH] cgroups: add lock for child->cgroups in cgroup_post

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Message-ID: <6599ad830811210959t22e0fe1ck33828f762a3bfdbd@mail.gmail.com>
Date:	Fri, 21 Nov 2008 09:59:05 -0800
From:	Paul Menage <menage@...gle.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH] cgroups: add lock for child->cgroups in 
	cgroup_post_fork()

On Fri, Nov 21, 2008 at 12:49 AM, Lai Jiangshan <laijs@...fujitsu.com> wrote:
> when cgroup_post_fork() called, child is seen by find_task_by_vpid(),
> so child->cgroups maybe be changed, It'll incorrect.
>
> child->cgroups<old>'s refcnt is decreased
> child->cgroups<new>'s refcnt is increased
> but child->cg_list is added to child->cgroups<old>'s list.
>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>

Reviewed-by: Paul Menage <menage@...gle.com>

Yeah, I guess this was a place where I equated "holding css_set_lock"
with "cgroups can't change". But in fact they can partially change.

Paul
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