linux-kernel - Re: [RFC][PATCH 7/9 v2] cgroup: avoid attaching task to a cgroup under rmdir()

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Message-ID: <20120427203336.GM26595@google.com>
Date:	Fri, 27 Apr 2012 13:33:36 -0700
From:	Tejun Heo <tj@...nel.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Han Ying <yinghan@...gle.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kamezawa.hiroyuki@...il.com
Subject: Re: [RFC][PATCH 7/9 v2] cgroup: avoid attaching task to a cgroup
 under rmdir()

On Fri, Apr 27, 2012 at 01:31:59PM -0700, Tejun Heo wrote:
> On Fri, Apr 27, 2012 at 03:02:22PM +0900, KAMEZAWA Hiroyuki wrote:
> > attach_task() is done under cgroup_mutex() but ->pre_destroy() callback
> > in rmdir() isn't called under cgroup_mutex().
> > 
> > It's better to avoid attaching a task to a cgroup which
> > is under pre_destroy(). Considering memcg, the attached task may
> > increase resource usage after memcg's pre_destroy() confirms that
> > memcg is empty. This is not good.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> Hmm... once memcg's pre_destroy() can't fail, I think what we should
> do is marking a cgroup DEAD before calling pre_destroy() and the
> existing cgroup_is_removed() check should be enough.  Patches upto
> this point already make ->pre_destroy() not fail, right?

Ooh, I was confused about patch order.  This patch, probably with the
update suggested by Frederic looks good as an interim solution for
now.

Thanks.

-- 
tejun
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