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

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Date:	Sat, 28 Apr 2012 09:06:20 +0900
From:	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	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>,
	Glauber Costa <glommer@...allels.com>,
	Tejun Heo <tj@...nel.org>, Han Ying <yinghan@...gle.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 7/9 v2] cgroup: avoid attaching task to a cgroup
 under rmdir()

On Fri, Apr 27, 2012 at 7:39 PM, Frederic Weisbecker <fweisbec@...il.com> 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>
>> ---
>>  kernel/cgroup.c |    5 ++++-
>>  1 files changed, 4 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index ad8eae5..7a3076b 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -1953,6 +1953,9 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
>>       if (cgrp == oldcgrp)
>>               return 0;
>>
>> +     if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
>> +             return -EBUSY;
>> +
>
> You probably need to update cgroup_attach_proc() as well?
>
Ahh...I missed that. Thank you for pointing out !

Thanks,
-Kame
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