Subject: Re: [PATCH 1/3] don't attach a task to a dead cgroup

From: Glauber Costa <[email-masked]>
Date: Fri, 20 Apr 2012 12:05:31 -0300

On 04/19/2012 07:53 PM, Tejun Heo wrote:
> On Thu, Apr 19, 2012 at 07:49:16PM -0300, Glauber Costa wrote:
>> Not all external callers of cgroup_attach_task() test to
>> see if the cgroup is still live - the internal callers at
>> cgroup.c does.
>>
>> With this test in cgroup_attach_task, we can assure that
>> no tasks are ever moved to a cgroup that is past its
>> destruction point and was already marked as dead.
>>
>> Signed-off-by: Glauber Costa<[email-masked]>
>> CC: Tejun Heo<[email-masked]>
>> CC: Li Zefan<[email-masked]>
>> CC: Kamezawa Hiroyuki<[email-masked]>
>> ---
>>   kernel/cgroup.c |    3 +++
>>   1 files changed, 3 insertions(+), 0 deletions(-)
>>
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index b61b938..932c318 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -1927,6 +1927,9 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
>>   	struct cgroup_taskset tset = { };
>>   	struct css_set *newcg;
>>
>> +	if (cgroup_is_removed(cgrp))
>> +		return -ENODEV;
>> +
>
> Isn't the test in cgroup_lock_live_group() enough?
>
Yes, when it is done.

Not all callers take it, specially the external ones.