Re: [PATCH] cgroup: Fix potential race between cgroup_exit and migrate path

[Neeraj Upadhyay <neeraju@codeaurora.org>]

On 08/31/2017 06:42 AM, Tejun Heo wrote:
> On Wed, Aug 30, 2017 at 06:03:19PM -0700, Tejun Heo wrote:
>> Oops, more like the following.
>>
>> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
>> index df2e0f1..6f34025 100644
>> --- a/kernel/cgroup/cgroup.c
>> +++ b/kernel/cgroup/cgroup.c
>> @@ -683,7 +683,7 @@ static void css_set_move_task(struct task_struct *task,
>>   			if (it->task_pos == &task->cg_list)
>>   				css_task_iter_advance(it);
>>   
>> -		list_del_init(&task->cg_list);
>> +		list_del(&task->cg_list);
>>   		if (!css_set_populated(from_cset))
>>   			css_set_update_populated(from_cset, false);
>>   	} else {
>> @@ -702,6 +702,8 @@ static void css_set_move_task(struct task_struct *task,
>>   		rcu_assign_pointer(task->cgroups, to_cset);
>>   		list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
>>   							     &to_cset->tasks);
>> +	} else {
>> +		INIT_LIST_HEAD(&task->cg_list);
>>   	}
>>   }
> On the third thought, I don't think this can happen either because now
> migration is strongly synchronized against exits.  Please take a look
> at the changes around cgroup_threadgroup_rwsem.
>
> Thanks.
>
Thank you for the suggestion; found below fix, which is not present in 
v4.4.86
stable code base. Please let me know in case I am missing something:

eedd0f4 cgroupns: Close race between cgroup_post_fork and copy_cgroup_ns

Thanks.

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