Re: [RFC][mm] [PATCH 4/4] Memory cgroup hierarchy feature selector (v3)

Balbir Singh
2008-11-13T01:35:24Z

Li Zefan wrote:
>> + /*
>> + * If parent's use_hiearchy is set, we can't make any modifications
>> + * in the child subtrees. If it is unset, then the change can
>> + * occur, provided the current cgroup has no children.
>> + *
>> + * For the root cgroup, parent_mem is NULL, we allow value to be
>> + * set if there are no children.
>> + */
>> + if (!parent_mem || (!parent_mem->use_hierarchy &&
>> + (val == 1 || val == 0))) {
>> + if (list_empty(&cont->children))
>> + mem->use_hierarchy = val;
>> + else
>> + retval = -EBUSY;
>> + } else
>> + retval = -EINVAL;
>> +
>> + return retval;
>> +}
>
> As I mentioned there is a race here. :(
>
> echo 1 > /memcg/memory.use_hierarchy
> =>if (list_empty(&cont->children))
> mkdir /memcg/0
> => mem->use_hierarchy = 0
> mem->use_hierarchy = 1;
>

Hi, Li,

I thought I had the cgroup_lock() around that check, but I seemed to have missed
it. I'll fix that in v4.

--
Balbir