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

Li Zefan
2008-11-13T01:31:16Z

> + /*
> + * 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;

Now it ends up with parent's use_hierarchy is set but its child's
use_hierarchy is not set.