memcg: fix css_is_ancestor() RCU locking

}

EXPORT_SYMBOL_GPL(css_depth);

/**

 *  css_is_ancestor - test "root" css is an ancestor of "child"

 * @child: the css to be tested.

 * @root: the css supporsed to be an ancestor of the child.

 *

 * Returns true if "root" is an ancestor of "child" in its hierarchy. Because

 * this function reads css->id, this use rcu_dereference() and rcu_read_lock().

 * But, considering usual usage, the csses should be valid objects after test.

 * Assuming that the caller will do some action to the child if this returns

 * returns true, the caller must take "child";s reference count.

 * If "child" is valid object and this returns true, "root" is valid, too.

 */

bool css_is_ancestor(struct cgroup_subsys_state *child,

		    const struct cgroup_subsys_state *root)

{

	struct css_id *child_id = rcu_dereference(child->id);

	struct css_id *root_id = rcu_dereference(root->id);

	struct css_id *child_id;

	struct css_id *root_id;

	bool ret = true;

	if (!child_id || !root_id || (child_id->depth < root_id->depth))

		return false;

	return child_id->stack[root_id->depth] == root_id->id;

	rcu_read_lock();

	child_id  = rcu_dereference(child->id);

	root_id = rcu_dereference(root->id);

	if (!child_id

	    || !root_id

	    || (child_id->depth < root_id->depth)

	    || (child_id->stack[root_id->depth] != root_id->id))

		ret = false;

	rcu_read_unlock();

	return ret;

}

static void __free_css_id_cb(struct rcu_head *head)

	 * enabled in "curr" and "curr" is a child of "mem" in *cgroup*

	 * hierarchy(even if use_hierarchy is disabled in "mem").

	 */

	rcu_read_lock();

	if (mem->use_hierarchy)

		ret = css_is_ancestor(&curr->css, &mem->css);

	else

		ret = (curr == mem);

	rcu_read_unlock();

	css_put(&curr->css);

	return ret;

}

			 * There is a small race that "from" or "to" can be

			 * freed by rmdir, so we use css_tryget().

			 */

			rcu_read_lock();

			from = mc.from;

			to = mc.to;

			if (from && css_tryget(&from->css)) {

					do_continue = (to == mem_over_limit);

				css_put(&to->css);

			}

			rcu_read_unlock();

			if (do_continue) {

				DEFINE_WAIT(wait);

				prepare_to_wait(&mc.waitq, &wait,