cgroup: use restart_syscall() for retries after offline waits in cgroup_subtree_control_write()

static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,

					struct cftype *cft, char *buffer)

{

	unsigned int enable_req = 0, disable_req = 0, enable, disable;

	unsigned int enable = 0, disable = 0;

	struct cgroup *cgrp = dummy_css->cgroup, *child;

	struct cgroup_subsys *ss;

	char *tok, *p;

				continue;

			if (*tok == '+') {

				enable_req |= 1 << ssid;

				disable_req &= ~(1 << ssid);

				enable |= 1 << ssid;

				disable &= ~(1 << ssid);

			} else if (*tok == '-') {

				disable_req |= 1 << ssid;

				enable_req &= ~(1 << ssid);

				disable |= 1 << ssid;

				enable &= ~(1 << ssid);

			} else {

				return -EINVAL;

			}

	 */

	cgroup_get(cgrp);

	kernfs_break_active_protection(cgrp->control_kn);

retry:

	enable = enable_req;

	disable = disable_req;

	mutex_lock(&cgroup_tree_mutex);

				schedule();

				finish_wait(&child->offline_waitq, &wait);

				cgroup_put(child);

				goto retry;

				ret = restart_syscall();

				goto out_unbreak;

			}

			/* unavailable or not enabled on the parent? */

	mutex_unlock(&cgroup_mutex);

out_unlock_tree:

	mutex_unlock(&cgroup_tree_mutex);

out_unbreak:

	kernfs_unbreak_active_protection(cgrp->control_kn);

	cgroup_put(cgrp);

	return ret;