[PATCH 5/8] cgroup: factor out cgroup_kn_lock_live() and cgroup_kn_unlock()

cgroup_mkdir(), cgroup_rmdir() and cgroup_subtree_control_write() share the logic to break active protection so that they can grab cgroup_tree_mutex which nests above active protection and/or remove self. Factor out this logic into cgroup_kn_lock_live() and cgroup_kn_unlock(). This patch doesn't

[PATCH 5/8] cgroup: factor out cgroup_kn_lock_live() and cgroup_kn_unlock()

cgroup_mkdir(), cgroup_rmdir() and cgroup_subtree_control_write() share the logic to break active protection so that they can grab cgroup_tree_mutex which nests above active protection and/or remove self. Factor out this logic into cgroup_kn_lock_live() and cgroup_kn_unlock(). This patch doesn't