[PATCH v2 3/9] cgroup: make for_each_subsys() useable under cgroup_root_mutex

We want to use for_each_subsys() in cgroupfs_root handling where only cgroup_root_mutex is held. The only way cgroup_subsys[] can change is through module load/unload, make cgroup_[un]load_subsys() grab cgroup_root_mutex too and update the lockdep annotation in for_each_subsys() to allow either

[PATCH v2 3/9] cgroup: make for_each_subsys() useable under cgroup_root_mutex

We want to use for_each_subsys() in cgroupfs_root handling where only cgroup_root_mutex is held. The only way cgroup_subsys[] can change is through module load/unload, make cgroup_[un]load_subsys() grab cgroup_root_mutex too and update the lockdep annotation in for_each_subsys() to allow either