Pull cgroup updates from Tejun Heo:
 "Nothing major. Two notable fixes are Li's second stab at fixing the
  long-standing race condition in the mount path and suppression of
  spurious warning from cgroup_get(). All other changes are trivial"

* 'for-4.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: mark cgroup_get() with __maybe_unused
  cgroup: avoid attaching a cgroup root to two different superblocks, take 2
  cgroup: fix spurious warnings on cgroup_is_dead() from cgroup_sk_alloc()
  cgroup: move cgroup_subsys_state parent field for cache locality
  cpuset: Remove cpuset_update_active_cpus()'s parameter.
  cgroup: switch to BUG_ON()
  cgroup: drop duplicate header nsproxy.h
  kernel: convert css_set.refcount from atomic_t to refcount_t
  kernel: convert cgroup_namespace.count from atomic_t to refcount_t