Commit bfb0b80d ("cgroup: avoid attaching a cgroup root to two
different superblocks") is broken.  Now we try to fix the race by
delaying the initialization of cgroup root refcnt until a superblock
has been allocated.
Reported-by: NDmitry Vyukov <dvyukov@google.com>
Reported-by: NAndrei Vagin <avagin@virtuozzo.com>
Tested-by: NAndrei Vagin <avagin@virtuozzo.com>
Signed-off-by: NZefan Li <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>