cgroup: Fixes for v7.1-rc1

- Fix UAF race in psi pressure_write() against cgroup file release by
  extending cgroup_mutex coverage and ordering of->priv access after
  cgroup_kn_lock_live().

- Fix integer overflow in rdmacg_try_charge() when usage equals INT_MAX
  by performing the increment in s64.

- Fix asymmetric DL bandwidth accounting on cpuset attach rollback by
  recording the CPU used by dl_bw_alloc() so cancel_attach() returns
  the reservation to the same root domain.

- Fix nr_dying_subsys_* race that briefly showed 0 in cgroup.stat after
  rmdir by incrementing from kill_css() instead of offline_css().

- Typo fix in cgroup-v2 documentation.

docs: cgroup: fix typo 'protetion' -> 'protection'

Fix a small typo in the description of the memory_hugetlb_accounting
mount option.

Signed-off-by: Petr Vaněk <arkamar@atlas.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>