mm/hugetlb_cgroup: move per-node usage on cgroup reparenting

hugetlb_cgroup_css_offline() hands the folios of a dying cgroup over to
its parent with hugetlb_cgroup_move_parent(), which moves the page_counter
charges and the hugetlb_cgroup pointer of the folio but not its per-node
usage.  The parent's hugetlb.<size>.numa_stat is short by that usage while
they are charged, and underflows once they are freed, exposing incorrect
per-node usage values to userspace.

Move the per-node usage to the parent as well.  The folios keep their node
here, so only the cgroup which holds the usage changes.

Link: https://lore.kernel.org/20260918-for-hugetlb-charge-v2-2-2b6d8c2bdc36@kylinos.cn
Fixes: f47761999052 ("hugetlb: add hugetlb.*.numa_stat file")
Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Muchun Song <muchun.song@linux.dev>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: <stable@vger.kernel.org>

0 files changed, 0 insertions, 0 deletions