[PATCH v2 2/2] mm/hugetlb_cgroup: move per-node usage on cgroup reparenting

[Hongfu Li]

From: Hongfu Li <lihongfu@xxxxxxxxxx>

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.

Fixes: f47761999052 ("hugetlb: add hugetlb.*.numa_stat file")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hongfu Li <lihongfu@xxxxxxxxxx>
Acked-by: Muchun Song <muchun.song@xxxxxxxxx>
---
 mm/hugetlb_cgroup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index 7cf7c18119b4..3fb41311e4c7 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -241,6 +241,8 @@ static void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,
 	/* Take the pages off the local counter */
 	page_counter_cancel(counter, nr_pages);
 
+	hugetlb_cgroup_move_usage(h_cg, parent, folio, folio);
+
 	set_hugetlb_cgroup(folio, parent);
 out:
 	return;

-- 
2.54.0