FAILED: patch "[PATCH] mm/hugetlb_cgroup: move per-node usage on cgroup reparenting" failed to apply to 6.1-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 23fac055c21176f66ed453394b533bdfc00f7fba
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107054727-failed-6.1-23fac055c211@kernel.org' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 23fac055c21176f66ed453394b533bdfc00f7fba Mon Sep 17 00:00:00 2001
From: Hongfu Li <lihongfu@kylinos.cn>
Date: Fri, 18 Sep 2026 10:56:11 +0800
Subject: [PATCH] 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>
---
 mm/hugetlb_cgroup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index 7cf7c18119b43..3fb41311e4c7d 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;
-- 
2.53.0