[PATCH 5.10 209/221] mm/memcg: fix 5.10 backport of splitting page memcg

[Greg Kroah-Hartman]

From: Hugh Dickins <hu...@google.com>

The straight backport of 5.12's e1baddf8475b ("mm/memcg: set memcg when
splitting page") works fine in 5.11, but turned out to be wrong for 5.10:
because that relies on a separate flag, which must also be set for the
memcg to be recognized and uncharged and cleared when freeing. Fix that.

Signed-off-by: Hugh Dickins <hu...@google.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 mm/memcontrol.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3274,13 +3274,17 @@ void obj_cgroup_uncharge(struct obj_cgro
 void split_page_memcg(struct page *head, unsigned int nr)
 {
        struct mem_cgroup *memcg = head->mem_cgroup;
+       int kmemcg = PageKmemcg(head);
        int i;
 
        if (mem_cgroup_disabled() || !memcg)
                return;
 
-       for (i = 1; i < nr; i++)
+       for (i = 1; i < nr; i++) {
                head[i].mem_cgroup = memcg;
+               if (kmemcg)
+                       __SetPageKmemcg(head + i);
+       }
        css_get_many(&memcg->css, nr - 1);
 }