[PATCH] mm: memcontrol: fix memsw uncharge for root_mem_cgroup

[Muchun Song]

The pages aren't accounted at the root level, so we cannot uncharge the
page to the memsw counter for the root memcg. Fix this.

Fixes: 1f47b61fb407 ("mm: memcontrol: fix swap counter leak on swapout from offline cgroup")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/memcontrol.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 533b4b31b464..7d765a106684 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7155,7 +7155,8 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	if (!cgroup_memory_noswap && memcg != swap_memcg) {
 		if (!mem_cgroup_is_root(swap_memcg))
 			page_counter_charge(&swap_memcg->memsw, nr_entries);
-		page_counter_uncharge(&memcg->memsw, nr_entries);
+		if (!mem_cgroup_is_root(memcg))
+			page_counter_uncharge(&memcg->memsw, nr_entries);
 	}
 
 	/*
-- 
2.11.0