[PATCH 1/9] mm: list_lru: fix list_lru_count_one() return value

Muchun Song
2021-04-28T09:54:07Z

Since commit 2788cf0c401c ("memcg: reparent list_lrus and free kmemcg_id
on css offline"), the ->nr_items can be negative during memory cgroup
reparenting. In this case, list_lru_count_one() can returns an unusually
large value. In order to not surprise the user. So return zero when
->nr_items is negative.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
mm/list_lru.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index cd58790d0fb3..4962d48d4410 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -176,13 +176,16 @@ unsigned long list_lru_count_one(struct list_lru *lru,
{
struct list_lru_node *nlru = &lru->node[nid];
struct list_lru_one *l;
- unsigned long count;
+ long count;

rcu_read_lock();
l = list_lru_from_memcg_idx(nlru, memcg_cache_id(memcg));
count = READ_ONCE(l->nr_items);
rcu_read_unlock();

+ if (unlikely(count < 0))
+ count = 0;
+
return count;
}
EXPORT_SYMBOL_GPL(list_lru_count_one);
--
2.11.0