[PATCH v2 01/21] mm: list_lru: fix list_lru_count_one() return value

[Muchun Song]

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() returns an unusual and
huge value. It can surprise users. So let it return zero when ->nr_items
is negative.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 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