[061/262] mm: list_lru: fix the return value of list_lru_count_one()

Commit Message

Andrew Morton Nov. 5, 2021, 8:37 p.m. UTC

From: Muchun Song <[e-mail]>
Subject: mm: list_lru: fix the return value of list_lru_count_one()

Since commit 2788cf0c401c ("memcg: reparent list_lrus and free kmemcg_id
on css offline"), ->nr_items can be negative during memory cgroup
reparenting.  In this case, list_lru_count_one() will return an unusual
and huge value, which can surprise users.  At least for now it hasn't
affected any users.  But it is better to let list_lru_count_ont() returns
zero when ->nr_items is negative.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Muchun Song <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Shakeel Butt <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/list_lru.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Patch

--- a/mm/list_lru.c~mm-list_lru-fix-the-return-value-of-list_lru_count_one
+++ a/mm/list_lru.c
@@ -176,13 +176,16 @@  unsigned long list_lru_count_one(struct
 {
 	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);