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mm: list_lru: fix the return value of list_lru_count_one() 

Since commit 2788cf0c40 ("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/20211025124910.56433-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Muchun Song 2021-11-05 13:37:50 -07:00 committed by Linus Torvalds
parent 60ec6a48ee
commit 41d17431df
1 changed files with 4 additions and 1 deletions
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5
mm/list_lru.c
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@ -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);