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From:   Muchun Song <songmuchun@bytedance.com>
To:     willy@infradead.org, akpm@linux-foundation.org, hannes@cmpxchg.org,
        mhocko@kernel.org, vdavydov.dev@gmail.com, shakeelb@google.com,
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        alexander.h.duyck@linux.intel.com, richard.weiyang@gmail.com
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH 1/9] mm: list_lru: fix list_lru_count_one() return value
Date:   Wed, 28 Apr 2021 17:49:41 +0800
Message-Id: <20210428094949.43579-2-songmuchun@bytedance.com>
In-Reply-To: <20210428094949.43579-1-songmuchun@bytedance.com>
References: <20210428094949.43579-1-songmuchun@bytedance.com>
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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