The commit b74a120bcf507 ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED_BP") added accesses to memcg structure without getting reference to it. This is unsafe. Let's get the reference before accessing the memcg. Fixes: b74a120bcf507 ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED_BP") Signed-off-by: Shakeel Butt --- mm/damon/core.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 4ad5f290d382..89982e0229f0 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2051,13 +2051,15 @@ static unsigned long damos_get_node_memcg_used_bp( rcu_read_lock(); memcg = mem_cgroup_from_id(goal->memcg_id); - rcu_read_unlock(); - if (!memcg) { + if (!memcg || !mem_cgroup_tryget(memcg)) { + rcu_read_unlock(); if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) return 0; else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ return 10000; } + rcu_read_unlock(); + mem_cgroup_flush_stats(memcg); lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(goal->nid)); used_pages = lruvec_page_state(lruvec, NR_ACTIVE_ANON); @@ -2065,6 +2067,8 @@ static unsigned long damos_get_node_memcg_used_bp( used_pages += lruvec_page_state(lruvec, NR_ACTIVE_FILE); used_pages += lruvec_page_state(lruvec, NR_INACTIVE_FILE); + mem_cgroup_put(memcg); + si_meminfo_node(&i, goal->nid); if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) numerator = used_pages; -- 2.47.3