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mm/damon/core: get memcg reference before access

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The commit b74a120bcf ("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.

Link: https://lkml.kernel.org/r/20251225002904.139543-1-shakeel.butt@linux.dev
Fixes: b74a120bcf ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED_BP")
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Shakeel Butt 2025-12-24 16:29:04 -08:00 committed by Andrew Morton
parent 582f0f3864
commit a38be54626
1 changed files with 6 additions and 2 deletions
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8
mm/damon/core.c
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@ -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;