set_shrinker_bit() reads info->unit[shrinker_id_to_index(shrinker_id)] before checking shrinker_id against info->map_nr_max, so an id past the currently visible map_nr_max reads past the unit[] array before the WARN_ON_ONCE() catches it. Move the load into the bounded branch. Fixes: 307bececcd12 ("mm: shrinker: add a secondary array for shrinker_info::{map, nr_deferred}") Signed-off-by: David Carlier --- mm/shrinker.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/shrinker.c b/mm/shrinker.c index 76b3f750cf65..49256f81199f 100644 --- a/mm/shrinker.c +++ b/mm/shrinker.c @@ -197,12 +197,13 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id) { if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) { struct shrinker_info *info; - struct shrinker_info_unit *unit; rcu_read_lock(); info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - unit = info->unit[shrinker_id_to_index(shrinker_id)]; if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) { + struct shrinker_info_unit *unit; + + unit = info->unit[shrinker_id_to_index(shrinker_id)]; /* Pairs with smp mb in shrink_slab() */ smp_mb__before_atomic(); set_bit(shrinker_id_to_offset(shrinker_id), unit->map); -- 2.53.0