[PATCH v2] mm: memcg: initialize *locked in memcg1_oom_prepare() stub

[Breno Leitao]

mem_cgroup_oom() passes an uninitialized "locked" to memcg1_oom_prepare()
and reads it back in memcg1_oom_finish():

	bool locked, ret;
	...
	if (!memcg1_oom_prepare(memcg, &locked))
		return false;
	ret = mem_cgroup_out_of_memory(memcg, mask, order);
	memcg1_oom_finish(memcg, locked);

This relies on memcg1_oom_prepare() setting *locked whenever it returns
true.  The CONFIG_MEMCG_V1=y version does, but the stub used when
CONFIG_MEMCG_V1=n returns true without touching *locked, so
memcg1_oom_finish() consumes an uninitialized value.  On a memcg OOM this
is reported by UBSAN:

  UBSAN: invalid-load in mm/memcontrol.c:1932:27
  load of value 0 is not a valid value for type 'bool' (aka '_Bool')

Initialize *locked to false in the stub; with cgroup v1 compiled out
there is no OOM lock to take.

Fixes: e93d4166b40a ("mm: memcg: put cgroup v1-specific code under a config option")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reviewed-by: SeongJae Park <sj@xxxxxxxxxx>
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
Changes in v2:
- added the reviews and acks.
- Link to v1: https://lore.kernel.org/r/20260626-memcg-oom-uninit-locked-v1-1-a00175936b39@xxxxxxxxxx
---
 mm/memcontrol-v1.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
index d3ed5b93290fb..0f703f239c80f 100644
--- a/mm/memcontrol-v1.h
+++ b/mm/memcontrol-v1.h
@@ -101,7 +101,11 @@ static inline void memcg1_remove_from_trees(struct mem_cgroup *memcg) {}
 static inline void memcg1_soft_limit_reset(struct mem_cgroup *memcg) {}
 static inline void memcg1_css_offline(struct mem_cgroup *memcg) {}
 
-static inline bool memcg1_oom_prepare(struct mem_cgroup *memcg, bool *locked) { return true; }
+static inline bool memcg1_oom_prepare(struct mem_cgroup *memcg, bool *locked)
+{
+	*locked = false;
+	return true;
+}
 static inline void memcg1_oom_finish(struct mem_cgroup *memcg, bool locked) {}
 static inline void memcg1_oom_recover(struct mem_cgroup *memcg) {}
 

---
base-commit: b8809969e1d7a591e0f49dd464a5d04b3cf02ab1
change-id: 20260626-memcg-oom-uninit-locked-5ec79dff4396

Best regards,
--  
Breno Leitao <leitao@xxxxxxxxxx>