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Subject[PATCH v3] mm: memcg/slab: Fix return child memcg objcg for root memcg
Date
Consider the following memcg hierarchy.

root
/ \
A B

If we failed to get the reference on objcg of memcg A, the
get_obj_cgroup_from_current can return the wrong objcg for
the root memcg.

Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Roman Gushchin <guro@fb.com>
---
changelog in v3:
1. Fix commit grammar, thanks to Shakeel.

changelog in v2:
1. Do not use a comparison with the root_mem_cgroup

mm/memcontrol.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1337775b04f3..8c8b4c3ed5a0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2961,6 +2961,7 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
objcg = rcu_dereference(memcg->objcg);
if (objcg && obj_cgroup_tryget(objcg))
break;
+ objcg = NULL;
}
rcu_read_unlock();

--
2.20.1
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