From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: mm: memcg/slab: fix return of child memcg objcg for root memcg
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.
Link: https://lkml.kernel.org/r/20201029164429.58703-1-songmuchun@xxxxxxxxxxxxx
Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Chris Down <chris@xxxxxxxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Eugene Syromiatnikov <esyr@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Adrian Reber <areber@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 1 +
1 file changed, 1 insertion(+)
--- a/mm/memcontrol.c~mm-memcg-slab-fix-return-child-memcg-objcg-for-root-memcg
+++ a/mm/memcontrol.c
@@ -2975,6 +2975,7 @@ __always_inline struct obj_cgroup *get_o
objcg = rcu_dereference(memcg->objcg);
if (objcg && obj_cgroup_tryget(objcg))
break;
+ objcg = NULL;
}
rcu_read_unlock();
_
