[v3] mm: memcg/slab: Fix return child memcg objcg for root memcg
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Message ID 20201029164429.58703-1-songmuchun@bytedance.com
State In Next
Commit 7327d455ef5c2bdc5f74f88c907cf0ed47061b79
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  • [v3] mm: memcg/slab: Fix return child memcg objcg for root memcg
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Commit Message

Muchun Song Oct. 29, 2020, 4:44 p.m. UTC
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(+)

Patch
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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();