[PATCH 5.10 449/717] mm: memcg/slab: fix return of child memcg objcg for root memcg

Greg Kroah-Hartman
2020-12-28T14:22:33Z

From: Muchun Song <songmuchun@bytedance.com>

[ Upstream commit 2f7659a314736b32b66273dbf91c19874a052fde ]

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@bytedance.com
Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Roman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Yafang Shao <laoar.shao@gmail.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Eugene Syromiatnikov <esyr@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Adrian Reber <areber@redhat.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/memcontrol.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 29459a6ce1c7a..74b85077f89ad 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2987,6 +2987,7 @@ __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();

--
2.27.0