From: Michal Hocko <mhocko@xxxxxxx>
Subject: memcg, kmem: fix reference count handling on the error path
mem_cgroup_css_online calls mem_cgroup_put if memcg_init_kmem fails. This
is not correct because only memcg_propagate_kmem takes an additional
reference while mem_cgroup_sockets_init is allowed to fail as well
(although no current implementation fails) but it doesn't take any
reference. This all suggests that it should be memcg_propagate_kmem that
should clean up after itself so this patch moves mem_cgroup_put over
there.
Unfortunately this is not that easy (as pointed out by Li Zefan) because
memcg_kmem_mark_dead marks the group dead (KMEM_ACCOUNTED_DEAD) if it is
marked active (KMEM_ACCOUNTED_ACTIVE) which is the case even if
memcg_propagate_kmem fails so the additional reference is dropped in that
case in kmem_cgroup_destroy which means that the reference would be
dropped two times.
The easiest way then would be to simply remove mem_cgrroup_put from
mem_cgroup_css_online and rely on kmem_cgroup_destroy doing the right
thing.
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Glauber Costa <glommer@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [3.8]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 8 --------
1 file changed, 8 deletions(-)
diff -puN mm/memcontrol.c~memcg-kmem-fix-reference-count-handling-on-the-error-path mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-kmem-fix-reference-count-handling-on-the-error-path
+++ a/mm/memcontrol.c
@@ -6345,14 +6345,6 @@ mem_cgroup_css_online(struct cgroup *con
error = memcg_init_kmem(memcg, &mem_cgroup_subsys);
mutex_unlock(&memcg_create_mutex);
- if (error) {
- /*
- * We call put now because our (and parent's) refcnts
- * are already in place. mem_cgroup_put() will internally
- * call __mem_cgroup_free, so return directly
- */
- mem_cgroup_put(memcg);
- }
return error;
}
_
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