Commit 48fe267c authored by Roman Gushchin's avatar Roman Gushchin Committed by Linus Torvalds
Browse files

mm: memcg: make tolerable to task migration

If a task is getting moved out of the OOMing cgroup, it might result in
unexpected OOM killings if is used anywhere in the cgroup

Imagine the following example:

          A ( = 1)
         / \
  (OOM) B   C

Let's say B's memory.max is exceeded and it's OOMing.  The OOM killer
selects a task in B as a victim, but someone asynchronously moves the task
into C.  mem_cgroup_get_oom_group() will iterate over all ancestors of C
up to the root cgroup.  In theory it had to stop at the oom_domain level -
the memory cgroup which is OOMing.  But because B is not an ancestor of C,
it's not happening.  Instead it chooses A (because it's is set),
and kills all tasks in A.  This behavior is wrong because the OOM happened
in B, so there is no reason to kill anything outside.

Fix this by checking it the memory cgroup to which the task belongs is a
descendant of the oom_domain.  If not, should be ignored,
and the OOM killer should kill only the victim task.
Reported-by: default avatarDan Schatzberg <>
Signed-off-by: default avatarRoman Gushchin <>
Signed-off-by: default avatarAndrew Morton <>
Acked-by: default avatarMichal Hocko <>
Acked-by: default avatarJohannes Weiner <>

Signed-off-by: default avatarLinus Torvalds <>
parent b3a7822e
......@@ -1930,6 +1930,14 @@ struct mem_cgroup *mem_cgroup_get_oom_group(struct task_struct *victim,
if (memcg == root_mem_cgroup)
goto out;
* If the victim task has been asynchronously moved to a different
* memory cgroup, we might end up killing tasks outside oom_domain.
* In this case it's better to ignore
if (unlikely(!mem_cgroup_is_descendant(memcg, oom_domain)))
goto out;
* Traverse the memory cgroup hierarchy from the victim task's
* cgroup up to the OOMing cgroup (or root) to find the
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