From 48fe267c503ec22014ba4e83d002b07caad034d0 Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Wed, 1 Apr 2020 21:07:39 -0700 Subject: [PATCH] mm: memcg: make memory.oom.group tolerable to task migration If a task is getting moved out of the OOMing cgroup, it might result in unexpected OOM killings if memory.oom.group is used anywhere in the cgroup tree. Imagine the following example: A (oom.group = 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 oom.group 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, memory.oom.group should be ignored, and the OOM killer should kill only the victim task. Reported-by: Dan Schatzberg Signed-off-by: Roman Gushchin Signed-off-by: Andrew Morton Acked-by: Michal Hocko Acked-by: Johannes Weiner Link: http://lkml.kernel.org/r/20200316223510.3176148-1-guro@fb.com Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a96d9015..ca19486 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1931,6 +1931,14 @@ struct mem_cgroup *mem_cgroup_get_oom_group(struct task_struct *victim, 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 memory.group.oom. + */ + 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 * highest-level memory cgroup with oom.group set. -- 2.7.4