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Hugh Dickins authored
Sometimes the cleanup after memcg hierarchy testing gets stuck in mem_cgroup_reparent_charges(), unable to bring non-kmem usage down to 0. There may turn out to be several causes, but a major cause is this: the workitem to offline parent can get run before workitem to offline child; parent's mem_cgroup_reparent_charges() circles around waiting for the child's pages to be reparented to its lrus, but it's holding cgroup_mutex which prevents the child from reaching its mem_cgroup_reparent_charges(). Just use an ordered workqueue for cgroup_destroy_wq. tj: Committing as the temporary fix until the reverse dependency can be removed from memcg. Comment updated accordingly. Fixes: e5fca243 ("cgroup: use a dedicated workqueue for cgroup destruction") Suggested-by:
Filipe Brandenburger <filbranden@google.com> Signed-off-by:
Hugh Dickins <hughd@google.com> Cc: stable@vger.kernel.org # 3.10+ Signed-off-by:
Tejun Heo <tj@kernel.org>
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