-
Filipe Brandenburger 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(). Further testing showed that an ordered workqueue for cgroup_destroy_wq is not always good enough: percpu_ref_kill_and_confirm's call_rcu_sched stage on the way can mess up the order before reaching the workqueue. Instead, when offlining a memcg, call mem_cgroup_reparent_charges() on all its children (and grandchildren, in the correct order) to have their charges reparented first. Fixes: e5fca243 ("cgroup: use a dedicated workqueue for cgroup destruction") Signed-off-by:
Filipe Brandenburger <filbranden@google.com> Signed-off-by:
Hugh Dickins <hughd@google.com> Reviewed-by:
Tejun Heo <tj@kernel.org> Acked-by:
Michal Hocko <mhocko@suse.cz> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: <stable@vger.kernel.org> [v3.10+] Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
4fb1a86f