From: Filipe Brandenburger Date: Mon, 3 Mar 2014 23:38:25 +0000 (-0800) Subject: memcg: reparent charges of children before processing parent X-Git-Tag: v3.14-rc6~32^2~13 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4fb1a86fb5e4209a7d4426d4e586c58e9edc74ac;p=pandora-kernel.git memcg: reparent charges of children before processing parent 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: e5fca243abae ("cgroup: use a dedicated workqueue for cgroup destruction") Signed-off-by: Filipe Brandenburger Signed-off-by: Hugh Dickins Reviewed-by: Tejun Heo Acked-by: Michal Hocko Cc: Johannes Weiner Cc: [v3.10+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed