3.11.10.7 -stable review patch. If anyone has any objections, please let me know.
------------------ From: Filipe Brandenburger <[email protected]> commit 4fb1a86fb5e4209a7d4426d4e586c58e9edc74ac upstream. 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 <[email protected]> Signed-off-by: Hugh Dickins <[email protected]> Reviewed-by: Tejun Heo <[email protected]> Acked-by: Michal Hocko <[email protected]> Cc: Johannes Weiner <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> [ Hugh: Yes, more differences, and the old mem_cgroup_reparent_charges line is intentionally left in for 3.10 whereas it was removed for 3.12+: that's because the css/cgroup iterator changed in between, it used not to supply the root of the subtree, but nowadays it does. ] [ luis: backported to 3.11: used Hugh's backport to 3.10 ] Signed-off-by: Luis Henriques <[email protected]> --- mm/memcontrol.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index bb13089..4e4b328 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6346,11 +6346,25 @@ static void mem_cgroup_invalidate_reclaim_iterators(struct mem_cgroup *memcg) static void mem_cgroup_css_offline(struct cgroup *cont) { struct mem_cgroup *memcg = mem_cgroup_from_cont(cont); + struct cgroup *iter; kmem_cgroup_css_offline(memcg); mem_cgroup_invalidate_reclaim_iterators(memcg); + + /* + * This requires that offlining is serialized. Right now that is + * guaranteed because css_killed_work_fn() holds the cgroup_mutex. + */ + rcu_read_lock(); + cgroup_for_each_descendant_post(iter, cont) { + rcu_read_unlock(); + mem_cgroup_reparent_charges(mem_cgroup_from_cont(iter)); + rcu_read_lock(); + } + rcu_read_unlock(); mem_cgroup_reparent_charges(memcg); + mem_cgroup_destroy_all_caches(memcg); vmpressure_cleanup(&memcg->vmpressure); } -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
