3.13-stable review patch. If anyone has any objections, please let me know.
------------------
From: Filipe Brandenburger <filbran...@google.com>
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 <filbran...@google.com>
Signed-off-by: Hugh Dickins <hu...@google.com>
Reviewed-by: Tejun Heo <t...@kernel.org>
Acked-by: Michal Hocko <mho...@suse.cz>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: <sta...@vger.kernel.org> [v3.10+]
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
mm/memcontrol.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6360,11 +6360,24 @@ static void mem_cgroup_invalidate_reclai
static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+ struct cgroup_subsys_state *iter;
kmem_cgroup_css_offline(memcg);
mem_cgroup_invalidate_reclaim_iterators(memcg);
- mem_cgroup_reparent_charges(memcg);
+
+ /*
+ * This requires that offlining is serialized. Right now that is
+ * guaranteed because css_killed_work_fn() holds the cgroup_mutex.
+ */
+ rcu_read_lock();
+ css_for_each_descendant_post(iter, css) {
+ rcu_read_unlock();
+ mem_cgroup_reparent_charges(mem_cgroup_from_css(iter));
+ rcu_read_lock();
+ }
+ rcu_read_unlock();
+
mem_cgroup_destroy_all_caches(memcg);
vmpressure_cleanup(&memcg->vmpressure);
}
--
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