From: Filipe Brandenburger <[email protected]>
This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.
===============
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]>
Cc: <[email protected]> [v3.10+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Jiri Slaby <[email protected]>
---
mm/memcontrol.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8e7adcba8176..a3be835d999f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6346,11 +6346,24 @@ static void
mem_cgroup_invalidate_reclaim_iterators(struct mem_cgroup *memcg)
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);
}
--
1.9.0
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