[Devel] [PATCH RH7] mm/memcontrol: remove excess put of memory cgroup id refcount on css free

[Pavel Tikhomirov]

The removed hunk comes from rhel partial porting of [1], there they
added mem_cgroup_id_put on memcg free instead of offline. But they also
didn't do refcounting in mem_cgroup_id_put, only removed id from idr.

Now we do actual refcounting in mem_cgroup_id_put, and atomic_set(1) and
css_get in mem_cgroup_css_online are paired with mem_cgroup_id_put in
mem_cgroup_css_offline. The call in free path is excess and we should
remove it.

This is not a critical excess refcount put, as it happened on late
cgroup freeing stage, which can only happen after this id refcount
reaches zero, which leads to css_put, which leads to freeing. So nobody
cares about id refcount at this point.

https://jira.vzint.dev/browse/PSBM-148818

Fixes: 9dcef96ce3e2 ("ms/mm: memcontrol: fix cgroup creation failure after many small jobs") [1]
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 mm/memcontrol.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3a5e89b913bd..c7c15c6dd6fb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6818,8 +6818,6 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
 
 	mem_cgroup_remove_from_trees(memcg);
 
-	mem_cgroup_id_put(memcg);
-
 	for_each_node(node)
 		free_mem_cgroup_per_zone_info(memcg, node);
 
-- 
2.41.0