[Devel] [PATCH RH7 6/9] memcg: remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure

[Pavel Tikhomirov]

From: Kirill Tkhai <ktkhai at virtuozzo.com>

In case of memcg_online_kmem() failure, memcg_cgroup::id remains hashed
in mem_cgroup_idr even after memcg memory is freed.  This leads to leak
of ID in mem_cgroup_idr.

This patch adds removal into mem_cgroup_css_alloc(), which fixes the
problem.  For better readability, it adds a generic helper which is used
in mem_cgroup_alloc() and mem_cgroup_id_put_many() as well.

Link: http://lkml.kernel.org/r/152354470916.22460.14397070748001974638.stgit@localhost.localdomain
Fixes 73f576c04b94 ("mm: memcontrol: fix cgroup creation failure after many small jobs")
Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
Acked-by: Johannes Weiner <hannes at cmpxchg.org>
Acked-by: Vladimir Davydov <vdavydov.dev at gmail.com>
Cc: Michal Hocko <mhocko at kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

Changes:
- skip hunk in mem_cgroup_css_alloc as there is no such error path yet,
patch is not strictly required but better have it as a small cleanup

https://jira.vzint.dev/browse/PSBM-147036

(cherry picked from commit 7e97de0b033bcac4fa9a35cef72e0c06e6a22c67)
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 mm/memcontrol.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8c14585f5e86..af99281292e5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6674,6 +6674,14 @@ unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
 	return memcg->id.id;
 }
 
+static void mem_cgroup_id_remove(struct mem_cgroup *memcg)
+{
+	if (memcg->id.id > 0) {
+		idr_remove(&mem_cgroup_idr, memcg->id.id);
+		memcg->id.id = 0;
+	}
+}
+
 static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
 {
 	atomic_add(n, &memcg->id.ref);
@@ -6700,8 +6708,7 @@ static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
 static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
 {
 	if (atomic_sub_and_test(n, &memcg->id.ref)) {
-		idr_remove(&mem_cgroup_idr, memcg->id.id);
-		memcg->id.id = 0;
+		mem_cgroup_id_remove(memcg);
 
 		/* Memcg ID pins CSS */
 		css_put(&memcg->css);
@@ -6811,8 +6818,7 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	for_each_node(node)
 		free_mem_cgroup_per_zone_info(memcg, node);
 
-	if (memcg->id.id > 0)
-		idr_remove(&mem_cgroup_idr, memcg->id.id);
+	mem_cgroup_id_remove(memcg);
 fail:
 	kfree(memcg);
 	return NULL;
-- 
2.40.1