[PATCH v2 3/3] mm: memcontrol: add sanity checks for memcg->id.ref on get/put

[Vladimir Davydov]

Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
---
 mm/memcontrol.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 67109d556a4a..32b2f33865f9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4033,6 +4033,7 @@ static DEFINE_IDR(mem_cgroup_idr);
 
 static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
 {
+	VM_BUG_ON(atomic_read(&memcg->id.ref) <= 0);
 	atomic_add(n, &memcg->id.ref);
 }
 
@@ -4056,6 +4057,7 @@ static struct mem_cgroup *mem_cgroup_id_get_active(struct mem_cgroup *memcg)
 
 static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
 {
+	VM_BUG_ON(atomic_read(&memcg->id.ref) < n);
 	if (atomic_sub_and_test(n, &memcg->id.ref)) {
 		idr_remove(&mem_cgroup_idr, memcg->id.id);
 		memcg->id.id = 0;
@@ -4176,6 +4178,7 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	INIT_LIST_HEAD(&memcg->cgwb_list);
 #endif
 	idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
+	atomic_set(&memcg->id.ref, 1);
 	return memcg;
 fail:
 	if (memcg->id.id > 0)
@@ -4245,7 +4248,6 @@ fail:
 static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 {
 	/* Online state pins memcg ID, memcg ID pins CSS */
-	mem_cgroup_id_get(mem_cgroup_from_css(css));
 	css_get(css);
 	return 0;
 }
-- 
2.1.4