[PATCH v3 3/3] mm: memcontrol: add sanity checks for memcg->id.ref on get/put

[Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>]

Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
Changes in v3:
 - move memcg->id.ref initialization to mem_cgroup_css_online to make the code
   easier to follow (Johannes)

 mm/memcontrol.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 18db8a490a93..1c0aa59fd333 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_online(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;
@@ -4244,8 +4246,10 @@ fail:
 
 static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 {
+	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+
 	/* Online state pins memcg ID, memcg ID pins CSS */
-	mem_cgroup_id_get(mem_cgroup_from_css(css));
+	atomic_set(&memcg->id.ref, 1);
 	css_get(css);
 	return 0;
 }
-- 
2.1.4

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