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

[Vladimir Davydov]

Signed-off-by: Vladimir Davydov <vdavy...@virtuozzo.com>
---
 mm/memcontrol.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 58c229071fb1..cf7fb63860e5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4032,18 +4032,22 @@ 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);
 }
 
 static struct mem_cgroup *mem_cgroup_id_get_active(struct mem_cgroup *memcg)
 {
-       while (!atomic_inc_not_zero(&memcg->id.ref))
+       while (!atomic_inc_not_zero(&memcg->id.ref)) {
+               VM_BUG_ON(mem_cgroup_is_root(memcg));
                memcg = parent_mem_cgroup(memcg);
+       }
        return 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;
@@ -4164,6 +4168,7 @@ 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)
@@ -4233,7 +4238,6 @@ 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