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

From: Vladimir Davydov
Date: Wed Aug 03 2016 - 06:54:48 EST


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