[PATCH v6 3/5] memcg: fail to create cgroup if the cgroup id is too big

[Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

memcg requires the cgroup id to be smaller than 65536.

This is a preparation to kill css id.

Signed-off-by: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Acked-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
---
 mm/memcontrol.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6719e2c..4e40ebe 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -498,6 +498,12 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
 	return (memcg == root_mem_cgroup);
 }
 
+/*
+ * We restrict the id in the range of [1, 65535], so it can fit into
+ * an unsigned short.
+ */
+#define MEM_CGROUP_ID_MAX	USHRT_MAX
+
 static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
 {
 	/*
@@ -6312,6 +6318,9 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(css));
 	int error = 0;
 
+	if (css->cgroup->id > MEM_CGROUP_ID_MAX)
+		return -ENOSPC;
+
 	if (!parent)
 		return 0;
 
-- 
1.8.0.2