[PATCH v5 3/5] memcg: fail to create cgroup if the cgroup id is toobig

[Li Zefan]

memcg requires the cgroup id to be smaller than 65536.

This is a preparation to kill css id.

Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
---
 mm/memcontrol.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3189f70..c0bb83c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -503,6 +503,12 @@ 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)
 {
 	/*
@@ -6056,6 +6062,9 @@ mem_cgroup_css_alloc(struct cgroup *cont)
 	long error = -ENOMEM;
 	int node;
 
+	if (cont->id > MEM_CGROUP_ID_MAX)
+		return ERR_PTR(-ENOSPC);
+
 	memcg = mem_cgroup_alloc();
 	if (!memcg)
 		return ERR_PTR(error);
-- 
1.8.0.2
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