v4.19.13 snapshot.
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
new file mode 100644
index 0000000..acb77dc
--- /dev/null
+++ b/include/linux/cgroup_subsys.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * List of cgroup subsystems.
+ *
+ * DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
+ */
+
+/*
+ * This file *must* be included with SUBSYS() defined.
+ */
+
+#if IS_ENABLED(CONFIG_CPUSETS)
+SUBSYS(cpuset)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_SCHED)
+SUBSYS(cpu)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_CPUACCT)
+SUBSYS(cpuacct)
+#endif
+
+#if IS_ENABLED(CONFIG_BLK_CGROUP)
+SUBSYS(io)
+#endif
+
+#if IS_ENABLED(CONFIG_MEMCG)
+SUBSYS(memory)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_DEVICE)
+SUBSYS(devices)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_FREEZER)
+SUBSYS(freezer)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_NET_CLASSID)
+SUBSYS(net_cls)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_PERF)
+SUBSYS(perf_event)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_NET_PRIO)
+SUBSYS(net_prio)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_HUGETLB)
+SUBSYS(hugetlb)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_PIDS)
+SUBSYS(pids)
+#endif
+
+#if IS_ENABLED(CONFIG_CGROUP_RDMA)
+SUBSYS(rdma)
+#endif
+
+/*
+ * The following subsystems are not supported on the default hierarchy.
+ */
+#if IS_ENABLED(CONFIG_CGROUP_DEBUG)
+SUBSYS(debug)
+#endif
+
+/*
+ * DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
+ */