+static inline kuid_t kuid_into_mnt(struct user_namespace *to, kuid_t kuid)
+{
+#ifdef CONFIG_IDMAP_MOUNTS
+	return make_kuid(to, __kuid_val(kuid));
+#else
+	return kuid;
+#endif
+}
+
+static inline kgid_t kgid_into_mnt(struct user_namespace *to, kgid_t kgid)
+{
+#ifdef CONFIG_IDMAP_MOUNTS
+	return make_kgid(to, __kgid_val(kgid));
+#else
+	return kgid;
+#endif

If you want to keep the config option please at least have on
#ifdef/#else/#endif instead of this mess.