v4.19.13 snapshot.
diff --git a/include/linux/once.h b/include/linux/once.h
new file mode 100644
index 0000000..9225ee6
--- /dev/null
+++ b/include/linux/once.h
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_ONCE_H
+#define _LINUX_ONCE_H
+
+#include <linux/types.h>
+#include <linux/jump_label.h>
+
+bool __do_once_start(bool *done, unsigned long *flags);
+void __do_once_done(bool *done, struct static_key_true *once_key,
+ unsigned long *flags);
+
+/* Call a function exactly once. The idea of DO_ONCE() is to perform
+ * a function call such as initialization of random seeds, etc, only
+ * once, where DO_ONCE() can live in the fast-path. After @func has
+ * been called with the passed arguments, the static key will patch
+ * out the condition into a nop. DO_ONCE() guarantees type safety of
+ * arguments!
+ *
+ * Not that the following is not equivalent ...
+ *
+ * DO_ONCE(func, arg);
+ * DO_ONCE(func, arg);
+ *
+ * ... to this version:
+ *
+ * void foo(void)
+ * {
+ * DO_ONCE(func, arg);
+ * }
+ *
+ * foo();
+ * foo();
+ *
+ * In case the one-time invocation could be triggered from multiple
+ * places, then a common helper function must be defined, so that only
+ * a single static key will be placed there!
+ */
+#define DO_ONCE(func, ...) \
+ ({ \
+ bool ___ret = false; \
+ static bool ___done = false; \
+ static DEFINE_STATIC_KEY_TRUE(___once_key); \
+ if (static_branch_unlikely(&___once_key)) { \
+ unsigned long ___flags; \
+ ___ret = __do_once_start(&___done, &___flags); \
+ if (unlikely(___ret)) { \
+ func(__VA_ARGS__); \
+ __do_once_done(&___done, &___once_key, \
+ &___flags); \
+ } \
+ } \
+ ___ret; \
+ })
+
+#define get_random_once(buf, nbytes) \
+ DO_ONCE(get_random_bytes, (buf), (nbytes))
+#define get_random_once_wait(buf, nbytes) \
+ DO_ONCE(get_random_bytes_wait, (buf), (nbytes)) \
+
+#endif /* _LINUX_ONCE_H */