v4.19.13 snapshot.
diff --git a/lib/once.c b/lib/once.c
new file mode 100644
index 0000000..8b7d623
--- /dev/null
+++ b/lib/once.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/once.h>
+#include <linux/random.h>
+
+struct once_work {
+ struct work_struct work;
+ struct static_key_true *key;
+};
+
+static void once_deferred(struct work_struct *w)
+{
+ struct once_work *work;
+
+ work = container_of(w, struct once_work, work);
+ BUG_ON(!static_key_enabled(work->key));
+ static_branch_disable(work->key);
+ kfree(work);
+}
+
+static void once_disable_jump(struct static_key_true *key)
+{
+ struct once_work *w;
+
+ w = kmalloc(sizeof(*w), GFP_ATOMIC);
+ if (!w)
+ return;
+
+ INIT_WORK(&w->work, once_deferred);
+ w->key = key;
+ schedule_work(&w->work);
+}
+
+static DEFINE_SPINLOCK(once_lock);
+
+bool __do_once_start(bool *done, unsigned long *flags)
+ __acquires(once_lock)
+{
+ spin_lock_irqsave(&once_lock, *flags);
+ if (*done) {
+ spin_unlock_irqrestore(&once_lock, *flags);
+ /* Keep sparse happy by restoring an even lock count on
+ * this lock. In case we return here, we don't call into
+ * __do_once_done but return early in the DO_ONCE() macro.
+ */
+ __acquire(once_lock);
+ return false;
+ }
+
+ return true;
+}
+EXPORT_SYMBOL(__do_once_start);
+
+void __do_once_done(bool *done, struct static_key_true *once_key,
+ unsigned long *flags)
+ __releases(once_lock)
+{
+ *done = true;
+ spin_unlock_irqrestore(&once_lock, *flags);
+ once_disable_jump(once_key);
+}
+EXPORT_SYMBOL(__do_once_done);