--- x/drivers/usb/core/devio.c
+++ y/drivers/usb/core/devio.c
@@ -417,6 +417,7 @@ static void free_async(struct async *as)
 {
 	int i;
 
+	usb_kill_urb(as->urb);
 	put_pid(as->pid);
 	if (as->cred)
 		put_cred(as->cred);