--- linux/drivers/usb/serial/usbserial.c-27	2006-06-27 10:26:06.294476250 +0200
+++ linux/drivers/usb/serial/usbserial.c	2006-06-27 10:30:31.011020000 +0200
@@ -528,8 +528,18 @@
 		down(&port->sem);
 		dbg("%s - port %d len %d backlog %d", __FUNCTION__,
 		    port->number, job->len, port->write_backlog);
-		if (port->tty != NULL)
-			__serial_write(port, 0, job->buff, job->len);
+		if (port->tty != NULL) {
+			int rc;
+			int sent = 0;
+			while (sent < job->len) {
+				rc = __serial_write(port, 0, job->buff + sent, job->len - sent);
+				if ((rc < 0) || signal_pending(current))
+					break;
+				sent += rc;
+				if ((sent < job->len) && current->need_resched)
+					schedule();
+			}
+		}
 		up(&port->sem);
 
 		spin_lock_irqsave(&post_lock, flags);
@@ -725,6 +735,9 @@
 	struct usb_serial_port *port = (struct usb_serial_port *) tty->driver_data;
 	int rc;
 
+	if (!port)
+		return -ENODEV;
+
 	if (!in_interrupt()) {
 		/*
 		 * Run post_list to reduce a possiblity of reordered writes.