diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 2138ba8..aea861e 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -401,11 +401,13 @@
 	struct usb_serial_port *port = tty->driver_data;
 	int retval = -ENODEV;
 
+	lock_kernel();
 	if (!port)
 		goto exit;
 
 	dbg("%s - port %d, cmd 0x%.4x", __FUNCTION__, port->number, cmd);
 
+	/* Caution - port->open_count is BKL protected */
 	if (!port->open_count) {
 		dbg ("%s - port not open", __FUNCTION__);
 		goto exit;
@@ -416,8 +418,8 @@
 		retval = port->serial->type->ioctl(port, file, cmd, arg);
 	else
 		retval = -ENOIOCTLCMD;
-
 exit:
+	unlock_kernel();
 	return retval;
 }
 
@@ -446,19 +448,24 @@
 {
 	struct usb_serial_port *port = tty->driver_data;
 
-	if (!port)
+	lock_kernel();
+	if (!port) {
+		unlock_kernel();
 		return;
+	}
 
 	dbg("%s - port %d", __FUNCTION__, port->number);
 
 	if (!port->open_count) {
 		dbg("%s - port not open", __FUNCTION__);
+		unlock_kernel();
 		return;
 	}
 
 	/* pass on to the driver specific version of this function if it is available */
 	if (port->serial->type->break_ctl)
 		port->serial->type->break_ctl(port, break_state);
+	unlock_kernel();
 }
 
 static int serial_read_proc (char *page, char **start, off_t off, int count, int *eof, void *data)