static int edge_port_remove(struct usb_serial_port *port)
{
	struct edgeport_port *edge_port;

	edge_port = usb_get_serial_port_data(port);
	edge_remove_sysfs_attrs(port);
	kfree(edge_port);

	return 0;
}

The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.