bus = list_entry(buslist, struct usb_bus, bus_list);
/* recurse through all children of the root hub */
+ if (!bus->root_hub)
+ continue;
down(&bus->root_hub->serialize);
ret = usb_device_dump(&buf, &nbytes, &skip_bytes, ppos, bus->root_hub, bus, 0, 0, 0);
up(&bus->root_hub->serialize);