Am Freitag, 22. Dezember 2006 23:45 schrieb J:
> > if (!port || port->serial->dev->state ==
> > USB_STATE_NOTATTACHED)
>
> > There's no use checking for attachement. The state
> > may have changed.
> > In fact, if a device is disconnected via sysfs, this
> > code will happily write
> > to a device somebody else has claimed.
>
> I don't understand. serial->dev is usb_device*
> and it is protected by ref counting (using
> usb_get_dev).
> So, it should not disappear or be claimed by
> anybody else, right?
Partially.
Yes, refcounting will make sure it does not disappear.
Refcounting will _not_ make sure it is not claimed.
The call path is as follows:
usbfs:
/* disconnect kernel driver from interface */
case USBDEVFS_DISCONNECT:
down_write(&usb_bus_type.subsys.rwsem);
if (intf->dev.driver) {
driver = to_usb_driver(intf->dev.driver);
dev_dbg (&intf->dev, "disconnect by usbfs\n");
usb_driver_release_interface(driver, intf);
} else
retval = -ENODATA;
up_write(&usb_bus_type.subsys.rwsem);
break;
--
usb_driver_release_interface():
/* don't release if the interface hasn't been added yet */
if (device_is_registered(dev)) {
iface->condition = USB_INTERFACE_UNBINDING;
device_release_driver(dev);
}
--
__device_release_driver():
if (dev->bus && dev->bus->remove)
dev->bus->remove(dev);
else if (drv->remove)
drv->remove(dev);
and a driver is unbound. After that ownership is in potential flux.
> As for the USB_STATE_NOTATTACHED, there is a long
> comment in hub.c about it. Also I see plenty of
> code, which checks it without any lock.
> So, I guess, it should not kill anybody.
It doesn't kill you.
USB_STATE_NOTATTACHED -> return with error code is valid.
However, the reverse is not.
Regards
Oliver
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