Am Samstag, 23. Dezember 2006 00:37 schrieb J:
> * usb_get_dev - increments the reference count of the
> usb device structure
> * @dev: the device being referenced
> *
> * Each live reference to a device should be
> refcounted.
> *
> * Drivers for USB interfaces should normally record
> such references in
> * their probe() methods, when they bind to an
> interface, and release
> * them by calling usb_put_dev(), in their
> disconnect() methods.
>
> But usb-serial.c breaks this rule because it calls
> usb_put_dev not in usb_serial_disconnect, but in
> destroy_serial. destroy_serial is usually called
> from usb_serial_disconnect except in case of
> the serial_open/usb_serial_disconnect race condition.
This isn't a rule but a sugestion. The rules are:
1. You must balance get/put
2. You must not do IO after returning from disconnect
> So, this seems to prove that we cannot simply
> ref-count usb_serial and execute destroy_serial
> after usb_serial_disconnect already returned.
The use in the code is valid, but insufficient.
> This means that usb_serial_disconnect have to wait
> on serial_open and any other serial_* functions
> to finish. And the body of destroy_serial
> (or at least, most of it)
> should be returned back to usb_serial_disconnect
It is perfectly valid to do (in pseudocode)
disconnect:
lock()
device->disconnect_flag = 1;
unlock()
rest()
put()
io-method:
lock()
if (device->disconnect_flag)
goto err_no_dev;
io()
unlock()
and to leave freeing the memory to refcounting
Regards
Oliver
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