Am Freitag, 4. Dezember 2009 22:36:22 schrieb Alan Stern:
> > > Typically the driver would take a reference during open() and drop it
> > > during close().
> >
> >
> > You can do that but then you must not do IO prior to open() or after
> > close(). That is you must actually wait for IO to finish in close() and
> > cannot prefill your buffers before open().
>
> If open() or close() is called before disconnect() then you don't have
> to worry.
>
> If close() is called after disconnect() there's nothing to wait for,
> because disconnect() should call usb_kill_urb() on all outstanding
> transfers (actually usbcore will do that for you). Likewise with
> open().
>
> The problem in this example stems from the fact that you are using
> instance->dev at a time when you don't know that it is valid -- in
> fact, you have good reason to believe it _isn't_ valid because
> instance->disconnected is set.
OK, yes. It's a bad example. However this is tricky.
This is a bug then:
mutex_lock(...);
if (instance->error) {
rv = instance->error;
instance->error = 0;
dev_dbg(instance->dev,...);
goto err_out;
}
rv = -ENODEV;
if (instance->disconnected)
goto err_out;
> One approach is to set instance->dev to NULL in disconnect(). That
> wouldn't do much good for your dev_dbg(), though. A better solution is
> to refcount the instance->dev pointer: Take a reference to the device
> when setting instance->dev and drop it when clearing instance->dev (or
> when instance is freed).
That would mean that I am forced to adopt refcounting just to print
something. This seems very inelegant.
Regards
Oliver
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