Oliver Neukum wrote:
> Am Dienstag, 27. Juni 2006 16:09 schrieb Franck Bui-Huu:
>> Oliver Neukum wrote:
>>> Am Dienstag, 27. Juni 2006 09:52 schrieb Franck Bui-Huu:
>>>> + expire = timeout ? msecs_to_jiffies(timeout) :
>>>> MAX_SCHEDULE_TIMEOUT;
>>>> + if (!wait_for_completion_timeout(&done, expire)) {
>>>> + usb_unlink_urb(urb);
>>>> }
>>>> -
>>>> + status = urb->status;
>>> Hm, is this racy?
>>> What happens if usb_unlink_urb() and the completion handler race?
>>> If usb_unlink_urb() fails to unlink the URB because it is too late,
>>> is it guaranteed that urb->status is valid?
>>> In the old version this could not happen because the completion was
>>> always done.
>> well, I'm not sure to understand. Do you mean "what happen if the timeout has
>> expired, but just before calling usb_unlink_urb() the urb is completed by the
>> hcd" ?
>>
>> If so, I think that usb_unlink_urb() handles this case by checking (with lock
>> held) that the urb is still queued.
>
> Precisely. If the URB is not queued it'll notice. But you read urb->status
> even in that case.
>
If URB is no more queued when calling usb_unlink_urb(), this function will leave
urb->status alone. So urb->status will have the value given by the hcd.
Therefore
usb_start_wait_urb() will behave like a normal case (no timeout). I don't see
what's wrong here...
Franck
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