Oliver Neukum <oliver@xxxxxxxxxx> writes:
> Am Dienstag, 17. November 2009 19:35:07 schrieb Eric W. Biederman:
>> Boiled down. ftdi_chars_in_buffer is essentially
>> priv->tx_outstanding_bytes. tx_outstanding_bytes is incremented when an
>> urb request is sent and tx_outstanding_bytes is decremented when an urb
>> request completes.
>>
>> It turns out I have a moderately noisy usb line, and so I occasionally
>> get messages like:
>>
>> ehci_hcd 0000:00:0a.1: detected XactErr len 0/7 retry 31
>>
>> Which as best as I can tell result in the urb getting abandoned and
>> neither completed nor canceled (because we have hit the maximum
>> retry count and they still don't succeed).
>
> The URB should be finished with an error code in urb->status.
> ftdi_write_bulk_callback() does decrement the counter even in
> the error case.
>
>> Which appears to result in tx_outstanding_bytes getting stuck at
>> some positive number.
>
> Do you see this message
>
> if (status) {
> dbg("nonzero write bulk status received: %d", status);
> return;
> }
>
> if you enable debugging output?
I will have to give that a try. The problem isn't that easy to reproduce.
But I do have a 100% correlation between urb retry counts and hangs
in tty_wait_until_sent.
Eric
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