Re: [Bisected] [Bug #13821] Replugging USB serial converter uses new device node

Ferenc Wagner
2009-07-27T15:53:30Z

Alan Stern <stern@rowland.harvard.edu> writes:

> On Mon, 27 Jul 2009, Carlos R. Mafra wrote:
>
>> On Sun 26.Jul'09 at 22:28:27 +0200, Rafael J. Wysocki wrote:
>>> Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=13821
>>> Subject : Replugging USB serial converter uses new device node
>>> Submitter : Ferenc Wagner <wferi@niif.hu>
>>> Date : 2009-07-18 20:04 (9 days old)
>>> References : http://marc.info/?l=linux-kernel&m=124794754015776&w=4
>>
>> I was scanning the regressions list and noticed that I could reproduce
>> this bug.
>>
>> So I bisected it to commit 335f8514f200e63d689113d29cb7253a5c282967
>> ("tty: Bring the usb tty port structure into more use"), from Alan
>> Cox.
>>
>> I did not double check if reverting it from -rc4 fixes the issue,
>> but I noticed that this patch touches drivers/usb/serial/option.c, which
>> is the driver I used to test this problem.
>>
>> If there is anything else I can do (give more info, test patches etc),
>> please let me know.
>
> Are you certain this really is a regression? Under 2.6.30 and 2.6.27
> the same thing happened if I unplugged a USB serial device while it was
> in use.

My original report is about unplugging the USB servial device *after*
using it.

> Can you check whether the device is still being used when you unplug
> it? For instance, is there still a pppd process trying to communicate
> with the device?

I checked and rechecked that the pppd process is already dead by the
time I unplug the device. However, the minor number did not increase
if I unplugged the device without using it beforehand, as expected.

> In short, it seems likely that this is not new behavior but rather the
> way usb-serial has worked all along.

I didn't experience this problem with 2.6.30: my ppp script was
hardwired to use ttyUSB0 and it always worked. Now with 2.6.31-rc3 it
does not, as the device node keeps changing.

I'll test this with opening ttyUSB directly from the shell, instead of
via pppd, and report back whether it makes a difference.
--
Regards,
Feri.