USB stack getting confused

[Hans Petter Selasky]

On 3/9/19 4:26 PM, Konstantin Belousov wrote:
> On Sat, Mar 09, 2019 at 08:59:30PM +1030, O'Connor, Daniel wrote:
>>
>>
>>> On 9 Mar 2019, at 19:30, Hans Petter Selasky <hps at selasky.org> wrote:
>>> On 3/9/19 12:08 AM, O'Connor, Daniel wrote:
>>>> My program normally runs continually doing acquisitions of data for N seconds, doing some checks and restarting. After a while (~30 1 minute acquisitions or ~8 30 minute ones) my program can't 'see' the device (it uses libusb10) any more (it reconnects each acquisition for $REASONS). Also pretty weirdly usbconfig can't see it either(!).
>>>
>>> What is printed in dmesg? Maybe the device has a problem.
>>
>> There is nothing in dmesg - no disconnect / reconnect etc.
>>
>> If I hold the user space process in gdb 'forever' (eg over night) usbconfig doesn't see the device, but the moment I quit the user space process it can be seen again.
> 
> Does it mean that the file descriptor opened for ugen has a chance to
> be closed ?

The USB stack will wait for all FDs to be closed during detach also via 
destroy_dev().

> 
> I suspect that usb subsystem tried to destroy the device but some internal
> refcounting prevents it.  Proper use of destroy_dev(_cb)(9) avoids
> the issue.

--HPS