On Monday 01 April 2013 22:05:47 Mike Verstegen wrote:
Hi,
> Such a simple question you asked -- but it lead to a useful discovery.
>
> My logs show that acm_tty_write is called multiple times
>
> - The application opens the device and then calls write() to send the 4 byte
> message to the fd. This results in a call to acm_tty_write
> - From somewhere else, acm_tty_write is called several times, each with a
> count=1 and one of the offending characters noted above.
>
> To get find out where the unexpected calls to acm_tty_write were coming from,
> I added a dump_stack at the entry point to acm_tty_write. From those stack
> frames, I can see that the first acm_tty_write call is from my application,
> but the second and subsequent calls are from a kworker thread.
This is unexpected.
> So at this point, it doesn't look like a cdc_acm driver problem, but instead
> an unexpected call to acm_tty_write from another process. Having briefly
> looked the trace output of the kworker queue, it may a challenge to find out
> what thread in there is making this call.
I am afraid I have no idea on debugging for worker threads but people on LKML
might know.
Regards
Oliver
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