On Tue, 2 Apr 2013, Oliver Neukum wrote: > 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. Mike, why don't you post one of the stack dumps for the kworker thread? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
