Re: Panic after USB deadlock followed by kldunload umass.ko

Hans Petter Selasky <hps_at_selasky.org> wrote:

> On 10/23/14 16:28, Fabian Keil wrote:

> > kldunload umass.ko lead to a panic, dumping didn't work.
> >
> > Screenshots are available at:
> > http://www.fabiankeil.de/bilder/freebsd/kernel-panic-r273434-usb/
> >
> > I've seen locked-up usbconfig processes in the past,
> > usually after executing a shell function that does:
> >
> > | usbconfig_output="$(sudo usbconfig -d ${device} add_quirk UQ_MSC_NO_INQUIRY)"
> > | [... error handling snipped ]
> > | usbconfig_output="$(sudo usbconfig -d ${device} reset)"
> >
> > Sometimes the second command seems to mess up the USB system.

> USB detach is synchronous. If for example umass fails to detach, due to 
> reference counts not reaching zero, that might be the root cause. Try to 
> get a backtrace from the "usb_process()" processes using kgdb, and 
> you'll see right away what is going on.

Thanks for the quick response. So far I haven't been able to intentionally
reproduce the issue, but I'll try the above the next time I unintentionally
run into this again.

Fabian