RPI2: Mutex related KASSERT when entering ddb(4)

[Stephan <stephanwib%googlemail.com@localhost>]

Hi

I´m running a pretty recent image of 7.0_RC3 on my RPI2. When I hit
Strg+Alt+Esc in order to enter ddb(4), a mutex related assertion
fires, ending up in a crash.

The assertion is in sys/dev/usb/usbdi.c

KASSERT(mutex_owned(pipe->device->bus->lock)); (line 950, in usbd_start_next())


The stack indicates an USB transfer in polling mode, originating
somewhere from ukbd(4). The top of the stack is this:

vpanic()
__udivmoddi4()
usbd_start_next()
dwc2_softintr()
...
dwc2_poll()
usbd_dopoll()
ukbd_cngetc()
...

From looking at the code, I would expect to see usb_tranfer_complete()
being called from dwc2_softintr(), which then calls usbd_start_next().
usb_transfer_complete() is however missing on the stack trace and I´m
not sure why that is.

I suspect this branch was taken in usb_transfer_complete() which
doesn´t deal with the bus lock, and usbd_start_next() expects it being
held:

    if (!repeat) {
        /* XXX should we stop the queue on all errors? */
        if (erred && pipe->iface != NULL)    /* not control pipe */
            pipe->running = 0;
        else
            usbd_start_next(pipe);
    }

I´m not an USB guy so I don´t really understand what this all is. I
hope someone can fix this.


Regards,

Stephan