USB lockup (was: ktrace-ing a command that locks up the machine)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

> Hmmm, this was usb, right?
Yes.

> Maybe turn on options USBHIST (and/or EHCIHIST, OHCIHIST, UHCIHIST,
> XHCIHIST).  None of these seem to be described in options(4) man
> page, but you can dump the debug data using ``vmstat -u histname''.
> And get a listof the actual histname's with ``vmstat -l''
Oh, thanks, I didn't knew of that. I don't even need any further options.

So, during the partial lockup, I see
	ohci_softintr#63@0: add TD 0xffff80013ec2de20
	ohci_softintr#63@0: add TD 0xffff80013ec2dea0
	ohci_softintr#63@0: add TD 0xffff80013ec2dee0
at .000001 intervals.

The ddb backtrace usually is
bus_space_read_4()
bintime()
ohci_softintr()
usb_soft_intr()
softint_dispatch()

The system call causing the lock-up is a USB_DEVICEINFO ioctl on /dev/usb0 
with udi_addr=2, which corresponds to ugen0.

Any hints how to debug this further? I tried a DIGNOSTIC+DEBUG+LOCKDEBUG 
kernel, but it didn't complain. The strange thing is that not only USB 
locks up, but any file system operation seems to stall, too. No, these 
are not USB discs.