usb/xhci lock issue on HEAD

[Phil Nelson <phil%NetBSD.org@localhost>]

Hello,

   Has anyone run into this?   I created a special kernel for my 802.11 work
that removes a lot of unneeded drivers from my setup, stuff like raid, ntfs
and so forth.   I got a working kernel out of it.   Then, to work on the 802.11,
I commented out every 802.11 driver except the urtwn driver.   This new
kernel without the the 802.11 drivers no panics as follows:

panic: kernel diagnostic assertion "mutex_owned(&sc->sc_lock)" failed: file "../../../../dev/usb/xhci.c", line 2049 
[    6.459749] cpu0: Begin traceback...
[    6.459749] vpanic() at netbsd:vpanic+0x16f
[    6.459749] ch_voltag_convert_in() at netbsd:ch_voltag_convert_in
[    6.459749] xhci_softintr() at netbsd:xhci_softintr+0x5d7
[    6.459749] xhci_poll() at netbsd:xhci_poll+0x37
[    6.459749] ukbd_cngetc() at netbsd:ukbd_cngetc+0x113
[    6.459749] wskbd_cngetc() at netbsd:wskbd_cngetc+0xc8
[    6.459749] wsdisplay_getc() at netbsd:wsdisplay_getc+0x2f
[    6.459749] cngetc() at netbsd:cngetc+0x4d
[    6.459749] cngetsn() at netbsd:cngetsn+0x71
[    6.459749] setroot() at netbsd:setroot+0x46f
[    6.459749] main() at netbsd:main+0x4a5
[    6.459749] cpu0: End traceback...
[    6.459749] fatal breakpoint trap in supervisor mode
[    6.459749] trap type 1 code 0 rip 0xffffffff8021de15 cs 0x8 rflags 0x202 cr2 0 ilevel 0x8 rsp 0xffffffff81451a70
[    6.459749] curlwp 0xffffffff81020920 pid 0.1 lowest kstack 0xffffffff8144d2c0
fatal protection fault in supervisor mode
[    6.459749] trap type 4 code 0 rip 0xffffffff8087caea cs 0x8 rflags 0x10282 cr2 0 ilevel 0x8 rsp 0xffffffff81451480
[    6.459749] curlwp 0xffffffff81020920 pid 0.1 lowest kstack 0xffffffff8144d2c0
rebooting...

I'm not sure why this kernel is calling cngetsn() at setroot() time. 

Has anyone seen this before?

--Phil