kern/53328: xhci panic on netboot

[prlw1%cam.ac.uk@localhost]

>Number:         53328
>Category:       kern
>Synopsis:       xhci panic on netboot
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue May 29 15:40:00 +0000 2018
>Originator:     Patrick Welche
>Release:        NetBSD-8.99.19/amd64
>Organization:
>Environment:
>Description:
Just tried to netboot a GENERIC kernel on a new computer over nfs. I'm not sure now whether I actually hit return/enter or not at the root on wm0 prompt. On screen, I see:

ums0: detached
uhidev2: detached
uhidev2: at uhub1 port 2 (addr 2) disconnected
panic: kernel diagnostic assertion "mutex_owned(&sc->sc_lock)" failed: file "/usr/src/sys/dev/usb/xhci.c", line 2049
cpu0: Begin traceback...
vpanic() at netbsd:vpanic+0x16f
ch_voltag_convert_in() at netbsd:ch_voltag_convert_in
xhci_softintr() at nebsd:xhci_softintr+0x5d7
xhci_poll() at netbsd:xhci_poll+0x37
ukbd_cngetc() at netbsd:ukbd_cngetc+0x113
wskbd_cngetc() at netbsd:wskbd_cngetc+0xc8
wsdisplay_getc() at netbsd:wsdisplay_getc+0x2f
cngetc() at netbsd:cngetc+0x4d
cngetsn() at netbsd:cngetsn+0x71
setroot() at netbsd:setroot+0x133
main() at netbsd:main+0x6af
cpu0: End traceback...
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip 0xffffffff8021eb75 cs 0x8 rflags 0x202 cr2 0 ilevel 0x8 rsp 0xffffffff87fda70
curlwp 0xffffffff81481f60 pid 0.1 lowest kstack 0xffffffff817f92c0

>How-To-Repeat:

>Fix: