kern/53447: usb lock problem, mutex_enter

[phil%netbsd.org@localhost]

>Number:         53447
>Category:       kern
>Synopsis:       usb lock problem, mutex_enter
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jul 12 21:25:00 +0000 2018
>Originator:     Phil Nelson
>Release:        NetBSD HEAD 8.99.21
>Organization:
>Environment:
8.99.21 NetBSD 8.99.21 (STEELHEAD) #8: Thu Jul 12 13:34:13 PDT 2018 amd64
>Description:
When asking for the root device using a USB console keyboard, typing a character to answer the root device name causes a Mutex_error, mutex_vector_enter 528: spin lock held.

Output (typed from picture)
root device: Mutex error: mutex_vector_enter 528: spin lock held
lock address:  0xffffe4010f5b99a0 type          spin
initialized:   0xffffffff80599151
shared holds:                       0 exclusive:            1
shares wanted:                      0 exclusive:            0
current cpu :                       1 last held:            1
current lwp  : 0xffffffff8124bda0   last held: 0xffffffff8124bda0
last locked* : 0xffffffff80596693   unlocked:  0xffffffff80599302
owner field  : 0x0000000000010600   wait/spin:                0/1

panic:  LOCKDEBUG:  Mutex error: mutex_vector_enter,528: spin lock held
cpu1: Begin traceback...
vpanic() at netbsd:vpanic+0x16f   (in future lines :func is netbsd:func)
snprintf() at :snprintf
lockdebug_more() at :lockdebug_more
mutex_enter() at :mutex_enter+0x6b6
xhci_device_intr_start() at xhci_device_intr_start+0x11e
usbd_start_next() at :usbd_start_next+0x73
xhci_softintr() at :xhci_softintr+0x492
xhci_poll() at :xhci_poll+x37
ukbd_cngetd() at :ukbd_cngetc+0x113
wskbd_cngetc() at :wskbd_cngetc+0xc8
wsdisplay_getc() at :wskbd_cngetc+0xc8
cngetc() at :cngetc+0x4d
cngetsn() at :cngetsn+0x71
setroot() at :setroot+0x46f
main() at :main+0x4a5
cpu1: End traceback...
>How-To-Repeat:
Build a kernel with "options LOCKDEBUG"
reboot and boot with "boot -a"
and use a usb console keyboard.
>Fix: