kern/52889: amd64 panic during audio tests

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         52889
>Category:       kern
>Synopsis:       amd64 panic during audio tests
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jan 02 21:55:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date 2017.12.27.21.34.12
>Organization:

>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

I ran the ATF tests on physical amd64 hardware, a 12-core HP DL369 G7
server, and they triggered a panic.  Here's the relevant part of the
serial console output:

    varcmd: [0.108315s] Passed.
    varmisc: [0.110863s] Passed
    varshell: [0.100081s] Passed
[14.685181s]

usr.bin/mpad0: outputs: 44100Hz, 16-bit, stereo
audio0 at pad0: half duplex, playback, capture, mmap
pad0: Virtual format configured - Format SLINEAR, precision 16, channels 2, frequency 44100
pad0: Latency: 139 milliseconds
spkr1 at audio0: PC Speaker (synthesized)
wsbell at spkr1 not configured
spkr1: detached
ixerctl/t_mixerctl (532/729): 4 test cases
    nflag: audio0: detached
pad0: detached
pad0: outputs: 44100Hz, 16-bit, stereo
audio0 at pad0: half duplex, playback, capture, mmap
pad0: Virtual format configured - Format SLINEAR, precision 16, channels 2, frequency 44100
pad0: Latency: 139 milliseconds
spkr1 at audio0: PC Speaker (synthesized)
wsbell at spkr1 not configured
spk[r1: detached
0.877622s] Passed.
    noargaudio0: detached
s_usage: [0.011678s] Skipped: no audipad0: detached
audio1 at pad0uvm_fault(0xffffffff8154a580, 0xffff80006708b000, 2) -> e
fatal page fault in supervisor mode
trap type 6 code 0x2 rip 0xffffffff80224d4c cs 0x8 rflags 0x10246 cr2 0xffff80006708b040 ilevel 0 rsp 0xffffe40158e87638
curlwp 0xffffe40bb11b9b40 pid 8882.1 lowest kstack 0xffffe40158e842c0
panic: trap
cpu0: Begin traceback...
vpanic() at netbsd:vpanic+0x140
snprintf() at netbsd:snprintf
trap() at netbsd:trap+0xcd2
--- trap (number 6) ---
mutex_enter() at netbsd:mutex_enter+0xc
config_attach_loc() at netbsd:config_attach_loc+0x17a
config_found_sm_loc() at netbsd:config_found_sm_loc+0x48
audio_attach_mi() at netbsd:audio_attach_mi+0x32
pad_open() at netbsd:pad_open+0x1ba
spec_open() at netbsd:spec_open+0x260
VOP_OPEN() at netbsd:VOP_OPEN+0x33
vn_open() at netbsd:vn_open+0x1ed
do_open() at netbsd:do_open+0x112
do_sys_openat() at netbsd:do_sys_openat+0x68
sys_open() at netbsd:sys_open+0x24
syscall() at netbsd:syscall+0x1d8
--- syscall (number 5) ---
7c5ae8a3e95a:
cpu0: End traceback...

dumping to dev 4,1 (offset=2226, size=12580302):
dump 1935 1934 1933 1932 [etc]

This server doesn't have any physical audio devices, only the "pad" device.

>How-To-Repeat:

>Fix: