lock error in [ 500.ADDR] do_sys

Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported
lock error in [ 81.ADDR] do_sys_accept				1	2082d	2082d
[ 500.0085618] panic: lock error: Mutex: mutex_vector_exit,761: assertion failed: MUTEX_OWNER(mtx->mtx_owner) == curthread: lock 0xffff940012fcf180 cpu 1 lwp 0xffff9400130e3140
[ 500.0185895] cpu1: Begin traceback...
[ 500.0286170] vpanic() at netbsd:vpanic+0x214
[ 500.0386479] snprintf() at netbsd:snprintf
[ 500.0486734] lockdebug_abort() at netbsd:lockdebug_abort+0x14c
[ 500.0587053] mutex_vector_exit() at netbsd:mutex_vector_exit+0x1bc
[ 500.0687298] do_sys_accept() at netbsd:do_sys_accept+0x346
[ 500.0787596] sys_accept() at netbsd:sys_accept+0xac
[ 500.0887838] sys___syscall() at netbsd:sys___syscall+0xe2
[ 500.0988108] syscall() at netbsd:syscall+0x32e
[ 500.1088392] --- syscall (number 198) ---
[ 500.1188690] 75ef4e43f4aa:
[ 500.1188690] cpu1: End traceback...

[ 500.1188690] dumping to dev 4,1 (offset=0, size=0): not possible
[ 500.1289119] rebooting...
SeaBIOS (version 1.8.2-20190122_225043-google)
Total RAM Size = 0x00000001e0000000 = 7680 MiB
CPUs found: 2     Max CPUs supported: 2
found virtio-scsi at 0:3
virtio-scsi vendor='Google' product='PersistentDisk' rev='1' type=0 removable=0
virtio-scsi blksize=512 sectors=4194304 = 2048 MiB
drive 0x000f29c0: PCHS=0/0/0 translation=lba LCHS=520/128/63 s=4194304
Booting from Hard Disk 0...

>> NetBSD/x86 BIOS Boot, Revision 5.10 (Tue Jul 17 14:59:51 UTC 2018) (from NetBSD 8.0)
>> Memory: 639/3144640 k

     1. Boot normally
     2. Boot single user
     3. Disable ACPI
     4. Disable ACPI and SMP
     5. Drop to boot prompt