NetBSD-8 panic

Does anyone know what may've happened here? It's a dual processor DS25 
running NetBSD-8 that's running a pbulk build.

panic: kernel diagnostic assertion "ff->ff_refcnt == 0" failed: file 
"/usr/src/sys/kern/kern_descrip.c", line 1565
cpu0: Begin traceback...
alpha trace requires known PC =eject=
cpu0: End traceback...
cpu1: shutting down...

dumping to dev 4,1 offset 8388607
dump
System Machine Check (660): Rev 0x1, Code 0x202, Flags 0x0

     Software Error Summary Flags   = 0x0000000000000002
     CPU Device Interrupt Requests  = 0x2000000000000010
         DIR = 0x2000000000000010<Pchip 1 error>
     Cchip Miscellaneous Register   = 0x00000012000000f0
     Pchip 0 Error Register         = 0x0000000000000000
     Pchip 1 Error Register         = 0x0000000000000000

unexpected machine check:

     mces    = 0x1
     vector  = 0x660
     param   = 0xfffffc00000060b0
     pc      = 0xfffffc0000a0c974
     ra      = 0xfffffc0000c5c06c
     code    = 0x100000202
     curlwp = 0xfffffc02e173f1a0
         pid = 5813.11, comm = virtuoso-iodbc-t

Skipping crash dump on recursive panic
panic: machine check
cpu0: Begin traceback...
alpha trace requires known PC =eject=
cpu0: End traceback...
rebooting...