witness_lock_list_get: witness exhausted

Hi!

I've recently up'd my processor count on our poudriere box and have 
started noticing the error
"witness_lock_list_get: witness exhausted" on the console.  The kernel 
*DOES NOT* crash but I
thought the report may be useful to someone.

$ uname -a
FreeBSD poudriere 12.0-CURRENT FreeBSD 12.0-CURRENT #1 r325999: Sun Nov 
19 18:41:20 EST 2017
mikej_at_poudriere:/usr/obj/usr/src/amd64.amd64/sys/GENERIC  amd64

The machine is pretty busy running four poudriere build instances.

last pid: 76584;  load averages: 115.07, 115.96, 98.30                   
                                                                          
                                      up 6+07:32:59  14:44:03
763 processes: 117 running, 581 sleeping, 2 zombie, 63 lock
CPU: 59.0% user,  0.0% nice, 40.7% system,  0.1% interrupt,  0.1% idle
Mem: 12G Active, 2003M Inact, 44G Wired, 29G Free
ARC: 28G Total, 11G MFU, 16G MRU, 122M Anon, 359M Header, 1184M Other
      25G Compressed, 32G Uncompressed, 1.24:1 Ratio

Let me know what additional information I might supply.


Thanks!
--mikej