Updated to HEAD, booted with WITNESS enabled, and the boot dies here:
ipfw2 initialized, divert disabled, rule-based forwarding enabled, default to accept,
logging unlimited
malloc() of 16 with the following non-sleepable locks held:
exclusive sleep mutex ifnet r = 0 (0xc07cc940) locked @ net
held:
exclusive sleep mutex ifnet r = 0 (0xc07cc940) locked @ net/if.c:459
Debugger(witness_warn)
Stopped at Debugger+0x54: xchgl %ebx,in_Debugger.0
db trace
Debugger(c070f058,c0c21ce8,1,c07396e3,c0778ec0) at Debugger+0x54
witness_warn(5,0,c074cdc7,c072620e,c07cc940) at witness_warn