db:0:kdb.enter.default> bt
Tracing pid 12 tid 100266 td 0xfffff8000d85e620
kdb_enter() at kdb_enter+0x3b/frame 0xfffffe0c580f6740
vpanic() at vpanic+0x19b/frame 0xfffffe0c580f67a0
panic() at panic+0x43/frame 0xfffffe0c580f6800
trap_pfault() at trap_pfault/frame 0xfffffe0c580f6850
trap_pfault() at trap_pfault+0x49/frame 0xfffffe0c580f68b0
trap() at trap+0x29d/frame 0xfffffe0c580f69c0
calltrap() at calltrap+0x8/frame 0xfffffe0c580f69c0
--- trap 0xc, rip = 0xffffffff8051fdd0, rsp = 0xfffffe0c580f6a90, rbp = 0xfffffe0c580f6b20 ---
bce_intr() at bce_intr+0x500/frame 0xfffffe0c580f6b20
intr_event_execute_handlers() at intr_event_execute_handlers+0xe9/frame 0xfffffe0c580f6b60
ithread_loop() at ithread_loop+0xe7/frame 0xfffffe0c580f6bb0
fork_exit() at fork_exit+0x83/frame 0xfffffe0c580f6bf0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe0c580f6bf0
--- trap 0, rip = 0, rsp = 0, rbp = 0 ---
<6>bce1: promiscuous mode enabled
bce2: Gigabit link up!
Fatal trap 12: page fault while in kernel mode
cpuid = 12; apic id = 20
fault virtual address = 0x10
fault code = supervisor read data, page not present
instruction pointer = 0x20:0xffffffff8051fcf0
stack pointer = 0x28:0xfffffe0c582fba90
frame pointer = 0x28:0xfffffe0c582fbb20
code segment = base 0x0, limit 0xfffff, type 0x1b
= DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags = interrupt enabled, resume, IOPL = 0
current process = 12 (irq258: bce1)
trap number = 12
panic: page fault
cpuid = 12
KDB: enter: panic
Unfortunately there isn't much in the backtrace that would point to a specific cause, except it's crashing in the bce driver, apparently while processing an interrupt. Could be a driver issue, could be hardware.