Fatal trap 12: page fault while in kernel mode, Stopped at _mtx_lock_spin_failed+0x2f: movl 0x78(%r12),%r8d

On amd64 r210786 booting kernel with iwn(4)
I get this fatal trap (copied by hand) :

*skip*
acpi_throttle0: <ACPI CPU Throttling> on cpu0
powernow0: <PowerNow! K8> on cpu0
acpi_throttle1: <ACPI CPU Throttling> on cpu1
acpi_throttle1: failed to attach P_CNT
device_attach: acpi_throttle1 attach returned 6
powernow1: <PowerNow! K8> on cpu1


Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address	= 0x20000000178
fault code		= supervisor read data, page not present
instruction pointer	= 0x20:0xffffffff803f2f9f
stack pointer		= 0x28:0xffffff80000adb10
frame pointer		= 0x28:0xffffff80000adb30
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		= 0 (bwi0 taskq)
[ thread pid 0 tid 100026 ]
Stopped at	_mtx_lock_spin_failed+0x2f:	movl	0x78(%r12),%r8d
db> bt
Tracing pid 0 tid 100026 td 0xffffff000251d880
_mtx_lock_spin_failed() at _mtx_lock_spin_failed+0x2f
_mtx_lock_spin() at _mtx_lock_spin+0x9e
_mtx_lock_spin_flags() at _mtx_lock_spin_flags+0x115
taskqueue_thread_loop() at taskqueue_thread_loop_0x3f
fork_exit() at fork_exit+0x12a
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffff80000adcf0, rbp = 0 ---
db> 

many thanks
anton

-- 
Anton Shterenlikht
Room 2.6, Queen's Building
Mech Eng Dept
Bristol University
University Walk, Bristol BS8 1TR, UK
Tel: +44 (0)117 331 5944
Fax: +44 (0)117 929 4423