I have twice gotten a kernel page fault trap while bringing my system up.
The backtrace is roughly:
	page fault trap, code=0
	_free+0x1de	movl %edx,0xc(%eax)
	free(f8664c60, 2b)
	cluster_callback(f8c66ae8, 0)
	biodone(...)
	scsi_error(...)
	sc_err1(...)
	scsi_done(..)
	aha_done(...)
	ahaintr()
I have cluster sizes of roughly 3 to 5 on all my disk drives.  I don't know
which disk drive generated the error, unfortunately, nor what error it was.