Jason,

I have vague memories of seeing this problem shortly after the bounce
buffer support went in and I upgraded my 486/33 (now retired to crash
& burn service) to 32mb from 16mb..

I didn't se as bad results, but the system in question had root on
wd0, and sd0 merely contained some "extra" stuff; the crash mostly
occurred while dumping sd0 to st0..

You sent me a patch to i386/i386/machdep.c and i386/isa/isa_machdep.c
which involved running the guts of _bus_dmamap_load(),
_isa_bus_dmamap_load(), and _isa_bus_dmamap_unload() at splimp(); this
made the problem go away, but it never got integrated into the main
tree; I ran with that fix until I retired the machine and moved the
controller into another machine where it currently gets much lighter
duty..

					- Bill