Hang booting 7-current on a dual-P3: isa_find_memory

I recently tried updating a P3 box to 7-CURRENT, and ran into a hang at boot. 
I can get into the debugger, interestingly, so trace below.  I'll try backing 
out kernel versions for a bit and see if I get anywhere.

Robert N M Watson
Computer Laboratory
University of Cambridge

sio2: not probed (disabled)
sio3: not probed (disabled)
sn0: not probed (disabled)
vga0: <Generic ISA VGA> at port 0x3c0-0x3df iomem 0xa0000-0xbffff on isa0
vt0: not probed (disabled)
isa_probe_children: probing PnP devices
unknown: <PNP0800> failed to probe at port 0x61 pnpid PNP0800 on isa0
unknown: <PNP0c01> can't assign resources (memory)
unknown: <PNP0c01> at iomem 0-0x9ffff pnpid PNP0c01 on isa0
~KDB: enter: Line break on console
[thread pid 0 tid 0 ]
Stopped at      kdb_enter+0x2b: nop
db> bt
Tracing pid 0 tid 0 td 0xc0a4d860
kdb_enter(c093b451) at kdb_enter+0x2b
siointr1(c1ea2400,c0abc52c,0,c096e5d5,56f,...) at siointr1+0xce
siointr(c1ea2400) at siointr+0x21
intr_execute_handlers(c1cfc8cc,c0c208a0,4,c0c20918,c08a88e4,...) at 
intr_execute_handlers+0xd9
lapic_handle_intr(38,c0c208a0) at lapic_handle_intr+0x2f
Xapic_isr1() at Xapic_isr1+0x34
--- interrupt, eip = 0xc06e420e, esp = 0xc0c208e0, ebp = 0xc0c20918 ---
rman_reserve_resource_bound(c0ac3b80,100000,ffffff,f00000,0,...) at 
rman_reserve_resource_bound+0x66
rman_reserve_resource(c0ac3b80,100000,ffffff,f00000,0,c1e5d400) at 
rman_reserve_resource+0x1c
nexus_alloc_resource(c1d6e300,c1e5d400,3,c0c20c38,100000,ffffff,f00000,0) at 
nexus_alloc_resource+0xcb
bus_generic_alloc_resource(c1d28b80,c1e5d400,3,c0c20c38,100000,ffffff,f00000,0) 
at bus_generic_alloc_resource+0x7f
bus_generic_alloc_resource(c1d28900,c1e5d400,3,c0c20c38,100000,...) at 
bus_generic_alloc_resource+0x7f
legacy_pcib_alloc_resource(c1d28900,c1e5d400,3,c0c20c38,100000,ffffff,f00000,0) 
at legacy_pcib_alloc_resource+0x4b
resource_list_alloc(c1e4a704,c1d28800,c1e5d400,3,c0c20c38,...) at 
resource_list_alloc+0xac
pci_alloc_resource(c1d28800,c1e5d400,3,c0c20c38,100000,ffffff,f00000,0) at 
pci_alloc_resource+0x1e0
bus_generic_alloc_resource(c1d28500,c1e5d400,3,c0c20c38,100000,ffffff,f00000,0) 
at bus_generic_alloc_resource+0x7f
resource_list_alloc(c1e4a700,c1de2200,c1e5d400,3,c0c20c38,...) at 
resource_list_alloc+0x180
isa_alloc_resource(c1de2200,c1e5d400,3,c0c20c38,0,ffffffff,1,0) at 
isa_alloc_resource+0x112
bus_alloc_resource(c1e5d400,3,c0c20c38,0,ffffffff,...) at 
bus_alloc_resource+0x7c
isa_find_memory(c1e5d400,c1e7780c,c1dcf800) at isa_find_memory+0x189
isa_assign_resources(c1e5d400) at isa_assign_resources+0x88
isa_probe_children(c1de2200) at isa_probe_children+0x14d
configure(0,c1ec00,c1e000,0,c0452825,...) at configure+0x1d
mi_startup() at mi_startup+0x96
begin() at begin+0x2c