current i386 SMP boot hang

My Friday and Saturday kernel builds have both hung at boot.  I'm
am getting the following message:

Timecounters tick every 10.000 msec
ad0: 39205MB <Maxtor 6E040L0> [79656/16/63] at ata2-master UDMA66
ahc0: PCI error Interrupt at seqaddr = 0x9
ahc0: Data Parity Error Detected during address or write data phase

and then it hangs.  Only reset will get a response.

Booting the previous kernel, I get these messages at this point:

Timecounters tick every 10.000 msec
ad0: 39205MB <Maxtor 6E040L0> [79656/16/63] at ata2-master UDMA66
SMP: AP CPU #1 Launched!
da0 at ahc0 bus 0 target 0 lun 0
... and so on, to a successful boot...

There haven't been any changes to ahc, that I can tell, so perhaps
this is related to the PCI changes.  I will back out those changes
and see if that fixes it.

Here is the relavent boot infomation for this machine:

CPU: Pentium III/Pentium III Xeon/Celeron (551.25-MHz 686-class CPU)
   Origin = "GenuineIntel"  Id = 0x673  Stepping = 3

Features=0x387fbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CM
OV,PAT,PSE36,PN,MMX,FXSR,SSE>
real memory  = 671076352 (639 MB)
avail memory = 646979584 (617 MB)
ACPI APIC Table: <ASUS   P2B-DS  >
FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
  cpu0 (BSP): APIC ID:  1
  cpu1 (AP): APIC ID:  0
MADT: Forcing active-lo polarity and level trigger for IRQ 9
ioapic0 <Version 1.1> irqs 0-23 on motherboard
netsmb_dev: loaded
Pentium Pro MTRR support enabled
VESA: v2.0, 16384k memory, flags:0x1, mode table:0xc082a9a2 (1000022)
VESA: Matrox Graphics Inc.
cpu0 on motherboard
cpu1 on motherboard
acpi0: <ASUS P2B-DS> on motherboard
acpi0: Overriding SCI Interrupt from IRQ 9 to IRQ 20
acpi0: [GIANT-LOCKED]
pcibios: BIOS version 2.10
Found $PIR table, 7 entries at 0xc00f0d20
acpi0: Power Button (fixed)
Timecounter "ACPI-safe" frequency 3579545 Hz quality 1000
acpi_timer0: <24-bit timer at 3.579545MHz> port 0xe408-0xe40b on acpi0
acpi_cpu0: <CPU> port 0x530-0x537 on acpi0
acpi_cpu1: <CPU> port 0x530-0x537 on acpi0
acpi_button0: <Power Button> on acpi0
pcib0: <ACPI Host-PCI bridge> port 0xcf8-0xcff on acpi0
pci0: <ACPI PCI bus> on pcib0
agp0: <Intel 82443BX (440 BX) host to PCI bridge> mem 
0xe4000000-0xe7ffffff at d
evice 0.0 on pci0
pcib1: <PCI-PCI bridge> at device 1.0 on pci0
pci1: <PCI bus> on pcib1
pcib1: slot 0 INTA is routed to irq 16
drm0: <Matrox G200 (AGP)> mem 
0xe1800000-0xe1ffffff,0xe2000000-0xe2003fff,0xe300
0000-0xe3ffffff irq 16 at device 0.0 on pci1
info: [drm] AGP at 0xe4000000 64MB
info: [drm] Initialized mga 3.1.0 20021029 on minor 0
isab0: <PCI-ISA bridge> at device 4.0 on pci0
isa0: <ISA bus> on isab0
atapci0: <Intel PIIX4 UDMA33 controller> port 0xd800-0xd80f at device 
4.1 on pci
0
ata0: at 0x1f0 irq 14 on atapci0
ata1: at 0x170 irq 15 on atapci0
uhci0: <Intel 82371AB/EB (PIIX4) USB controller> port 0xd400-0xd41f irq 
19 at de
vice 4.2 on pci0
uhci0: [GIANT-LOCKED]
usb0: <Intel 82371AB/EB (PIIX4) USB controller> on uhci0
usb0: USB revision 1.0
uhub0: Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
uhub1: Atmel UHB124 hub, class 9/0, rev 1.00/1.00, addr 2
uhub1: 4 ports with 4 removable, self powered
ums0: Logitech USB Mouse, rev 1.10/6.10, addr 3, iclass 3/1
ums0: 4 buttons and Z dir.
intpm0: <Intel 82371AB Power management controller> port 0xe800-0xe80f 
irq 9 at
device 4.3 on pci0
intpm0: I/O mapped e800
intpm0: intr IRQ 9 enabled revision 0
intpm0: [GIANT-LOCKED]
intsmb0: <Intel PIIX4 SMBUS Interface> on intpm0
smbus0: <System Management Bus> on intsmb0
smb0: <SMBus generic I/O> on smbus0
intpm0: PM I/O mapped e400
ahc0: <Adaptec aic7890/91 Ultra2 SCSI adapter> port 0xd000-0xd0ff mem 
0xe1000000
-0xe1000fff irq 19 at device 6.0 on pci0
ahc0: [GIANT-LOCKED]
aic7890/91: Ultra2 Wide Channel A, SCSI Id=7, 32/253 SCBs
pcm0: <AudioPCI ES1371-B> port 0xb800-0xb83f irq 18 at device 10.0 on pci0
pcm0: <Cirrus Logic CS4297A AC97 Codec>
pcm0: [GIANT-LOCKED]
atapci1: <Promise PDC20262 UDMA66 controller> port 
0xa000-0xa03f,0xa400-0xa403,0
xa800-0xa807,0xb000-0xb003,0xb400-0xb407 mem 0xe0800000-0xe081ffff irq 
17 at dev
ice 11.0 on pci0
ata2: at 0xb400 on atapci1
ata3: at 0xa800 on atapci1
...