The Machine is a HP DL385 with two AMD 280s in it (dual cpu, dual core 2.4GHz). Booting the x86_64 Flight 4 dapper live CD, I get this oops on the dmesg:
[ 148.143131] tg3: eth0: Link is up at 100 Mbps, full duplex.
[ 148.143135] tg3: eth0: Flow control is off for TX and off for RX.
[ 148.459912] device-mapper: 4.4.0-ioctl (2005-01-12) initialised: <email address hidden>
[ 151.754302] Unable to handle kernel NULL pointer dereference at 0000000000000000 RIP:
[ 151.754309] <0000000000000000>{_stext+2146431208}
[ 151.754316] PGD f3a5f067 PUD 8209d067 PMD 0
[ 151.754320] Oops: 0010 [1] PREEMPT SMP
[ 151.754323] CPU 1
[ 151.754324] Modules linked in: dm_mod md_mod tsdev hw_random shpchp psmouse pcspkr af_packet i2c_amd756 i2c_core serio_raw pci_hotplug floppy evdev tg3 squashfs unionfs loop nls_cp437 isofs ohci_hcd usbcore cciss scsi_mod ide_generic ide_cd cdrom generic amd74xx thermal processor fan capability commoncap vga16fb cfbcopyarea vgastate cfbimgblt cfbfillrect fbcon tileblit font bitblit softcursor
[ 151.754342] Pid: 4457, comm: readahead-list Not tainted 2.6.15-15-amd64-generic #1
[ 151.754344] RIP: 0010:[<0000000000000000>] <0000000000000000>{_stext+2146431208}
[ 151.754348] RSP: 0018:ffff81007d0cfc80 EFLAGS: 00010246
[ 151.754350] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff81007d0cfcc8
[ 151.754353] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff8100f43e86a8
[ 151.754356] RBP: ffff8100f44ab280 R08: 0000000000000000 R09: ffff81007d0cfdd4
[ 151.754358] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
[ 151.754361] R13: ffff810081989c08 R14: 0000000000000000 R15: ffff8100f43e87f0
[ 151.754364] FS: 00002aaaaadfb6d0(0000) GS:ffffffff80428880(0000) knlGS:0000000000000000
[ 151.754367] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 151.754369] CR2: 0000000000000000 CR3: 00000000f3ae1000 CR4: 00000000000006e0
[ 151.754372] Process readahead-list (pid: 4457, threadinfo ffff81007d0ce000, task ffff81007b570e40)
[ 151.754374] Stack: ffffffff880fe169 ffff8100f43e86a8 ffff8100f44ab280 ffff8100f28e3438
[ 151.754381] 000000008020a650 ffff8100f29ff000 0000000000000000 000ffffff50ad2c0
[ 151.754385] ffff8100f43e8680 ffff810080000300
[ 151.754389] Call Trace:<ffffffff880fe169>{:squashfs:squashfs_readpage+217}
[ 151.754398] <ffffffff8020c603>{radix_tree_node_alloc+19} <ffffffff8020cacd>{radix_tree_insert+317}
[ 151.754414] <ffffffff8016c824>{__alloc_pages+116} <ffffffff8016e340>{__do_page_cache_readahead+480}
[ 151.754425] <ffffffff8016e489>{force_page_cache_readahead+105} <ffffffff80166508>{sys_readahead+136}
[ 151.754440] <ffffffff8010fede>{system_call+126}
[ 151.754448]
[ 151.754449] Code: Bad RIP value.
[ 151.754451] RIP <0000000000000000>{_stext+2146431208} RSP <ffff81007d0cfc80>
[ 151.754455] CR2: 0000000000000000
[ 151.754456] <6>ACPI: Power Button (FF) [PWRF]
[ 152.651068] ibm_acpi: ec object not found
-------
I have seen a similar OOPS on my work desktop booting dapper live CD flight 2 (#21223)
I also see this segfault from powernowd in my dmesg, but that may be because I tried to kill it with /etc/init.d/powernowd stop... and it only partially died (1 cpu went back to full throttle, the other one didn't)... so I ended up -9'ing it.
[ 180.038433] powernow-k8: Found 4 AMD Athlon 64 / Opteron processors (version 1.50.4)
[ 180.040518] powernow-k8: 0 : fid 0x10 (2400 MHz), vid 0x8 (1350 mV)
[ 180.040524] powernow-k8: 1 : fid 0xe (2200 MHz), vid 0xa (1300 mV)
[ 180.040528] powernow-k8: 2 : fid 0xc (2000 MHz), vid 0xc (1250 mV)
[ 180.040532] powernow-k8: 3 : fid 0xa (1800 MHz), vid 0xe (1200 mV)
[ 180.040538] cpu_init done, current fid 0x10, vid 0x8
[ 180.043377] powernow-k8: 0 : fid 0x10 (2400 MHz), vid 0x8 (1350 mV)
[ 180.043385] powernow-k8: 1 : fid 0xe (2200 MHz), vid 0xa (1300 mV)
[ 180.043387] powernow-k8: 2 : fid 0xc (2000 MHz), vid 0xc (1250 mV)
[ 180.043390] powernow-k8: 3 : fid 0xa (1800 MHz), vid 0xe (1200 mV)
[ 180.043396] cpu_init done, current fid 0x10, vid 0x8
[ 180.337876] Bluetooth: Core ver 2.8
[ 180.337882] NET: Registered protocol family 31
[ 180.337884] Bluetooth: HCI device and connection manager initialized
[ 180.337897] Bluetooth: HCI socket layer initialized
[ 180.583305] Bluetooth: L2CAP ver 2.8
[ 180.583312] Bluetooth: L2CAP socket layer initialized
[ 180.585993] Bluetooth: RFCOMM socket layer initialized
[ 180.586012] Bluetooth: RFCOMM TTY layer initialized
[ 180.586014] Bluetooth: RFCOMM ver 1.6
[ 188.716986] eth0: no IPv6 routers present
[ 248.584946] powernowd[5576]: segfault at 0000000000500000 rip 00002aaaaac2bc23 rsp 00007fffff80dae0 error 4
I also found it wierd that powernowd was loaded at all on the opteron chip. I'm almost positive that previous ubuntu releases (hoary, Breezy) didn't load powernowd for opterons. Clearly it freaked out, but I don't know if that's because it's dual core or what.
Lemme know if you need anything... I will be visiting the datacenter where these machines are housed this weekend and can gather further info if you need it.