Sorry for posting it twice, but it seems to me that it didn't make it to the 
LKML previously:

I tried the software suspend (echo 4 > /proc/acpi/sleep) on 2.6.9-rc1-mm4 
(AMD64) and it reported a LOCKUP on CPU0:

Stopping tasks: ==============================|
Freeing memory: .....................................|
PM: Attempting to suspend to disk.
PM: snapshotting memory.
swsusp: critical section:
..<7>[nosave pfn 
0x618].........................................................swsusp: Need 
to copy 11534 pages
suspend: (pages needed: 11534 + 512 free: 119345)
..<7>[nosave pfn 0x618]...............................................NMI 
Watchdog detected LOCKUP on CPU0, registers:
CPU 0
Modules linked in: usbserial parport_pc lp parport joydev sg st sd_mod sr_mod 
scsi_mod nvram usbhid powernow_k8 freq_table snd_d
Pid: 11700, comm: bash Not tainted 2.6.9-rc1-mm4
RIP: 0010:[<ffffffff801737a4>] <ffffffff801737a4>{is_head_of_free_region+244}
RSP: 0018:000001001482bd70  EFLAGS: 00000003
RAX: 0000010001679080 RBX: ffffffff804ad220 RCX: 0000000000000002
RDX: 00000100016790a8 RSI: 0000000000000030 RDI: ffffffff804ad250
RBP: 000001000163cc08 R08: 0000000000000002 R09: 0000000000000030
R10: 000001000140c108 R11: 0000000000000000 R12: 0000000000000004
R13: 6db6db6db6db6db7 R14: cccccccccccccccd R15: 0000000000000000
FS:  0000002a95d330a0(0000) GS:ffffffff805e7500(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000002a955a5000 CR3: 0000000000101000 CR4: 00000000000006e0
Process bash (pid: 11700, threadinfo 000001001482a000, task 000001001f702270)
Stack: cccccccccccccccd 0000000000000012 000000000001c837 000001001482bdc0
       0000010000000000 ffffffff8016774c 0000000000002d8e ffffffff804ad220
       000001000bf425e0 ffffffff80167cdb
Call Trace:<ffffffff8016774c>{saveable+284} 
<ffffffff80167cdb>{suspend_prepare_image+971}
       <ffffffff802ef1ef>{pci_device_suspend+63} 
<ffffffff80167db6>{swsusp_swap_check+22}
       <ffffffff8036f9c2>{suspend_device+50} 
<ffffffff8012233c>{swsusp_arch_suspend+124}
       <ffffffff8016702c>{swsusp_suspend+12} 
<ffffffff8016837a>{pm_suspend_disk+90}
       <ffffffff80165d26>{enter_state+70} 
<ffffffff80330615>{acpi_system_write_sleep+100}
       <ffffffff8019c284>{vfs_write+228} <ffffffff8019c3c3>{sys_write+83}
       <ffffffff8011102a>{system_call+126}

Code: 48 39 c5 0f 85 9b 00 00 00 48 81 3b 3c 4b 24 1d 74 1d 48 89
console shuts up ...

This is 100% reproducible and always happens in is_head_of_free_region().

The .config and the output of dmesg are attached.

Greets,
RJW

-- 
- Would you tell me, please, which way I ought to go from here?
- That depends a good deal on where you want to get to.
		-- Lewis Carroll "Alice's Adventures in Wonderland"