Using linux-2.6.19, "init 0" properly shutdown and powered off the machine.
Using linux-2.6.20, the machine resets and reboots instead of power off.
Distro: OpenSuse 10.2
System: Intel SE7525GP2 Dual Xeon Server - x86_64
in both cases, dmesg ends with this:
Stopping udevd: done
The system will be halted immediately.
Synchronizing SCSI cache for disk sda:
ACPI: PCI interrupt for device 0000:06:03.0 disabled
ACPI: PCI interrupt for device 0000:05:06.1 disabled
ACPI: PCI interrupt for device 0000:05:06.0 disabled
ACPI: PCI interrupt for device 0000:05:04.1 disabled
ACPI: PCI interrupt for device 0000:05:04.0 disabled
hwsleep-0285  enter_sleep_state : Entering sleep state [S5]
If I enter BIOS SETUP and disable USB, then 2.6.20 powers off properly.
Leaving USB enabled in BIOS and booting with "nousb" doesn't help.
CONFIG_USB=n fixes poweroff.
Created attachment 10308 [details]
Disabling CONFIG_USB_SUSPEND is sufficient to prevent this failure.
Attached is the config file that I'm using -- just set
CONFIG_USB_SUSPEND=y to cause poweroff to fail.
The system behaves the same no matter if USB devices
(I use a kbd+mouse over IOGEAR KVM) are attached or not.
*** This bug has been marked as a duplicate of 7828 ***