Kdump broken in ACPI initialization upon reading SCI_EN bit

[Vivek Goyal <vgoyal@in.ibm.com>]

Hi,

On one of my machines (Intel Xeon 2.00GHz), Kdump is broken. Second
kernel hangs during boot during ACPI initialization. I am
using 2.6.19-rc2.

It basically hangs when it tries to read from hardware whether system
is already in ACPI mode or not. It tries to read SCI_ENABLE bit from
PM1 control register.

Interestingly this phenomenon is observed only if the code is running 
on a non-boot cpu (cpu id is not zero). I system crashes on cpu 0 and
second kernel is booting on cpu 0 then everything is fine.

Following is the code sequence.

  acpi_early_init()
   acpi_enable_subsystem()
     acpi_hw_get_mode
       acpi_hw_get_register
	  acpi_hw_register_read
	    acpi_hw_low_level_read
		acpi_os_read_port()

In acpi_os_read_port() it tries to read port 0x804 (inw()) and then it hangs.

Any idea what's happening? Are there any dependencies of this port being
read by a boot cpu only? Any suggestions how can I debug further?

Thanks
Vivek