percpu: fix first chunk match in per_cpu_ptr_to_phys()

percpu: fix first chunk match in per_cpu_ptr_to_phys()

commit 9983b6f0cf8263e51bcf4c8a9dc0c1ef175b3c60 upstream.

per_cpu_ptr_to_phys() determines whether the passed in @addr belongs
to the first_chunk or not by just matching the address against the
address range of the base unit (unit0, used by cpu0).  When an adress
from another cpu was passed in, it will always determine that the
address doesn't belong to the first chunk even when it does.  This
makes the function return a bogus physical address which may lead to
crash.

This problem was discovered by Cliff Wickman while investigating a
crash during kdump on a SGI UV system.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Cliff Wickman <cpw@sgi.com>
Tested-by: Cliff Wickman <cpw@sgi.com>
[PG: for 2.6.34, diffstat differs slightly due to a trivial indenting
 difference, and 34 does not have the _maybe_unused annotation to delete]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>