[patch] x86: 2.6.31-rc7 crash due to buggy flat_phys_pkg_id

[Ravikiran G Thirumalai]

2.6.31-rc7 does not boot on vSMPowered systems.  The sched domains
seem to build incorrectly with error messages of the sort:

[    8.501108] CPU31: Thermal monitoring enabled (TM1)
[    8.501127] CPU 31 MCA banks SHD:2 SHD:3 SHD:5 SHD:6 SHD:8
[    8.650254] CPU31: Intel(R) Xeon(R) CPU           E5540  @ 2.53GHz
stepping 04
[    8.710324] Brought up 32 CPUs
[    8.713916] Total of 32 processors activated (162314.96 BogoMIPS).
[    8.721489] ERROR: parent span is not a superset of domain->span
[    8.727686] ERROR: domain->groups does not contain CPU0
[    8.733091] ERROR: groups don't span domain->span
[    8.737975] ERROR: domain->cpu_power not set
[    8.742416]

This is followed by oopsen in the scheduler code
with NULL pointer deference in find_busiest_group.

Git bisection pointed to the following commit:

commit 2759c3287de27266e06f1f4e82cbd2d65f6a044c
x86: don't call read_apic_id if !cpu_has_apic

Upon examining the history of the commit, the above commit seems to be a fix
for:

commit 4797f6b021a3fa399942245d07a1feb30df81bb8
x86: read apic ID in the !acpi_lapic case

However, there appears to be bug in the commit
2759c3287de27266e06f1f4e82cbd2d65f6a044c, where flat_phys_pkg_id
uses initial apic id instead of hard_smp_processor_id() on SMP machines.
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=2759c3287de27266e06f1f4e82cbd2d65f6a044c

This patch fixes the bug and causes vSMPowered systems to boot up
correctly,

Signed-off-by: Ravikiran Thirumalai <kiran@xxxxxxxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>

Index: linux-2.6.31-rc6/arch/x86/kernel/apic/apic_flat_64.c
===================================================================
--- linux-2.6.31-rc6.orig/arch/x86/kernel/apic/apic_flat_64.c	2009-08-21 12:42:16.000000000 -0700
+++ linux-2.6.31-rc6/arch/x86/kernel/apic/apic_flat_64.c	2009-08-21 14:12:21.654837472 -0700
@@ -161,7 +161,8 @@ static int flat_apic_id_registered(void)
 
 static int flat_phys_pkg_id(int initial_apic_id, int index_msb)
 {
-	return initial_apic_id >> index_msb;
+	return cpu_has_apic ? hard_smp_processor_id() >> index_msb :
+	    initial_apic_id >> index_msb;
 }
 
 struct apic apic_flat =  {
--
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