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

From: Ravikiran G Thirumalai
Date: Mon Aug 24 2009 - 15:07:26 EST

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

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.

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

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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