[tip:x86/urgent] x86, amd, mce: Avoid NULL pointer reference on CPU northbridge lookup

[tip-bot for Daniel J Blueman <daniel@numascale-asia.com>]

Commit-ID:  21c5e50e15b1abd797e62f18fd7f90b9cc004cbd
Gitweb:     http://git.kernel.org/tip/21c5e50e15b1abd797e62f18fd7f90b9cc004cbd
Author:     Daniel J Blueman <daniel@numascale-asia.com>
AuthorDate: Mon, 1 Oct 2012 14:42:05 +0800
Committer:  H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Wed, 17 Oct 2012 11:25:32 -0700

x86, amd, mce: Avoid NULL pointer reference on CPU northbridge lookup

When booting on a federated multi-server system (NumaScale), the
processor Northbridge lookup returns NULL; add guards to prevent this
causing an oops.

On those systems, the northbridge is accessed through MMIO and the
"normal" northbridge enumeration in amd_nb.c doesn't work since we're
generating the northbridge ID from the initial APIC ID and the last
is not unique on those systems. Long story short, we end up without
northbridge descriptors.

Signed-off-by: Daniel J Blueman <daniel@numascale-asia.com>
Cc: stable@vger.kernel.org # 3.6
Link: http://lkml.kernel.org/r/1349073725-14093-1-git-send-email-daniel@numascale-asia.com
[ Boris: beef up commit message ]
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
 arch/x86/kernel/cpu/mcheck/mce_amd.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index c4e916d..698b6ec 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -576,12 +576,10 @@ static __cpuinit int threshold_create_bank(unsigned int cpu, unsigned int bank)
 	int err = 0;
 
 	if (shared_bank[bank]) {
-
 		nb = node_to_amd_nb(amd_get_nb_id(cpu));
-		WARN_ON(!nb);
 
 		/* threshold descriptor already initialized on this node? */
-		if (nb->bank4) {
+		if (nb && nb->bank4) {
 			/* yes, use it */
 			b = nb->bank4;
 			err = kobject_add(b->kobj, &dev->kobj, name);
@@ -615,8 +613,10 @@ static __cpuinit int threshold_create_bank(unsigned int cpu, unsigned int bank)
 		atomic_set(&b->cpus, 1);
 
 		/* nb is already initialized, see above */
-		WARN_ON(nb->bank4);
-		nb->bank4 = b;
+		if (nb) {
+			WARN_ON(nb->bank4);
+			nb->bank4 = b;
+		}
 	}
 
 	err = allocate_threshold_blocks(cpu, bank, 0,