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>

diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index c4e916d773780f4239ac831478c15aa2325c7382..698b6ec12e0f40f9c292b9f84206b38214d9fe7e 100644 (file)
--- 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,