[PATCH] x86, amd, mce: Prevent potential cpu-online oops

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

On platforms where all Northbridges may not be visible (due to routing, eg on
NumaConnect systems), prevent oopsing due to stale pointer access when
offlining cores.

Signed-off-by: Steffen Persvold <sp@numascale.com>
Signed-off-by: Daniel J Blueman <daniel@numascale-asia.com>

---
 arch/x86/kernel/cpu/mcheck/mce_amd.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index 1ac581f..53a58c2 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -578,8 +578,11 @@ static __cpuinit int threshold_create_bank(unsigned int cpu, unsigned int bank)
 	if (shared_bank[bank]) {
 		nb = node_to_amd_nb(amd_get_nb_id(cpu));
 
+		if (WARN_ON_ONCE(!nb))
+			goto out;
+
 		/* threshold descriptor already initialized on this node? */
-		if (nb && nb->bank4) {
+		if (nb->bank4) {
 			/* yes, use it */
 			b = nb->bank4;
 			err = kobject_add(b->kobj, &dev->kobj, name);
@@ -613,10 +616,8 @@ static __cpuinit int threshold_create_bank(unsigned int cpu, unsigned int bank)
 		atomic_set(&b->cpus, 1);
 
 		/* nb is already initialized, see above */
-		if (nb) {
-			WARN_ON(nb->bank4);
-			nb->bank4 = b;
-		}
+		WARN_ON(nb->bank4);
+		nb->bank4 = b;
 	}
 
 	err = allocate_threshold_blocks(cpu, bank, 0,
-- 
1.7.4.1