[PATCH] powerpc/pseries: fix oops in hotplug memory notifier

During post-migration device tree updates, we can oops in
pseries_update_drconf_memory if the source device tree has an
ibm,dynamic-memory-v2 property and the destination has a
ibm,dynamic_memory (v1) property. The notifier processes an "update"
for the ibm,dynamic-memory property but it's really an add in this
scenario. So make sure the old property object is there before
dereferencing it.

Signed-off-by: Nathan Lynch <redacted>
---
 arch/powerpc/platforms/pseries/hotplug-memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 47087832f8b2..e6bd172bcf30 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c

@@ -980,6 +980,9 @@ static int pseries_update_drconf_memory(struct of_reconfig_data *pr)
 	if (!memblock_size)
 		return -EINVAL;
 
+	if (!pr->old_prop)
+		return 0;
+
 	p = (__be32 *) pr->old_prop->value;
 	if (!p)
 		return -EINVAL;

-- 
2.20.1