[PATCH] mm: Fix ZONE_DEVICE usage in move_pfn_range_to_zone()

[Dan Williams]

Randy reports the build breaks with recent additions of
section_taint_zone_device() in move_pfn_range_to_zone(). Fix that by
including a conditionally stubbed out zone_is_zone_device() helper.

Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
Andrew, apologies for the thrash. Please fold this into:

mm-teach-pfn_to_online_page-about-zone_device-section-collisions.patch

 include/linux/mmzone.h |   12 ++++++++++++
 mm/memory_hotplug.c    |    2 +-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0b5c44f730b4..66ba38dae9ba 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -885,6 +885,18 @@ static inline int local_memory_node(int node_id) { return node_id; };
  */
 #define zone_idx(zone)		((zone) - (zone)->zone_pgdat->node_zones)
 
+#ifdef CONFIG_ZONE_DEVICE
+static inline bool zone_is_zone_device(struct zone *zone)
+{
+	return zone_idx(zone) == ZONE_DEVICE;
+}
+#else
+static inline bool zone_is_zone_device(struct zone *zone)
+{
+	return false;
+}
+#endif
+
 /*
  * Returns true if a zone has pages managed by the buddy allocator.
  * All the reclaim decisions have to use this function rather than
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c78a1bef561b..710e469fb3a1 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -769,7 +769,7 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
 	 * ZONE_DEVICE pages in an otherwise  ZONE_{NORMAL,MOVABLE}
 	 * section.
 	 */
-	if (zone_idx(zone) == ZONE_DEVICE) {
+	if (zone_is_zone_device(zone)) {
 		if (!IS_ALIGNED(start_pfn, PAGES_PER_SECTION))
 			section_taint_zone_device(start_pfn);
 		if (!IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION))