[PATCH v5 12/12] mm/mmzone: remove zonelist_node_idx()

[Gregory Price (Meta)]

zonelist_node_idx() looks like it returns a field of the zoneref, as
zonelist_zone_idx() does, but it loads the zone from the slot again.

Memory hotplug rewrites zonelists in place, so a caller that has already
checked the slot can get a different zone, or the NULL terminator, from
that second load.

__next_zones_zonelist() and mempolicy_slab_node() had this bug.

Remove the helper and open-code it in its two remaining callers, neither
of which can race with a rebuild.  local_memory_node() runs either inside
__build_all_zonelists() or during CPU bring-up, which holds
cpu_hotplug_lock for write and so excludes mem_hotplug_begin().

The lookup in mpol_misplaced() is unreachable: it needs a policy with
MPOL_F_MOF but not MPOL_F_MORON, and nothing sets one without the other.

Signed-off-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
---
 include/linux/mmzone.h | 6 ------
 mm/mempolicy.c         | 2 +-
 mm/page_alloc.c        | 2 +-
 3 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 4bc2318ac37f..72ffb2959c4f 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1439,7 +1439,6 @@ struct zoneref {
  *
  * zonelist_zone()	- Return the struct zone * for an entry in _zonerefs
  * zonelist_zone_idx()	- Return the index of the zone for an entry
- * zonelist_node_idx()	- Return the index of the node for an entry
  */
 struct zonelist {
 	struct zoneref _zonerefs[MAX_ZONES_PER_ZONELIST + 1];
@@ -1864,11 +1863,6 @@ static inline int zonelist_zone_idx(const struct zoneref *zoneref)
 	return zoneref->zone_idx;
 }
 
-static inline int zonelist_node_idx(const struct zoneref *zoneref)
-{
-	return zone_to_nid(zoneref->zone);
-}
-
 struct zoneref *__next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
 					const nodemask_t *nodes);
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index cd63c3e2c029..267576054980 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -3087,7 +3087,7 @@ int mpol_misplaced(struct folio *folio, struct vm_fault *vmf,
 				node_zonelist(thisnid, GFP_HIGHUSER),
 				gfp_zone(GFP_HIGHUSER),
 				&pol->nodes);
-		polnid = zonelist_node_idx(z);
+		polnid = zone_to_nid(zonelist_zone(z));
 		break;
 
 	default:
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 91ad979409e5..81c1de714658 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5973,7 +5973,7 @@ int local_memory_node(int node)
 	z = first_zones_zonelist(node_zonelist(node, GFP_KERNEL),
 				   gfp_zone(GFP_KERNEL),
 				   NULL);
-	return zonelist_node_idx(z);
+	return zone_to_nid(zonelist_zone(z));
 }
 #endif
 
-- 
2.56.0