[RFC PATCH] mm/init: fix zone boundary creation

["Oliver O'Halloran" <oohall@xxxxxxxxx>]

As a part of memory initialisation the architecture passes an array to
free_area_init_nodes() which specifies the max PFN of each memory zone.
This array is not necessarily monotonic (due to unused zones) so this
array is parsed to build monotonic lists of the min and max PFN for
each zone. ZONE_MOVABLE is special cased here as its limits are managed by
the mm subsystem rather than the architecture. Unfortunately, this special
casing is broken when ZONE_MOVABLE is the not the last zone in the zone
list. The core of the issue is:

	if (i == ZONE_MOVABLE)
		continue;
	arch_zone_lowest_possible_pfn[i] =
		arch_zone_highest_possible_pfn[i-1];

As ZONE_MOVABLE is skipped the lowest_possible_pfn of the next zone
will be set to zero. This patch fixes this bug by adding explicitly
tracking where the next zone should start rather than relying on the
contents arch_zone_highest_possible_pfn[].

Signed-off-by: Oliver O'Halloran <oohall@xxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
---
 mm/page_alloc.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 59de90d5d3a3..fc78306ce087 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5980,15 +5980,18 @@ void __init free_area_init_nodes(unsigned long *max_zone_pfn)
 				sizeof(arch_zone_lowest_possible_pfn));
 	memset(arch_zone_highest_possible_pfn, 0,
 				sizeof(arch_zone_highest_possible_pfn));
-	arch_zone_lowest_possible_pfn[0] = find_min_pfn_with_active_regions();
-	arch_zone_highest_possible_pfn[0] = max_zone_pfn[0];
-	for (i = 1; i < MAX_NR_ZONES; i++) {
+
+	start_pfn = find_min_pfn_with_active_regions();
+
+	for (i = 0; i < MAX_NR_ZONES; i++) {
 		if (i == ZONE_MOVABLE)
 			continue;
-		arch_zone_lowest_possible_pfn[i] =
-			arch_zone_highest_possible_pfn[i-1];
-		arch_zone_highest_possible_pfn[i] =
-			max(max_zone_pfn[i], arch_zone_lowest_possible_pfn[i]);
+
+		end_pfn = max(max_zone_pfn[i], start_pfn);
+		arch_zone_lowest_possible_pfn[i] = start_pfn;
+		arch_zone_highest_possible_pfn[i] = end_pfn;
+
+		start_pfn = end_pfn;
 	}
 	arch_zone_lowest_possible_pfn[ZONE_MOVABLE] = 0;
 	arch_zone_highest_possible_pfn[ZONE_MOVABLE] = 0;
-- 
2.5.5

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