[PATCH] memory hotplug: fix page_zone() calculation in test_pages_isolated()

[Gerald Schaefer <gerald.schaefer@de.ibm.com>]

My last bugfix here (adding zone->lock) introduced a new problem: Using
pfn_to_page(pfn) to get the zone after the for() loop is wrong. pfn then
points to the first pfn after end_pfn, which may be in a different zone
or not present at all. This may lead to an addressing exception in
page_zone() or spin_lock_irqsave().

Using the last valid page that was found inside the for() loop, instead
of pfn_to_page(), should fix this.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>

---
 mm/page_isolation.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6/mm/page_isolation.c
===================================================================
--- linux-2.6.orig/mm/page_isolation.c
+++ linux-2.6/mm/page_isolation.c
@@ -115,7 +115,7 @@ __test_page_isolated_in_pageblock(unsign
 int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
 {
 	unsigned long pfn, flags;
-	struct page *page;
+	struct page *page = NULL;
 	struct zone *zone;
 	int ret;
 
@@ -130,10 +130,10 @@ int test_pages_isolated(unsigned long st
 		if (page && get_pageblock_migratetype(page) != MIGRATE_ISOLATE)
 			break;
 	}
-	if (pfn < end_pfn)
+	if ((pfn < end_pfn) || !page)
 		return -EBUSY;
 	/* Check all pages are free or Marked as ISOLATED */
-	zone = page_zone(pfn_to_page(pfn));
+	zone = page_zone(page);
 	spin_lock_irqsave(&zone->lock, flags);
 	ret = __test_page_isolated_in_pageblock(start_pfn, end_pfn);
 	spin_unlock_irqrestore(&zone->lock, flags);

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