[PATCH] Use correct page frame number to grab page zone lock

[Nathan Fontenot <nfont@austin.ibm.com>]

There are situations in which the 'pfn' variable used to calculate the
page zone can be invalid.  One case is in the hotplug memory remove path
where we are trying to remove memory the last valid page frame for the
system.  Passing an invalid page frame number to the pfn_to_page() macro
will cause the system to oops.

Additionally I think this also solves an issue where we may be grabbing
the wrong zone->lock.  This would occur when 'pfn' refers to a page
frame beyond what we are examining and lies in a different zone.

Using the starting page frame number passed in appears to resolve
both of these issues.  This patch also removes the redundant
initialization of 'pfn', it is set explicitly and then again in the for loop.


Signed-off-by: Nathan Fontenot <nfont@austin.ibm.com>
---

Index: linux-2.6/mm/page_isolation.c
===================================================================
--- linux-2.6.orig/mm/page_isolation.c	2008-10-13 12:00:46.000000000 -0500
+++ linux-2.6/mm/page_isolation.c	2008-10-29 11:18:39.000000000 -0500
@@ -119,7 +119,6 @@
 	struct zone *zone;
 	int ret;
 
-	pfn = start_pfn;
 	/*
 	 * Note: pageblock_nr_page != MAX_ORDER. Then, chunks of free page
 	 * is not aligned to pageblock_nr_pages.
@@ -133,7 +132,7 @@
 	if (pfn < end_pfn)
 		return -EBUSY;
 	/* Check all pages are free or Marked as ISOLATED */
-	zone = page_zone(pfn_to_page(pfn));
+	zone = page_zone(pfn_to_page(start_pfn));
 	spin_lock_irqsave(&zone->lock, flags);
 	ret = __test_page_isolated_in_pageblock(start_pfn, end_pfn);
 	spin_unlock_irqrestore(&zone->lock, flags);