page migration: replace radix_tree_lookup_slot with radix_tree_lockup

The radix tree rcu code runs into trouble when we use radix_tree_lookup
slot and use the slot to update the page reference. Use radix_tree_lookup
instead and update the page reference via radix_tree_delete and
radix_tree_insert.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc3-mm2/mm/migrate.c
===================================================================
--- linux-2.6.18-rc3-mm2.orig/mm/migrate.c	2006-08-07 20:21:12.985022791 -0700
+++ linux-2.6.18-rc3-mm2/mm/migrate.c	2006-08-08 09:15:29.352637207 -0700
@@ -294,7 +294,8 @@ out:
 static int migrate_page_move_mapping(struct address_space *mapping,
 		struct page *newpage, struct page *page)
 {
-	struct page **radix_pointer;
+	struct page *current_page;
+	long index;
 
 	if (!mapping) {
 		/* Anonymous page */
@@ -305,12 +306,14 @@ static int migrate_page_move_mapping(str
 
 	write_lock_irq(&mapping->tree_lock);
 
-	radix_pointer = (struct page **)radix_tree_lookup_slot(
+	index = page_index(page);
+
+	current_page = (struct page *)radix_tree_lookup(
 						&mapping->page_tree,
-						page_index(page));
+						index);
 
 	if (page_count(page) != 2 + !!PagePrivate(page) ||
-			radix_tree_deref_slot(radix_pointer) != page) {
+			current_page != page) {
 		write_unlock_irq(&mapping->tree_lock);
 		return -EAGAIN;
 	}
@@ -326,7 +329,8 @@ static int migrate_page_move_mapping(str
 	}
 #endif
 
-	radix_tree_replace_slot(radix_pointer, newpage);
+	radix_tree_delete(&mapping->page_tree, index);
+	radix_tree_insert(&mapping->page_tree, index, newpage);
 	__put_page(page);
 	write_unlock_irq(&mapping->tree_lock);