1 files changed, 22 insertions, 7 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index d8c65a6..153572f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -285,7 +285,15 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 
 	page = migration_entry_to_page(entry);
 
-	get_page(page);
+	/*
+	 * Once radix-tree replacement of page migration started, page_count
+	 * *must* be zero. And, we don't want to call wait_on_page_locked()
+	 * against a page without get_page().
+	 * So, we use get_page_unless_zero(), here. Even failed, page fault
+	 * will occur again.
+	 */
+	if (!get_page_unless_zero(page))
+		goto out;
 	pte_unmap_unlock(ptep, ptl);
 	wait_on_page_locked(page);
 	put_page(page);
@@ -305,6 +313,7 @@ out:
 static int migrate_page_move_mapping(struct address_space *mapping,
 		struct page *newpage, struct page *page)
 {
+	int expected_count;
 	void **pslot;
 
 	if (!mapping) {
@@ -314,14 +323,20 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 		return 0;
 	}
 
-	write_lock_irq(&mapping->tree_lock);
+	spin_lock_irq(&mapping->tree_lock);
 
 	pslot = radix_tree_lookup_slot(&mapping->page_tree,
  					page_index(page));
 
-	if (page_count(page) != 2 + !!PagePrivate(page) ||
+	expected_count = 2 + !!PagePrivate(page);
+	if (page_count(page) != expected_count ||
 			(struct page *)radix_tree_deref_slot(pslot) != page) {
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
+		return -EAGAIN;
+	}
+
+	if (!page_freeze_refs(page, expected_count)) {
+		spin_unlock_irq(&mapping->tree_lock);
 		return -EAGAIN;
 	}
 
@@ -338,6 +353,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 
 	radix_tree_replace_slot(pslot, newpage);
 
+	page_unfreeze_refs(page, expected_count);
 	/*
 	 * Drop cache reference from old page.
 	 * We know this isn't the last reference.
@@ -357,10 +373,9 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 	__dec_zone_page_state(page, NR_FILE_PAGES);
 	__inc_zone_page_state(newpage, NR_FILE_PAGES);
 
-	write_unlock_irq(&mapping->tree_lock);
-	if (!PageSwapCache(newpage)) {
+	spin_unlock_irq(&mapping->tree_lock);
+	if (!PageSwapCache(newpage))
 		mem_cgroup_uncharge_cache_page(page);
-	}
 
 	return 0;
 }