---

yaml
---
r: 62984
b: refs/heads/master
c: dc386d4
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 098284020c47c1212d211e39ae2b41c21182e056
+refs/heads/master: dc386d4d1e98bb39fb967ee156cd456c802fc692

trunk/mm/migrate.c

@@ -632,18 +632,35 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
 			goto unlock;
 		wait_on_page_writeback(page);
 	}
-
 	/*
-	 * Establish migration ptes or remove ptes
+	 * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
+	 * we cannot notice that anon_vma is freed while we migrates a page.
+	 * This rcu_read_lock() delays freeing anon_vma pointer until the end
+	 * of migration. File cache pages are no problem because of page_lock()
+	 */
+	rcu_read_lock();
+	/*
+	 * This is a corner case handling.
+	 * When a new swap-cache is read into, it is linked to LRU
+	 * and treated as swapcache but has no rmap yet.
+	 * Calling try_to_unmap() against a page->mapping==NULL page is
+	 * BUG. So handle it here.
 	 */
+	if (!page->mapping)
+		goto rcu_unlock;
+	/* Establish migration ptes or remove ptes */
 	try_to_unmap(page, 1);
+
 	if (!page_mapped(page))
 		rc = move_to_new_page(newpage, page);
 
 	if (rc)
 		remove_migration_ptes(page, page);
+rcu_unlock:
+	rcu_read_unlock();
 
 unlock:
+
 	unlock_page(page);
 
 	if (rc != -EAGAIN) {