1 files changed, 11 insertions, 0 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 42a3d24..b114635 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -600,6 +600,17 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
 	if (PageAnon(page)) {
 		rcu_read_lock();
 		rcu_locked = 1;
+
+		/*
+		 * If the page has no mappings any more, just bail. An
+		 * unmapped anon page is likely to be freed soon but worse,
+		 * it's possible its anon_vma disappeared between when
+		 * the page was isolated and when we reached here while
+		 * the RCU lock was not held
+		 */
+		if (!page_mapped(page))
+			goto rcu_unlock;
+
 		anon_vma = page_anon_vma(page);
 		atomic_inc(&anon_vma->external_refcount);
 	}