Release page reference during page fault retry

This slipped by when unifying the filemap and swap versions of
lock_page_or_retry()...

Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -1563,8 +1563,10 @@ retry_find:
 			goto no_cached_page;
 	}
 
-	if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags))
+	if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
+		page_cache_release(page);
 		return ret | VM_FAULT_RETRY;
+	}
 
 	/* Did it get truncated? */
 	if (unlikely(page->mapping != mapping)) {