mm/migrate.c: also overwrite error when it is bigger than zero

If we get here after successfully adding page to list, err would be 1 to
indicate the page is queued in the list.

Current code has two problems:

  * on success, 0 is not returned
  * on error, if add_page_for_migratioin() return 1, and the following err1
    from do_move_pages_to_node() is set, the err1 is not returned since err
    is 1

And these behaviors break the user interface.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: e0153fc ("mm: move_pages: return valid node id in status if the page is already on the target node").
Signed-off-by: Wei Yang <[email protected]>
Acked-by: Yang Shi <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Wei Yang

mm/migrate.c

@@ -1676,7 +1676,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 	err1 = do_move_pages_to_node(mm, &pagelist, current_node);
 	if (!err1)
 		err1 = store_status(status, start, current_node, i - start);
-	if (!err)
+	if (err >= 0)
 		err = err1;
 out:
 	return err;