[Patch v2] mm/migrate.c: also overwrite error when it is bigger than zero

[Wei Yang <richardw.yang@linux.intel.com>]

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.

Fixes: e0153fc2c760 ("mm: move_pages: return valid node id in status if the
page is already on the target node").
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

---
v2:
  * put more words to explain the error case
---
 mm/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 86873b6f38a7..430fdccc733e 100644
--- a/mm/migrate.c
+++ b/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;
-- 
2.17.1