Re: [PATCH 1/3] mm, numa: rework do_pages_move

[Andrew Morton]

On Mon, 29 Jan 2018 17:06:14 -0500 "Zi Yan" <zi.yan@xxxxxxxxxxxxxx> wrote:

> I discover that this patch does not hold mmap_sem while migrating pages in
> do_move_pages_to_node().
> 
> A simple fix below moves mmap_sem from add_page_for_migration()
> to the outmost do_pages_move():

I'm not surprised.  Why does do_move_pages_to_node() need mmap_sem
and how is a reader to discover that fact???