Messages in this thread |  | | Date | Mon, 29 Jan 2018 15:48:02 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 1/3] mm, numa: rework do_pages_move |
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On Mon, 29 Jan 2018 18:39:01 -0500 "Zi Yan" <zi.yan@cs.rutgers.edu> wrote:
> On 29 Jan 2018, at 17:35, Andrew Morton wrote: > > > On Mon, 29 Jan 2018 17:06:14 -0500 "Zi Yan" <zi.yan@cs.rutgers.edu> 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??? > > do_move_pages_to_node() calls migrate_pages(), which requires down_read(&mmap_sem). > > In the outmost do_pages_move(), both add_page_for_migration() and > do_move_pages_to_node() inside it need to hold read lock of mmap_sem. > > Do we need to add comments for both functions?
Just for migrate_pages(), I guess. Let's include a description of *why* mmap_sem is needed. What it is protecting.
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