On 29 Jan 2018, at 17:35, Andrew Morton wrote: > 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??? 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? -- Best Regards Yan Zi
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