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SubjectRe: [PATCH 15/16] mm/migration: fix possible do_pages_stat_array racing with memory offline
Date
Miaohe Lin <linmiaohe@huawei.com> writes:

> When follow_page peeks a page, the page could be reclaimed under heavy
> memory pressure

I don't think that memory pressure and reclaiming will be an issue.

> and thus be offlined while it's still being used by the
> do_pages_stat_array().

"offline" seems a possible problem.

Best Regards,
Huang, Ying

> Use FOLL_GET to hold the page refcnt to fix this
> potential issue.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
> mm/migrate.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 7b1c0b988234..98a968e6f465 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1788,13 +1788,18 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
> goto set_status;
>
> /* FOLL_DUMP to ignore special (like zero) pages */
> - page = follow_page(vma, addr, FOLL_DUMP);
> + page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
>
> err = PTR_ERR(page);
> if (IS_ERR(page))
> goto set_status;
>
> - err = page ? page_to_nid(page) : -ENOENT;
> + if (page) {
> + err = page_to_nid(page);
> + put_page(page);
> + } else {
> + err = -ENOENT;
> + }
> set_status:
> *status = err;

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