linux-kernel - Re: [PATCH 12/16] mm/migration: fix potential page refcounts leak in migrate

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Date:   Fri, 04 Mar 2022 10:21:58 -0500
From:   Zi Yan <ziy@...dia.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, mike.kravetz@...cle.com,
        shy828301@...il.com, willy@...radead.org, ying.huang@...el.com,
        minchan@...nel.org, apopple@...dia.com, ave.hansen@...ux.intel.com,
        o451686892@...il.com, almasrymina@...gle.com, jhubbard@...dia.com,
        rcampbell@...dia.com, peterx@...hat.com, naoya.horiguchi@....com,
        mhocko@...e.com, riel@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/16] mm/migration: fix potential page refcounts leak in migrate_pages

On 4 Mar 2022, at 4:34, Miaohe Lin wrote:

> In -ENOMEM case, there might be some subpages of fail-to-migrate THPs
> left in thp_split_pages list. We should move them back to migration
> list so that they could be put back to the right list by the caller
> otherwise the page refcnt will be leaked here. Also adjust nr_failed
> and nr_thp_failed accordingly to make vm events account more accurate.
>
> Fixes: b5bade978e9b ("mm: migrate: fix the return value of migrate_pages()")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/migrate.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index e0db06927f02..6c2dfed2ddb8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1422,6 +1422,15 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  				}
>
>  				nr_failed_pages += nr_subpages;
> +				/*
> +				 * There might be some subpages of fail-to-migrate THPs
> +				 * left in thp_split_pages list. Move them back to migration
> +				 * list so that they could be put back to the right list by
> +				 * the caller otherwise the page refcnt will be leaked.
> +				 */
> +				list_splice_init(&thp_split_pages, from);
> +				nr_failed += retry;
> +				nr_thp_failed += thp_retry;
>  				goto out;
>  			case -EAGAIN:
>  				if (is_thp)
> -- 
> 2.23.0

LGTM. Thanks. Reviewed-by: Zi Yan <ziy@...dia.com>


--
Best Regards,
Yan, Zi

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