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

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Message-ID: <87r17e5pat.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Mon, 07 Mar 2022 13:01:30 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     <akpm@...ux-foundation.org>, <mike.kravetz@...cle.com>,
        <shy828301@...il.com>, <willy@...radead.org>, <ziy@...dia.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

Miaohe Lin <linmiaohe@...wei.com> writes:

> 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;

It appears that we don't need to change nr_failed, because we don't use
it for this situation.  Otherwise looks good to me.

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

Best Regards,
Huang, Ying

> +				nr_thp_failed += thp_retry;
>  				goto out;
>  			case -EAGAIN:
>  				if (is_thp)