linux-kernel - Re: [PATCH] mm: migrate: fix missing update page_private to hugetlb_page

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Message-Id: <20210519212412.5653163f94904b141d5d74ce@linux-foundation.org>
Date:   Wed, 19 May 2021 21:24:12 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     osalvador@...e.de, mike.kravetz@...cle.com, mhocko@...e.com,
        david@...hat.com, willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, duanxiongchun@...edance.com,
        zhengqi.arch@...edance.com, fam.zheng@...edance.com,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH] mm: migrate: fix missing update page_private to
 hugetlb_page_subpool

On Thu, 20 May 2021 10:59:49 +0800 Muchun Song <songmuchun@...edance.com> wrote:

> Since commit d6995da31122 ("hugetlb: use page.private for hugetlb specific
> page flags") converts page.private for hugetlb specific page flags. We
> should use hugetlb_page_subpool() to get the subpool pointer instead of
> page_private(). The commit forgot to update it in the page migration
> routine. So fix it.
> 
> ...
>
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1290,7 +1290,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
>  	 * page_mapping() set, hugetlbfs specific move page routine will not
>  	 * be called and we could leak usage counts for subpools.
>  	 */
> -	if (page_private(hpage) && !page_mapping(hpage)) {
> +	if (hugetlb_page_subpool(hpage) && !page_mapping(hpage)) {
>  		rc = -EBUSY;
>  		goto out_unlock;
>  	}

So it uses the wrong page*, so this isn't just a cosmetic fix.  One
cannot tell from this changelog.

Please describe the runtime effects of this bug.  Please always include
this information when fixing bugs.  And when adding them.