linux-kernel - Re: [PATCH v2 06/10] mm/hugetlb: Make hugetlb_follow_page

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Date:   Wed, 7 Dec 2022 15:21:56 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Peter Xu <peterx@...hat.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
CC:     Muchun Song <songmuchun@...edance.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        James Houghton <jthoughton@...gle.com>,
        Jann Horn <jannh@...gle.com>, Rik van Riel <riel@...riel.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Mike Kravetz" <mike.kravetz@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        Nadav Amit <nadav.amit@...il.com>
Subject: Re: [PATCH v2 06/10] mm/hugetlb: Make hugetlb_follow_page_mask() safe
 to pmd unshare

On 12/7/22 12:30, Peter Xu wrote:
> Since hugetlb_follow_page_mask() walks the pgtable, it needs the vma lock
> to make sure the pgtable page will not be freed concurrently.
> 
> Acked-by: David Hildenbrand <david@...hat.com>
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>   mm/hugetlb.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)

Reviewed-by: John Hubbard <jhubbard@...dia.com>


thanks,
-- 
John Hubbard
NVIDIA

> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 49f73677a418..3fbbd599d015 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6226,9 +6226,10 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
>   	if (WARN_ON_ONCE(flags & FOLL_PIN))
>   		return NULL;
>   
> +	hugetlb_vma_lock_read(vma);
>   	pte = huge_pte_offset(mm, haddr, huge_page_size(h));
>   	if (!pte)
> -		return NULL;
> +		goto out_unlock;
>   
>   	ptl = huge_pte_lock(h, mm, pte);
>   	entry = huge_ptep_get(pte);
> @@ -6251,6 +6252,8 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
>   	}
>   out:
>   	spin_unlock(ptl);
> +out_unlock:
> +	hugetlb_vma_unlock_read(vma);
>   	return page;
>   }
>