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Message-ID: <4daab76b-aa00-dbb2-3761-d782b00fab72@nvidia.com>
Date:   Wed, 7 Dec 2022 15:21:56 -0800
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Subject: Re: [PATCH v2 06/10] mm/hugetlb: Make hugetlb_follow_page_mask() safe
 to pmd unshare
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To:     Peter Xu <peterx@redhat.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>
CC:     Muchun Song <songmuchun@bytedance.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        James Houghton <jthoughton@google.com>,
        Jann Horn <jannh@google.com>, Rik van Riel <riel@surriel.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Mike Kravetz" <mike.kravetz@oracle.com>,
        David Hildenbrand <david@redhat.com>,
        Nadav Amit <nadav.amit@gmail.com>
References: <20221207203034.650899-1-peterx@redhat.com>
 <20221207203034.650899-7-peterx@redhat.com>
From:   John Hubbard <jhubbard@nvidia.com>
In-Reply-To: <20221207203034.650899-7-peterx@redhat.com>
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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@redhat.com>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>   mm/hugetlb.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)

Reviewed-by: John Hubbard <jhubbard@nvidia.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;
>   }
>