Re: [PATCH v2 06/10] mm/hugetlb: Make hugetlb_follow_page_mask() safe to pmd unshare

[John Hubbard]

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@xxxxxxxxxx>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
>   mm/hugetlb.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)

Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>


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;
>   }
>