Re: [PATCH v2 10/10] mm/hugetlb: Document why page_vma_mapped_walk() is safe to walk

[David Hildenbrand]

On 07.12.22 21:31, Peter Xu wrote:
> Taking vma lock here is not needed for now because all potential hugetlb
> walkers here should have i_mmap_rwsem held.  Document the fact.
>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
>   mm/page_vma_mapped.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index e97b2e23bd28..2e59a0419d22 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -168,8 +168,14 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>   		/* The only possible mapping was handled on last iteration */
>   		if (pvmw->pte)
>   			return not_found(pvmw);
> -
> -		/* when pud is not present, pte will be NULL */
> +		/*
> +		 * NOTE: we don't need explicit lock here to walk the
> +		 * hugetlb pgtable because either (1) potential callers of
> +		 * hugetlb pvmw currently holds i_mmap_rwsem, or (2) the
> +		 * caller will not walk a hugetlb vma (e.g. ksm or uprobe).
> +		 * When one day this rule breaks, one will get a warning
> +		 * in hugetlb_walk(), and then we'll figure out what to do.
> +		 */
>   		pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
>   		if (!pvmw->pte)
>   			return false;

Would it make sense to squash that into the previous commit?

--
Thanks,

David / dhildenb