Re: [PATCH v4 6/7] mm/khugepaged: unmap pte before releasing vma write lock

[Lorenzo Stoakes (ARM)]

On Tue, Aug 11, 2026 at 06:48:38AM -0600, Nico Pache (Red Hat) wrote:
> We are currently dropping the anon_vma write lock before unmapping the
> PTE. Although this is safe, due to us still holding the mmap_write_lock,
> its safer and less confusing to switch the order of these two operations.
>
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Signed-off-by: Nico Pache (Red Hat) <nico.pache@xxxxxxxxx>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
>  mm/khugepaged.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b7372aba4417..0ba637df9c48 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1546,10 +1546,10 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long s
>
>  	result = SCAN_SUCCEED;
>  out_up_write:
> -	if (anon_vma_locked)
> -		anon_vma_unlock_write(vma->anon_vma);
>  	if (pte)
>  		pte_unmap(pte);
> +	if (anon_vma_locked)
> +		anon_vma_unlock_write(vma->anon_vma);
>  	mmap_write_unlock(mm);
>  out_nolock:
>  	if (folio)
>
> --
> 2.55.0
>

--
Cheers, Lorenzo