RE: [PATCH V1 4/5] mm/gup: fix memfd_pin_folios hugetlb page allocation

["Kasireddy, Vivek" <vivek.kasireddy@intel.com>]

Hi Steve,

> Subject: [PATCH V1 4/5] mm/gup: fix memfd_pin_folios hugetlb page
> allocation
> 
> When memfd_pin_folios -> memfd_alloc_folio creates a hugetlb page, the
> index is wrong.  The subsequent call to filemap_get_folios_contig thus
> cannot find it, and fails, and memfd_pin_folios loops forever.
> To fix, adjust the index for the huge_page_order.
> 
> memfd_alloc_folio also forgets to unlock the folio, so the next touch
> of the page calls hugetlb_fault which blocks forever trying to take
> the lock.  Unlock it.
Where exactly is the lock taken from? I did a quick search but couldn't
immediately figure out in which function is the lock taken, while allocating
the folio.

> 
> Fixes: 89c1905d9c14 ("mm/gup: introduce memfd_pin_folios() for pinning
> memfd folios")
> 
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>  mm/memfd.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memfd.c b/mm/memfd.c
> index bfe0e71..bcb131d 100644
> --- a/mm/memfd.c
> +++ b/mm/memfd.c
> @@ -79,10 +79,13 @@ struct folio *memfd_alloc_folio(struct file *memfd,
> pgoff_t idx)
>  		 * alloc from. Also, the folio will be pinned for an indefinite
>  		 * amount of time, so it is not expected to be migrated away.
>  		 */
> -		gfp_mask = htlb_alloc_mask(hstate_file(memfd));
> +		struct hstate *h = hstate_file(memfd);
> +
> +		gfp_mask = htlb_alloc_mask(h);
>  		gfp_mask &= ~(__GFP_HIGHMEM | __GFP_MOVABLE);
> +		idx >>= huge_page_order(h);
> 
> -		folio = alloc_hugetlb_folio_reserve(hstate_file(memfd),
> +		folio = alloc_hugetlb_folio_reserve(h,
>  						    numa_node_id(),
>  						    NULL,
>  						    gfp_mask);
> @@ -95,6 +98,7 @@ struct folio *memfd_alloc_folio(struct file *memfd,
> pgoff_t idx)
>  				free_huge_folio(folio);
>  				return ERR_PTR(err);
>  			}
> +			folio_unlock(folio);
Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com>

Thanks,
Vivek

>  			return folio;
>  		}
>  		return ERR_PTR(-ENOMEM);
> --
> 1.8.3.1