Re: mbind() fails to fail with EIO

[Oscar Salvador <osalvador@suse.de>]

+CC Kirill

On Mon, Mar 18, 2019 at 11:12:19AM -0700, Yang Shi wrote:
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index abe7a67..6ba45aa 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -521,11 +521,14 @@ static int queue_pages_pte_range(pmd_t *pmd,
> unsigned long addr,
>                         continue;
>                 if (!queue_pages_required(page, qp))
>                         continue;
> -               migrate_page_add(page, qp->pagelist, flags);
> +               if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
> +                       migrate_page_add(page, qp->pagelist, flags);
> +               else
> +                       break;
>         }
>         pte_unmap_unlock(pte - 1, ptl);
>         cond_resched();
> -       return 0;
> +       return addr != end ? -EIO : 0;
>  }
> 
>  static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask,

This alone is not going to help.

The problem is that we do skip the vma early in queue_pages_test_walk() in
case MPOL_MF_MOVE and MPOL_MF_MOVE_ALL are not set.

walk_page_range
 walk_page_test
  queue_pages_test_walk

	...
 	...
	/* queue pages from current vma */
	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
		return 0;
	return 1;

So, we skip the vma and keep going.

Before ("77bf45e78050: mempolicy: do not try to queue pages from !vma_migratable()"),
queue_pages_test_walk() would not have skipped the vma in case we had MPOL_MF_STRICT
or MPOL_MF_MOVE | MPOL_MF_MOVE_ALL.

I did not give it a lot of thought, but it seems to me that we might need to reach
queue_pages_to_pte_range() in order to see whether the page is in the required node
or not by calling queue_pages_required(), and if it is not, check for
MPOL_MF_MOVE | MPOL_MF_MOVE_ALL like the above patch does, so we would be able to
return -EIO.
That would imply that we would need to re-add MPOL_MF_STRICT in queue_pages_test_walk().

-- 
Oscar Salvador
SUSE L3