Re: [PATCH] mm/memfd_luo: report error when restoring a folio fails mid-loop

[Pratyush Yadav]

On Wed, Apr 15 2026, David Carlier wrote:

> memfd_luo_retrieve_folios() initialises err to -EIO, but the per-iteration
> calls to mem_cgroup_charge(), shmem_add_to_page_cache() and
> shmem_inode_acct_blocks() reuse and overwrite err.  Once any iteration
> completes successfully, err becomes zero.
>
> If a later iteration's kho_restore_folio() returns NULL, the failure path
> jumps to put_folios without resetting err, so the function returns 0.
> The caller memfd_luo_retrieve() then takes the success path, sets
> args->file and reports the restore as successful, leaving userspace with
> a partially populated memfd and no indication that anything went wrong.
>
> Set err to -EIO in the kho_restore_folio() failure branch so the error
> is propagated to the caller.
>
> Signed-off-by: David Carlier <devnexen@xxxxxxxxx>

Reviewed-by: Pratyush Yadav <pratyush@xxxxxxxxxx>

Please add these when applying:

Cc: stable@xxxxxxxxxxxxxxx
Fixes: b3749f174d68 ("mm: memfd_luo: allow preserving memfd")

[...]

-- 
Regards,
Pratyush Yadav