Re: [PATCH 10/16] mm/shmem: discard whole new large folios on fallocate rollback

[Baolin Wang]

On 10/26/26 5:40 PM, David Hildenbrand (Arm) wrote:
> When undoing a failed fallocate(), shmem_undo_range() must discard each
> newly allocated folio. Its second scan instead passes large
> folios to truncate_inode_partial_folio(), which does not necessarily
> discard the entire large folio, but instead tries splitting it to
> discard only the requested range.
>
> For example, with huge=always, a failed allocation starting at offset
> 4 KiB can leave page 0 allocated in an otherwise empty file.
>
> Discard the whole folio when unfalloc is set. Note that we enter this
> path only for folios that are not uptodate, and can consequently be
> dropped without losing any data.
>
> Fixes: 55ac8bbe358b ("mm/shmem: fix race in shmem_undo_range w/THP")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> ---

Good catch. LGTM.
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>