Re: [PATCH v2 06/14] mm/shmem: stop retrying folios that cannot be split

[Zi Yan]

On Tue Oct 27, 2026 at 9:03 AM EDT, David Hildenbrand (Arm) wrote:
> From: Chris Mason <mason@xxxxxxxxxx>
>
> A fault or collapse can insert a large folio crossing EOF after
> shmem_undo_range() has handled the boundary folios. If splitting that
> folio fails, truncate_inode_partial_folio() retains it when it is dirty.
> The final scan then repeatedly finds it because it restarts from an
> unchanged start.
>
> Truncation keeps the inode lock and ignores fatal signals while looping.
> A concurrent unlink() can then block other directory operations while
> holding the directory lock and waiting for the file's lock.
>
> Advance start past the retained folio, whose truncated part has already
> been zeroed. Do not move start backwards if the failed split has shrunk
> the folio.
>
> Fix generated by an LLM and sent by Chris Mason in private.
>
> Fixes: 55ac8bbe358b ("mm/shmem: fix race in shmem_undo_range w/THP")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Chris Mason <mason@xxxxxxxxxx>
> Tested-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
> [ david: split fixes, simplify descriptions, adjust comments ]
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> ---
>  mm/shmem.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>

Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>



-- 
Best Regards,
Yan, Zi