Re: [PATCH v2] shmem: skip empty unmap ranges when punching holes

[Baolin Wang]

On 11/5/26 1:56 PM, Hungyu Lin wrote:
> When a hole ends before the first page boundary, shmem_fallocate()
> calculates unmap_end as -1. Casting it to u64 makes the range check
> succeed even though the hole contains no complete pages.
>
> For example, punching one byte at offset zero calls unmap_mapping_range()
> with a zero length, which means unmap to the end of the file. The file
> contents are preserved outside the hole, but unrelated mappings are
> removed and must fault back in. This can be reproduced with fallocate -p
> -o 0 -l 1 on a mapped tmpfs file.
>
> Keep unmap_end as the exclusive rounded end instead of subtracting one,
> and adjust shmem_falloc.next and the unmap length accordingly. A hole
> ending before the first page boundary then has an end of zero, so the
> unsigned range check skips the empty range. Retain the unsigned
> comparison so rounding the start near the maximum file offset continues
> to be handled correctly.
>
> Fixes: 83e4fa9c16e4 ("tmpfs: support fallocate FALLOC_FL_PUNCH_HOLE")
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Hungyu Lin <dennylin0707@xxxxxxxxx>
> ---
> Changes in v2:
> - Use an exclusive unmap_end throughout, following David's suggestion.
> - Add Baolin's Reviewed-by.

Thanks. This still looks good to me.