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

[Baolin Wang]

On 10/28/26 1:17 AM, Hungyu Lin wrote:
> When a hole ends within the first page, 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.
>
> Compare the exclusive rounded end against the rounded start to skip
> empty ranges. Keep 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")
> Signed-off-by: Hungyu Lin <dennylin0707@xxxxxxxxx>
> ---

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