Re: [PATCH v2 1/1] mm/slab_common: reject zero object_size before calculate_alignment

[Harry Yoo]

On Wed, Aug 26, 2026 at 09:55:06AM +0800, Longlong Xia wrote:
> From: Longlong Xia <xialonglong@xxxxxxxxxx>
> 
> calculate_alignment() with SLAB_HWCACHE_ALIGN halves ralign in a
> while (size <= ralign / 2) loop. When size is 0, ralign eventually
> reaches 0 and the condition stays true indefinitely, hanging the
> kernel.
> 
> kmem_cache_sanity_check() rejected size > KMALLOC_MAX_SIZE but not
> size == 0. Add !size to the check so a 0-size kmem_cache_create() is
> caught on CONFIG_DEBUG_VM builds, where it can be diagnosed when it
> surfaces.
> 
> Suggested-by: Hao Li <hao.li@xxxxxxxxx>
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Longlong Xia <xialonglong@xxxxxxxxxx>
> ---
> Changes in v2:
> - Drop the !object_size check in __kmem_cache_create_args() that v1
>   added to the always-compiled path, and keep the guard only in the
>   debug-only kmem_cache_sanity_check(), as suggested by Hao Li.
> 
> Link: https://lore.kernel.org/all/20260824092454.1693745-1-xialonglong2025@xxxxxxx/
> ---

The patch is small and benign enough, so:
Reviewed-by: Harry Yoo (Meta) <harry@xxxxxxxxxx>

However, to be honest I don't understand why anyone would ever try to
create a kmem_cache with size == 0. It doesn't make any sense.

I'd strongly encourage not addressing every theoretical issue raised
by an LLM that doesn't bother you or somebody else.

-- 
Cheers,
Harry / Hyeonggon