Re: [PATCH] slub: Fix Off-By-One in the While condition in on_freelist()

From: Harry Yoo
Date: Thu Feb 20 2025 - 03:21:26 EST


On Sat, Feb 15, 2025 at 06:57:01PM +0200, Lilitha Persefoni Gkini wrote:
> The condition `nr <= slab->objects` in the `on_freelist()` serves as
> bound while walking through the `freelist` linked list because we can't
> have more free objects than the maximum amount of objects in the slab.
> But the `=` can result in an extra unnecessary iteration.
>
> The patch changes it to `nr < slab->objects` to ensure it iterates
> at most `slab->objects` number of times.
>
> Signed-off-by: Lilitha Persefoni Gkini <lilithpgkini@xxxxxxxxx>
> ---
> mm/slub.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 1f50129dcfb3..ad42450d4b0f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1435,7 +1435,7 @@ static int on_freelist(struct kmem_cache *s, struct slab *slab, void *search)
> int max_objects;
>
> fp = slab->freelist;
> - while (fp && nr <= slab->objects) {
> + while (fp && nr < slab->objects) {

Hi, this makes sense to me.

But based on what the name of the variable suggests (nr of objects),
I think it makes clearer to initialize it to 1 instead?

--
Cheers,
Harry