Re: [syzbot] [mm?] [f2fs?] [exfat?] memory leak in __kfree_rcu_sheaf

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 3/2/26 04:41, Qing Wang wrote:
> #syz test
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index cdc1e652ec52..387979b89120 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -6307,15 +6307,21 @@ bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj)
>  			goto fail;
>  
>  		if (!local_trylock(&s->cpu_sheaves->lock)) {
> -			barn_put_empty_sheaf(barn, empty);
> +			if (barn && data_race(barn->nr_empty) < MAX_EMPTY_SHEAVES)
> +				barn_put_empty_sheaf(barn, empty);
> +			else
> +				free_empty_sheaf(s, empty);
>  			goto fail;
>  		}
>  
>  		pcs = this_cpu_ptr(s->cpu_sheaves);
>  
> -		if (unlikely(pcs->rcu_free))
> -			barn_put_empty_sheaf(barn, empty);
> -		else
> +		if (unlikely(pcs->rcu_free)) {
> +			if (barn && data_race(barn->nr_empty) < MAX_EMPTY_SHEAVES)
> +				barn_put_empty_sheaf(barn, empty);
> +			else
> +				free_empty_sheaf(s, empty);
> +		} else
>  			pcs->rcu_free = empty;
>  	}

I don't think this would fix any leak, and syzbot agrees. It would limit the
empty sheaves in barn more strictly, but they are not leaked.
Hm I don't see any leak in __kfree_rcu_sheaf() or rcu_free_sheaf(). Wonder
if kmemleak lacks visibility into barns or pcs's as roots for searching what
objects are considered referenced, or something?