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

Harry Yoo
2026-03-11T11:23:54Z

On Wed, Mar 11, 2026 at 06:48:55PM +0800, Qing Wang wrote:
> #syz test
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 20cb4f3b636d..73b2cfd0e123 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2797,6 +2797,7 @@ static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf)
> if (s->flags & SLAB_KMALLOC)
> mark_obj_codetag_empty(sheaf);
>
> + WARN_ON(sheaf->size > 0);
> kfree(sheaf);
>
> stat(s, SHEAF_FREE);
> @@ -2828,6 +2829,7 @@ static int refill_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf,
> return 0;
> }
>
> +static void sheaf_flush_unused(struct kmem_cache *s, struct slab_sheaf *sheaf);
>
> static struct slab_sheaf *alloc_full_sheaf(struct kmem_cache *s, gfp_t gfp)
> {
> @@ -2837,6 +2839,7 @@ static struct slab_sheaf *alloc_full_sheaf(struct kmem_cache *s, gfp_t gfp)
> return NULL;
>
> if (refill_sheaf(s, sheaf, gfp | __GFP_NOMEMALLOC | __GFP_NOWARN)) {
> + sheaf_flush_unused(s, sheaf);
> free_empty_sheaf(s, sheaf);
> return NULL;
> }
> @@ -4623,6 +4626,7 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
> * we must be very low on memory so don't bother
> * with the barn
> */
> + sheaf_flush_unused(s, empty);
> free_empty_sheaf(s, empty);
> }
> } else {

This won't fix any kmemleak reports because kmemleak couldn't detect this
in the first place. kmemleak doesn't know that those objects exist
until they are allocated and kmemleak_alloc() is called for them.

--
Cheers,
Harry / Hyeonggon