Re: [PATCH bpf-next 1/5] bpf: Add KF_ACQUIRE and KF_RELEASE support for iterators

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2026-02-18 at 10:25 -0800, Puranjay Mohan wrote:

[...]

> @@ -13797,7 +13826,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
>  		}
>  	}
>  
> -	if (is_kfunc_release(meta) && !meta->release_regno) {
> +	if (is_kfunc_release(meta) && !meta->release_regno && !meta->has_iter_arg) {

This makes the check too strict, right?
E.g. for most of the release kfuncs there would be no iter arg,
hence the check won't ever be true for those kfuncs.
Do we have tests for this check?
Either we don't have the tests or the check itself is redundant.

>  		verbose(env, "release kernel function %s expects refcounted PTR_TO_BTF_ID\n",
>  			func_name);
>  		return -EINVAL;

[...]

> @@ -14356,6 +14400,18 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>  			regs[BPF_REG_0].id = ++env->id_gen;
>  		}
>  		mark_btf_func_reg_size(env, BPF_REG_0, sizeof(void *));
> +		/* For iterators with KF_ACQUIRE, auto-release the previous
> +		 * iteration's ref before acquiring a new one, and after
> +		 * acquisition track the new ref on the iter slot.
> +		 */
> +		struct bpf_reg_state *iter_acquire_st = NULL;
> +
> +		if (is_iter_next_kfunc(&meta) && is_kfunc_acquire(&meta)) {
> +			iter_acquire_st = get_iter_from_state(env->cur_state, &meta);
> +			err = iter_release_acquired_ref(env, iter_acquire_st);
> +			if (err)
> +				return err;
> +		}

I second Mykyta's points here.

[...]