Re: [PATCH bpf-next v4 4/6] bpf/helpers: mark the callback of bpf_timer_set_sleepable_cb() as sleepable

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2024-03-15 at 15:29 +0100, Benjamin Tissoires wrote:
[...]

> @@ -5279,7 +5281,8 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
>  
>  static bool in_sleepable(struct bpf_verifier_env *env)
>  {
> -	return env->prog->sleepable;
> +	return env->prog->sleepable ||
> +	       (env->cur_state && env->cur_state->in_sleepable);
>  }

I was curious why 'env->cur_state &&' check was needed and found that
removing it caused an error in the following fragment:

static int do_misc_fixups(struct bpf_verifier_env *env)
{
		...
		if (is_storage_get_function(insn->imm)) {
			if (!in_sleepable(env) ||
			    env->insn_aux_data[i + delta].storage_get_func_atomic)
				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__force __s32)GFP_ATOMIC);
			else
				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__force __s32)GFP_KERNEL);
			...
		}
		...
}

When do_misc_fixups() is done env->cur_state is NULL.
Current implementation would use GFP_ATOMIC allocation even for
sleepable callbacks, where GFP_KERNEL is sufficient.
Is this is something we want to address?

>  
>  /* The non-sleepable programs and sleepable programs with explicit bpf_rcu_read_lock()