linux-kernel - Re: [PATCH bpf-next v4 3/6] bpf/helpers: introduce bpf_timer_set_sleepable

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Date: Tue, 19 Mar 2024 00:52:33 +0200
From: Eduard Zingerman <eddyz87@...il.com>
To: Benjamin Tissoires <bentiss@...nel.org>, Alexei Starovoitov
 <ast@...nel.org>,  Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,  Song Liu
 <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend
 <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav
 Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>,  Mykola Lysenko <mykolal@...com>, Shuah Khan
 <shuah@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 3/6] bpf/helpers: introduce
 bpf_timer_set_sleepable_cb() kfunc

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

This patch looks good to me, please see two nitpicks below.
Acked-by: Eduard Zingerman <eddyz87@...il.com>

[...]

> @@ -1350,6 +1358,11 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla
>  		goto out;
>  	}
>  
> +	if (t->is_sleepable && !(flags & BPF_F_TIMER_SLEEPABLE)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}

Nit:
the BPF_F_TIMER_ABS and BPF_F_TIMER_CPU_PIN don't affect
sleepable timers, should this check be changed to:
'(t->is_sleepable && flags != BPF_F_TIMER_SLEEPABLE)' ?

[...]

> @@ -12151,6 +12175,16 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>  		}
>  	}
>  
> +	if (is_async_callback_calling_kfunc(meta.func_id)) {
> +		err = push_callback_call(env, insn, insn_idx, meta.subprogno,
> +					 set_timer_callback_state);

Nit: still think that this fragment would be better as:

	if (is_bpf_timer_set_sleepable_cb_impl_kfunc(meta.func_id)) {
		err = push_callback_call(env, insn, insn_idx, meta.subprogno,
					 set_timer_callback_state);

Because of the 'set_timer_callback_state' passed to push_callback_call().

> +		if (err) {
> +			verbose(env, "kfunc %s#%d failed callback verification\n",
> +				func_name, meta.func_id);
> +			return err;
> +		}
> +	}
> +
>  	rcu_lock = is_kfunc_bpf_rcu_read_lock(&meta);
>  	rcu_unlock = is_kfunc_bpf_rcu_read_unlock(&meta);
>