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

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Date: Thu, 21 Mar 2024 16:44:01 +0100
From: Benjamin Tissoires <benjamin.tissoires@...hat.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: 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>, 
	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 Mon, Mar 18, 2024 at 11:52 PM Eduard Zingerman <eddyz87@...il.com> wrote:
>
> 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>

Thanks!

>
> [...]
>
> > @@ -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)' ?

Sounds fair enough. Scheduled this for v5

>
> [...]
>
> > @@ -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().

Yeah, sorry I missed that part from the previous reviews.

Fixed in v5

Cheers,
Benjamin

>
> > +             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);
> >
>