Re: [PATCH RFC bpf-next v3 04/16] bpf/helpers: introduce sleepable bpf_timers

From: Eduard Zingerman <eddyz87@gmail.com>
To: Benjamin Tissoires <bentiss@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	 Daniel Borkmann <daniel@iogearbox.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>,
	Yonghong Song <yonghong.song@linux.dev>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>, Jiri Kosina <jikos@kernel.org>,
	 Benjamin Tissoires <benjamin.tissoires@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
	 linux-input@vger.kernel.org, linux-doc@vger.kernel.org,
	 linux-kselftest@vger.kernel.org
Subject: Re: [PATCH RFC bpf-next v3 04/16] bpf/helpers: introduce sleepable bpf_timers
Date: Fri, 23 Feb 2024 00:40:23 +0200	[thread overview]
Message-ID: <818e43447651af1a659993897c14d05fec5038e4.camel@gmail.com> (raw)
In-Reply-To: <20240221-hid-bpf-sleepable-v3-4-1fb378ca6301@kernel.org>

On Wed, 2024-02-21 at 17:25 +0100, Benjamin Tissoires wrote:

[...]

> @@ -1282,7 +1333,7 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla
>  
>  	if (in_nmi())
>  		return -EOPNOTSUPP;
> -	if (flags & ~(BPF_F_TIMER_ABS | BPF_F_TIMER_CPU_PIN))
> +	if (flags & ~(BPF_F_TIMER_ABS | BPF_F_TIMER_CPU_PIN | BPF_F_TIMER_SLEEPABLE))
>  		return -EINVAL;
>  	__bpf_spin_lock_irqsave(&timer->lock);
>  	t = timer->timer;
> @@ -1299,7 +1350,10 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla
>  	if (flags & BPF_F_TIMER_CPU_PIN)
>  		mode |= HRTIMER_MODE_PINNED;
>  
> -	hrtimer_start(&t->timer, ns_to_ktime(nsecs), mode);
> +	if (flags & BPF_F_TIMER_SLEEPABLE)
> +		schedule_work(&t->work);
> +	else
> +		hrtimer_start(&t->timer, ns_to_ktime(nsecs), mode);

It looks like nsecs is simply ignored for sleepable timers.
Should this be hrtimer_start() that waits nsecs and schedules work,
or schedule_delayed_work()? (but it takes delay in jiffies, which is
probably too coarse). Sorry if I miss something.