linux-kernel - Re: [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints

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Date:   Wed, 2 Mar 2022 18:29:35 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     Hao Luo <haoluo@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        KP Singh <kpsingh@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Joe Burton <jevburton.kernel@...il.com>,
        Tejun Heo <tj@...nel.org>, Josh Don <joshdon@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>, bpf <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints

On Wed, Mar 2, 2022 at 5:09 PM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 3/2/22 1:30 PM, Alexei Starovoitov wrote:
> > On Wed, Mar 2, 2022 at 1:23 PM Yonghong Song <yhs@...com> wrote:
> >>
> >>
> >>
> >> On 2/25/22 3:43 PM, Hao Luo wrote:
> >>> Add a new type of bpf tracepoints: sleepable tracepoints, which allows
> >>> the handler to make calls that may sleep. With sleepable tracepoints, a
> >>> set of syscall helpers (which may sleep) may also be called from
> >>> sleepable tracepoints.
> >>
> >> There are some old discussions on sleepable tracepoints, maybe
> >> worthwhile to take a look.
> >>
> >> https://lore.kernel.org/bpf/20210218222125.46565-5-mjeanson@efficios.com/T/
> >
> > Right. It's very much related, but obsolete too.
> > We don't need any of that for sleeptable _raw_ tps.
> > I prefer to stay with "sleepable" name as well to
> > match the rest of the bpf sleepable code.
> > In all cases it's faultable.
>
> sounds good to me. Agree that for the bpf user case, Hao's
> implementation should be enough.

Just remembered that we can also do trivial noinline __weak
nop function and mark it sleepable on the verifier side.
That's what we were planning to do to trace map update/delete ops
in Joe Burton's series.
Then we don't need to extend tp infra.
I'm fine whichever way. I see pros and cons in both options.