linux-kernel - Re: [PATCH v2 2/3] perf/bpf: Allow a bpf program to suppress all sample side effects.

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Message-ID: <CAEf4Bza5LWs8nQhJ78QRAU78PU8DOjs5aZkbsgdggr_a+GdEjQ@mail.gmail.com>
Date:   Thu, 7 Dec 2023 11:12:38 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Kyle Huey <me@...ehuey.com>
Cc:     Kyle Huey <khuey@...ehuey.com>, linux-kernel@...r.kernel.org,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Marco Elver <elver@...gle.com>,
        Yonghong Song <yonghong.song@...ux.dev>,
        "Robert O'Callahan" <robert@...llahan.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v2 2/3] perf/bpf: Allow a bpf program to suppress all
 sample side effects.

On Thu, Dec 7, 2023 at 8:35 AM Kyle Huey <me@...ehuey.com> wrote:
>
> Returning zero from a bpf program attached to a perf event already
> suppresses any data output. By clearing pending_kill, returning zero from a
> bpf program will effectively pretend the sample never happened for all
> userspace purposes.
>
> Signed-off-by: Kyle Huey <khuey@...ehuey.com>
> ---
>  kernel/events/core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>

LGTM

Acked-by: Andrii Nakryiko <andrii@...nel.org>

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 19fddfc27a4a..6cda05a4969d 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -10421,8 +10421,10 @@ static void bpf_overflow_handler(struct perf_event *event,
>         rcu_read_unlock();
>  out:
>         __this_cpu_dec(bpf_prog_active);
> -       if (!ret)
> +       if (!ret) {
> +               event->pending_kill = 0;
>                 return;
> +       }
>
>         event->orig_overflow_handler(event, data, regs);
>  }
> --
> 2.34.1
>