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References: <20231207163458.5554-1-khuey@kylehuey.com> <20231207163458.5554-3-khuey@kylehuey.com>
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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Thu, 7 Dec 2023 11:12:38 -0800
Message-ID: <CAEf4Bza5LWs8nQhJ78QRAU78PU8DOjs5aZkbsgdggr_a+GdEjQ@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] perf/bpf: Allow a bpf program to suppress all
 sample side effects.
To:     Kyle Huey <me@kylehuey.com>
Cc:     Kyle Huey <khuey@kylehuey.com>, linux-kernel@vger.kernel.org,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Marco Elver <elver@google.com>,
        Yonghong Song <yonghong.song@linux.dev>,
        "Robert O'Callahan" <robert@ocallahan.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Ian Rogers <irogers@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        linux-perf-users@vger.kernel.org, bpf@vger.kernel.org
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On Thu, Dec 7, 2023 at 8:35=E2=80=AFAM Kyle Huey <me@kylehuey.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@kylehuey.com>
> ---
>  kernel/events/core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>

LGTM

Acked-by: Andrii Nakryiko <andrii@kernel.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_eve=
nt *event,
>         rcu_read_unlock();
>  out:
>         __this_cpu_dec(bpf_prog_active);
> -       if (!ret)
> +       if (!ret) {
> +               event->pending_kill =3D 0;
>                 return;
> +       }
>
>         event->orig_overflow_handler(event, data, regs);
>  }
> --
> 2.34.1
>