Re: [PATCH 1/2] perf/bpf: Allow a bpf program to suppress I/O signals.

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Kyle Huey <me@kylehuey.com>
Cc: Kyle Huey <khuey@kylehuey.com>,
	linux-kernel@vger.kernel.org,
	"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>,
	Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
	Ian Rogers <irogers@google.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	linux-perf-users@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH 1/2] perf/bpf: Allow a bpf program to suppress I/O signals.
Date: Mon, 4 Dec 2023 14:18:49 -0800	[thread overview]
Message-ID: <CAEf4BzYtSXtgdO9C2w9OOKni68H-7UOExFJRBEij3HG2Qwn1Rg@mail.gmail.com> (raw)
In-Reply-To: <20231204201406.341074-2-khuey@kylehuey.com>

On Mon, Dec 4, 2023 at 12:14 PM Kyle Huey <me@kylehuey.com> wrote:
>
> Returning zero from a bpf program attached to a perf event already
> suppresses any data output. This allows it to suppress I/O availability
> signals too.

make sense, just one question below

>
> Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> ---
>  kernel/events/core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b704d83a28b2..34d7b19d45eb 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -10417,8 +10417,10 @@ 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;
> +       }

What's the distinction between event->pending_kill and
event->pending_wakeup? Should we do something about pending_wakeup?
Asking out of complete ignorance of all these perf specifics.

>
>         event->orig_overflow_handler(event, data, regs);
>  }
> --
> 2.34.1
>
>