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Message-ID: <CAPhsuW6yhHQ1WRx5jXN3M=Bx3t=OdRY3V+DGcLFU8y-MJS3QLA@mail.gmail.com>
Date: Tue, 2 Jan 2024 15:10:12 -0800
From: Song Liu <song@...nel.org>
To: Kyle Huey <me@...ehuey.com>
Cc: Kyle Huey <khuey@...ehuey.com>, linux-kernel@...r.kernel.org,
Andrii Nakryiko <andrii.nakryiko@...il.com>, 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 v3 3/4] perf/bpf: Allow a bpf program to suppress all
sample side effects
On Sun, Dec 10, 2023 at 8:56 PM Kyle Huey <me@...ehuey.com> wrote:
>
> Returning zero from a bpf program attached to a perf event already
> suppresses any data output. Return early from __perf_event_overflow() in
> this case so it will also suppress event_limit accounting, SIGTRAP
> generation, and F_ASYNC signalling.
>
> Signed-off-by: Kyle Huey <khuey@...ehuey.com>
Acked-by: Song Liu <song@...nel.org>
> ---
> kernel/events/core.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 54f6372d2634..d6093fe893c8 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9541,6 +9541,11 @@ static int __perf_event_overflow(struct perf_event *event,
>
> ret = __perf_event_account_interrupt(event, throttle);
>
> +#ifdef CONFIG_BPF_SYSCALL
> + if (event->prog && !bpf_overflow_handler(event, data, regs))
> + return ret;
> +#endif
> +
> /*
> * XXX event_limit might not quite work as expected on inherited
> * events
> @@ -9590,10 +9595,7 @@ static int __perf_event_overflow(struct perf_event *event,
> irq_work_queue(&event->pending_irq);
> }
>
> -#ifdef CONFIG_BPF_SYSCALL
> - if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
> -#endif
> - READ_ONCE(event->overflow_handler)(event, data, regs);
> + READ_ONCE(event->overflow_handler)(event, data, regs);
>
> if (*perf_event_fasync(event) && event->pending_kill) {
> event->pending_wakeup = 1;
> --
> 2.34.1
>
>
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