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

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Date:   Thu,  7 Dec 2023 08:34:57 -0800
From:   Kyle Huey <me@...ehuey.com>
To:     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>
Cc:     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: [PATCH v2 2/3] perf/bpf: Allow a bpf program to suppress all sample side effects.

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(-)

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