linux-kernel - [PATCH v5 3/4] perf/bpf: Allow a bpf program to suppress all sample side effects

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Message-Id: <20240122062535.8265-4-khuey@kylehuey.com>
Date: Sun, 21 Jan 2024 22:25:34 -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>,
	Song Liu <song@...nel.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 v5 3/4] 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. 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>
Acked-by: Jiri Olsa <jolsa@...nel.org>
Acked-by: Namhyung Kim <namhyung@...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 24a718e7eb98..a329bec42c4d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9574,6 +9574,11 @@ 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
@@ -9623,10 +9628,7 @@ 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