linux-kernel - [PATCH v2 1/3] perf: Reorder overflow handler ahead of event

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Message-Id: <20231207163458.5554-2-khuey@kylehuey.com>
Date:   Thu,  7 Dec 2023 08:34:56 -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
Subject: [PATCH v2 1/3] perf: Reorder overflow handler ahead of event_limit/sigtrap

The perf subsystem already allows an overflow handler to clear pending_kill
to suppress a fasync signal (although nobody currently does this). Allow an
overflow handler to suppress the other visible side effects of an overflow,
namely event_limit accounting and SIGTRAP generation.

Signed-off-by: Kyle Huey <khuey@...ehuey.com>
---
 kernel/events/core.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index b704d83a28b2..19fddfc27a4a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9541,6 +9541,12 @@ static int __perf_event_overflow(struct perf_event *event,
 	 */
 
 	event->pending_kill = POLL_IN;
+
+	READ_ONCE(event->overflow_handler)(event, data, regs);
+
+	if (!event->pending_kill)
+		return ret;
+
 	if (events && atomic_dec_and_test(&event->event_limit)) {
 		ret = 1;
 		event->pending_kill = POLL_HUP;
@@ -9584,9 +9590,7 @@ static int __perf_event_overflow(struct perf_event *event,
 		irq_work_queue(&event->pending_irq);
 	}
 
-	READ_ONCE(event->overflow_handler)(event, data, regs);
-
-	if (*perf_event_fasync(event) && event->pending_kill) {
+	if (*perf_event_fasync(event)) {
 		event->pending_wakeup = 1;
 		irq_work_queue(&event->pending_irq);
 	}
-- 
2.34.1