[PATCH v4 3/4] perf/bpf: Allow a bpf program to suppress all sample side effects

[Kyle Huey <me@kylehuey.com>]

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@kylehuey.com>
Acked-by: Song Liu <song@kernel.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