[PATCH v3 3/4] perf/bpf: Allow a bpf program to suppress all sample side effects

From: Kyle Huey
Date: Sun Dec 10 2023 - 23:56:09 EST


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@xxxxxxxxxxxx>
---
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