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Date: Thu, 18 Jan 2024 16:13:48 -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>,
Song Liu <song@...nel.org>
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 v4 1/4] perf/bpf: Call bpf handler directly, not through overflow machinery
To ultimately allow bpf programs attached to perf events to completely
suppress all of the effects of a perf event overflow (rather than just the
sample output, as they do today), call bpf_overflow_handler() from
__perf_event_overflow() directly rather than modifying struct perf_event's
overflow_handler. Return the bpf program's return value from
bpf_overflow_handler() so that __perf_event_overflow() knows how to
proceed. Remove the now unnecessary orig_overflow_handler from struct
perf_event.
This patch is solely a refactoring and results in no behavior change.
Signed-off-by: Kyle Huey <khuey@...ehuey.com>
Suggested-by: Namhyung Kim <namhyung@...nel.org>
Acked-by: Song Liu <song@...nel.org>
---
include/linux/perf_event.h | 6 +-----
kernel/events/core.c | 28 +++++++++++++++-------------
2 files changed, 16 insertions(+), 18 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index d2a15c0c6f8a..c7f54fd74d89 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -810,7 +810,6 @@ struct perf_event {
perf_overflow_handler_t overflow_handler;
void *overflow_handler_context;
#ifdef CONFIG_BPF_SYSCALL
- perf_overflow_handler_t orig_overflow_handler;
struct bpf_prog *prog;
u64 bpf_cookie;
#endif
@@ -1357,10 +1356,7 @@ __is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
#ifdef CONFIG_BPF_SYSCALL
static inline bool uses_default_overflow_handler(struct perf_event *event)
{
- if (likely(is_default_overflow_handler(event)))
- return true;
-
- return __is_default_overflow_handler(event->orig_overflow_handler);
+ return is_default_overflow_handler(event);
}
#else
#define uses_default_overflow_handler(event) \
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f0f0f71213a1..24a718e7eb98 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9548,6 +9548,12 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r
return true;
}
+#ifdef CONFIG_BPF_SYSCALL
+static int bpf_overflow_handler(struct perf_event *event,
+ struct perf_sample_data *data,
+ struct pt_regs *regs);
+#endif
+
/*
* Generic event overflow handling, sampling.
*/
@@ -9617,7 +9623,10 @@ static int __perf_event_overflow(struct perf_event *event,
irq_work_queue(&event->pending_irq);
}
- READ_ONCE(event->overflow_handler)(event, data, regs);
+#ifdef CONFIG_BPF_SYSCALL
+ if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
+#endif
+ READ_ONCE(event->overflow_handler)(event, data, regs);
if (*perf_event_fasync(event) && event->pending_kill) {
event->pending_wakeup = 1;
@@ -10427,9 +10436,9 @@ static void perf_event_free_filter(struct perf_event *event)
}
#ifdef CONFIG_BPF_SYSCALL
-static void bpf_overflow_handler(struct perf_event *event,
- struct perf_sample_data *data,
- struct pt_regs *regs)
+static int bpf_overflow_handler(struct perf_event *event,
+ struct perf_sample_data *data,
+ struct pt_regs *regs)
{
struct bpf_perf_event_data_kern ctx = {
.data = data,
@@ -10450,10 +10459,8 @@ static void bpf_overflow_handler(struct perf_event *event,
rcu_read_unlock();
out:
__this_cpu_dec(bpf_prog_active);
- if (!ret)
- return;
- event->orig_overflow_handler(event, data, regs);
+ return ret;
}
static int perf_event_set_bpf_handler(struct perf_event *event,
@@ -10489,8 +10496,6 @@ static int perf_event_set_bpf_handler(struct perf_event *event,
event->prog = prog;
event->bpf_cookie = bpf_cookie;
- event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
- WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
return 0;
}
@@ -10501,7 +10506,6 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
if (!prog)
return;
- WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
event->prog = NULL;
bpf_prog_put(prog);
}
@@ -11975,13 +11979,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
overflow_handler = parent_event->overflow_handler;
context = parent_event->overflow_handler_context;
#if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING)
- if (overflow_handler == bpf_overflow_handler) {
+ if (parent_event->prog) {
struct bpf_prog *prog = parent_event->prog;
bpf_prog_inc(prog);
event->prog = prog;
- event->orig_overflow_handler =
- parent_event->orig_overflow_handler;
}
#endif
}
--
2.34.1
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