perf/bpf: Reorder bpf_overflow_handler() ahead of __perf_event_overflow()

This will allow __perf_event_overflow() to call bpf_overflow_handler().
Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240412015019.7060-2-khuey@kylehuey.com

kernel/events/core.c

@@ -9563,6 +9563,98 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r
 	return true;
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+static void 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,
+		.event = event,
+	};
+	struct bpf_prog *prog;
+	int ret = 0;
+
+	ctx.regs = perf_arch_bpf_user_pt_regs(regs);
+	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1))
+		goto out;
+	rcu_read_lock();
+	prog = READ_ONCE(event->prog);
+	if (prog) {
+		perf_prepare_sample(data, event, regs);
+		ret = bpf_prog_run(prog, &ctx);
+	}
+	rcu_read_unlock();
+out:
+	__this_cpu_dec(bpf_prog_active);
+	if (!ret)
+		return;
+
+	event->orig_overflow_handler(event, data, regs);
+}
+
+static int perf_event_set_bpf_handler(struct perf_event *event,
+				      struct bpf_prog *prog,
+				      u64 bpf_cookie)
+{
+	if (event->overflow_handler_context)
+		/* hw breakpoint or kernel counter */
+		return -EINVAL;
+
+	if (event->prog)
+		return -EEXIST;
+
+	if (prog->type != BPF_PROG_TYPE_PERF_EVENT)
+		return -EINVAL;
+
+	if (event->attr.precise_ip &&
+	    prog->call_get_stack &&
+	    (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) ||
+	     event->attr.exclude_callchain_kernel ||
+	     event->attr.exclude_callchain_user)) {
+		/*
+		 * On perf_event with precise_ip, calling bpf_get_stack()
+		 * may trigger unwinder warnings and occasional crashes.
+		 * bpf_get_[stack|stackid] works around this issue by using
+		 * callchain attached to perf_sample_data. If the
+		 * perf_event does not full (kernel and user) callchain
+		 * attached to perf_sample_data, do not allow attaching BPF
+		 * program that calls bpf_get_[stack|stackid].
+		 */
+		return -EPROTO;
+	}
+
+	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;
+}
+
+static void perf_event_free_bpf_handler(struct perf_event *event)
+{
+	struct bpf_prog *prog = event->prog;
+
+	if (!prog)
+		return;
+
+	WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
+	event->prog = NULL;
+	bpf_prog_put(prog);
+}
+#else
+static int perf_event_set_bpf_handler(struct perf_event *event,
+				      struct bpf_prog *prog,
+				      u64 bpf_cookie)
+{
+	return -EOPNOTSUPP;
+}
+
+static void perf_event_free_bpf_handler(struct perf_event *event)
+{
+}
+#endif
+
 /*
  * Generic event overflow handling, sampling.
  */
@@ -10441,97 +10533,6 @@ static void perf_event_free_filter(struct perf_event *event)
 	ftrace_profile_free_filter(event);
 }
 
-#ifdef CONFIG_BPF_SYSCALL
-static void 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,
-		.event = event,
-	};
-	struct bpf_prog *prog;
-	int ret = 0;
-
-	ctx.regs = perf_arch_bpf_user_pt_regs(regs);
-	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1))
-		goto out;
-	rcu_read_lock();
-	prog = READ_ONCE(event->prog);
-	if (prog) {
-		perf_prepare_sample(data, event, regs);
-		ret = bpf_prog_run(prog, &ctx);
-	}
-	rcu_read_unlock();
-out:
-	__this_cpu_dec(bpf_prog_active);
-	if (!ret)
-		return;
-
-	event->orig_overflow_handler(event, data, regs);
-}
-
-static int perf_event_set_bpf_handler(struct perf_event *event,
-				      struct bpf_prog *prog,
-				      u64 bpf_cookie)
-{
-	if (event->overflow_handler_context)
-		/* hw breakpoint or kernel counter */
-		return -EINVAL;
-
-	if (event->prog)
-		return -EEXIST;
-
-	if (prog->type != BPF_PROG_TYPE_PERF_EVENT)
-		return -EINVAL;
-
-	if (event->attr.precise_ip &&
-	    prog->call_get_stack &&
-	    (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) ||
-	     event->attr.exclude_callchain_kernel ||
-	     event->attr.exclude_callchain_user)) {
-		/*
-		 * On perf_event with precise_ip, calling bpf_get_stack()
-		 * may trigger unwinder warnings and occasional crashes.
-		 * bpf_get_[stack|stackid] works around this issue by using
-		 * callchain attached to perf_sample_data. If the
-		 * perf_event does not full (kernel and user) callchain
-		 * attached to perf_sample_data, do not allow attaching BPF
-		 * program that calls bpf_get_[stack|stackid].
-		 */
-		return -EPROTO;
-	}
-
-	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;
-}
-
-static void perf_event_free_bpf_handler(struct perf_event *event)
-{
-	struct bpf_prog *prog = event->prog;
-
-	if (!prog)
-		return;
-
-	WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
-	event->prog = NULL;
-	bpf_prog_put(prog);
-}
-#else
-static int perf_event_set_bpf_handler(struct perf_event *event,
-				      struct bpf_prog *prog,
-				      u64 bpf_cookie)
-{
-	return -EOPNOTSUPP;
-}
-static void perf_event_free_bpf_handler(struct perf_event *event)
-{
-}
-#endif
-
 /*
  * returns true if the event is a tracepoint, or a kprobe/upprobe created
  * with perf_event_open()