From 957968e25f87cc5d3881389b636de34d89dbd200 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Wed, 7 Feb 2018 17:29:46 -0500
Subject: [PATCH 112/518] tracing: Use the ring-buffer nesting to allow
 synthetic events to be traced

Synthetic events can be done within the recording of other events. Notify
the ring buffer via ring_buffer_nest_start() and ring_buffer_nest_end() that
this is intended and not to block it due to its recursion protection.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
(cherry picked from commit 92c571543120ffed5e725f5b57b9de0b535e9d0a)
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/trace/trace_events_hist.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index a4ef34a797321..46e020a89d335 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -640,6 +640,7 @@ static notrace void trace_event_raw_event_synth(void *__data,
 	struct trace_event_file *trace_file = __data;
 	struct synth_trace_event *entry;
 	struct trace_event_buffer fbuffer;
+	struct ring_buffer *buffer;
 	struct synth_event *event;
 	unsigned int i, n_u64;
 	int fields_size = 0;
@@ -651,10 +652,17 @@ static notrace void trace_event_raw_event_synth(void *__data,
 
 	fields_size = event->n_u64 * sizeof(u64);
 
+	/*
+	 * Avoid ring buffer recursion detection, as this event
+	 * is being performed within another event.
+	 */
+	buffer = trace_file->tr->trace_buffer.buffer;
+	ring_buffer_nest_start(buffer);
+
 	entry = trace_event_buffer_reserve(&fbuffer, trace_file,
 					   sizeof(*entry) + fields_size);
 	if (!entry)
-		return;
+		goto out;
 
 	for (i = 0, n_u64 = 0; i < event->n_fields; i++) {
 		if (event->fields[i]->is_string) {
@@ -670,6 +678,8 @@ static notrace void trace_event_raw_event_synth(void *__data,
 	}
 
 	trace_event_buffer_commit(&fbuffer);
+out:
+	ring_buffer_nest_end(buffer);
 }
 
 static void free_synth_event_print_fmt(struct trace_event_call *call)
-- 
2.41.0

