[for-next][PATCH 36/46] tracing: Use the ring-buffer nesting to allow synthetic events to be traced

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rost...@goodmis.org>

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) <rost...@goodmis.org>
---
 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 f7d0da20c5c8..4f027642ceef 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)
-- 
2.15.1