[PATCH 04/10] perf python: Fix pyrf_evlist__read_on_cpu event consuming

[Jiri Olsa]

We can't consume the event before parsing it. Under heavy
load we could get caught by kernel writer overwriting the
event we're trying to parse.

Link: http://lkml.kernel.org/n/tip-8dbalvrufeisa4cioyd9k65i@xxxxxxxxxxxxxx
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 tools/perf/util/python.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
index d0c1267741ee..c68ef0319114 100644
--- a/tools/perf/util/python.c
+++ b/tools/perf/util/python.c
@@ -865,12 +865,14 @@ static PyObject *pyrf_evlist__read_on_cpu(struct pyrf_evlist *pevlist,
 		PyObject *pyevent = pyrf_event__new(event);
 		struct pyrf_event *pevent = (struct pyrf_event *)pyevent;
 
-		perf_evlist__mmap_consume(evlist, cpu);
-
 		if (pyevent == NULL)
 			return PyErr_NoMemory();
 
 		err = perf_evlist__parse_sample(evlist, event, &pevent->sample);
+
+		/* Consume the even only after we parsed it out. */
+		perf_evlist__mmap_consume(evlist, cpu);
+
 		if (err)
 			return PyErr_Format(PyExc_OSError,
 					    "perf: can't parse sample, err=%d", err);
-- 
2.4.11