perf python: Fix pyrf_evlist__read_on_cpu event consuming

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.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1468148882-10362-5-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
index d0c1267741eecb70b7d94239b93db69e0815ccd1..c68ef03191142c5c0626164b3490e262e5da0d04 100644 (file)
--- 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);