linux-kernel - [PATCH] perf script python: Fix dict reference counting

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Date:   Fri, 6 Jul 2018 09:53:44 +0300
From:   Janne Huttunen <janne.huttunen@...ia.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jaroslav Škarvada <jskarvad@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Janne Huttunen <janne.huttunen@...ia.com>
Subject: [PATCH] perf script python: Fix dict reference counting

The dictionaries are attached to the parameter tuple that steals the
references. The code should not decrement the reference counters
explicitly. Otherwise the objects might be released while they are
still in use which may cause perf crashes, assertions or just plain
weird behavior like unexpected data changes in stored objects.

Signed-off-by: Janne Huttunen <janne.huttunen@...ia.com>
---
 tools/perf/util/scripting-engines/trace-event-python.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
index 46e9e19..60fce44 100644
--- a/tools/perf/util/scripting-engines/trace-event-python.c
+++ b/tools/perf/util/scripting-engines/trace-event-python.c
@@ -908,14 +908,11 @@ static void python_process_tracepoint(struct perf_sample *sample,
 	if (_PyTuple_Resize(&t, n) == -1)
 		Py_FatalError("error resizing Python tuple");
 
-	if (!dict) {
+	if (!dict)
 		call_object(handler, t, handler_name);
-	} else {
+	else
 		call_object(handler, t, default_handler_name);
-		Py_DECREF(dict);
-	}
 
-	Py_XDECREF(all_entries_dict);
 	Py_DECREF(t);
 }
 
@@ -1235,7 +1232,6 @@ static void python_process_general_event(struct perf_sample *sample,
 
 	call_object(handler, t, handler_name);
 
-	Py_DECREF(dict);
 	Py_DECREF(t);
 }
 
-- 
2.5.5