perf script python: Fix dict reference counting

The dictionaries are attached to the parameter tuple that steals the
references and takes care of releasing them when appropriate.  The code
should not decrement the reference counts explicitly.  E.g. if libpython
has been built with reference debugging enabled, the superfluous DECREFs
will trigger this error when running perf script:

  Fatal Python error: Objects/tupleobject.c:238 object at
  0x7f10f2041b40 has negative ref count -1
  Aborted (core dumped)

If the reference debugging is not enabled, the superfluous DECREFs might
cause the dict objects to be silently released while they are still in
use. This may trigger various other assertions or just cause perf
crashes and/or weird and unexpected data changes in the stored Python
objects.

Signed-off-by: Janne Huttunen <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Jaroslav Skarvada <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

1 files 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 8b2eb6dbff4d..bc32e57d17be 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);
 }