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

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Date:   Sun, 8 Jul 2018 13:17:07 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Janne Huttunen <janne.huttunen@...ia.com>
Cc:     linux-kernel@...r.kernel.org,
        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>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] perf script python: Fix dict reference counting

On Fri, Jul 06, 2018 at 09:53:44AM +0300, Janne Huttunen wrote:
> 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);

so the dict is released when the tuple is released?

jirka