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Message-ID: <56A9D887.8030508@huawei.com>
Date: Thu, 28 Jan 2016 16:59:51 +0800
From: "Wangnan (F)" <wangnan0@...wei.com>
To: Jiri Olsa <jolsa@...nel.org>
CC: <acme@...hat.com>, <linux-kernel@...r.kernel.org>,
Jérémie Galarneau
<jeremie.galarneau@...icios.com>, Zefan Li <lizefan@...wei.com>,
<pi3orama@....com>
Subject: Re: [PATCH] perf data: Fix releasing event_class
Hi Jiri, What's your opinion on this patch?
Thank you.
On 2016/1/27 19:21, Wang Nan wrote:
> A new patch of libbabeltrace [1] reveals a object leak problem in
> perf data CTF support: perf code never release event_class which is
> allocated in add_event() and stored in evsel's private field.
>
> If libbabeltrace has the above patch applied, leaking event_class
> prevent writer being destroied and flushing metadata. For example:
>
> $ ./perf record ls
> Lowering default frequency rate to 500.
> Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
> perf.data
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.012 MB perf.data (12 samples) ]
> $ ./perf data convert --to-ctf ./out.ctf
> [ perf data convert: Converted 'perf.data' into CTF data './out.ctf' ]
> [ perf data convert: Converted and wrote 0.000 MB (12 samples) ]
> $ cat ./out.ctf/metadata
> $ ls -l ./out.ctf/metadata
> -rw-r----- 1 w00229757 mm 0 Jan 27 10:49 ./out.ctf/metadata
>
> The correct result should be:
> ...
> $ cat ./out.ctf/metadata
> /* CTF 1.8 */
>
> trace {
> [SNIP]
>
> $ ls -l ./out.ctf/metadata
> -rw-r----- 1 w00229757 mm 2446 Jan 27 10:52 ./out.ctf/metadata
>
> The full story is:
>
> Patch [1] of babeltrace redesign reference counting scheme. In that
> patch:
>
> * writer <- trace (bt_ctf_writer_create)
> * trace <- stream_class (bt_ctf_trace_add_stream_class)
> * stream_class <- event_class (bt_ctf_stream_class_add_event_class)
> ('<-' means 'is a parent of')
>
> Holding of event_class causes reference count of corresponding
> 'writer' increases through parent chain. Perf expect 'writer' is
> released (so metadata is flushed) through bt_ctf_writer_put() in
> ctf_writer__cleanup(). However, since it never release event_class,
> the reference of 'writer' won't be reduced, so bt_ctf_writer_put()
> won't lead releasing of writer.
>
> Before this CTF patch, !(writer <- trace). Even event_class leak,
> writer is able to be released.
>
> [1] https://github.com/efficios/babeltrace/commit/e6a8e8e4744633807083a077ff9f101eb97d9801
>
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Jérémie Galarneau <jeremie.galarneau@...icios.com>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: pi3orama@....com
> ---
> tools/perf/util/data-convert-bt.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/tools/perf/util/data-convert-bt.c b/tools/perf/util/data-convert-bt.c
> index 34cd1e4..e553321 100644
> --- a/tools/perf/util/data-convert-bt.c
> +++ b/tools/perf/util/data-convert-bt.c
> @@ -858,6 +858,19 @@ static int setup_events(struct ctf_writer *cw, struct perf_session *session)
> return 0;
> }
>
> +static void cleanup_events(struct perf_session *session)
> +{
> + struct perf_evlist *evlist = session->evlist;
> + struct perf_evsel *evsel;
> +
> + evlist__for_each(evlist, evsel) {
> + struct evsel_priv *priv;
> +
> + priv = evsel->priv;
> + bt_ctf_event_class_put(priv->event_class);
> + }
> +}
> +
> static int setup_streams(struct ctf_writer *cw, struct perf_session *session)
> {
> struct ctf_stream **stream;
> @@ -1171,6 +1184,7 @@ int bt_convert__perf2ctf(const char *input, const char *path, bool force)
> (double) c.events_size / 1024.0 / 1024.0,
> c.events_count);
>
> + cleanup_events(session);
> perf_session__delete(session);
> ctf_writer__cleanup(cw);
>
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