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    Subject[tip:perf/core] perf data: Fix releasing event_class
    Commit-ID:  5141d7350d3d8a12f1f76b1015b937f14d2b97e2
    Gitweb: http://git.kernel.org/tip/5141d7350d3d8a12f1f76b1015b937f14d2b97e2
    Author: Wang Nan <wangnan0@huawei.com>
    AuthorDate: Fri, 5 Feb 2016 14:01:30 +0000
    Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
    CommitDate: Fri, 12 Feb 2016 17:27:48 -0300

    perf data: Fix releasing event_class

    A new patch in libbabeltrace [1] reveals a object leak problem in
    'perf data' CTF support: perf code never releases the 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
    prevents the writer from being destroyed and flushing metadata. For
    example:

    $ perf record ls
    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 redesigns its 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'
    to increase through parent chain. Perf expects that 'writer' is released
    (so metadata is flushed) through bt_ctf_writer_put() in
    ctf_writer__cleanup(). However, since it never releases event_class, the
    reference of 'writer' won't be dropped, so bt_ctf_writer_put() won't
    lead to the release of writer.

    Before this CTF patch, !(writer <- trace). Even with event_class leaking,
    the writer ends up being released.

    [1] https://github.com/efficios/babeltrace/commit/e6a8e8e4744633807083a077ff9f101eb97d9801

    Signed-off-by: Wang Nan <wangnan0@huawei.com>
    Acked-by: Jiri Olsa <jolsa@kernel.org>
    Cc: Adrian Hunter <adrian.hunter@intel.com>
    Cc: Alexei Starovoitov <ast@kernel.org>
    Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
    Cc: Cody P Schafer <dev@codyps.com>
    Cc: He Kuang <hekuang@huawei.com>
    Cc: Jeremie Galarneau <jeremie.galarneau@efficios.com>
    Cc: Kirill Smelkov <kirr@nexedi.com>
    Cc: Li Zefan <lizefan@huawei.com>
    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Zefan Li <lizefan@huawei.com>
    Cc: pi3orama@163.com
    Link: http://lkml.kernel.org/r/1454680939-24963-6-git-send-email-wangnan0@huawei.com
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    ---
    tools/perf/util/data-convert-bt.c | 18 ++++++++++++++++++
    1 file changed, 18 insertions(+)

    diff --git a/tools/perf/util/data-convert-bt.c b/tools/perf/util/data-convert-bt.c
    index 34cd1e4..b722e57 100644
    --- a/tools/perf/util/data-convert-bt.c
    +++ b/tools/perf/util/data-convert-bt.c
    @@ -858,6 +858,23 @@ 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);
    + zfree(&evsel->priv);
    + }
    +
    + perf_evlist__delete(evlist);
    + session->evlist = NULL;
    +}
    +
    static int setup_streams(struct ctf_writer *cw, struct perf_session *session)
    {
    struct ctf_stream **stream;
    @@ -1171,6 +1188,7 @@ 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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