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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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