linux-kernel - Re: [PATCH v2] perf data: Fix releasing event

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Date:	Thu, 28 Jan 2016 15:59:23 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	acme@...hat.com, jolsa@...nel.org, linux-kernel@...r.kernel.org,
	Jérémie Galarneau 
	<jeremie.galarneau@...icios.com>, Zefan Li <lizefan@...wei.com>,
	pi3orama@....com
Subject: Re: [PATCH v2] perf data: Fix releasing event_class

On Thu, Jan 28, 2016 at 01:20:28PM +0000, 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
> ---
> 
> v1 -> v2: Free evsel->priv, destroy evlist
>           (even 'perf report' doesn't destroy evlist created by
> 	   perf_session__open)

Acked-by: Jiri Olsa <jolsa@...nel.org>


Arnaldo,
we're missing perf_evlist__delete in report command

I remember there were several cleanups skipped intentionaly,
but I dont think this one is the case.. also report TUI provides
the 's' key to load new data file.. which makes this leak
important

however even with this patch I can see perf report getting
more memory every time it reloads the data.. either there's
something else, or I'm looking at it wrong ;-)

thanks,
jirka


---
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 2bf537f190a0..7a4a27a6f053 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -970,12 +970,14 @@ repeat:
 
 	ret = __cmd_report(&report);
 	if (ret == K_SWITCH_INPUT_DATA) {
+		perf_evlist__delete(session->evlist);
 		perf_session__delete(session);
 		goto repeat;
 	} else
 		ret = 0;
 
 error:
+	perf_evlist__delete(session->evlist);
 	perf_session__delete(session);
 	return ret;
 }