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

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Date:	Thu, 28 Jan 2016 17:09:30 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Wang Nan <wangnan0@...wei.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

Em Thu, Jan 28, 2016 at 03:59:23PM +0100, Jiri Olsa escreveu:
> 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 ;-)

So, for the last delete, IIRC that teardown was removed because it made
the exit operation to be slower than just not calling
perf_evlist__delete (or was it perf_session__delete, don't recall right
now, probably the later, because it would delete all the threads, mmaps,
etc).

But yeah, for switching perf.data files on the fly, we better free all
that up...
 
> 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;
>  }