linux-kernel - Re: [GIT PULL 00/21] perf/core improvements and fixes

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Message-ID: <20131210120143.GJ8098@ghostprotocols.net>
Date:	Tue, 10 Dec 2013 09:01:43 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Ben Cheng <bccheng@...gle.com>,
	David Ahern <dsahern@...il.com>,
	Dongsheng Yang <yangds.fnst@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung.kim@....com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [GIT PULL 00/21] perf/core improvements and fixes

Em Tue, Dec 10, 2013 at 12:47:57PM +0100, Ingo Molnar escreveu:
> * Arnaldo Carvalho de Melo <acme@...stprotocols.net> wrote:
> > Em Tue, Dec 10, 2013 at 12:12:29PM +0100, Ingo Molnar escreveu:
> > > Hm, I've unpulled it because 'perf top' crashes on exit, in 
> > > dso__delete():

> > 495		if (dso->sname_alloc)
> > 496			free((char *)dso->short_name)

> Btw., instead of trusting flags I'd argue that using the pointer as a 
> flag and clearing the pointer too is a much more robust freeing 
> pattern in general:

> 		if (dso->short_name) {
> 			free(dso->short_name);
> 			dso->short_name = NULL;
> 		}
> 
> or so ...

This is not an unusual idiom, if you look at tools/perf/util/ev{list,sel}.c,
for instance, you'll see it in many destructors.

In this case there is a micro optimization where sometimes the shortname
is just a pointer to the tail part of the long name, hence the flag.

- Arnaldo
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