linux-kernel - Re: [PATCH v2 perf/core] perf script: fix a use after free crash.

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Message-ID: <20170103003033.GD27864@kernel.org>
Date:   Mon, 2 Jan 2017 21:30:33 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Krister Johansen <kjlx@...pleofstupid.com>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 perf/core] perf script: fix a use after free crash.

Em Mon, Jan 02, 2017 at 04:39:04PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Mon, Jan 02, 2017 at 02:36:57PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Mon, Jan 02, 2017 at 02:35:30PM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Mon, Jan 02, 2017 at 12:15:14PM -0300, Arnaldo Carvalho de Melo escreveu:
> >  {
> >         zfree(&iter->priv);
> >         iter->he = NULL;
> > +       map__zput(al->map);
> 
> What this pairs to? I was expecting that since this is called via:
> 
>    hist_entry_iter__add()
>    {
>            <SNIP>
>            err2 = iter->ops->finish_entry(iter, al);
>    }
> 
> Then it would have to match something done earlier in
> hist_entry_iter__add(), most likely by some iter->ops->() method, but I
> couldn'd find anything to that extent, can you clarify?

With the following patch it has been running all day, care to explain
why it is needed? I need to run this on valgrind or with Masami's
refcount debugger to get more clues :-\

- Arnaldo

diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 72f5c82798e9..c27bda16e9cd 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -980,7 +980,6 @@ iter_finish_cumulative_entry(struct hist_entry_iter *iter,
 {
 	zfree(&iter->priv);
 	iter->he = NULL;
-	map__zput(al->map);
 
 	return 0;
 }