linux-kernel - Re: [PATCH] perf hist: fix memory leak if histogram entry is reused

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Date:   Sat, 23 Feb 2019 12:18:18 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf hist: fix memory leak if histogram entry is reused

Hi,

On Fri, Feb 22, 2019 at 1:29 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Thu, Feb 21, 2019 at 02:53:20PM +0100, Jonas Rabenstein wrote:
> > On Thu, Feb 21, 2019 at 01:39:09PM +0100, Jiri Olsa wrote:
> > > On Thu, Feb 21, 2019 at 01:23:06PM +0100, Jonas Rabenstein wrote:
> > > > In __hists__add_entry the srcline of the addr_location is duplicated
> > > > for the hist_entry. If hists__findnew_entry returns an already existing
> > > > hist_entry the srcline has to be freed again as no further reference to
> > > > that duplicated srcline would exists anymore.
> > > >
> > > > Signed-off-by: Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>
> > > > ---
> > > >  tools/perf/util/hist.c | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
> > > > index 8aad8330e392..25b8dbdbbe87 100644
> > > > --- a/tools/perf/util/hist.c
> > > > +++ b/tools/perf/util/hist.c
> > > > @@ -623,6 +623,9 @@ __hists__add_entry(struct hists *hists,
> > > >           .ops = ops,
> > > >   }, *he = hists__findnew_entry(hists, &entry, al, sample_self);
> > > >
> > > > + if (he && he->srcline != entry.srcline)
> > > > +         free(entry.srcline);
> > > > +
> > > >   if (!hists->has_callchains && he && he->callchain_size != 0)
> > > >           hists->has_callchains = true;
> > > >   return he;
> > >
> > > nice, do we have similar issue in here?
> > >
> > > jirka
> > >
> > >
> > > ---
> > > diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
> > > index 216388003dea..e65e6822c848 100644
> > > --- a/tools/perf/util/hist.c
> > > +++ b/tools/perf/util/hist.c
> > > @@ -966,7 +966,7 @@ iter_add_next_cumulative_entry(struct hist_entry_iter *iter,
> > >                     .map = al->map,
> > >                     .sym = al->sym,
> > >             },
> > > -           .srcline = al->srcline ? strdup(al->srcline) : NULL,
> > > +           .srcline = al->srcline,
> > While this shouldn't leak the memory, we may end up with an al->srcline
> > to get free afterwards while still having a reference on it within the
> > hist_entry... Also I could not find where/how the hist_entry is freed up
> > so we may get an double free if both of al and he clean the srcline.
> > Of course, with your solution we could spare the useless strdup/free if
> > we find an hist_entry (which should be the typical case for hotspots..).
> > Taking a deeper look thus should be beneficial - but I do not have the
> > time for that right now because I'm still working on the inline-symbol
> > integration which is more important for me...
>
> ok, I'll check it

I think we can defer calling strdup() to hist_entry__init().

Thanks,
Namhyung