linux-kernel - Re: [PATCH] perf config: fix caching and memory leak in perf_home

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Date:   Fri, 20 Aug 2021 21:58:16 +0200
From:   Riccardo Mancini <rickyman7@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Ian Rogers <irogers@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Jin Yao <yao.jin@...ux.intel.com>, Song Liu <song@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf config: fix caching and memory leak in
 perf_home_perfconfig

Hi,

On Fri, 2021-08-20 at 11:13 -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Aug 20, 2021 at 03:08:17PM +0200, Riccardo Mancini escreveu:
> > Acaict, perf_home_perfconfig is supposed to cache the result of
> > home_perfconfig, which returns the default location of perfconfig for
> > the user, given the HOME environment variable.
> > However, the current implementation calls home_perfconfig every time
> > perf_home_perfconfig is called (so no caching is actually performed),
> > replacing the previous pointer, thus also causing a memory leak.
> > 
> > This patch adds a check of whether either config or failed is set and,
> > in that case, directly returns config without calling home_perfconfig at
> > each invocation.
> > 
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > Fixes: f5f03e19ce14fc31 ("perf config: Add perf_home_perfconfig function")
> > Signed-off-by: Riccardo Mancini <rickyman7@...il.com>
> > ---
> >  tools/perf/util/config.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/tools/perf/util/config.c b/tools/perf/util/config.c
> > index 63d472b336de21d4..6ab670cdf512507e 100644
> > --- a/tools/perf/util/config.c
> > +++ b/tools/perf/util/config.c
> > @@ -581,6 +581,9 @@ const char *perf_home_perfconfig(void)
> >         static const char *config;
> >         static bool failed;
> >  
> > +       if (config || failed)
> > +               return config;
> > +
> >         config = failed ? NULL : home_perfconfig();
> 
> humm, why keep the above failed test then?

Sorry, I forgot about that, it should be removed.

> 
> >         if (!config)
> >                 failed = true;
> 
> I.e. please check this:
> 
> 
> diff --git a/tools/perf/util/config.c b/tools/perf/util/config.c
> index 63d472b336de21d4..4fb5e90d7a57ae48 100644
> --- a/tools/perf/util/config.c
> +++ b/tools/perf/util/config.c
> @@ -581,7 +581,10 @@ const char *perf_home_perfconfig(void)
>         static const char *config;
>         static bool failed;
>  
> -       config = failed ? NULL : home_perfconfig();
> +       if (failed || config)
> +               return config;
> +
> +       config = home_perfconfig();
>         if (!config)
>                 failed = true;
>  

Looks good to me.
Shall I resend it fixed?

Thanks,
Riccardo