linux-kernel - Re: [PATCH 1/3] perf tools: Protect reading thread's namespace

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Message-ID: <20190523023636.GA196218@google.com>
Date:   Thu, 23 May 2019 11:36:38 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
        Krister Johansen <kjlx@...pleofstupid.com>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] perf tools: Protect reading thread's namespace

Hi Arnaldo,

On Wed, May 22, 2019 at 10:18:32AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, May 22, 2019 at 02:32:48PM +0900, Namhyung Kim escreveu:
> > It seems that the current code lacks holding the namespace lock in
> > thread__namespaces().  Otherwise it can see inconsistent results.
> > 
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > ---
> >  tools/perf/util/thread.c | 15 +++++++++++++--
> >  1 file changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> > index 403045a2bbea..b413ba5b9835 100644
> > --- a/tools/perf/util/thread.c
> > +++ b/tools/perf/util/thread.c
> > @@ -133,7 +133,7 @@ void thread__put(struct thread *thread)
> >  	}
> >  }
> >  
> > -struct namespaces *thread__namespaces(const struct thread *thread)
> > +static struct namespaces *__thread__namespaces(const struct thread *thread)
> >  {
> >  	if (list_empty(&thread->namespaces_list))
> >  		return NULL;
> > @@ -141,10 +141,21 @@ struct namespaces *thread__namespaces(const struct thread *thread)
> >  	return list_first_entry(&thread->namespaces_list, struct namespaces, list);
> >  }
> >  
> > +struct namespaces *thread__namespaces(const struct thread *thread)
> > +{
> > +	struct namespaces *ns;
> > +
> > +	down_read((struct rw_semaphore *)&thread->namespaces_lock);
> > +	ns = __thread__namespaces(thread);
> > +	up_read((struct rw_semaphore *)&thread->namespaces_lock);
> > +
> 
> Humm, so we need to change thread__namespaces() to remove that const
> instead of throwing it away with that cast, right?

Yes, that's possible too.  Note that thread__comm_str() has the same issue
as well.

Thanks,
Namhyung