linux-kernel - Re: [PATCH] perf: fix uninitialized variable in thread__set

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Message-ID: <20111007204521.GA7813@ghostprotocols.net>
Date:	Fri, 7 Oct 2011 17:45:21 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	dsahern@...il.com
Subject: Re: [PATCH] perf: fix uninitialized variable in thread__set_comm()

Em Fri, Oct 07, 2011 at 12:14:18PM +0200, Stephane Eranian escreveu:
> Arnaldo,
> 
> Did you also integrate this patch?
> 
> 
> On Tue, Sep 6, 2011 at 5:00 PM, Stephane Eranian <eranian@...gle.com> wrote:
> >
> > In thread__set_comm(), a command string could be freed and then
> > reused to point to a new command. Yet, the length was never reset
> > nor recomputed. This could lead to bogus column formatting.

Perhaps I'm out of coffee right now, but how can it be reused in such a
way?

I don't have a problem in doing the strlen in thread__set_comm, just
want to understand the sequence of events that lead to this
inconsistency.

- Arnaldo

> > This patch below fixes the problem by having thread__set_comm()
> > immediately compute the string length in thread->comm_len. It
> > gets rid of thread__comm_len() which is not needed anymore.
> > It was doing the lazy eval of strlen() which could cause the
> > issue.
> >
> > Signed-off-by: Stephane Eranian <eranian@...gle.com>
> > ---
> >
> > diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
> > index 677e1da..b883821 100644
> > --- a/tools/perf/util/hist.c
> > +++ b/tools/perf/util/hist.c
> > @@ -61,7 +61,7 @@ static void hists__calc_col_len(struct hists *self, struct hist_entry *h)
> >                                           unresolved_col_width);
> >        }
> >
> > -       len = thread__comm_len(h->thread);
> > +       len = h->thread->comm_len;
> >        if (hists__new_col_len(self, HISTC_COMM, len))
> >                hists__set_col_len(self, HISTC_THREAD, len + 6);
> >
> > @@ -731,7 +731,7 @@ static size_t hist_entry__fprintf_callchain(struct hist_entry *self,
> >                struct sort_entry *se = list_first_entry(&hist_entry__sort_list,
> >                                                         typeof(*se), list);
> >                left_margin = hists__col_len(hists, se->se_width_idx);
> > -               left_margin -= thread__comm_len(self->thread);
> > +               left_margin -= self->thread->comm_len;
> >        }
> >
> >        return hist_entry_callchain__fprintf(fp, self, session_total,
> > diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> > index d5d3b22..3ce2a80 100644
> > --- a/tools/perf/util/thread.c
> > +++ b/tools/perf/util/thread.c
> > @@ -35,26 +35,18 @@ int thread__set_comm(struct thread *self, const char *comm)
> >
> >        if (self->comm)
> >                free(self->comm);
> > +
> >        self->comm = strdup(comm);
> > +
> >        err = self->comm == NULL ? -ENOMEM : 0;
> >        if (!err) {
> >                self->comm_set = true;
> > +               self->comm_len = strlen(self->comm);
> >                map_groups__flush(&self->mg);
> >        }
> >        return err;
> >  }
> >
> > -int thread__comm_len(struct thread *self)
> > -{
> > -       if (!self->comm_len) {
> > -               if (!self->comm)
> > -                       return 0;
> > -               self->comm_len = strlen(self->comm);
> > -       }
> > -
> > -       return self->comm_len;
> > -}
> > -
> >  static size_t thread__fprintf(struct thread *self, FILE *fp)
> >  {
> >        return fprintf(fp, "Thread %d %s\n", self->pid, self->comm) +
> > diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
> > index e5f2401..701ea09 100644
> > --- a/tools/perf/util/thread.h
> > +++ b/tools/perf/util/thread.h
> > @@ -23,7 +23,6 @@ struct perf_session;
> >  void thread__delete(struct thread *self);
> >
> >  int thread__set_comm(struct thread *self, const char *comm);
> > -int thread__comm_len(struct thread *self);
> >  struct thread *perf_session__findnew(struct perf_session *self, pid_t pid);
> >  void thread__insert_map(struct thread *self, struct map *map);
> >  int thread__fork(struct thread *self, struct thread *parent);
> >
--
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