Re: [PATCH] perf tools: Fix segfault in 'perf top'

[Wangnan (F)]

On 2015/9/12 0:22, Namhyung Kim wrote:
> On Fri, Sep 11, 2015 at 04:59:11AM +0000, Wang Nan wrote:
> > 'perf top' segfaults with following operation:
> >
> >   # perf top -e page-faults -p 15173 # 15173 never generate page-fault
> >
> > Then on the resulting empty interface, press right key:
> >
> >   # ./perf top -e page-faults -p 11400
> >   perf: Segmentation fault
> >   -------- backtrace --------
> >   ./perf[0x535428]
> >   /lib64/libc.so.6(+0x3545f)[0x7f0dd360745f]
> >   ./perf[0x531d46]
> >   ./perf(perf_evlist__tui_browse_hists+0x96)[0x5340d6]
> >   ./perf[0x44ba2f]
> >   /lib64/libpthread.so.0(+0x81d0)[0x7f0dd49dc1d0]
> >   /lib64/libc.so.6(clone+0x6c)[0x7f0dd36b90dc]
> >
> > The bug reside in perf_evsel__hists_browse() that, in the above circumstance
> > browser->selection can be NULL, but code after skip_annotation doesn't consider
> > it.
> >
> > This patch fix it by checing browser->selection before fetching
> > browser->selection->map and browser->selection->sym.
> I'm ok with this change, just a nitpick below..
>
>
> > Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > ---
> >   tools/perf/ui/browsers/hists.c | 8 ++++++--
> >   1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
> > index e4fd40f..b00fa92 100644
> > --- a/tools/perf/ui/browsers/hists.c
> > +++ b/tools/perf/ui/browsers/hists.c
> > @@ -2017,7 +2017,8 @@ skip_annotation:
> >   					  &options[nr_options], dso);
> >   		nr_options += add_map_opt(browser, &actions[nr_options],
> >   					  &options[nr_options],
> > -					  browser->selection->map);
> > +					  browser->selection ?
> > +					  	browser->selection->map : NULL);
> >   		nr_options += add_socket_opt(browser, &actions[nr_options],
> >   					     &options[nr_options],
> >   					     socket);
> > @@ -2030,7 +2031,10 @@ skip_annotation:
> >   			nr_options += add_script_opt(browser,
> >   						     &actions[nr_options],
> >   						     &options[nr_options],
> > -						     NULL, browser->selection->sym);
> > +						     NULL,
> > +						     browser->selection ?
> > +						     	browser->selection->sym :
> > +							NULL);
> Is this really needed?  IIUC browser->selection is not NULL if
> browser->he_selection is not NULL.  Did you see a case it's NULL?
> Also passing a NULL thread and a NULL sym is meaningless here since
> it's a duplication..

Actually I didn't see the case when browser->he_selection is not NULL but
browser->selection is NULL. I add the testing only for safety reason because
we have

        if (browser->selection == NULL)
            goto skip_annotation;

So I guess we'd better to check browser->selection in the codeblock 
leading by
skip_annotation, so if someone breaks the assumption the code still work.

But yes, we can add the checker back when the assumption *does* be broken.
Currently let's add a comment here for code readers.

Please have a look for v2 patch.

Thank you.


> Thanks,
> Namhyung
>
>
> >   		}
> >   		nr_options += add_script_opt(browser, &actions[nr_options],
> >   					     &options[nr_options], NULL, NULL);
> > --
> > 1.8.3.4


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