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

[Namhyung Kim <namhyung@kernel.org>]

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@huawei.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Namhyung Kim <namhyung@kernel.org>
> ---
>  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..

Thanks,
Namhyung


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