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

["Wangnan (F)" <wangnan0@huawei.com>]

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@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..

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
>>