Re: perf list dumps core using 5.13.0.rc2

[Thomas Richter <tmricht@linux.ibm.com>]

On 5/19/21 7:18 PM, Arnaldo Carvalho de Melo wrote:
> Em Wed, May 19, 2021 at 09:27:14AM -0700, Ian Rogers escreveu:
>> On Wed, May 19, 2021 at 7:57 AM Thomas Richter <tmricht@linux.ibm.com> wrote:
>>>
>>> Using kernel 5.13.0.rc2 command perf list dumps core on my x86
>>> virtual machine:
>>>
>>> [root@f34 perf]# ./perf list
>>> Segmentation fault (core dumped)
>>> ^C
>>> [root@f34 perf]#
>>>
>>> The root case this this change in file ../include/uapi/linux/perf_event.h:
>>> enum perf_sw_ids {
>>>         PERF_COUNT_SW_CPU_CLOCK                 = 0,
>>>         ...
>>>  --->   PERF_COUNT_SW_CGROUP_SWITCHES           = 11,
>>>
>>>         PERF_COUNT_SW_MAX,                      /* non-ABI */
>>> };
>>>
>>> This change increases PERF_COUNT_SW_MAX to 12. However this
>>> change is not reflected in file util/parse-events.c where data structure
>>>
>>> struct event_symbol event_symbols_sw[PERF_COUNT_SW_MAX] = {
>>>         ....
>>> }
>>>
>>> is defined and it misses the symbol name and alias for this new software
>>> event. So when command 'perf list' is called, the call chain sequence
>>> is
>>>   cmd_list()
>>>     print_events()
>>>       print_symbol_events(event_glob, PERF_TYPE_SOFTWARE,
>>>                           event_symbols_sw, PERF_COUNT_SW_MAX, name_only);
>>>
>>> where PERF_COUNT_SW_MAX is 12 and  structure event_symbols_sw[] contains
>>> only 11 elements. This ends up with the last element of the array being
>>> all zeroes and the line:
>>>
>>>     if (!name_only && strlen(syms->alias))
>>>
>>> dumps core because syms->alias is a NULL pointer.
>>>
>>> Is this dummy event PERF_COUNT_SW_CGROUP_SWITCHES simply missing in the
>>> event_symbols_sw[] array or is there more to it (which I am missing).
>>>
>>> Thanks.
>>>
>>> PS: I can sent a patch if needed....
>>
>> I believe Namhyung's pending change will fix this:
>> https://lore.kernel.org/lkml/20210210083327.22726-3-namhyung@kernel.org/
> 
> Ok, I'll pick that one instead of the one I did, similar one.
> 
> - Arnaldo
> 

Thanks for looking into this, Namhyung's patch fixes this issue.

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
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