linux-kernel - Re: [PATCH 02/31] perf tools: Don't set cmdline_group

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Date:	Tue, 1 Sep 2015 18:37:40 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>
CC:	<mingo@...nel.org>, <ast@...mgrid.com>,
	<linux-kernel@...r.kernel.org>, <lizefan@...wei.com>,
	<pi3orama@....com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 02/31] perf tools: Don't set cmdline_group_boundary if
 no evsel is collected



On 2015/9/1 3:20, Arnaldo Carvalho de Melo wrote:
> Em Sat, Aug 29, 2015 at 04:21:36AM +0000, Wang Nan escreveu:
>> If parse_events__scanner() collects no entry, perf_evlist__last(evlist)
>> is invalid. Then setting of cmdline_group_boundary touches invalid.
>>
>> It could happend in currect BPF implementation. See [1]. Although it
>> can be fixed, for safety reason it whould be better to introduce this
>> check.
>>
>> Instead of checking number of entries, check data.list instead, so we
>> can add dummy evsel here.
> Event parsing fixes should have Jiri Olsa on the CC list, Jiri, is this
> ok?
>
>  From what I can see it looks Ok, my question, just from looking at this
> patch, is if it is valid to get to this point with an empty data.list,
> i.e. was it ever possible and this is a bug irrespective of eBPF?

It should not be a existing bug in perf. There are other places rely on
non-empty of the list. For example, in parse_events__set_leader(). 
Furtunately,
it won't triggered problem because we don't allow a BPF object to be 
wrapped with "{}"
lexically ("{./aaa.o}" will be interpreterd as file '{./aaa.o' and a 
extra '}').


> - Arnaldo
>   
>> [1]: http://lkml.kernel.org/n/1436445342-1402-19-git-send-email-wangnan0@huawei.com
>>
>> Signed-off-by: Wang Nan <wangnan0@...wei.com>
>> Cc: Alexei Starovoitov <ast@...mgrid.com>
>> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>> Cc: Namhyung Kim <namhyung@...nel.org>
>> Cc: Zefan Li <lizefan@...wei.com>
>> Cc: pi3orama@....com
>> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
>> Link: http://lkml.kernel.org/r/1440742821-44548-3-git-send-email-wangnan0@huawei.com
>> ---
>>   tools/perf/util/parse-events.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
>> index d826e6f..14cd7e3 100644
>> --- a/tools/perf/util/parse-events.c
>> +++ b/tools/perf/util/parse-events.c
>> @@ -1143,10 +1143,14 @@ int parse_events(struct perf_evlist *evlist, const char *str,
>>   		int entries = data.idx - evlist->nr_entries;
>>   		struct perf_evsel *last;
>>   
>> +		if (!list_empty(&data.list)) {
>> +			last = list_entry(data.list.prev,
>> +					  struct perf_evsel, node);
>> +			last->cmdline_group_boundary = true;
>> +		}
>> +
>>   		perf_evlist__splice_list_tail(evlist, &data.list, entries);
>>   		evlist->nr_groups += data.nr_groups;
>> -		last = perf_evlist__last(evlist);
>> -		last->cmdline_group_boundary = true;
>>   
>>   		return 0;
>>   	}
>> -- 
>> 2.1.0


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