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SubjectRe: [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@huawei.com>
>> Cc: Alexei Starovoitov <ast@plumgrid.com>
>> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>> Cc: Namhyung Kim <namhyung@kernel.org>
>> Cc: Zefan Li <lizefan@huawei.com>
>> Cc: pi3orama@163.com
>> Cc: Arnaldo Carvalho de Melo <acme@redhat.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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