Re: [PATCH 02/31] perf tools: Don't set cmdline_group_boundary if no evsel is collected

[Wangnan (F)]

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@xxxxxxxxxx
> >
> > Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> > Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > Cc: Zefan Li <lizefan@xxxxxxxxxx>
> > Cc: pi3orama@xxxxxxx
> > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > Link: http://lkml.kernel.org/r/1440742821-44548-3-git-send-email-wangnan0@xxxxxxxxxx
> > ---
> >   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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