linux-kernel - RE: [PATCH] perf tools: Don't write to evsel if parser doesn't collect evsel

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Date:	Wed, 2 Sep 2015 10:31:03 +0000
From:	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
To:	"'Wangnan (F)'" <wangnan0@...wei.com>,
	"acme@...hat.com" <acme@...hat.com>
CC:	Alexei Starovoitov <ast@...mgrid.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.com>,
	"pi3orama@....com" <pi3orama@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] perf tools: Don't write to evsel if parser doesn't
 collect evsel

> From: Wangnan (F) [mailto:wangnan0@...wei.com]
> 
> Sorry, forget to CC kernel mailing list...
> 
> On 2015/9/2 14:49, Wang Nan wrote:
> > If parse_events__scanner() collects no entry, perf_evlist__last(evlist)
> > is invalid.
> >
> > Although it shouldn't happen at this point, before calling
> > perf_evlist__last(), we should ensure the list is not empty for safety
> > reason.
> >
> > There are 3 places need this checking:
> >
> >   1. Before setting cmdline_group_boundary;
> >   2. Before __perf_evlist__set_leader();
> >   3. In foreach_evsel_in_last_glob.
> >

This looks OK to me.

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Thanks!

> > Signed-off-by: Wang Nan <wangnan0@...wei.com>
> > Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> > Cc: Alexei Starovoitov <ast@...mgrid.com>
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Cc: Zefan Li <lizefan@...wei.com>
> > Cc: pi3orama@....com
> > ---
> >
> > Merge all 3 list_empty() test together into one patch.
> >
> > Add warning messages.
> >
> > Improve commit message.
> >
> > ---
> >   tools/perf/util/parse-events.c | 22 +++++++++++++++++++---
> >   1 file changed, 19 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> > index d826e6f..069848d 100644
> > --- a/tools/perf/util/parse-events.c
> > +++ b/tools/perf/util/parse-events.c
> > @@ -793,6 +793,11 @@ void parse_events__set_leader(char *name, struct list_head *list)
> >   {
> >   	struct perf_evsel *leader;
> >
> > +	if (list_empty(list)) {
> > +		__WARN_printf("WARNING: failed to set leader: empty list");
> > +		return;
> > +	}
> > +
> >   	__perf_evlist__set_leader(list);
> >   	leader = list_entry(list->next, struct perf_evsel, node);
> >   	leader->group_name = name ? strdup(name) : NULL;
> > @@ -1143,10 +1148,15 @@ 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;
> > +		} else
> > +			__WARN_printf("WARNING: event parser found nothing");
> > +
> >   		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;
> >   	}
> > @@ -1252,7 +1262,13 @@ foreach_evsel_in_last_glob(struct perf_evlist *evlist,
> >   	struct perf_evsel *last = NULL;
> >   	int err;
> >
> > -	if (evlist->nr_entries > 0)
> > +	/*
> > +	 * Don't return when list_empty, give func a chance to report
> > +	 * error when it found last == NULL.
> > +	 *
> > +	 * So no need to WARN here, let *func do this.
> > +	 */
> > +	if (!list_empty(&evlist->entries))
> >   		last = perf_evlist__last(evlist);
> >
> >   	do {
>