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 13:54:15 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	masami.hiramatsu.pt@...achi.com, acme@...hat.com,
	Alexei Starovoitov <ast@...mgrid.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.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

On Wed, Sep 02, 2015 at 02:53:58PM +0800, Wangnan (F) wrote:
> 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.
> >
> >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");

we need to unify error printing in this object ;-) with this one it's 3

__WARN_printf(...
fprintf(stderr,...
printf(...
WARN_ONCE(...

;-)


> >+
> >  		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))

why is it better than to check evlist->nr_entries?
evlist->nr_entries is equivalent to !list_empty(&evlist->entries) in here, right?


jirka
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