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 14:53:58 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	<masami.hiramatsu.pt@...achi.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>,
	"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

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");
> +
>   		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 {


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