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