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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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