Messages in this thread | | | Date | Wed, 16 Mar 2022 15:08:00 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf evlist: Avoid iteration for empty evlist. |
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On Wed, Mar 16, 2022 at 12:10:49AM -0700, Ian Rogers wrote: > As seen with 'perf stat --null ..' and reported in: > https://lore.kernel.org/lkml/YjCLcpcX2peeQVCH@kernel.org/ > > Fixes: 472832d2c000 ("perf evlist: Refactor evlist__for_each_cpu()") > Signed-off-by: Ian Rogers <irogers@google.com> > --- > tools/perf/util/evlist.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c > index 8134d45e2164..a2dba9e00765 100644 > --- a/tools/perf/util/evlist.c > +++ b/tools/perf/util/evlist.c > @@ -354,7 +354,10 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin > .affinity = affinity, > }; > > - if (itr.affinity) { > + if (evlist__empty(evlist)) { > + /* Ensure the empty list doesn't iterate. */ > + itr.evlist_cpu_map_idx = itr.evlist_cpu_map_nr;
I can't see the crash anymore, but I'm bit confused with the code
if evlist is empty then itr.evsel is bogus.. and the loop code __run_perf_stat is just lucky, right?
I think we need to set itr.evsel to NULL and skip the loop in case evlist is empty
thanks, jirka
> + } else if (itr.affinity) { > itr.cpu = perf_cpu_map__cpu(evlist->core.all_cpus, 0); > affinity__set(itr.affinity, itr.cpu.cpu); > itr.cpu_map_idx = perf_cpu_map__idx(itr.evsel->core.cpus, itr.cpu); > -- > 2.35.1.723.g4982287a31-goog >
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