perf stat: Propagate supported flag to follower cgroup BPF events

When using BPF counters with cgroups, follower events (for cgroups
other than the first one) are not opened. Because they are not opened,
their `supported` flag was left as `false`.

During metric calculation, `prepare_metric` checks if the event is
supported. If it is not supported (like the follower events), it
explicitly sets the value to `NAN`, which eventually causes the metric
to be reported as `nan %`.

Fix this by propagating the `supported` flag from the "leader" events
(the ones opened for the first cgroup) to the "follower" events.

Also add a validation check to `bperf_load_program` to ensure `nr_cgroups`
is not zero and the number of events is a multiple of `nr_cgroups`,
preventing a potential division-by-zero (SIGFPE) exception when
`num_events` evaluates to 0 (e.g., with a trailing comma in cgroups list).

Reported-by: Svilen Kanev <skanev@google.com>
Assisted-by: Antigravity:gemini-3-flash
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/tools/perf/util/bpf_counter_cgroup.c b/tools/perf/util/bpf_counter_cgroup.c
index 519fee3dc3d0..e1ce5aa3b957 100644
--- a/tools/perf/util/bpf_counter_cgroup.c
+++ b/tools/perf/util/bpf_counter_cgroup.c
@@ -104,6 +104,11 @@ static int bperf_load_program(struct evlist *evlist)
 
 	set_max_rlimit();
 
+	if (nr_cgroups == 0 || evlist->core.nr_entries % nr_cgroups != 0) {
+		pr_err("Invalid cgroup or event count\n");
+		return -EINVAL;
+	}
+
 	test_max_events_program_load();
 
 	skel = bperf_cgroup_bpf__open();
@@ -187,6 +192,21 @@ static int bperf_load_program(struct evlist *evlist)
 	}
 
 	/*
+	 * Propagate supported flag from leaders to followers. Follower events
+	 * are not opened, so their supported flag remains false.
+	 */
+	{
+		struct evsel *leader;
+		int num_events = evlist->core.nr_entries / nr_cgroups;
+
+		evlist__for_each_entry(evlist, evsel) {
+			leader = evlist__find_evsel(evlist, evsel->core.idx % num_events);
+			if (leader)
+				evsel->supported = leader->supported;
+		}
+	}
+
+	/*
 	 * bperf uses BPF_PROG_TEST_RUN to get accurate reading. Check
 	 * whether the kernel support it
 	 */