[PATCH v4 07/21] perf evsel: Mark the event as supported when retrying an open

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

Opening a group with perf record on a machine with perf_event_paranoid >
1 and no CAP_PERFMON fails the first perf_event_open() with EACCES, after
which evsel__open_cpu() clears evsel->supported; evsel__fallback() then
adds exclude_kernel and record__open() retries, and the retry succeeds
with supported left false.  get_group_fd() treats unsupported events as
ungroupable, so the retry opens the group members without their leader:

  sys_perf_event_open: pid 12345 cpu 0 group_fd -1
  FAILED '.../test-record-group-sampling1' - group failure

which fails the group subtests of "perf test 82", the Perf attribute
expectations test, when it is run as a regular user, while it passes as
root or with CAP_PERFMON, where the first open doesn't fail.

commit 2cc7aa995ce9 ("perf stat: Refactor retry/skip/fatal error handling")
dropped the pos->supported = true that record__open() did after a
successful open and moved the resets into the stat code only, while
saying "When an event is tried the supported is set to true again".  Do
that in evsel__open_cpu(), which every open entry point funnels through,
so that a retry describes its own try instead of the previous failure.

Fixes: 2cc7aa995ce9ecd8 ("perf stat: Refactor retry/skip/fatal error handling")
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Assisted-by: LLM
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/evsel.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 9c5e7510f0c019c3..e61f309e93dccc7f 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -3014,6 +3014,12 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 	enum rlimit_action set_rlimit = NO_CHANGE;
 	struct perf_cpu cpu;
 
+	/*
+	 * A failed attempt being retried after evsel__fallback() would
+	 * otherwise keep group members out of their group in get_group_fd().
+	 */
+	evsel->supported = true;
+
 	if (evsel__is_retire_lat(evsel)) {
 		err = evsel__tpebs_open(evsel);
 		goto out;
-- 
2.55.0