selftests/bpf: fix flaky bpf_cookie selftest

Problem:
bpf_cookie selftest fails if it runs after task_work selftest:
perf_event_open fails with errno=EINVAL.
EINVAL indicates incorrect/invalid input argument, which in case of
bpf_cookie can only point to sample_freq attribute.

Possible root cause:
When running task_work test, we can see that perf subsystem lowers
kernel.perf_event_max_sample_rate which probably is the side-effect of
the test that make bpf_cookie fail.

Solution:
Set perf_event_open sampling rate attribute for bpf_cookie the same as
task_work - this is the most reliable solution for this, changing
task_work sampling rate resulted in task_work test becoming flaky.

Signed-off-by: Mykyta Yatsenko <[email protected]>

Author: mykyta5

tools/testing/selftests/bpf/prog_tests/bpf_cookie.c

@@ -450,8 +450,7 @@ static void pe_subtest(struct test_bpf_cookie *skel)
 	attr.size = sizeof(attr);
 	attr.type = PERF_TYPE_SOFTWARE;
 	attr.config = PERF_COUNT_SW_CPU_CLOCK;
-	attr.freq = 1;
-	attr.sample_freq = 10000;
+	attr.sample_period = 100000;
 	pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
 	if (!ASSERT_GE(pfd, 0, "perf_fd"))
 		goto cleanup;