selftests/bpf: Fix flaky bpf_cookie selftest

bpf_cookie can fail on perf_event_open(), when it runs after the task_work
selftest. The task_work test causes perf to lower
sysctl_perf_event_sample_rate, and bpf_cookie uses sample_freq,
which is validated against that sysctl. As a result,
perf_event_open() rejects the attr if the (now tighter) limit is
exceeded.

>From perf_event_open():
if (attr.freq) {
	if (attr.sample_freq > sysctl_perf_event_sample_rate)
		return -EINVAL;
} else {
	if (attr.sample_period & (1ULL << 63))
		return -EINVAL;
}

Switch bpf_cookie to use sample_period, which is not checked against
sysctl_perf_event_sample_rate.

Signed-off-by: Mykyta Yatsenko <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[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;