selftests/bpf: Reduce flakyness in timer_mim

This patch extends wait time in timer_mim. As observed in slow CI environment,
it is possible to have interrupt/preemption long enough to cause the test to
fail, almost 1 failure in 5 runs.

Signed-off-by: Yucong Sun <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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

···
 
 	/* check that timer_cb[12] are incrementing 'cnt' */
 	cnt1 = READ_ONCE(timer_skel->bss->cnt);
-	usleep(200); /* 100 times more than interval */
-	cnt2 = READ_ONCE(timer_skel->bss->cnt);
+	for (int i = 0; i < 100; i++) {
+		cnt2 = READ_ONCE(timer_skel->bss->cnt);
+		if (cnt2 != cnt1)
+			break;
+		usleep(200); /* 100 times more than interval */
+	}
 	ASSERT_GT(cnt2, cnt1, "cnt");
 
 	ASSERT_EQ(timer_skel->bss->err, 0, "err");
···
 
 	/* check that timer_cb[12] are no longer running */
 	cnt1 = READ_ONCE(timer_skel->bss->cnt);
-	usleep(200);
-	cnt2 = READ_ONCE(timer_skel->bss->cnt);
+	for (int i = 0; i < 100; i++) {
+		usleep(200); /* 100 times more than interval */
+		cnt2 = READ_ONCE(timer_skel->bss->cnt);
+		if (cnt2 == cnt1)
+			break;
+	}
 	ASSERT_EQ(cnt2, cnt1, "cnt");
 
 	return 0;