selftests/harness: Move test child waiting logic

In order to better handle timeout failures, rearrange the child waiting
logic into a separate function. This is mostly a copy/paste with an
indentation change. To handle pid tracking, a new field is added for
the child pid. Also move the alarm() pairing into the function.
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/kselftest_harness.h

@@ -635,6 +635,7 @@
 struct __test_metadata {
 	const char *name;
 	void (*fn)(struct __test_metadata *);
+	pid_t pid;	/* pid of test when being run */
 	int termsig;
 	int passed;
 	int trigger; /* extra handler after the evaluation */
@@ -695,26 +696,14 @@ static inline int __bail(int for_realz, bool no_print, __u8 step)
 	return 0;
 }
 
-void __run_test(struct __test_metadata *t)
+void __wait_for_test(struct __test_metadata *t)
 {
-	pid_t child_pid;
 	int status;
 
-	t->passed = 1;
-	t->trigger = 0;
-	printf("[ RUN      ] %s\n", t->name);
 	alarm(t->timeout);
-	child_pid = fork();
-	if (child_pid < 0) {
-		printf("ERROR SPAWNING TEST CHILD\n");
-		t->passed = 0;
-	} else if (child_pid == 0) {
-		t->fn(t);
-		/* return the step that failed or 0 */
-		_exit(t->passed ? 0 : t->step);
-	} else {
-		/* TODO(wad) add timeout support. */
-		waitpid(child_pid, &status, 0);
+	waitpid(t->pid, &status, 0);
+	alarm(0);
+
 	if (WIFEXITED(status)) {
 		t->passed = t->termsig == -1 ? !WEXITSTATUS(status) : 0;
 		if (t->termsig != -1) {
@@ -750,9 +739,25 @@ void __run_test(struct __test_metadata *t)
 			t->name,
 			status);
 	}
+}
+
+void __run_test(struct __test_metadata *t)
+{
+	t->passed = 1;
+	t->trigger = 0;
+	printf("[ RUN      ] %s\n", t->name);
+	t->pid = fork();
+	if (t->pid < 0) {
+		printf("ERROR SPAWNING TEST CHILD\n");
+		t->passed = 0;
+	} else if (t->pid == 0) {
+		t->fn(t);
+		/* return the step that failed or 0 */
+		_exit(t->passed ? 0 : t->step);
+	} else {
+		__wait_for_test(t);
 	}
 	printf("[     %4s ] %s\n", (t->passed ? "OK" : "FAIL"), t->name);
-	alarm(0);
 }
 
 static int test_harness_run(int __attribute__((unused)) argc,