selftests/pidfd: add third PIDFD_INFO_EXIT selftest

Add a selftest for PIDFD_INFO_EXIT behavior.

Link: https://lore.kernel.org/r/20250305-work-pidfs-kill_on_last_close-v3-12-c8c3d8361705@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

tools/testing/selftests/pidfd/pidfd_info_test.c

@@ -161,4 +161,20 @@ TEST_F(pidfd_info, sigkill_reaped)
 	ASSERT_EQ(WTERMSIG(info.exit_code), SIGKILL);
 }
 
+TEST_F(pidfd_info, success_exit)
+{
+	struct pidfd_info info = {
+		.mask = PIDFD_INFO_CGROUPID,
+	};
+
+	/* Process has exited but not been reaped so this must work. */
+	ASSERT_EQ(ioctl(self->child_pidfd3, PIDFD_GET_INFO, &info), 0);
+
+	info.mask = PIDFD_INFO_CGROUPID | PIDFD_INFO_EXIT;
+	ASSERT_EQ(ioctl(self->child_pidfd3, PIDFD_GET_INFO, &info), 0);
+	ASSERT_TRUE(!!(info.mask & PIDFD_INFO_CREDS));
+	/* Process has exited but not been reaped, so no PIDFD_INFO_EXIT information yet. */
+	ASSERT_FALSE(!!(info.mask & PIDFD_INFO_EXIT));
+}
+
 TEST_HARNESS_MAIN