hello驱动自动创建设备节点，不能卸载模块

各位大侠，按照书上自动创建设备节点，结果insmod hello.ko 提示已杀死。然后卸载，提示设备忙，卸载不了，请问这是怎么回事啊，程序如下

  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/cdev.h>
  #include <linux/device.h>

MODULE_LICENSE ("GPL");

int hello_major = 555;
  int hello_minor = 0;
  int number_of_devices = 1;

struct cdev cdev;
  dev_t dev = 0;

struct file_operations hello_fops = {
  .owner = THIS_MODULE
  };

static void char_reg_setup_cdev (void)
  {
  int error, devno = MKDEV (hello_major, hello_minor);
  cdev_init (&cdev, &hello_fops);
  cdev.owner = THIS_MODULE;
  cdev.ops = &hello_fops;
  error = cdev_add (&cdev, devno , 1);
  if (error)
  printk (KERN_NOTICE "Error %d adding char_reg_setup_cdev", error);

}

struct class *my_class;

static int __init hello_2_init (void)
  {
  int result;
  dev = MKDEV (hello_major, hello_minor);
  result = register_chrdev_region (dev, number_of_devices, "hello");
  if (result<0) {
  printk (KERN_WARNING "hello: can't get major number %d\n", hello_major);
  return result;
  }

 char_reg_setup_cdev ();

 /* create your own class under /sysfs */
  my_class = class_create(THIS_MODULE, "my_class");
  if(IS_ERR(my_class))
  {
  printk("Err: failed in creating class.\n");
  return -1;
  }

  /* register your own device in sysfs, and this will cause udev to create corresponding device node */
  device_create( my_class, NULL, MKDEV(hello_major, 0), "hello" "%d", 0 );

  printk (KERN_INFO "Registered character driver\n");
  return 0;
  }

static void __exit hello_2_exit (void)
  {
  dev_t devno = MKDEV (hello_major, hello_minor);

  cdev_del (&cdev);

  device_destroy(my_class, MKDEV(hello_major, 0)); //delete device node under /dev
  class_destroy(my_class); //delete class created by us

  unregister_chrdev_region (devno, number_of_devices);

  printk (KERN_INFO "char driver cleaned up\n");
  }

module_init (hello_2_init);
module_exit (hello_2_exit);

按照书上自动创建设备节点，结果insmod hello.ko 提示已杀死。然后卸载，提示设备忙，卸载不了，请问这是怎么回事啊，程序如下


你这insmod提示已经杀死什么意思，没有加载成功？
最好lsmod把内容贴出来看看