V4L/DVB (9668): em28xx: fix a race condition with hald

Newer versions of hald tries to open it to call QUERYCAP.

Due to the lack of a proper locking, it is possible to open the device
before it finishes initialization.

This patch adds a lock to avoid this risk, and to protect the list of
em28xx devices.

While here, remove the uneeded BKL lock.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-video.c

@@ -73,6 +73,7 @@ MODULE_DESCRIPTION(DRIVER_DESC);
 MODULE_LICENSE("GPL");
 
 static LIST_HEAD(em28xx_devlist);
+static DEFINE_MUTEX(em28xx_devlist_mutex);
 
 static unsigned int card[]     = {[0 ... (EM28XX_MAXBOARDS - 1)] = UNSET };
 static unsigned int video_nr[] = {[0 ... (EM28XX_MAXBOARDS - 1)] = UNSET };
@@ -1519,7 +1520,7 @@ static int em28xx_v4l2_open(struct inode *inode, struct file *filp)
 	struct em28xx_fh *fh;
 	enum v4l2_buf_type fh_type = 0;
 
-	lock_kernel();
+	mutex_lock(&em28xx_devlist_mutex);
 	list_for_each_entry(h, &em28xx_devlist, devlist) {
 		if (h->vdev->minor == minor) {
 			dev  = h;
@@ -1535,10 +1536,11 @@ static int em28xx_v4l2_open(struct inode *inode, struct file *filp)
 			dev   = h;
 		}
 	}
-	if (NULL == dev) {
-		unlock_kernel();
+	mutex_unlock(&em28xx_devlist_mutex);
+	if (NULL == dev)
 		return -ENODEV;
-	}
+
+	mutex_lock(&dev->lock);
 
 	em28xx_videodbg("open minor=%d type=%s users=%d\n",
 				minor, v4l2_type_names[fh_type], dev->users);
@@ -1547,10 +1549,9 @@ static int em28xx_v4l2_open(struct inode *inode, struct file *filp)
 	fh = kzalloc(sizeof(struct em28xx_fh), GFP_KERNEL);
 	if (!fh) {
 		em28xx_errdev("em28xx-video.c: Out of memory?!\n");
-		unlock_kernel();
+		mutex_unlock(&dev->lock);
 		return -ENOMEM;
 	}
-	mutex_lock(&dev->lock);
 	fh->dev = dev;
 	fh->radio = radio;
 	fh->type = fh_type;
@@ -1584,7 +1585,6 @@ static int em28xx_v4l2_open(struct inode *inode, struct file *filp)
 			sizeof(struct em28xx_buffer), fh);
 
 	mutex_unlock(&dev->lock);
-	unlock_kernel();
 
 	return errCode;
 }
@@ -1871,6 +1871,7 @@ int em28xx_register_extension(struct em28xx_ops *ops)
 {
 	struct em28xx *dev = NULL;
 
+	mutex_lock(&em28xx_devlist_mutex);
 	mutex_lock(&em28xx_extension_devlist_lock);
 	list_add_tail(&ops->next, &em28xx_extension_devlist);
 	list_for_each_entry(dev, &em28xx_devlist, devlist) {
@@ -1879,6 +1880,7 @@ int em28xx_register_extension(struct em28xx_ops *ops)
 	}
 	printk(KERN_INFO "Em28xx: Initialized (%s) extension\n", ops->name);
 	mutex_unlock(&em28xx_extension_devlist_lock);
+	mutex_unlock(&em28xx_devlist_mutex);
 	return 0;
 }
 EXPORT_SYMBOL(em28xx_register_extension);
@@ -1887,6 +1889,7 @@ void em28xx_unregister_extension(struct em28xx_ops *ops)
 {
 	struct em28xx *dev = NULL;
 
+	mutex_lock(&em28xx_devlist_mutex);
 	list_for_each_entry(dev, &em28xx_devlist, devlist) {
 		if (dev)
 			ops->fini(dev);
@@ -1896,6 +1899,7 @@ void em28xx_unregister_extension(struct em28xx_ops *ops)
 	printk(KERN_INFO "Em28xx: Removed (%s) extension\n", ops->name);
 	list_del(&ops->next);
 	mutex_unlock(&em28xx_extension_devlist_lock);
+	mutex_unlock(&em28xx_devlist_mutex);
 }
 EXPORT_SYMBOL(em28xx_unregister_extension);
 
@@ -1921,6 +1925,60 @@ static struct video_device *em28xx_vdev_init(struct em28xx *dev,
 }
 
 
+static int register_analog_devices(struct em28xx *dev)
+{
+	int ret;
+
+	/* allocate and fill video video_device struct */
+	dev->vdev = em28xx_vdev_init(dev, &em28xx_video_template, "video");
+	if (!dev->vdev) {
+		em28xx_errdev("cannot allocate video_device.\n");
+		return -ENODEV;
+	}
+
+	/* register v4l2 video video_device */
+	ret = video_register_device(dev->vdev, VFL_TYPE_GRABBER,
+				       video_nr[dev->devno]);
+	if (ret) {
+		em28xx_errdev("unable to register video device (error=%i).\n",
+			      ret);
+		return ret;
+	}
+
+	/* Allocate and fill vbi video_device struct */
+	dev->vbi_dev = em28xx_vdev_init(dev, &em28xx_video_template, "vbi");
+
+	/* register v4l2 vbi video_device */
+	ret = video_register_device(dev->vbi_dev, VFL_TYPE_VBI,
+					vbi_nr[dev->devno]);
+	if (ret < 0) {
+		em28xx_errdev("unable to register vbi device\n");
+		return ret;
+	}
+
+	if (em28xx_boards[dev->model].radio.type == EM28XX_RADIO) {
+		dev->radio_dev = em28xx_vdev_init(dev, &em28xx_radio_template, "radio");
+		if (!dev->radio_dev) {
+			em28xx_errdev("cannot allocate video_device.\n");
+			return -ENODEV;
+		}
+		ret = video_register_device(dev->radio_dev, VFL_TYPE_RADIO,
+					    radio_nr[dev->devno]);
+		if (ret < 0) {
+			em28xx_errdev("can't register radio device\n");
+			return ret;
+		}
+		em28xx_info("Registered radio device as /dev/radio%d\n",
+			    dev->radio_dev->num);
+	}
+
+	em28xx_info("V4L2 device registered as /dev/video%d and /dev/vbi%d\n",
+				dev->vdev->num, dev->vbi_dev->num);
+
+	return 0;
+}
+
+
 /*
  * em28xx_init_dev()
  * allocates and inits the device structs, registers i2c bus and v4l device
@@ -2000,50 +2058,6 @@ static int em28xx_init_dev(struct em28xx **devhandle, struct usb_device *udev,
 		return errCode;
 	}
 
-	list_add_tail(&dev->devlist, &em28xx_devlist);
-
-	/* allocate and fill video video_device struct */
-	dev->vdev = em28xx_vdev_init(dev, &em28xx_video_template, "video");
-	if (NULL == dev->vdev) {
-		em28xx_errdev("cannot allocate video_device.\n");
-		goto fail_unreg;
-	}
-
-	/* register v4l2 video video_device */
-	retval = video_register_device(dev->vdev, VFL_TYPE_GRABBER,
-				       video_nr[dev->devno]);
-	if (retval) {
-		em28xx_errdev("unable to register video device (error=%i).\n",
-			      retval);
-		goto fail_unreg;
-	}
-
-	/* Allocate and fill vbi video_device struct */
-	dev->vbi_dev = em28xx_vdev_init(dev, &em28xx_video_template, "vbi");
-	/* register v4l2 vbi video_device */
-	if (video_register_device(dev->vbi_dev, VFL_TYPE_VBI,
-					vbi_nr[dev->devno]) < 0) {
-		em28xx_errdev("unable to register vbi device\n");
-		retval = -ENODEV;
-		goto fail_unreg;
-	}
-
-	if (em28xx_boards[dev->model].radio.type == EM28XX_RADIO) {
-		dev->radio_dev = em28xx_vdev_init(dev, &em28xx_radio_template, "radio");
-		if (NULL == dev->radio_dev) {
-			em28xx_errdev("cannot allocate video_device.\n");
-			goto fail_unreg;
-		}
-		retval = video_register_device(dev->radio_dev, VFL_TYPE_RADIO,
-					    radio_nr[dev->devno]);
-		if (retval < 0) {
-			em28xx_errdev("can't register radio device\n");
-			goto fail_unreg;
-		}
-		em28xx_info("Registered radio device as /dev/radio%d\n",
-			    dev->radio_dev->num);
-	}
-
 	/* init video dma queues */
 	INIT_LIST_HEAD(&dev->vidq.active);
 	INIT_LIST_HEAD(&dev->vidq.queued);
@@ -2070,8 +2084,14 @@ static int em28xx_init_dev(struct em28xx **devhandle, struct usb_device *udev,
 
 	video_mux(dev, 0);
 
-	em28xx_info("V4L2 device registered as /dev/video%d and /dev/vbi%d\n",
-				dev->vdev->num, dev->vbi_dev->num);
+	mutex_lock(&em28xx_devlist_mutex);
+	list_add_tail(&dev->devlist, &em28xx_devlist);
+	retval = register_analog_devices(dev);
+	if (retval < 0) {
+		em28xx_release_resources(dev);
+		mutex_unlock(&em28xx_devlist_mutex);
+		goto fail_reg_devices;
+	}
 
 	mutex_lock(&em28xx_extension_devlist_lock);
 	if (!list_empty(&em28xx_extension_devlist)) {
@@ -2081,11 +2101,13 @@ static int em28xx_init_dev(struct em28xx **devhandle, struct usb_device *udev,
 		}
 	}
 	mutex_unlock(&em28xx_extension_devlist_lock);
+	mutex_unlock(&em28xx_devlist_mutex);
 
 	return 0;
 
 fail_unreg:
 	em28xx_release_resources(dev);
+fail_reg_devices:
 	mutex_unlock(&dev->lock);
 	return retval;
 }