[media] v4l: Don't access media entity after is has been destroyed

Entities associated with video device nodes are unregistered in
video_unregister_device(). This destroys the entity even though it can
still be accessed through open video device nodes.

Move the media_device_unregister_entity() call from
video_unregister_device() to v4l2_device_release() to ensure that the
entity isn't unregistered until the last reference to the video device
is released.

Also remove the media_entity_get()/put() calls from v4l2-dev.c. Those
functions were designed for subdevs, to avoid a parent module from being
removed while still accessible through board code. They're not currently
needed for video device nodes, and will oops when a hotpluggable device
is disconnected during streaming, as media_entity_put() called in
v4l2_device_release() tries to access entity->parent->dev->driver which
is set to NULL when the device is disconnected.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/v4l2-dev.c

@@ -167,6 +167,12 @@ static void v4l2_device_release(struct device *cd)
 
 	mutex_unlock(&videodev_lock);
 
+#if defined(CONFIG_MEDIA_CONTROLLER)
+	if (vdev->v4l2_dev && vdev->v4l2_dev->mdev &&
+	    vdev->vfl_type != VFL_TYPE_SUBDEV)
+		media_device_unregister_entity(&vdev->entity);
+#endif
+
 	/* Release video_device and perform other
 	   cleanups as needed. */
 	vdev->release(vdev);
@@ -389,9 +395,6 @@ static int v4l2_mmap(struct file *filp, struct vm_area_struct *vm)
 static int v4l2_open(struct inode *inode, struct file *filp)
 {
 	struct video_device *vdev;
-#if defined(CONFIG_MEDIA_CONTROLLER)
-	struct media_entity *entity = NULL;
-#endif
 	int ret = 0;
 
 	/* Check if the video device is available */
@@ -405,17 +408,6 @@ static int v4l2_open(struct inode *inode, struct file *filp)
 	/* and increase the device refcount */
 	video_get(vdev);
 	mutex_unlock(&videodev_lock);
-#if defined(CONFIG_MEDIA_CONTROLLER)
-	if (vdev->v4l2_dev && vdev->v4l2_dev->mdev &&
-	    vdev->vfl_type != VFL_TYPE_SUBDEV) {
-		entity = media_entity_get(&vdev->entity);
-		if (!entity) {
-			ret = -EBUSY;
-			video_put(vdev);
-			return ret;
-		}
-	}
-#endif
 	if (vdev->fops->open) {
 		if (vdev->lock && mutex_lock_interruptible(vdev->lock)) {
 			ret = -ERESTARTSYS;
@@ -431,14 +423,8 @@ static int v4l2_open(struct inode *inode, struct file *filp)
 
 err:
 	/* decrease the refcount in case of an error */
-	if (ret) {
-#if defined(CONFIG_MEDIA_CONTROLLER)
-		if (vdev->v4l2_dev && vdev->v4l2_dev->mdev &&
-		    vdev->vfl_type != VFL_TYPE_SUBDEV)
-			media_entity_put(entity);
-#endif
+	if (ret)
 		video_put(vdev);
-	}
 	return ret;
 }
 
@@ -455,11 +441,6 @@ static int v4l2_release(struct inode *inode, struct file *filp)
 		if (vdev->lock)
 			mutex_unlock(vdev->lock);
 	}
-#if defined(CONFIG_MEDIA_CONTROLLER)
-	if (vdev->v4l2_dev && vdev->v4l2_dev->mdev &&
-	    vdev->vfl_type != VFL_TYPE_SUBDEV)
-		media_entity_put(&vdev->entity);
-#endif
 	/* decrease the refcount unconditionally since the release()
 	   return value is ignored. */
 	video_put(vdev);
@@ -754,12 +735,6 @@ void video_unregister_device(struct video_device *vdev)
 	if (!vdev || !video_is_registered(vdev))
 		return;
 
-#if defined(CONFIG_MEDIA_CONTROLLER)
-	if (vdev->v4l2_dev && vdev->v4l2_dev->mdev &&
-	    vdev->vfl_type != VFL_TYPE_SUBDEV)
-		media_device_unregister_entity(&vdev->entity);
-#endif
-
 	mutex_lock(&videodev_lock);
 	/* This must be in a critical section to prevent a race with v4l2_open.
 	 * Once this bit has been cleared video_get may never be called again.