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Subject: Re: [PATCH v6] media: em28xx: Fix race condition between open and
 init function
To:     Hans Verkuil <hverkuil-cisco@xs4all.nl>, mchehab@kernel.org,
        skhan@linuxfoundation.org, hdanton@sina.com
Cc:     linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        kernel test robot <lkp@intel.com>,
        syzbot+b2391895514ed9ef4a8e@syzkaller.appspotmail.com
References: <20210614195230.28691-1-igormtorrente@gmail.com>
 <0763c5bc-b7f7-b0da-e48c-d61c61fc5499@xs4all.nl>
From:   Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
Message-ID: <463f2e15-179c-7047-9803-e7103e7c2d9a@gmail.com>
Date:   Mon, 13 Sep 2021 12:11:54 -0300
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Hi Hans,

On 9/13/21 6:35 AM, Hans Verkuil wrote:
> On 14/06/2021 21:52, Igor Matheus Andrade Torrente wrote:
>> Fixes a race condition - for lack of a more precise term - between
>> em28xx_v4l2_open and em28xx_v4l2_init, by managing the em28xx_v4l2
>> and v4l2_dev life-time with the v4l2_dev->release() callback.
>>
>> The race happens when a thread[1] - containing the em28xx_v4l2_init()
>> code - calls the v4l2_mc_create_media_graph(), and it return a error,
>> if a thread[2] - running v4l2_open() - pass the verification point
>> and reaches the em28xx_v4l2_open() before the thread[1] finishes
>> the deregistration of v4l2 subsystem, the thread[1] will free all
>> resources before the em28xx_v4l2_open() can process their things,
>> because the em28xx_v4l2_init() has the dev->lock. And all this lead
>> the thread[2] to cause a user-after-free.
>>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Reported-and-tested-by: syzbot+b2391895514ed9ef4a8e@syzkaller.appspotmail.com
>> Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
>> ---
>>
>> V2: Add v4l2_i2c_new_subdev null check
>>      Deal with v4l2 subdevs dependencies
>>
>> V3: Fix link error when compiled as a module
>>
>> V4: Remove duplicated v4l2_device_disconnect
>>      in the em28xx_v4l2_fini
>>
>> V5: Move all the v4l2 resources management
>>      to the v4l2_dev->release() callback.
>>
>> V6: Address some Hans comments regarding
>>      video_unregister_device and struct v4l2_device
>>      inside the struct v4l2_device.
>>
>>      I'm sending this v6 that way but I'm totally open
>>      to the Hilt approach, if it is a more desirable
>>      way to fix this issue.
>> ---
>>   drivers/media/usb/em28xx/em28xx-cards.c |   3 +-
>>   drivers/media/usb/em28xx/em28xx-video.c | 232 +++++++++++++++---------
>>   drivers/media/usb/em28xx/em28xx.h       |   1 -
>>   3 files changed, 151 insertions(+), 85 deletions(-)
>>
>> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
>> index ba9292e2a587..6e67cf0a1e04 100644
>> --- a/drivers/media/usb/em28xx/em28xx-cards.c
>> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
>> @@ -4120,7 +4120,6 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
>>   	struct em28xx *dev;
>>   
>>   	dev = usb_get_intfdata(intf);
>> -	usb_set_intfdata(intf, NULL);
>>   
>>   	if (!dev)
>>   		return;
>> @@ -4148,6 +4147,8 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
>>   		dev->dev_next = NULL;
>>   	}
>>   	kref_put(&dev->ref, em28xx_free_device);
>> +
>> +	usb_set_intfdata(intf, NULL);
>>   }
>>   
>>   static int em28xx_usb_suspend(struct usb_interface *intf,
>> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
>> index 6b84c3413e83..abf9b325eae4 100644
>> --- a/drivers/media/usb/em28xx/em28xx-video.c
>> +++ b/drivers/media/usb/em28xx/em28xx-video.c
>> @@ -1897,7 +1897,7 @@ static int vidioc_g_chip_info(struct file *file, void *priv,
>>   		strscpy(chip->name, "ac97", sizeof(chip->name));
>>   	else
>>   		strscpy(chip->name,
>> -			dev->v4l2->v4l2_dev.name, sizeof(chip->name));
>> +			dev->v4l2->v4l2_dev->name, sizeof(chip->name));
>>   	return 0;
>>   }
>>   
>> @@ -2113,21 +2113,6 @@ static int radio_s_tuner(struct file *file, void *priv,
>>   	return 0;
>>   }
>>   
>> -/*
>> - * em28xx_free_v4l2() - Free struct em28xx_v4l2
>> - *
>> - * @ref: struct kref for struct em28xx_v4l2
>> - *
>> - * Called when all users of struct em28xx_v4l2 are gone
>> - */
>> -static void em28xx_free_v4l2(struct kref *ref)
>> -{
>> -	struct em28xx_v4l2 *v4l2 = container_of(ref, struct em28xx_v4l2, ref);
>> -
>> -	v4l2->dev->v4l2 = NULL;
>> -	kfree(v4l2);
>> -}
>> -
>>   /*
>>    * em28xx_v4l2_open()
>>    * inits the device and starts isoc transfer
>> @@ -2153,12 +2138,21 @@ static int em28xx_v4l2_open(struct file *filp)
>>   		return -EINVAL;
>>   	}
>>   
>> +	/* To prevent the case when the v4l2_device_put() has already being called,
>> +	 * the ref is now 0, we call a v4l2_device_get, and end up accessing freed
>> +	 * resources. Or straigth accessing a freed v4l2.
>> +	 */
>> +	if (!v4l2 || !kref_get_unless_zero(&v4l2->v4l2_dev.ref))
>> +		return -ENODEV;
>> +
> 
> This should not be needed: once the video devices are unregistered, it is no longer
> possible to open the video device. So this can't happen.
If a thread[1] with the `open` syscall pass verification point at 
v4l2_open() before the deregistration in the `em28xx_v4l2_fini`.

And If for some reason (e.g page fault) the thread[1] get stuck and 
can't get the `dev->lock` before the thread[2](which is in 
`em28xx_v4l2_dev_release`).*

The thread[1] will end up accessing freed resources.

Thread[1]                                                     |
Open()                                                        |
                                                               | Time
Thread[1]                  Thread[2]                          |
if(vdev==NULL...           em28xx_v4l2_fini(em28xx_v4l2_fini) |
                                                               ▽
Thread[1]                  Thread[2]
em28xx_v4l2_open(...)      b2_video_unregister_device(...)

Thread[1]                  Thread[2]
PAGE-FAULT                 v4l2_device_put(&v4l2->v4l2_dev)

Thread[1]                  Thread[2]
PAGE-FAULT                 if (refcount_dec_and_test(...))

Thread[1]                  Thread[2]
PAGE-FAULT                 em28xx_v4l2_dev_release(...)

Thread[1]                  Thread[2]
PAGE-FAULT                 mutex_lock(&dev->lock);

Thread[1]                  Thread[2]
mutex_lock_interruptible() em28xx_v4l2_dev_unregistr(dev);

Thread[1]                  Thread[2]
mutex_lock_interruptible() mutex_unlock(&dev->lock)0

Thread[1]                  Thread[2]
access freed resources     kref_put(&dev->ref, em28xx_free_device)

The case above is possible, isn't it?

> 
>>   	em28xx_videodbg("open dev=%s type=%s users=%d\n",
>>   			video_device_node_name(vdev), v4l2_type_names[fh_type],
>>   			v4l2->users);
>>   
>> -	if (mutex_lock_interruptible(&dev->lock))
>> +	if (mutex_lock_interruptible(&dev->lock)) {
>> +		v4l2_device_put(&v4l2->v4l2_dev);
> 
> So this is also not needed...
> 
>>   		return -ERESTARTSYS;
>> +	}
>>   
>>   	ret = v4l2_fh_open(filp);
>>   	if (ret) {
>> @@ -2166,6 +2160,7 @@ static int em28xx_v4l2_open(struct file *filp)
>>   			"%s: v4l2_fh_open() returned error %d\n",
>>   		       __func__, ret);
>>   		mutex_unlock(&dev->lock);
>> +		v4l2_device_put(&v4l2->v4l2_dev);
> 
> ...and neither is this.
> 
>>   		return ret;
>>   	}
>>   
>> @@ -2187,8 +2182,6 @@ static int em28xx_v4l2_open(struct file *filp)
>>   		v4l2_device_call_all(&v4l2->v4l2_dev, 0, tuner, s_radio);
>>   	}
>>   
>> -	kref_get(&dev->ref);
>> -	kref_get(&v4l2->ref);
>>   	v4l2->users++;
>>   
>>   	mutex_unlock(&dev->lock);
>> @@ -2222,36 +2215,30 @@ static int em28xx_v4l2_fini(struct em28xx *dev)
>>   
>>   	mutex_lock(&dev->lock);
>>   
>> -	v4l2_device_disconnect(&v4l2->v4l2_dev);
>> -
>>   	em28xx_uninit_usb_xfer(dev, EM28XX_ANALOG_MODE);
>>   
>> -	em28xx_v4l2_media_release(dev);
>> -
>>   	if (video_is_registered(&v4l2->radio_dev)) {
>> -		dev_info(&dev->intf->dev, "V4L2 device %s deregistered\n",
>> +		dev_info(&dev->intf->dev,
>> +			 "V4L2 device %s deregistered\n",
>>   			 video_device_node_name(&v4l2->radio_dev));
>> -		video_unregister_device(&v4l2->radio_dev);
>> +		vb2_video_unregister_device(&v4l2->radio_dev);
>>   	}
>>   	if (video_is_registered(&v4l2->vbi_dev)) {
>> -		dev_info(&dev->intf->dev, "V4L2 device %s deregistered\n",
>> +		dev_info(&dev->intf->dev,
>> +			 "V4L2 device %s deregistered\n",
>>   			 video_device_node_name(&v4l2->vbi_dev));
>> -		video_unregister_device(&v4l2->vbi_dev);
>> +		vb2_video_unregister_device(&v4l2->vbi_dev);
>>   	}
>>   	if (video_is_registered(&v4l2->vdev)) {
>> -		dev_info(&dev->intf->dev, "V4L2 device %s deregistered\n",
>> +		dev_info(&dev->intf->dev,
>> +			 "V4L2 device %s deregistered\n",
>>   			 video_device_node_name(&v4l2->vdev));
>> -		video_unregister_device(&v4l2->vdev);
>> +		vb2_video_unregister_device(&v4l2->vdev);
>>   	}
>>   
>> -	v4l2_ctrl_handler_free(&v4l2->ctrl_handler);
>> -	v4l2_device_unregister(&v4l2->v4l2_dev);
>> -
>> -	kref_put(&v4l2->ref, em28xx_free_v4l2);
>> -
>>   	mutex_unlock(&dev->lock);
>>   
>> -	kref_put(&dev->ref, em28xx_free_device);
>> +	v4l2_device_put(&v4l2->v4l2_dev);
>>   
>>   	return 0;
>>   }
>> @@ -2323,9 +2310,8 @@ static int em28xx_v4l2_close(struct file *filp)
>>   
>>   exit:
>>   	v4l2->users--;
>> -	kref_put(&v4l2->ref, em28xx_free_v4l2);
>>   	mutex_unlock(&dev->lock);
>> -	kref_put(&dev->ref, em28xx_free_device);
>> +	v4l2_device_put(&v4l2->v4l2_dev);
> 
> ...and neither is this v4l2_device_put.
> 
>>   
>>   	return 0;
>>   }
>> @@ -2517,6 +2503,28 @@ static void em28xx_tuner_setup(struct em28xx *dev, unsigned short tuner_addr)
>>   	v4l2_device_call_all(v4l2_dev, 0, tuner, s_frequency, &f);
>>   }
>>   
>> +static void em28xx_v4l2_dev_unregister(struct em28xx *dev)
>> +{
>> +	struct em28xx_v4l2 *v4l2 = dev->v4l2;
>> +
>> +	v4l2_device_unregister(&v4l2->v4l2_dev);
>> +	em28xx_v4l2_media_release(dev);
>> +	v4l2_ctrl_handler_free(&v4l2->ctrl_handler);
>> +}
>> +
>> +static void em28xx_v4l2_dev_release(struct v4l2_device *v4l2_dev)
>> +{
>> +	struct em28xx *dev = v4l2_dev->dev->driver_data;
>> +
>> +	mutex_lock(&dev->lock);
>> +	em28xx_v4l2_dev_unregister(dev);
>> +	kfree(dev->v4l2);
>> +	dev->v4l2 = NULL;
>> +	mutex_unlock(&dev->lock);
>> +
>> +	kref_put(&dev->ref, em28xx_free_device);
>> +}
>> +
>>   static int em28xx_v4l2_init(struct em28xx *dev)
>>   {
>>   	u8 val;
>> @@ -2524,6 +2532,7 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>   	unsigned int maxw;
>>   	struct v4l2_ctrl_handler *hdl;
>>   	struct em28xx_v4l2 *v4l2;
>> +	struct v4l2_subdev *sd;
>>   
>>   	if (dev->is_audio_only) {
>>   		/* Shouldn't initialize IR for this interface */
>> @@ -2541,12 +2550,13 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>   
>>   	v4l2 = kzalloc(sizeof(*v4l2), GFP_KERNEL);
>>   	if (!v4l2) {
>> -		mutex_unlock(&dev->lock);
>> -		return -ENOMEM;
>> +		ret = -ENOMEM;
>> +		goto err;
>>   	}
>> -	kref_init(&v4l2->ref);
>> +
>>   	v4l2->dev = dev;
>>   	dev->v4l2 = v4l2;
>> +	v4l2->v4l2_dev.release = em28xx_v4l2_dev_release;
>>   
>>   #ifdef CONFIG_MEDIA_CONTROLLER
>>   	v4l2->v4l2_dev.mdev = dev->media_dev;
>> @@ -2555,7 +2565,7 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>   	if (ret < 0) {
>>   		dev_err(&dev->intf->dev,
>>   			"Call to v4l2_device_register() failed!\n");
>> -		goto err;
>> +		goto free_v4l2;
>>   	}
>>   
>>   	hdl = &v4l2->ctrl_handler;
>> @@ -2574,25 +2584,53 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>   
>>   	/* request some modules */
>>   
>> -	if (dev->has_msp34xx)
>> -		v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> -				    &dev->i2c_adap[dev->def_i2c_bus],
>> -				    "msp3400", 0, msp3400_addrs);
>> +	if (dev->has_msp34xx) {
>> +		sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> +					 &dev->i2c_adap[dev->def_i2c_bus],
>> +					 "msp3400", 0, msp3400_addrs);
>> +		if (!sd) {
>> +			dev_err(&dev->intf->dev,
>> +				"Error while registering 'msp34xx' v4l2 subdevice!\n");
>> +			ret = -EINVAL;
>> +			goto unregister_dev;
>> +		}
>> +	}
>>   
>> -	if (dev->board.decoder == EM28XX_SAA711X)
>> -		v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> -				    &dev->i2c_adap[dev->def_i2c_bus],
>> -				    "saa7115_auto", 0, saa711x_addrs);
>> +	if (dev->board.decoder == EM28XX_SAA711X) {
>> +		sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> +					 &dev->i2c_adap[dev->def_i2c_bus],
>> +					 "saa7115_auto", 0, saa711x_addrs);
>> +		if (!sd) {
>> +			dev_err(&dev->intf->dev,
>> +				"Error while registering 'EM28XX_SAA711X' v4l2 subdevice!\n");
>> +			ret = -EINVAL;
>> +			goto unregister_dev;
>> +		}
>> +	}
>>   
>> -	if (dev->board.decoder == EM28XX_TVP5150)
>> -		v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> -				    &dev->i2c_adap[dev->def_i2c_bus],
>> -				    "tvp5150", 0, tvp5150_addrs);
>> +	if (dev->board.decoder == EM28XX_TVP5150) {
>> +		sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> +					 &dev->i2c_adap[dev->def_i2c_bus],
>> +					 "tvp5150", 0, tvp5150_addrs);
>> +		if (!sd) {
>> +			dev_err(&dev->intf->dev,
>> +				"Error while registering 'EM28XX_TVP5150' v4l2 subdevice!\n");
>> +			ret = -EINVAL;
>> +			goto unregister_dev;
>> +		}
>> +	}
>>   
>> -	if (dev->board.adecoder == EM28XX_TVAUDIO)
>> -		v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> -				    &dev->i2c_adap[dev->def_i2c_bus],
>> -				    "tvaudio", dev->board.tvaudio_addr, NULL);
>> +	if (dev->board.adecoder == EM28XX_TVAUDIO) {
>> +		sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> +					 &dev->i2c_adap[dev->def_i2c_bus],
>> +					 "tvaudio", dev->board.tvaudio_addr, NULL);
>> +		if (!sd) {
>> +			dev_err(&dev->intf->dev,
>> +				"Error while registering 'EM28XX_TVAUDIO' v4l2 subdevice!\n");
>> +			ret = -EINVAL;
>> +			goto unregister_dev;
>> +		}
>> +	}
>>   
>>   	/* Initialize tuner and camera */
>>   
>> @@ -2600,33 +2638,63 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>   		unsigned short tuner_addr = dev->board.tuner_addr;
>>   		int has_demod = (dev->board.tda9887_conf & TDA9887_PRESENT);
>>   
>> -		if (dev->board.radio.type)
>> -			v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> -					    &dev->i2c_adap[dev->def_i2c_bus],
>> -					    "tuner", dev->board.radio_addr,
>> -					    NULL);
>> -
>> -		if (has_demod)
>> -			v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> -					    &dev->i2c_adap[dev->def_i2c_bus],
>> -					    "tuner", 0,
>> -					    v4l2_i2c_tuner_addrs(ADDRS_DEMOD));
>> +		if (dev->board.radio.type) {
>> +			sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> +						 &dev->i2c_adap[dev->def_i2c_bus],
>> +						 "tuner", dev->board.radio_addr,
>> +						 NULL);
>> +			if (!sd) {
>> +				dev_err(&dev->intf->dev,
>> +					"Error while registering '%s' v4l2 subdevice!\n",
>> +					 dev->board.name);
>> +				ret = -EINVAL;
>> +				goto unregister_dev;
>> +			}
>> +		}
>> +
>> +		if (has_demod) {
>> +			sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> +						 &dev->i2c_adap[dev->def_i2c_bus],
>> +						 "tuner", 0,
>> +						 v4l2_i2c_tuner_addrs(ADDRS_DEMOD));
>> +			if (!sd) {
>> +				dev_err(&dev->intf->dev,
>> +					"Error while registering '%s' v4l2 subdevice!\n",
>> +					 dev->i2c_adap[dev->def_i2c_bus].name);
>> +				ret = -EINVAL;
>> +				goto unregister_dev;
>> +			}
>> +		}
>> +
>>   		if (tuner_addr == 0) {
>>   			enum v4l2_i2c_tuner_type type =
>>   				has_demod ? ADDRS_TV_WITH_DEMOD : ADDRS_TV;
>> -			struct v4l2_subdev *sd;
>>   
>>   			sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>>   						 &dev->i2c_adap[dev->def_i2c_bus],
>>   						 "tuner", 0,
>>   						 v4l2_i2c_tuner_addrs(type));
>> -
>> -			if (sd)
>> +			if (sd) {
>>   				tuner_addr = v4l2_i2c_subdev_addr(sd);
>> +			} else {
>> +				dev_err(&dev->intf->dev,
>> +					"Error while registering '%s' v4l2 subdevice!\n",
>> +					 dev->i2c_adap[dev->def_i2c_bus].name);
>> +				ret = -EINVAL;
>> +				goto unregister_dev;
>> +			}
>> +
>>   		} else {
>> -			v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> -					    &dev->i2c_adap[dev->def_i2c_bus],
>> -					    "tuner", tuner_addr, NULL);
>> +			sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
>> +						 &dev->i2c_adap[dev->def_i2c_bus],
>> +						 "tuner", tuner_addr, NULL);
>> +			if (!sd) {
>> +				dev_err(&dev->intf->dev,
>> +					"Error while registering '%s' v4l2 subdevice!\n",
>> +					 dev->i2c_adap[dev->def_i2c_bus].name);
>> +				ret = -EINVAL;
>> +				goto unregister_dev;
>> +			}
>>   		}
>>   
>>   		em28xx_tuner_setup(dev, tuner_addr);
>> @@ -2755,7 +2823,6 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>   	if (ret)
>>   		goto unregister_dev;
>>   
>> -	/* allocate and fill video video_device struct */
>>   	em28xx_vdev_init(dev, &v4l2->vdev, &em28xx_video_template, "video");
>>   	mutex_init(&v4l2->vb_queue_lock);
>>   	mutex_init(&v4l2->vb_vbi_queue_lock);
>> @@ -2768,7 +2835,6 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>   	if (dev->tuner_type != TUNER_ABSENT)
>>   		v4l2->vdev.device_caps |= V4L2_CAP_TUNER;
>>   
>> -
>>   	/* disable inapplicable ioctls */
>>   	if (dev->is_webcam) {
>>   		v4l2_disable_ioctl(&v4l2->vdev, VIDIOC_QUERYSTD);
>> @@ -2889,26 +2955,26 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>   		dev_info(&dev->intf->dev,
>>   			 "V4L2 device %s deregistered\n",
>>   			 video_device_node_name(&v4l2->radio_dev));
>> -		video_unregister_device(&v4l2->radio_dev);
>> +		vb2_video_unregister_device(&v4l2->radio_dev);
>>   	}
>>   	if (video_is_registered(&v4l2->vbi_dev)) {
>>   		dev_info(&dev->intf->dev,
>>   			 "V4L2 device %s deregistered\n",
>>   			 video_device_node_name(&v4l2->vbi_dev));
>> -		video_unregister_device(&v4l2->vbi_dev);
>> +		vb2_video_unregister_device(&v4l2->vbi_dev);
>>   	}
>>   	if (video_is_registered(&v4l2->vdev)) {
>>   		dev_info(&dev->intf->dev,
>>   			 "V4L2 device %s deregistered\n",
>>   			 video_device_node_name(&v4l2->vdev));
>> -		video_unregister_device(&v4l2->vdev);
>> +		vb2_video_unregister_device(&v4l2->vdev);
>>   	}
>>   
>> -	v4l2_ctrl_handler_free(&v4l2->ctrl_handler);
>> -	v4l2_device_unregister(&v4l2->v4l2_dev);
>> -err:
>> +	em28xx_v4l2_dev_unregister(dev);
>> +free_v4l2:
>> +	kfree(v4l2);
>>   	dev->v4l2 = NULL;
>> -	kref_put(&v4l2->ref, em28xx_free_v4l2);
>> +err:
>>   	mutex_unlock(&dev->lock);
>>   	return ret;
>>   }
>> diff --git a/drivers/media/usb/em28xx/em28xx.h b/drivers/media/usb/em28xx/em28xx.h
>> index ab167cd1f400..666b7eff55f4 100644
>> --- a/drivers/media/usb/em28xx/em28xx.h
>> +++ b/drivers/media/usb/em28xx/em28xx.h
>> @@ -549,7 +549,6 @@ struct em28xx_eeprom {
>>   #define EM28XX_RESOURCE_VBI   0x02
>>   
>>   struct em28xx_v4l2 {
>> -	struct kref ref;
>>   	struct em28xx *dev;
>>   
>>   	struct v4l2_device v4l2_dev;
>>
> 
> With the suggested changes it should be ready (pending testing on my side).
> 
> Regards,
> 
> 	Hans
>