Once device_register() failed, we should call put_device() to
decrement reference count for cleanup. Or it could cause memory leak.
And move callback function before put_device().

As comment of device_register() says, 'NOTE: _Never_ directly free
@dev after calling this function, even if it returned an error! Always
use put_device() to give up the reference initialized in this function
instead.'

Found by code review.

Cc: stable@vger.kernel.org
Fixes: baa057e29b58 ("media: v4l2-dev: use pr_foo() for printing messages")
Signed-off-by: Ma Ke <make24@iscas.ac.cn>
---
Changes in v2:
- modified the patch as no callback function before put_device().
---
 drivers/media/v4l2-core/v4l2-dev.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
index 5bcaeeba4d09..4a8fdf8115c0 100644
--- a/drivers/media/v4l2-core/v4l2-dev.c
+++ b/drivers/media/v4l2-core/v4l2-dev.c
@@ -1054,17 +1054,16 @@ int __video_register_device(struct video_device *vdev,
 	vdev->dev.class = &video_class;
 	vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
 	vdev->dev.parent = vdev->dev_parent;
+	vdev->dev.release = v4l2_device_release;
 	dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
 	mutex_lock(&videodev_lock);
 	ret = device_register(&vdev->dev);
 	if (ret < 0) {
 		mutex_unlock(&videodev_lock);
 		pr_err("%s: device_register failed\n", __func__);
-		goto cleanup;
+		put_device(&vdev->dev);
+		return ret;
 	}
-	/* Register the release callback that will be called when the last
-	   reference to the device goes away. */
-	vdev->dev.release = v4l2_device_release;
 
 	if (nr != -1 && nr != vdev->num && warn_if_nr_in_use)
 		pr_warn("%s: requested %s%d, got %s\n", __func__,
-- 
2.25.1

On Tue, Mar 18, 2025 at 05:09:45PM +0800, Ma Ke wrote:
> Once device_register() failed, we should call put_device() to
> decrement reference count for cleanup. Or it could cause memory leak.
> And move callback function before put_device().
> 
> As comment of device_register() says, 'NOTE: _Never_ directly free
> @dev after calling this function, even if it returned an error! Always
> use put_device() to give up the reference initialized in this function
> instead.'
> 
> Found by code review.
> 
> Cc: stable@vger.kernel.org
> Fixes: baa057e29b58 ("media: v4l2-dev: use pr_foo() for printing messages")

This tag does not seems to be right, the commit just change printk calls.

Regards
Stanislaw


> Signed-off-by: Ma Ke <make24@iscas.ac.cn>
> ---
> Changes in v2:
> - modified the patch as no callback function before put_device().
> ---
>  drivers/media/v4l2-core/v4l2-dev.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> index 5bcaeeba4d09..4a8fdf8115c0 100644
> --- a/drivers/media/v4l2-core/v4l2-dev.c
> +++ b/drivers/media/v4l2-core/v4l2-dev.c
> @@ -1054,17 +1054,16 @@ int __video_register_device(struct video_device *vdev,
>  	vdev->dev.class = &video_class;
>  	vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
>  	vdev->dev.parent = vdev->dev_parent;
> +	vdev->dev.release = v4l2_device_release;
>  	dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
>  	mutex_lock(&videodev_lock);
>  	ret = device_register(&vdev->dev);
>  	if (ret < 0) {
>  		mutex_unlock(&videodev_lock);
>  		pr_err("%s: device_register failed\n", __func__);
> -		goto cleanup;
> +		put_device(&vdev->dev);
> +		return ret;
>  	}
> -	/* Register the release callback that will be called when the last
> -	   reference to the device goes away. */
> -	vdev->dev.release = v4l2_device_release;
>  
>  	if (nr != -1 && nr != vdev->num && warn_if_nr_in_use)
>  		pr_warn("%s: requested %s%d, got %s\n", __func__,
> -- 
> 2.25.1
> 
>

Hi Ma,

Thanks for the update.

On Tue, Mar 18, 2025 at 05:09:45PM +0800, Ma Ke wrote:
> Once device_register() failed, we should call put_device() to
> decrement reference count for cleanup. Or it could cause memory leak.
> And move callback function before put_device().
> 
> As comment of device_register() says, 'NOTE: _Never_ directly free
> @dev after calling this function, even if it returned an error! Always
> use put_device() to give up the reference initialized in this function
> instead.'
> 
> Found by code review.
> 
> Cc: stable@vger.kernel.org
> Fixes: baa057e29b58 ("media: v4l2-dev: use pr_foo() for printing messages")
> Signed-off-by: Ma Ke <make24@iscas.ac.cn>
> ---
> Changes in v2:
> - modified the patch as no callback function before put_device().
> ---
>  drivers/media/v4l2-core/v4l2-dev.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> index 5bcaeeba4d09..4a8fdf8115c0 100644
> --- a/drivers/media/v4l2-core/v4l2-dev.c
> +++ b/drivers/media/v4l2-core/v4l2-dev.c
> @@ -1054,17 +1054,16 @@ int __video_register_device(struct video_device *vdev,
>  	vdev->dev.class = &video_class;
>  	vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
>  	vdev->dev.parent = vdev->dev_parent;
> +	vdev->dev.release = v4l2_device_release;
>  	dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
>  	mutex_lock(&videodev_lock);
>  	ret = device_register(&vdev->dev);
>  	if (ret < 0) {
>  		mutex_unlock(&videodev_lock);
>  		pr_err("%s: device_register failed\n", __func__);
> -		goto cleanup;
> +		put_device(&vdev->dev);
> +		return ret;
>  	}
> -	/* Register the release callback that will be called when the last
> -	   reference to the device goes away. */
> -	vdev->dev.release = v4l2_device_release;
>  
>  	if (nr != -1 && nr != vdev->num && warn_if_nr_in_use)
>  		pr_warn("%s: requested %s%d, got %s\n", __func__,

I think this still needs some work. E.g. v4l2_device_get() hasn't been
called yet here, but still v4l2_device_release() will call
v4l2_device_put().

-- 
Regards,

Sakari Ailus