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

device_register() includes device_add(). As comment of device_add()
says, 'if device_add() succeeds, you should call device_del() when you
want to get rid of it. If device_add() has not succeeded, use only
put_device() to drop the reference count'.

Found by code review.

Cc: stable@vger.kernel.org
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Ma Ke <make24@iscas.ac.cn>
---
Changes in v4:
- deleted the redundant initialization;
Changes in v3:
- modified the patch as suggestions;
Changes in v2:
- modified the patch as suggestions.
---
 arch/arm/common/locomo.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/arm/common/locomo.c b/arch/arm/common/locomo.c
index cb6ef449b987..45106066a17f 100644
--- a/arch/arm/common/locomo.c
+++ b/arch/arm/common/locomo.c
@@ -223,10 +223,8 @@ locomo_init_one_child(struct locomo *lchip, struct locomo_dev_info *info)
 	int ret;
 
 	dev = kzalloc(sizeof(struct locomo_dev), GFP_KERNEL);
-	if (!dev) {
-		ret = -ENOMEM;
-		goto out;
-	}
+	if (!dev)
+		return -ENOMEM;
 
 	/*
 	 * If the parent device has a DMA mask associated with it,
@@ -254,10 +252,9 @@ locomo_init_one_child(struct locomo *lchip, struct locomo_dev_info *info)
 			NO_IRQ : lchip->irq_base + info->irq[0];
 
 	ret = device_register(&dev->dev);
-	if (ret) {
- out:
-		kfree(dev);
-	}
+	if (ret)
+		put_device(&dev->dev);
+
 	return ret;
 }
 
-- 
2.25.1

On Wed, Jan 08, 2025 at 11:30:49AM +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.
> 
> device_register() includes device_add(). As comment of device_add()
> says, 'if device_add() succeeds, you should call device_del() when you
> want to get rid of it. If device_add() has not succeeded, use only
> put_device() to drop the reference count'.

I reviewed a previous version of this patch, and commented about the
commit message:

 The commit message is not quite correct:

 "After calling device_register(), the correct way to dispose of the
 device is to call put_device() as per the device_register()
 documentation rather than kfree()."

Alex Elder also commented about this. Please fix the commit message.
What device_add() doesn't matter, this code isn't calling device_add(),
it's calling device_register(), and the comments against
device_register() should be appearing in the commit message, not
the comments against device_add().

Thanks.

> 
> Found by code review.
> 
> Cc: stable@vger.kernel.org
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Ma Ke <make24@iscas.ac.cn>
> ---
> Changes in v4:
> - deleted the redundant initialization;
> Changes in v3:
> - modified the patch as suggestions;
> Changes in v2:
> - modified the patch as suggestions.
> ---
>  arch/arm/common/locomo.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/common/locomo.c b/arch/arm/common/locomo.c
> index cb6ef449b987..45106066a17f 100644
> --- a/arch/arm/common/locomo.c
> +++ b/arch/arm/common/locomo.c
> @@ -223,10 +223,8 @@ locomo_init_one_child(struct locomo *lchip, struct locomo_dev_info *info)
>  	int ret;
>  
>  	dev = kzalloc(sizeof(struct locomo_dev), GFP_KERNEL);
> -	if (!dev) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> +	if (!dev)
> +		return -ENOMEM;
>  
>  	/*
>  	 * If the parent device has a DMA mask associated with it,
> @@ -254,10 +252,9 @@ locomo_init_one_child(struct locomo *lchip, struct locomo_dev_info *info)
>  			NO_IRQ : lchip->irq_base + info->irq[0];
>  
>  	ret = device_register(&dev->dev);
> -	if (ret) {
> - out:
> -		kfree(dev);
> -	}
> +	if (ret)
> +		put_device(&dev->dev);
> +
>  	return ret;
>  }
>  
> -- 
> 2.25.1
> 
> 

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

On 1/7/25 9:30 PM, Ma Ke wrote:
> Once device_register() failed, we should call put_device() to
> decrement reference count for cleanup. Or it could cause memory leak.
> 
> device_register() includes device_add(). As comment of device_add()
> says, 'if device_add() succeeds, you should call device_del() when you
> want to get rid of it. If device_add() has not succeeded, use only
> put_device() to drop the reference count'.

And above device_register() it 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: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Ma Ke <make24@iscas.ac.cn>

Looks good to me.  Much cleaner result.

Reviewed-by: Alex Elder <elder@kernel.org>

> ---
> Changes in v4:
> - deleted the redundant initialization;
> Changes in v3:
> - modified the patch as suggestions;
> Changes in v2:
> - modified the patch as suggestions.
> ---
>   arch/arm/common/locomo.c | 13 +++++--------
>   1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/common/locomo.c b/arch/arm/common/locomo.c
> index cb6ef449b987..45106066a17f 100644
> --- a/arch/arm/common/locomo.c
> +++ b/arch/arm/common/locomo.c
> @@ -223,10 +223,8 @@ locomo_init_one_child(struct locomo *lchip, struct locomo_dev_info *info)
>   	int ret;
>   
>   	dev = kzalloc(sizeof(struct locomo_dev), GFP_KERNEL);
> -	if (!dev) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> +	if (!dev)
> +		return -ENOMEM;
>   
>   	/*
>   	 * If the parent device has a DMA mask associated with it,
> @@ -254,10 +252,9 @@ locomo_init_one_child(struct locomo *lchip, struct locomo_dev_info *info)
>   			NO_IRQ : lchip->irq_base + info->irq[0];
>   
>   	ret = device_register(&dev->dev);
> -	if (ret) {
> - out:
> -		kfree(dev);
> -	}
> +	if (ret)
> +		put_device(&dev->dev);
> +
>   	return ret;
>   }
>