linux-kernel - Re: [PATCH v2] chardev: Switch to guard(mutex) and _

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Message-ID: <v2y34qyxaz2foko67wsrfudqzvmplukb6sck7maij2r7a3xhv2@jy2f5hjwgqk3>
Date: Mon, 15 Dec 2025 13:43:50 +0100
From: Jan Kara <jack@...e.cz>
To: chen zhang <chenzhang@...inos.cn>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, chenzhang_0901@....com
Subject: Re: [PATCH v2] chardev: Switch to guard(mutex) and __free(kfree)

On Mon 15-12-25 19:15:00, chen zhang wrote:
> Instead of using the 'goto label; mutex_unlock()' pattern use
> 'guard(mutex)' which will release the mutex when it goes out of scope.
> Use the __free(kfree) cleanup to replace instances of manually
> calling kfree(). Also make some code path simplifications that this
> allows.
> 
> Signed-off-by: chen zhang <chenzhang@...inos.cn>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/char_dev.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/char_dev.c b/fs/char_dev.c
> index c2ddb998f3c9..74d4bdfaa9ae 100644
> --- a/fs/char_dev.c
> +++ b/fs/char_dev.c
> @@ -10,6 +10,7 @@
>  #include <linux/kdev_t.h>
>  #include <linux/slab.h>
>  #include <linux/string.h>
> +#include <linux/cleanup.h>
>  
>  #include <linux/major.h>
>  #include <linux/errno.h>
> @@ -97,7 +98,8 @@ static struct char_device_struct *
>  __register_chrdev_region(unsigned int major, unsigned int baseminor,
>  			   int minorct, const char *name)
>  {
> -	struct char_device_struct *cd, *curr, *prev = NULL;
> +	struct char_device_struct *cd __free(kfree) = NULL;
> +	struct char_device_struct *curr, *prev = NULL;
>  	int ret;
>  	int i;
>  
> @@ -117,14 +119,14 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor,
>  	if (cd == NULL)
>  		return ERR_PTR(-ENOMEM);
>  
> -	mutex_lock(&chrdevs_lock);
> +	guard(mutex)(&chrdevs_lock);
>  
>  	if (major == 0) {
>  		ret = find_dynamic_major();
>  		if (ret < 0) {
>  			pr_err("CHRDEV \"%s\" dynamic allocation region is full\n",
>  			       name);
> -			goto out;
> +			return ERR_PTR(ret);
>  		}
>  		major = ret;
>  	}
> @@ -144,7 +146,7 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor,
>  		if (curr->baseminor >= baseminor + minorct)
>  			break;
>  
> -		goto out;
> +		return ERR_PTR(ret);
>  	}
>  
>  	cd->major = major;
> @@ -160,12 +162,7 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor,
>  		prev->next = cd;
>  	}
>  
> -	mutex_unlock(&chrdevs_lock);
> -	return cd;
> -out:
> -	mutex_unlock(&chrdevs_lock);
> -	kfree(cd);
> -	return ERR_PTR(ret);
> +	return_ptr(cd);
>  }
>  
>  static struct char_device_struct *
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR