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

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Message-ID: <twm7w7grcgw6h4s5iyzifgmaazlx2u2awl3l4sjm24unq64ath@erjimgt3u4wi>
Date: Mon, 15 Dec 2025 10:46:17 +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] chardev: Switch to guard(mutex)

On Mon 15-12-25 14:06:57, 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.
> 
> Signed-off-by: chen zhang <chenzhang@...inos.cn>

Thanks for the patch. I agree guards can simplify this function but why not
handle 'cd' variable with __free as well then? The kfree() calls you have
to add otherwise kind of defeat the purpose of guards...

								Honza

> ---
>  fs/char_dev.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/char_dev.c b/fs/char_dev.c
> index c2ddb998f3c9..ca6037304e19 100644
> --- a/fs/char_dev.c
> +++ b/fs/char_dev.c
> @@ -117,14 +117,15 @@ __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;
> +			kfree(cd);
> +			return ERR_PTR(ret);
>  		}
>  		major = ret;
>  	}
> @@ -144,7 +145,8 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor,
>  		if (curr->baseminor >= baseminor + minorct)
>  			break;
>  
> -		goto out;
> +		kfree(cd);
> +		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);
>  }
>  
>  static struct char_device_struct *
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR