linux-kernel - Re: [RFC PATCH] fs: introduce check for drop/inc

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Message-ID: <20231013-tyrannisieren-umfassen-0047ab6279aa@brauner>
Date:   Fri, 13 Oct 2023 10:02:39 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     cheng.lin130@....com.cn
Cc:     viro@...iv.linux.org.uk, djwong@...nel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        david@...morbit.com, hch@...radead.org, jiang.yong5@....com.cn,
        wang.liang82@....com.cn, liu.dong3@....com.cn
Subject: Re: [RFC PATCH] fs: introduce check for drop/inc_nlink

On Fri, Oct 13, 2023 at 03:27:30PM +0800, cheng.lin130@....com.cn wrote:
> From: Cheng Lin <cheng.lin130@....com.cn>
> 
> Avoid inode nlink overflow or underflow.
> 
> Signed-off-by: Cheng Lin <cheng.lin130@....com.cn>
> ---

I'm very confused. There's no explanation why that's needed. As it
stands it's not possible to provide a useful review.

I'm not saying it's wrong. I just don't understand why and even if this
should please show up in the commit message.

>  fs/inode.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 67611a360..8e6d62dc4 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -328,6 +328,9 @@ static void destroy_inode(struct inode *inode)
>  void drop_nlink(struct inode *inode)
>  {
>  	WARN_ON(inode->i_nlink == 0);
> +	if (unlikely(inode->i_nlink == 0))
> +		return;
> +
>  	inode->__i_nlink--;
>  	if (!inode->i_nlink)
>  		atomic_long_inc(&inode->i_sb->s_remove_count);
> @@ -388,6 +391,9 @@ void inc_nlink(struct inode *inode)
>  		atomic_long_dec(&inode->i_sb->s_remove_count);
>  	}
>  
> +	if (unlikely(inode->i_nlink == ~0U))
> +		return;
> +
>  	inode->__i_nlink++;
>  }
>  EXPORT_SYMBOL(inc_nlink);
> -- 
> 2.18.1