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

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Date:   Fri, 13 Oct 2023 17:40:57 +0800 (CST)
From:   <cheng.lin130@....com.cn>
To:     <brauner@...nel.org>
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.
In an xfs issue, there was an nlink underflow of a directory inode. There
is a key information in the kernel messages, that is the WARN_ON from
drop_nlink(). However, VFS did not prevent the underflow. I'm not sure
if this behavior is inadvertent or specifically designed. As an abnormal
situation, perhaps prohibiting nlink overflow or underflow is a better way
to handle it.
Request for your comment.