Re: [RFC PATCH] fs: introduce check for drop/inc_nlink

[Darrick J. Wong]

On Fri, Oct 13, 2023 at 05:40:57PM +0800, cheng.lin130@xxxxxxxxxx wrote:
> > On Fri, Oct 13, 2023 at 03:27:30PM +0800, cheng.lin130@xxxxxxxxxx wrote:
> > > From: Cheng Lin <cheng.lin130@xxxxxxxxxx>
> > >
> > > Avoid inode nlink overflow or underflow.
> > >
> > > Signed-off-by: Cheng Lin <cheng.lin130@xxxxxxxxxx>
> > > ---
> > 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.

I was trying to steer you towards modifying vfs_rmdir and vfs_unlink to
check that i_nlink of the files involved aren't somehow already zero
and returning -EFSCORRUPTED if they are.  Not messing around with
drop_nlink.

--D