linux-kernel - Re: [PATCH v3] xfs: introduce protection for drop nlink

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Date:   Fri, 15 Sep 2023 17:50:56 +0800 (CST)
From:   <cheng.lin130@....com.cn>
To:     <david@...morbit.com>
Cc:     <djwong@...nel.org>, <linux-xfs@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <jiang.yong5@....com.cn>,
        <wang.liang82@....com.cn>, <liu.dong3@....com.cn>
Subject: Re: [PATCH v3] xfs: introduce protection for drop nlink

> On Wed, Sep 13, 2023 at 05:44:45PM +0800, cheng.lin130@....com.cn wrote:
> > From: Cheng Lin <cheng.lin130@....com.cn>
> >
> > When abnormal drop_nlink are detected on the inode,
> > shutdown filesystem, to avoid corruption propagation.
> >
> > Signed-off-by: Cheng Lin <cheng.lin130@....com.cn>
> > ---
> >  fs/xfs/xfs_inode.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > index 9e62cc500..40cc106ae 100644
> > --- a/fs/xfs/xfs_inode.c
> > +++ b/fs/xfs/xfs_inode.c
> > @@ -919,6 +919,15 @@ xfs_droplink(
> >      xfs_trans_t *tp,
> >      xfs_inode_t *ip)
> >  {
> > +
> > +    if (VFS_I(ip)->i_nlink == 0) {
> > +        xfs_alert(ip->i_mount,
> > +              "%s: Deleting inode %llu with no links.",
> > +              __func__, ip->i_ino);
> > +        tp->t_flags |= XFS_TRANS_DIRTY;
> Marking the transaction dirty is not necessary.
> Otherwise this seems fine.
Another strategy: 
Set nlink to an invalid value(like XFS_NLINK_PINNED), and
Complete this transaction before shutdown fs. To make sure
nlink not be zero. If the nlink of a directory are zero, it may
be cleaned up.
Is that appropriate?
> -Dave.
> --
> Dave Chinner
> david@...morbit.com