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

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Message-ID: <ZOfhoLql0TYiD5JW@dread.disaster.area>
Date:   Fri, 25 Aug 2023 09:02:56 +1000
From:   Dave Chinner <david@...morbit.com>
To:     cheng.lin130@....com.cn
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] xfs: introduce protection for drop nlink

On Thu, Aug 24, 2023 at 03:43:52PM +0800, cheng.lin130@....com.cn wrote:
> From: Cheng Lin <cheng.lin130@....com.cn>
> An dir nlinks overflow which down form 0 to 0xffffffff, cause the
> directory to become unusable until the next xfs_repair run.

Hmmm.  How does this ever happen?

IMO, if it does happen, we need to fix whatever bug that causes it
to happen, not issue a warning and do nothing about the fact we
just hit a corrupt inode state...

> Introduce protection for drop nlink to reduce the impact of this.
> And produce a warning for directory nlink error during remove.
> 
> Signed-off-by: Cheng Lin <cheng.lin130@....com.cn>
> ---
>  fs/xfs/xfs_inode.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 9e62cc5..536dbe4 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -919,6 +919,15 @@ STATIC int xfs_iunlink_remove(struct xfs_trans *tp, struct xfs_perag *pag,
>  	xfs_trans_t *tp,
>  	xfs_inode_t *ip)
>  {
> +	xfs_mount_t     *mp;
> +
> +	if (VFS_I(ip)->i_nlink == 0) {
> +		mp = ip->i_mount;
> +		xfs_warn(mp, "%s: Deleting inode %llu with no links.",
> +			 __func__, ip->i_ino);
> +		return 0;
> +	}

This is obviously incorrect - whiteout inodes (RENAME_WHITEOUT) have an
i_nlink of zero when they are removed from the unlinked list. As do
O_TMPFILE inodes - when they are linked into the filesystem, we
explicitly check for i_nlink being zero before calling
xfs_iunlink_remove().

> +
>  	xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);
> 
>  	drop_nlink(VFS_I(ip));

Wait a second - this code doesn't match an upstream kernel. What
kernel did you make this patch against?

-Dave.
-- 
Dave Chinner
david@...morbit.com