Re: [PATCH] xfs: introduce protection for drop nlink
From: Darrick J. Wong
Date: Thu Aug 24 2023 - 12:13:24 EST
On Thu, Aug 24, 2023 at 03:43:52PM +0800, cheng.lin130@xxxxxxxxxx wrote:
> From: Cheng Lin <cheng.lin130@xxxxxxxxxx>
> An dir nlinks overflow which down form 0 to 0xffffffff, cause the
> directory to become unusable until the next xfs_repair run.
>
> 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@xxxxxxxxxx>
> ---
> 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;
> + }
> +
> xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);
>
> drop_nlink(VFS_I(ip));
I'm not sure how nlink would ever get to 0xFFFFFFFF since the VFS won't
let a link count exceed s_max_links, and XFS sets that to 0x7FFFFFFF.
Unless, of course, you did that outside of Linux.
That said, why wouldn't you /pin/ the link count at -1U instead of
allowing it to overflow to zero?
Could you please take a look at this patch that's waiting in my
submission queue?
https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?h=inode-repair-improvements&id=05f5a82efa6395c92038e18e008aaf7154238f27
--D
> @@ -2442,7 +2451,12 @@ STATIC int xfs_iunlink_remove(struct xfs_trans *tp, struct xfs_perag *pag,
> */
> if (is_dir) {
> ASSERT(VFS_I(ip)->i_nlink >= 2);
> - if (VFS_I(ip)->i_nlink != 2) {
> + if (VFS_I(ip)->i_nlink < 2) {
> + xfs_warn(ip->i_mount,
> + "%s: Remove dir (inode %llu) with invalid links.",
> + __func__, ip->i_ino);
> + }
> + if (VFS_I(ip)->i_nlink > 2) {
> error = -ENOTEMPTY;
> goto out_trans_cancel;
> }
> --
> 1.8.3.1