[PATCH] xfs: introduce protection for drop nlink

[<cheng.lin130@zte.com.cn>]

From: Cheng Lin <cheng.lin130@zte.com.cn>
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@zte.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;
+	}
+
 	xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);

 	drop_nlink(VFS_I(ip));
@@ -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