The test steps are as follows：
- Have a bind mount point,like this
# /dev/sda4 UUID=xxxx /data xfs rw,relatime,attr2,inode64,sunit=128,swidth=256,noquota 0 2 /data/home /home none defaults,bind 0 0
Mount the disk to the subdirectory of the bind mount point，
mount /dev/sdb /home/test
Open the GParted graphics tool and umount /dev/sdb
An error message will be displayed:
#umount -v '/home/test' umount: /home/test: not mounted.
In bind mode, the gparted tool displays two mount points: /data/home/test and /home/test.
During the unmounting, two mount points will be umount in a circular manner. After the first mount point is successfully unmounted, the second mount point fails to be unmounted.