Two *different* mount points having the *same* absolute path (bind-mount problem)

Scenario -------- - a NFS share is mounted on /mnt/temp/dir (and other shares are mounted in subdirectories), - I umount everything there but supposedly, it doesn't work well (maybe I start with umount /mnt/temp/dir instead of umounting "nested" shares like /mnt/temp/dir/subdir* first), - I do mount -o bind /data/temp /mnt/temp, - I do mount /mnt/temp/dir, - I do mount /mnt/temp/dir/subdir1... and it works well. Note: /mnt/temp is initially hosted on the root (/) filesystem /dev/sda6, and /data is another filesystem from /dev/sda8. Problem ------- I cannot delete the /mnt/temp/dir directory on the root filesystem: # mount -o bind / /test/root # rmdir /test/root/mnt/temp/dir rmdir: failed to remove `dir': Device or resource busy Some explanation ----------------- /mnt/temp/dir is mounted ***twice***, probably once on the root fs, and once on the /data fs. Here is cat /proc/mounts: nfsserver:/some/share/ /mnt/temp/dir nfs rw,relatime(...) 0 0 nfsserver:/some/share/ /mnt/temp/dir nfs rw,relatime,(...) 0 0 More interesting, here is cat /proc/1/mountinfo: 29 20 0:18 / /mnt/temp/dir rw,relatime - nfs nfsserver:/some/share/ rw,(...) 33 31 0:18 / /mnt/temp/dir rw,relatime - nfs nfsserver:/some/share/ rw,(...) See, the two numbers at the beginning are *different*. Kernel doc says for these two fields: (1) mount ID: unique identifier of the mount (may be reused after umount) (2) parent ID: ID of parent (or of self for the top of the mount tree) They also have different parents 20 and 31 (root fs and /data fs), see: 20 1 8:6 / / rw,relatime - ext4 /dev/sda6 rw,(...) 31 20 8:8 /temp /mnt/temp rw,relatime - ext4 /dev/sda8 rw,(...) If I try to umount /mnt/temp/dir, I get 2 error messages: umount.nfs: /mnt/temp/dir: device is busy umount.nfs: /mnt/temp/dir: device is busy Question ======== **How can I umount the "bad" one (mount ID 29)?** Even the umount(2) system call takes a path for argument, and not a "mount ID".