Comment 18 for bug 506798

Description of problem: in the vicinity of a mount point directory, two directories may have the same device and inode number. This is a serious problem because many tools treat the condition as indicating a hard directory cycle, which usually indicates file system corruption.

Version-Release number of selected component (if applicable):
2.6.31.5-122.fc12.x86_64

How reproducible: every time

Steps to Reproduce:
Based on the set-up from Kamil Dudka in https://bugzilla.redhat.com/show_bug.cgi?id=501848#c45

# mount | grep ^/
...
/dev/sda8 on /home type ext4 (rw,noatime)
...
# top=/home
# cat /etc/exports
# printf "/ *(fsid=0,crossmnt)\n$top *(crossmnt)\n" >> /etc/exports
# service nfs restart
...
# mkdir /tmp/mnt
# mount -t nfs4 localhost:/ /tmp/mnt
# stat --printf "%d %i %n\n" /tmp/mnt{,$top}
22 2 /tmp/mnt
22 2 /tmp/mnt/home

Then, using the very latest du from upstream coreutils.git,
I see this:

    $ du /tmp/mnt > /dev/null
    du: WARNING: Circular directory structure.
    This almost certainly means that you have a corrupted file system.
    NOTIFY YOUR SYSTEM MANAGER.
    The following directory is part of the cycle:
      `/tmp/mnt/home'

Actual results: above

Expected results: different dev and/or inode, no du failure

Additional info: