+++ This bug was initially created as a clone of Bug #237538 +++

make a local gfs2 fs and try to mount it via loopback:

[root@neon tmp]# dd if=/dev/zero of=fsfile bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.239597 seconds, 438 MB/s
[root@neon tmp]# mkfs.gfs2 -p lock_nolock -j 1 fsfile 
This will destroy any data on fsfile.

Are you sure you want to proceed? [y/n] y

Device:                    fsfile
Blocksize:                 4096
Device Size                0.10 GB (25600 blocks)
Filesystem Size:           0.10 GB (25599 blocks)
Journals:                  1
Resource Groups:           1
Locking Protocol:          "lock_nolock"
Lock Table:                ""

[root@neon tmp]# dmesg -c > /dev/null
[root@neon tmp]# mount -o loop fsfile mnt/
/sbin/mount.gfs2: can't find /proc/mounts entry for directory mnt
[root@neon tmp]# dmesg
GFS2: fsid=: Trying to join cluster "lock_nolock", "loop0"
GFS2: fsid=loop0.0: Joined cluster. Now mounting FS...
GFS2: fsid=loop0.0: jid=0, already locked for use
GFS2: fsid=loop0.0: jid=0: Looking at journal...
GFS2: fsid=loop0.0: jid=0: Done

loop0 is still set up though:

[root@neon tmp]# losetup /dev/loop0
/dev/loop0: [0802]:33847258 (fsfile)
[root@neon tmp]# losetup /dev/loop1
loop: can't get info on device /dev/loop1: No such device or address

now bypass mount.gfs2:

[root@neon tmp]# mount -i -o loop fsfile mnt/

mounts and sets up another loopback device:

[root@neon tmp]# losetup /dev/loop1
/dev/loop1: [0802]:33847258 (fsfile)

umount fails too:

[root@neon tmp]# umount mnt/
/sbin/umount.gfs2: file system mounted on /tmp/mnt not found in mtab

works if you bypass umount.gfs2:

[root@neon tmp]# umount -i mnt/

original failed mount never cleaned up loop0:

[root@neon tmp]# losetup /dev/loop0
/dev/loop0: [0802]:33847258 (fsfile)
[root@neon tmp]# losetup /dev/loop1
loop: can't get info on device /dev/loop1: No such device or address

this was all on a reasonably uptodate FC6 box

-- Additional comment from esandeen@redhat.com on 2007-04-23 14:10 EST --
mount -v output at dct's request:

[root@neon tmp]# mount -v -o loop fsfile mnt/
mount: going to use the loop device /dev/loop0
mount: you didn't specify a filesystem type for /dev/loop0
       I will try type gfs2
/sbin/mount.gfs2: mount /dev/loop0 mnt
/sbin/mount.gfs2: parse_opts: opts = "rw"
/sbin/mount.gfs2:   clear flag 1 for "rw", flags = 0
/sbin/mount.gfs2: parse_opts: flags = 0
/sbin/mount.gfs2: parse_opts: extra = ""
/sbin/mount.gfs2: parse_opts: hostdata = ""
/sbin/mount.gfs2: parse_opts: lockproto = ""
/sbin/mount.gfs2: parse_opts: locktable = ""
/sbin/mount.gfs2: mount(2) ok
/sbin/mount.gfs2: can't find /proc/mounts entry for directory mnt


-- Additional comment from teigland@redhat.com on 2007-04-23 14:23 EST --
This is caused by the lack of a preceding "/" before "mnt".
/proc/mounts always shows the preceding "/" in the mountpoint
and mount.gfs2 fails to match "mnt" and "/mnt".