[Bug 30995] dm_mod causes false busy on mount attempts

[Ryan Lovett]

Public bug reported:
https://launchpad.net/malone/bugs/30995

Affects: linux-meta linux-image-amd64-k8 (Ubuntu)
       Severity: Normal
       Priority: (none set)
         Status: Unconfirmed

Description:
With dm_mod loaded, partitions on secondary disks fail to mount. We were
trying to, e.g.

  mount -t ext3 /dev/sdb1 /any/new/mountpoint

right after creating the partition/filesystem with fdisk or cfdisk and
mke2fs, or parted and tune2fs. The mount attempts would indicate the
filesystem or mountpoint was busy. After exhausting all known tools like
lsof, strace, etc. we found that dm-mod.ko was at fault. Hotplug
blacklisting didn't work, nor did preventing the startup of mdadm, evms,
or lvm. I eventually had to move the module aside to prevent it from
loading.

I tried building a kernel from kernel.org (2.6.15.3), but that produces
the same problem on Breezy.

Other Ubuntu users see similar problems:
http://www.google.com/search?q=ubuntu+%22already+mounted%22+busy+-cdrom+-usb&hl=en&lr=&c2coff=1&start=10&sa=N