I just wrote:

> Thomas Ulrich Nockmann writes:
>
>> On Saturday 30 April 2011 Alex Schuster wrote:
>
>>> weird ~ # umount /32/dev
>>> umount: /32/dev: device is busy.
>>>         (In some cases useful info about processes that use
>>>          the device is found by lsof(8) or fuser(1))
>> try 'umount -l /32/de'
>
> Cool, this does the trick!

But it does not help :(  After unmounting /32/dev, I can finally unmount
/32, but now the fsck fails:

weird ~ # fsck -Cf /dev/mapper/32
fsck from util-linux 2.19
e2fsck 1.41.14 (22-Dec-2010)
fsck.ext3: Device or resource busy while trying to open /dev/mapper/32
Filesystem mounted or opened exclusively by another program?

lsof and fuser report nothing. I guess I will have to reboot then.

       Wonko