[Unionfs] unionfs freezes with no apparent reason on Knoppix

[Klaus Knopper]

Hi list,

In the Knoppix 3.9 release, we encountered a strange bug with the
unionfs snapshot from 26 May 2005, but the problem is still present in
the current snapshot.

When running update-menus, which just goes through all the files in
/usr/lib/menu/* and creating the corresponding .desktop-files in the KDE
menu, unionfs freezes the entire machine shortly after accessing a
number of files in the aforementioned directory. While all files there
are perfectly safe to be cat'ed and stat'ed, it looks like there is a
problem with scripts that open and close these files rapidly.

Strangely enough, if you force a copyup of one file in /usr/lib/menu/ to
the upper ramdisk directory by editing and saving it (with unchanged
content), update-menus runs through without problems and the system
remains stable.

The unionfs configuration has a mount -o rw,dirs=/ramdisk=rw:/KNOPPIX=ro
none /UNIONFS, where /KNOPPIX is a read-only mounted (c)loopback image
(ISO9660 filesystem), and /ramdisk is of type tmpfs.

unionfs-1.0.11 does not show these sudden freezes, but causes kernel
oopses sometimes when files are rewritten on the ramdisk. 

Unfortunately, I cannot describe the problem more precisely because
there is not even a kernel panic message shown anymore, and even the
magic keys stop working.

With kind regards
-Klaus Knopper