Problem with loop mount

[Jon Forsberg <zzed@cyberdude.com>]

I do this:

# cd /tmp
# dd bs=1M seek=300 count=0 of=bigfile
# mke2fs bigfile
# mount -o loop bigfile /mnt
# cd /mnt

Then I start to copy a directory tree, that has around 200 MB of files, from
another place into /mnt. Everytime I've tried it just stops after 50 to 100 MB.
The hd isn't working and neither Ctrl-C or Ctrl-Z works to cancel cp. ps shows
cp's status as "D" (uninterruptible sleep). With kernel 2.2.17 I then can't
login, run commands, or do anything that needs access to files on the root
partition it seems. With 2.4.0 cp still freezes but the rest of the system
seems to work.

I've left it like this overnight one time just to see if anything happens - it
doesn't.

If I create the loopfile with "dd bs=1M count=300 if=/dev/zero of=bigfile"
instead (which is the "normal" way to do it, I guess) everything works.

So is this
A. A known problem/limitation in the kernel (can't use loopfiles with holes(?))
B. An actual (new) kernel bug
C. I who am missing something
?

--zzed