After some searching I found out that you apparently need lvm2 2.02.01 or later and devmapper 1.02.02 or later to successfully remove snapshot volumes now. Unfortunately neither of these versions is available for sarge from Debian or backports.org yet, so I had to make my own backports.
As it turned out (see below), it is also necessary to use 2.6.16.12 or to apply the patch from this email to older 2.6.16 versions in order to reliably remove snapshots.

If you are brave enough, you can get the backported packages by adding

deb http://blog.blackdown.de/static/debian/lvm/ sarge main
deb-src http://blog.blackdown.de/static/debian/lvm/ sarge main

to /etc/apt/sources.list.

The repository contains debs for devmapper, dlm, lvm2, and lvm-common. The Release files is signed with my GPG key. If you have a recent apt version, you can authenticate the packages after importing the key with apt-key:

wget http://blog.blackdown.de/static/gpg.asc -O - | \
    sudo apt-key add -

April 15th, 2006: In about 40 backup cycles I’ve seen three lockups with 2.6.16.2 now. Until snapshots get fixed in 2.6.16, I’d recommend to stay with 2.6.15. I’m using 2.6.15.3 again now.

April 24th, 2006: Added note about “dm snapshot: fix kcopyd destructor” patch from Alasdair G Kergon. With this patch snapshots work fine for me again.

May 2nd, 2006: Alasdair G Kergon’s patch has been included in 2.6.16.12.

The official sarge installer still uses a 2.4 kernel by default but includes a 2.6 kernel that can be used by booting with "install26" or "expert26". But even that kernel, 2.6.8, is too old for the Inspiron 9300. It still doesn’t recognize the hard disk.

Ubuntu’s installer, which uses a 2.6.11 kernel, works fine on the machine. Although Ubuntu is a nice distribution, I like pure Debian better. Unfortunately I wasn’t able to find any 2.6.11 based Debian installer on the net, even a question on debian-boot yielded nothing.

Anyhow, I finally had the time to build one myself:
debian-2.6.11-i386-businesscard.iso (GPG signature)

The image is basically a sarge businesscard ISO with a 2.6.11 kernel from Debian testing instead of the original 2.6.8 kernel.

Unlike with Ubuntu, installation on the Inspiron 9300 still doesn’t work out of the box but with a few tricks I was able to install Debian sarge:

• Boot with expert26
• When the installer starts up, switch to the second console (Alt-F2) and enter these commands:

  ~ # modprobe ide_generic
  ~ # modprobe ata_piix

  Without this the installer won’t find the CD-ROM.

• If network configuration via DHCP fails, just retry — worked for me
• When asked what version of Debian you would like to install, choose stable. Installing testing or unstable directly doesn’t work.
• It doesn’t matter which kernel you choose to install, we have to replace it with a 2.6.11 kernel later anyway
• Just before the first reboot, that means right after the installer ejects the CD-ROM, switch back to console two. Now download and install the latest available Debian kernel. I’ve used 2.6.11-1-686:

  ~ # mount -t proc proc /target/proc
  ~ # chroot /target
  sh-2.05b# cd /root
  sh-2.05b# wget http://blog.blackdown.de/static/debian/kernel-image-2.6.11-1-686_2.6.11-7_i386.deb
  sh-2.05b# dpkg -i kernel-image-2.6.11-1-686_2.6.11-7_i386.deb
  …
  sh-2.05b# exit
  ~ # umount /target/proc

• Reboot (using the kernel just installed) and complete the installation
• Upgrade to testing or unstable
• Build a custom kernel (2.6.12 or newer). It’s probably a good idea to include some additional libata patches. To get the DVD drive working you have to apply this patch.

A closer look at ipt_recent.c revealed that the time tests did not work like intended if one of the last hits was more than LONG_MAX jiffies ago or if the list of last hits contained empty slots and jiffies is greater than LONG_MAX.

To fix this, I replaced jiffies with seconds since ’00:00:00 1970-01-01 UTC’. I have sent the patch to linux-kernel and netfilter-devel. The patch also includes some 64-bit fixes.

May 12th, 2005: The patch has been added to Linux 2.6.12-rc4-mm1

September 8th, 2005: Please note that only the 64-bit parts of my patch have made it into 2.6.12. I’m working on an updated fix for the time comparison problems which will hopefully get accepted for 2.6.14 or later.

September 12th, 2005: These issues have CAN numbers now: CAN-2005-2872 and CAN-2005-2873 (which supersede CAN-2005-2802)

July 10th, 2006: The jiffies issue is fixed in the vanilla kernel now. Also note that 2.6.18 will contain a rewrite of ipt_recent.c.

I have not found a bug in these patches yet but I am pretty sure that it is no GCC bug.

Now if 2.6.12-rc kernels were just a tiny bit more stable on my G5…

As my old work-around (providing a uname command that returns ‘ppc’) didn’t work anymore, this forced me to look at the root cause of the problem.

I’ve finally found two issues with the PER_LINUX32 personality:

• uname(2) didn’t respect PER_LINUX32
• Child processes didn’t inherit PER_LINUX32

This patch for 2.6.12-rc1-mm4 fixes both issues:

$ uname -m
ppc64
$ linux32 uname -m
ppc
$ linux32 sh -c "uname -m"
ppc

Without the patch all three commands return ‘ppc64’.

March 18th, 2005: The patch has been integrated into inotify 0.21-2

March 17th, 2005: Updated patch available here

March 16th, 2005: The patch has been integrated into 2.6.11-mm3