Bug#375116: lvm2: Snapshotting the root logical volume crashes the machine, makes it unbootable, and the snapshot can't even be removed when booting from a recovery system

[Sam Morris]

Package: lvm2
Severity: critical
Justification: breaks the whole system

I unwittingly ran into bug #288354 today. Creating the snapshot froze my
machine, as described in that bug report.

After a while I rebooted the machine, but it will no longer boot up:

	device-mapper: 4.1.0-ioctl (2003-12-10) initialised: dm at uk.sistina.com
	  Can't expand LV: Snapshot support missing from kernel?
	  2 logical volume(s) in volume group "main" now active
	pivot_root: No sKernel panic: Attempted to kill init!
	uch file or dire ctory
	/sbin/init: 432: cannot open dev/console: No such file

I booted into a recovery system and the various filesystems and volumes
seemed fine:

	rescue:~# lvdisplay
	  --- Logical volume ---
	  LV Name                /dev/main/root
	  VG Name                main
	  LV UUID                x6pkSm-EeXo-a5Mq-B4Qh-JC9K-kxEy-yhtHua
	  LV Write Access        read/write
	  LV snapshot status     source of
							 /dev/main/rootbackup [active]
	  LV Status              available
	  # open                 0
	  LV Size                5.00 GB
	  Current LE             1280
	  Segments               1
	  Allocation             inherit
	  Read ahead sectors     0
	  Block device           253:3

	  --- Logical volume ---
	  LV Name                /dev/main/home
	  VG Name                main
	  LV UUID                mMAlEY-4w0M-rhxD-Er2R-0Z8S-K1nG-CuBBzC
	  LV Write Access        read/write
	  LV Status              available
	  # open                 0
	  LV Size                5.00 GB
	  Current LE             1280
	  Segments               1
	  Allocation             inherit
	  Read ahead sectors     0
	  Block device           253:4

	  --- Logical volume ---
	  LV Name                /dev/main/srv
	  VG Name                main
	  LV UUID                3DoKN8-foaO-AkYv-XVyh-x59G-n1zT-OV8LBP
	  LV Write Access        read/write
	  LV Status              available
	  # open                 0
	  LV Size                10.00 GB
	  Current LE             2560
	  Segments               1
	  Allocation             inherit
	  Read ahead sectors     0
	  Block device           253:5

	  --- Logical volume ---
	  LV Name                /dev/main/rootbackup
	  VG Name                main
	  LV UUID                Zg7bQo-iQT3-w2Sq-voLN-Yj2H-6Owo-Cmjii6
	  LV Write Access        read/write
	  LV snapshot status     active destination for /dev/main/root
	  LV Status              available
	  # open                 0
	  LV Size                5.00 GB
	  Current LE             1280
	  Segments               1
	  Snapshot chunk size    8.00 KB
	  Allocated to snapshot  0.01%
	  Allocation             inherit
	  Read ahead sectors     0
	  Block device           253:2

However, when I try to remove the rootbackup snapshot:

	rescue:~# lvremove -v /dev/main/rootbackup
		Using logical volume(s) on command line
	Do you really want to remove active logical volume "rootbackup"? [y/n]: y
		Archiving volume group "main" metadata.
		Found volume group "main"
		Loading main-root-real
		Loading main-rootbackup-cow
		Loading main-rootbackup

At this point, the machine crashes as before. I can still ping it, but
user space seems totally dead.

-- System Information:
Debian Release: testing/unstable
  APT prefers testing
  APT policy: (530, 'testing'), (520, 'unstable'), (510, 'experimental')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/bash
Kernel: Linux 2.6.16-2-k7
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)