Bug#439136: unable to create LVM snapshots on FC-device

[Christian Schwamborn]

Package: lvm2
Version: 2.02.06-4
Severity: important

When I'm creating snapshots on internal devices all works fine, but when
I try to create snapshots on a FC-device (using multipath), there is a
fifty-fifty chance that it will fail:

xen-7:~# lvcreate -s -L1G -vv -n test /dev/ERBACH/erbach 
      Setting global/locking_type to 1
      Setting global/locking_dir to /var/lock/lvm
      File-based locking enabled.
    Setting chunksize to 16 sectors.
      Getting target version for snapshot
      Getting target version for snapshot-origin
      Setting activation/mirror_region_size to 512
      Locking /var/lock/lvm/V_ERBACH WB
    Finding volume group "ERBACH"
      /dev/ram0: No label detected
      /dev/dm-0: lvm2 label detected
      /dev/ram1: No label detected
      /dev/dm-1: No label detected
      /dev/ram2: No label detected
      /dev/dm-2: No label detected
      /dev/ram3: No label detected
      /dev/dm-3: No label detected
      /dev/ram4: No label detected
      /dev/dm-4: No label detected
      /dev/ram5: No label detected
      /dev/sda5: No label detected
      /dev/dm-5: No label detected
      /dev/ram6: No label detected
      /dev/sda6: No label detected
      /dev/dm-6: No label detected
      /dev/ram7: No label detected
      /dev/sda7: lvm2 label detected
      /dev/dm-7: No label detected
      /dev/ram8: No label detected
      /dev/dm-8: No label detected
      /dev/ram9: No label detected
      /dev/dm-9: No label detected
      /dev/ram10: No label detected
      /dev/dm-10: No label detected
      /dev/ram11: No label detected
      /dev/ram12: No label detected
      /dev/ram13: No label detected
      /dev/ram14: No label detected
      /dev/ram15: No label detected
      /dev/dm-0: lvm2 label detected
      /dev/dm-0: lvm2 label detected
    Archiving volume group "ERBACH" metadata (seqno 78).
    Creating logical volume test
    Creating volume group backup "/etc/lvm/backup/ERBACH" (seqno 79).
      Finding volume group for uuid
MMp80E936wrmbc21Q3HjJWjqXgpEtdRdth2lrK70o3vFxYywI7onH1LWS37fkVFb
      /dev/dm-0: lvm2 label detected
      /dev/dm-0: lvm2 label detected
    Found volume group "ERBACH"
      Locking memory
      Setting activation/missing_stripe_filler to /dev/ioerror
      Getting target version for linear
      Getting target version for striped
    Creating ERBACH-test
    Loading ERBACH-test table
    Resuming ERBACH-test (254:11)
      Unlocking memory
      Linking /dev/ERBACH/test -> /dev/mapper/ERBACH-test
    Clearing start of logical volume "test"
      Finding volume group for uuid
MMp80E936wrmbc21Q3HjJWjqXgpEtdRdth2lrK70o3vFxYywI7onH1LWS37fkVFb
      /dev/dm-0: lvm2 label detected
      /dev/dm-0: lvm2 label detected
    Found volume group "ERBACH"
  LV ERBACH/test in use: not deactivating
  Couldn't deactivate new snapshot.
      Unlocking /var/lock/lvm/V_ERBACH


I figured out that if I stop udev it works just fine. So maybe it's also
a problem of udev.
After setting udev to debug loglevel (udevcontrol log_priority=debug),
the chance of a success was significanty increased, so I belief its a
timing-problem between udev and lvmcreate.

udev logs as follows:

Aug 22 16:12:03 xen-7 multipathd: dm-11: add map (uevent) 
Aug 22 16:12:03 xen-7 udevd[4103]: udev_event_run: seq 1838 forked, pid
[5815], 'add' 'block', 0 seconds old
Aug 22 16:12:03 xen-7 udevd-event[5815]: run_program: '/sbin/dmsetup -j
254 -m 11 --noopencount --noheadings -c -o name info'
Aug 22 16:12:03 xen-7 udevd-event[5815]: run_program:
'/sbin/dmsetup' (stdout) 'ERBACH-test'
Aug 22 16:12:03 xen-7 udevd-event[5815]: run_program: '/sbin/dmsetup'
returned with status 0
Aug 22 16:12:03 xen-7 udevd-event[5815]: udev_rules_get_name: no node
name set, will use kernel name 'dm-11'
Aug 22 16:12:03 xen-7 udevd-event[5815]: udev_db_get_device: no db file
to read /dev/.udev/db/block at dm-11: No such file or directory
Aug 22 16:12:03 xen-7 udevd-event[5815]: udev_node_add: creating device
node '/dev/dm-11', major = '254', minor = '11', mode = '0660', uid =
'0', gid = '6'
Aug 22 16:12:03 xen-7 udevd-event[5815]: run_program: '/sbin/kpartx
-a /dev/mapper/ERBACH-test'
Aug 22 16:12:03 xen-7 udevd-event[5815]: run_program: '/sbin/kpartx'
returned with status 0
Aug 22 16:12:03 xen-7 udevd-event[5815]: pass_env_to_socket: passed -1
bytes to socket '/org/kernel/udev/monitor', 
Aug 22 16:12:03 xen-7 udevd-event[5815]: pass_env_to_socket: passed 140
bytes to socket '/org/freedesktop/hal/udev_event', 
Aug 22 16:12:03 xen-7 udevd-event[5815]: udev_event_run: seq 1838
finished
Aug 22 16:12:03 xen-7 udevd[4103]: udev_done: seq 1838, pid [5815] exit
with 0, 0 seconds old


I'm running Debian Etch, kernel 2.6.18-4-xen-amd64, libc6 2.3.6.ds1-13,
udev 0.105-4

Cheers Christian