[linux-lvm] lvm2 2.02.105 breaks snapshots

[Christian Hesse]

Zdenek Kabelac <zkabelac at redhat.com> on Tue, 2014/02/04 17:47:
> Dne 4.2.2014 09:55, Christian Hesse napsal(a):
> > Christian Hesse <list at eworm.de> on Thu, 2014/01/23 14:27:
> >> Hello everybody,
> >>
> >> looks like lvm2 2.02.105 breaks snapshots. This is my block device tree:
> >>
> >> NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
> >> sda                   8:0    0   477G  0 disk
> >> |-sda1                8:1    0   767M  0 part
> >> | `-vg0-boot        254:0    0    64M  0 lvm   /boot
> >> |-sda2                8:2    0 444,2G  0 part
> >> | `-cvg             254:3    0 444,2G  0 crypt
> >> |   |-cvg-root      254:4    0    40G  0 lvm   /
> >> |   |-cvg-swap      254:5    0     4G  0 lvm   [SWAP]
> >> |   |-cvg-log       254:6    0     1G  0 lvm   /var/log
> >> |   `-cvg-home      254:8    0   320G  0 lvm   /home
> >> |-sda3                8:3    0    32G  0 part
> >> `-sda128            259:0    0     1M  0 part
> >>
> >> Creating a snapshot succeeds, but it is broken and can not be mounted:
> >>
> >> # lvcreate -s -pr -l50%free -n snap-home cvg/home
> >>    Logical volume "snap-home" created
> >> # mount /dev/cvg/snap-home /mnt/tmp
> >> mount: /dev/mapper/cvg-snap--home is write-protected, mounting read-only
> >> mount: wrong fs type, bad option, bad superblock on
> >> /dev/mapper/cvg-snap--home, missing codepage or helper program, or other
> >> error
> >>
> >> Syslog has a lot of these messages:
> >>
> >> [ 4823.002220] EXT4-fs (dm-7): ext4_check_descriptors: Checksum for group
> >> 256 failed (43470!=57954)
> >>
> >> Downgrading to lvm2 2.02.104 fixes the problem:
> >>
> >> # lvcreate -s -pr -l50%free -n snap-home
> >> cvg/home Logical volume "snap-home" created
> >> # mount /dev/cvg/snap-home /mnt/tmp
> >> mount: /dev/mapper/cvg-snap--home is write-protected, mounting read-only
> >>
> >> This is an Arch Linux system with Linux 3.12.8.
> >
> > Hello everybody,
> >
> > did anybody notice my mail? This is a real regression for me and I would
> > like to get this sorted. I will help with whatever is needed to find the
> > problem.
> >
> 
> 
> Ok -  could you test this:
> 
> Create an lv  -  ('lvcreate -Lsmallsize  vg'
> mount this lv somewhere
> modify this filesystem (via dd)

Do you want me to write to the block device here? I am not surprised if
anything break modifying a mounted filesystem.

> 'fsfreeze --freeze  mountpoint'
> 
> now  - copy whole frozen device somewhere (via dd)
> 
> 'fsfreeze --unfreeze mountpoint'
> 
> umount mountpoint
> 
> losetup -r  /dev/loop_free_number    frozen_copy_of_device
> 
> and now - try to mount your  read-only loop device copy.
> 
> Does it work for you ?
> 
> I've been testing this - and it seem fsfreeze API in kernel is not working 
> properly and you need to reply journal.
> 
> Then try to repeat the same with 3.10 kernel and 3.4 kernel.
> 
> So far I'm not convinced lvm2 version has anything to do with this problem
> 
> For 3.10  ext4 seems to work, but xfs is broken.

As said this is perfectly stable with lvm2 2.02.104. It breaks reliable with
lvm2 2.02.105. So I am sure lvm userspace tools are at least involved.

Looks like even the parent volume gets corrupted. My GnuPG keyring got
corrupted after creating a snapshot (with lvm2 2.02.105).

Just wondering... Is this mailing list just about the kernel part of lvm or
does it cover userspace as well?

-- 
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