[dm-devel] [PATCH 0/6] Support DAX for device-mapper dm-linear devices

[Mike Snitzer]

On Mon, Jun 20 2016 at  3:40pm -0400,
Mike Snitzer <snitzer at redhat.com> wrote:
 
> # dd if=/dev/zero of=/mnt/dax/meh bs=1024K oflag=direct
> [11729.754671] XFS (dm-4): Metadata corruption detected at xfs_agf_read_verify+0x70/0x120 [xfs], xfs_agf block 0x45a808
> [11729.766423] XFS (dm-4): Unmount and run xfs_repair
> [11729.771774] XFS (dm-4): First 64 bytes of corrupted metadata buffer:
> [11729.778869] ffff8800b8038000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [11729.788582] ffff8800b8038010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [11729.798293] ffff8800b8038020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [11729.808002] ffff8800b8038030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [11729.817715] XFS (dm-4): metadata I/O error: block 0x45a808 ("xfs_trans_read_buf_map") error 117 numblks 8
> 
> When this XFS corruption occurs corruption then also manifests in lvm2's
> metadata:
> 
> # vgremove pmem
> Do you really want to remove volume group "pmem" containing 1 logical volumes? [y/n]: y
> Do you really want to remove active logical volume lv? [y/n]: y
>   Incorrect metadata area header checksum on /dev/pmem0p1 at offset 4096
>   WARNING: Failed to write an MDA of VG pmem.
>   Incorrect metadata area header checksum on /dev/pmem0p2 at offset 4096
>   WARNING: Failed to write an MDA of VG pmem.
>   Failed to write VG pmem.
>   Incorrect metadata area header checksum on /dev/pmem0p2 at offset 4096
>   Incorrect metadata area header checksum on /dev/pmem0p1 at offset 4096
> 
> If I don't use XFS, and only issue IO directly to the /dev/pmem/lv, I
> don't see this corruption.

I did the same test with ext4 instead of xfs and it resulted in the same
type of systemic corruption (lvm2 metadata corrupted too):

[12816.407147] EXT4-fs (dm-4): DAX enabled. Warning: EXPERIMENTAL, use at your own risk
[12816.416123] EXT4-fs (dm-4): mounted filesystem with ordered data mode. Opts: dax
[12816.766855] EXT4-fs error (device dm-4): ext4_mb_generate_buddy:758: group 9, block bitmap and bg descriptor inconsistent: 32768 vs 32395 free clusters
[12816.782016] EXT4-fs error (device dm-4): ext4_mb_generate_buddy:758: group 10, block bitmap and bg descriptor inconsistent: 32768 vs 16384 free clusters
[12816.797491] JBD2: Spotted dirty metadata buffer (dev = dm-4, blocknr = 0). There's a risk of filesystem corruption in case of system crash.

# vgremove pmem
Do you really want to remove volume group "pmem" containing 1 logical volumes? [y/n]: y
Do you really want to remove active logical volume lv? [y/n]: y
  Incorrect metadata area header checksum on /dev/pmem0p1 at offset 4096
  WARNING: Failed to write an MDA of VG pmem.
  Incorrect metadata area header checksum on /dev/pmem0p2 at offset 4096
  WARNING: Failed to write an MDA of VG pmem.
  Failed to write VG pmem.
  Incorrect metadata area header checksum on /dev/pmem0p2 at offset 4096
  Incorrect metadata area header checksum on /dev/pmem0p1 at offset 4096