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

[Kani, Toshimitsu]

On Mon, 2016-06-20 at 15:52 -0400, Mike Snitzer wrote:
> 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

I will look into the issue.

Thanks for the testing!
-Toshi