Hi,

I'm experiencing I/O errors in a guest machine after migrating it from one 
host to another, and then back to the original host. After doing this, I find 
the following in the dmesg output of the guest machine:

[  345.390543] end_request: I/O error, dev vda, sector 273871
[  345.391125] end_request: I/O error, dev vda, sector 273871
[  345.391705] end_request: I/O error, dev vda, sector 273871
[  345.394796] end_request: I/O error, dev vda, sector 1745983
[  345.396005] end_request: I/O error, dev vda, sector 1745983
[  346.083160] end_request: I/O error, dev vdb, sector 54528008
[  346.083179] Buffer I/O error on device dm-0, logical block 6815745
[  346.083181] lost page write due to I/O error on dm-0
[  346.083193] end_request: I/O error, dev vdb, sector 54528264
[  346.083195] Buffer I/O error on device dm-0, logical block 6815777
[  346.083197] lost page write due to I/O error on dm-0
[  346.083201] end_request: I/O error, dev vdb, sector 2056
[  346.083204] Buffer I/O error on device dm-0, logical block 1
[  346.083206] lost page write due to I/O error on dm-0
[  346.083209] Buffer I/O error on device dm-0, logical block 2
[  346.083211] lost page write due to I/O error on dm-0
[  346.083215] end_request: I/O error, dev vdb, sector 10248
[  346.083217] Buffer I/O error on device dm-0, logical block 1025
[  346.083219] lost page write due to I/O error on dm-0
[  346.091499] end_request: I/O error, dev vdb, sector 76240
[  346.091506] Buffer I/O error on device dm-0, logical block 9274
[  346.091508] lost page write due to I/O error on dm-0
[  346.091572] JBD2: Detected IO errors while flushing file data on dm-0-8
[  346.091915] end_request: I/O error, dev vdb, sector 38017360
[  346.091956] Aborting journal on device dm-0-8.
[  346.092557] end_request: I/O error, dev vdb, sector 38012928
[  346.092566] Buffer I/O error on device dm-0, logical block 4751360
[  346.092569] lost page write due to I/O error on dm-0
[  346.092624] JBD2: I/O error detected when updating journal superblock for 
dm-0-8.
[  346.100940] end_request: I/O error, dev vdb, sector 2048
[  346.100948] Buffer I/O error on device dm-0, logical block 0
[  346.100952] lost page write due to I/O error on dm-0
[  346.101027] EXT4-fs error (device dm-0): ext4_journal_start_sb:327: 
Detected aborted journal
[  346.101038] EXT4-fs (dm-0): Remounting filesystem read-only
[  346.101051] EXT4-fs (dm-0): previous I/O error to superblock detected
[  346.101836] end_request: I/O error, dev vdb, sector 2048
[  346.101845] Buffer I/O error on device dm-0, logical block 0
[  346.101849] lost page write due to I/O error on dm-0
[  373.006680] end_request: I/O error, dev vda, sector 624319
[  373.007543] end_request: I/O error, dev vda, sector 624319
[  373.008327] end_request: I/O error, dev vda, sector 624319
[  374.886674] end_request: I/O error, dev vda, sector 624319
[  374.887563] end_request: I/O error, dev vda, sector 624319

The hosts are both running Fedora 17 with qemu-kvm-1.0.1-1.fc17.x86_64. The 
guest machine has been started and migrated using libvirt (0.9.11). Kernel 
version is 3.5.6-1.fc17.x86_64 on the first host and 3.5.5-2.fc17.x86_64 on 
the second.
The guest machine is on Kernel 3.3.8 and uses ext4 on its disks.

The commandline, as generated by libvirtd, looks like this:

LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin 
QEMU_AUDIO_DRV=none /usr/bin/qemu-kvm -S -M pc-0.15 -enable-kvm -m 1024 -smp 
1,sockets=1,cores=1,threads=1 -name migratetest2 -uuid 
ddbf11e9-387e-902b-4849-8c3067dc42a2 -nodefconfig -nodefaults -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/migratetest2.monitor,server,nowait
 
-mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-reboot -no-
shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive 
file=/data/migratetest2_system,if=none,id=drive-virtio-
disk0,format=qcow2,cache=none -device virtio-blk-
pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-
disk0,bootindex=1 -drive file=/data/migratetest2_data-1,if=none,id=drive-
virtio-disk1,format=qcow2,cache=none -device virtio-blk-
pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk1,id=virtio-disk1 -
netdev tap,fd=27,id=hostnet0,vhost=on,vhostfd=28 -device virtio-net-
pci,netdev=hostnet0,id=net0,mac=02:00:00:00:00:0c,bus=pci.0,addr=0x3 -vnc 
127.0.0.1:2,password -k de -vga cirrus -incoming tcp:0.0.0.0:49153 -device 
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6

The second host has an ext4 filesystem mounted under /data, which it exports 
using NFSv3 over TCP to the first host, which also mounts it under /data.

So far, the problem seems reproducible: When I start another guest machine and 
do the same thing with it, the same problem happens.

Can anybody help me with this problem?

        Guido

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