Description of problem:
Run kvm autotest 'ioquit' with virtio + qcow2 format image, will failed during checking image got some errors like this:

ERROR cluster 1617900 refcount=1 reference=0


Sometimes can find many such kind of errors though image is not corrupted. 
Confirmed with Kevin, these errors are harmless besides wasting some disk space for guest.


Version-Release number of selected component (if applicable):
kvm-83-105.el5_4.18

How reproducible:
So often

Steps to Reproduce:
1. run autotest kvm subtest 'ioquit'
(This test mainly runs dbench within guest and during dbench is running in guest, kill the autotest process along with all its child-processes including 'qemu-kvm'.
2. 
3.
  
Actual results:
Got some errors though they are harmless

Expected results:
Should not got these harmless errors if image is actually not corrupted.
Maybe let qemu-img fix this or replace 'Error' with 'Warning' as Kevin referred.

Additional info: