What were you trying to do that didn't work?

Set device weight on VM disk.

Please provide the package NVR for which bug is seen:

libvirt-10.4.0-1.el10

How reproducible:

100%

Steps to reproduce

1. Given a running VM booted from disk

   <disk type="file" device="disk">
     <driver name="qemu" type="qcow2"/>
     <source file="/var/lib/avocado/data/avocado-vt/images/jeos-27-x86_64.qcow2" index="1"/>
     <backingStore/>
     <target dev="vda" bus="virtio"/>
     <alias name="virtio-disk0"/>
     <address type="pci" domain="0x0000" bus="0x04" slot="0x00" function="0x0"/>
   </disk>
   

2. Try set device weight

   # virsh blkiotune avocado-vt-vm1 --live --device-weights /dev/vda,100

Expected results

Error message

error: 

Unable to change blkio parameters
error: Requested operation is not valid: blkio device weight is valid only for cfq scheduler

Actual results

A different error and a coredump for virtqemud.

Additional info

1. It seems setting weight isn't expected to work with cgroup2 https://bugzilla.redhat.com/show_bug.cgi?id=1970830 but given now we see a coredump it seems to be worth reporting. Setting severity low still.
2. On other test runs with the same libvirt version the expected behavior is observed. The qemu and kernel versions are different:
   • where it reproduces: qemu-kvm-9.0.0-2.el10.x86_64 kernel-6.10.0-0.rc4.11.el10.x86_64
   • where it doesn't reproduce: qemu-kvm-9.0.0-1.el10.x86_64 kernel-6.9.0-7.el10.x86_64
3. Attaching crash info