Comment 2 for bug 1029201

StacktraceTop:
 virtio_pci_mask_vq (vector=vector@entry=1, vq=0x7f7e7a00f100, masked=masked@entry=0, dev=<error reading variable: Unhandled dwarf expression opcode 0xfa>) at /build/buildd/qemu-kvm-1.1~rc+dfsg/hw/virtio-pci.c:546
 virtio_pci_mask_notifier (dev=0x7f7e79ff5670, vector=1, masked=0) at /build/buildd/qemu-kvm-1.1~rc+dfsg/hw/virtio-pci.c:576
 msix_set_mask_notifier_for_vector (vector=1, dev=0x7f7e79ff5670) at /build/buildd/qemu-kvm-1.1~rc+dfsg/hw/msix.c:562
 msix_set_mask_notifier (dev=dev@entry=0x7f7e79ff5670, f=f@entry=0x7f7e78cdb930 <virtio_pci_mask_notifier>) at /build/buildd/qemu-kvm-1.1~rc+dfsg/hw/msix.c:577
 virtio_pci_set_guest_notifiers (opaque=0x7f7e79ff5670, assign=true) at /build/buildd/qemu-kvm-1.1~rc+dfsg/hw/virtio-pci.c:651