Re: [Qemu-devel] Guest unresponsive after Virtqueue size exceeded error

[Fernando Casas Schössow]

Hi Ladi,

Thanks a lot for looking into this and replying.
I will do my best to rebuild and deploy Alpine's qemu packages with this patch 
included but not sure its feasible yet.
In any case, would it be possible to have this patch included in the next qemu 
release?
The current error message is helpful but knowing which device was involved will 
be much more helpful.

Regarding the environment, I'm not doing migrations and only managed save is 
done in case the host needs to be rebooted or shutdown. The QEMU process is 
running the VM since the host is started and this failuire is ocurring randomly 
without any previous manage save done.

As part of troubleshooting on one of the guests I switched from virtio_blk to 
virtio_scsi for the guest disks but I will need more time to see if that helped.
If I have this problem again I will follow your advise and remove 
virtio_balloon.

Another question: is there any way to monitor the virtqueue size either from 
the guest itself or from the host? Any file in sysfs or proc?
This may help to understand in which conditions this is happening and to react 
faster to mitigate the problem.

Thanks again for your help with this!

Fer

On vie, jun 16, 2017 at 8:58 , Ladi Prosek <address@hidden> wrote:
Hi,
Would you be able to enhance the error message and rebuild QEMU? --- 
a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -856,7 +856,7 @@ void 
*virtqueue_pop(VirtQueue *vq, size_t sz) max = vq->vring.num; if (vq->inuse >= 
vq->vring.num) { - virtio_error(vdev, "Virtqueue size exceeded"); + 
virtio_error(vdev, "Virtqueue %u device %s size exceeded", vq->queue_index, 
vdev->name); goto done; } This would at least confirm the theory that it's 
caused by virtio-blk-pci. If rebuilding is not feasible I would start by 
removing other virtio devices -- particularly balloon which has had quite a few 
virtio related bugs fixed recently. Does your environment involve VM migrations 
or saving/resuming, or does the crashing QEMU process always run the VM from 
its boot? Thanks!