On Tue, Aug 25, 2026 at 11:48:54AM -0400, Stefan Hajnoczi wrote:
> Commit e24a47c5b73e ("virtio-scsi: do not use vring in dataplane") set
> dataplane_started to true when virtio_scsi_dataplane_start() fails. This
> is likely a typo since dataplane is not functional after failure.
> 
> The non-ioeventfd fallback is broken because dataplane_started is true
> after virtio_scsi_dataplane_start() failure. As a result, the following
> assertion failure occurs when a virtio-scsi device exceeds the open file
> descriptor ulimit when setting up notifiers (eventfds):
> 
>   $ ulimit -n 104 # exact number can vary based on QEMU version
>   $ qemu-system-x86_64 -M q35,accel=kvm -m 1G -cpu host -smp 14 \
>          --blockdev file,node-name=drive0,filename=test.img,cache.direct=on,aio=native \
>          --blockdev file,node-name=drive1,filename=data01.img,cache.direct=on,aio=native \
>          --device virtio-scsi-pci,id=virtio-scsi-pci0 \
>          --device scsi-hd,drive=drive0,bus=virtio-scsi-pci0.0 \
>          --device virtio-scsi-pci,id=virtio-scsi-pci1 \
>          --device scsi-hd,drive=drive1,bus=virtio-scsi-pci1.0
>   qemu: virtio-scsi: Failed to set guest notifiers (-24), ensure -accel kvm is set.
>   qemu: virtio_bus_start_ioeventfd: failed. Fallback to userspace (slower).
>   qemu-system-x86_64: ../hw/scsi/virtio-scsi.c:1017: virtio_scsi_reset: Assertion `!s->dataplane_started' failed.
>   Aborted                    (core dumped)
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>

Ping

Paolo: Can you take this through your SCSI tree? Thanks!

Stefan

> Fixes: e24a47c5b73e ("virtio-scsi: do not use vring in dataplane")
> Buglink: https://redhat.atlassian.net/browse/RHEL-193328
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  hw/scsi/virtio-scsi-dataplane.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
> index 95f13fb7c28..bcb6e441335 100644
> --- a/hw/scsi/virtio-scsi-dataplane.c
> +++ b/hw/scsi/virtio-scsi-dataplane.c
> @@ -230,7 +230,7 @@ fail_host_notifiers:
>  fail_guest_notifiers:
>      s->dataplane_fenced = true;
>      s->dataplane_starting = false;
> -    s->dataplane_started = true;
> +    s->dataplane_started = false;
>      return -ENOSYS;
>  }
>  
> -- 
> 2.55.0
> 
>