On Mon, 22 Jan 2024 at 12:27, Stefan Hajnoczi <stefa...@redhat.com> wrote:
>
> Requests that complete in an IOThread use irqfd to notify the guest
> while requests that complete in the main loop thread use the traditional
> qdev irq code path. The reason for this conditional is that the irq code
> path requires the BQL:
>
> if (s->ioeventfd_started && !s->ioeventfd_disabled) {
> virtio_notify_irqfd(vdev, req->vq);
> } else {
> virtio_notify(vdev, req->vq);
> }
>
> There is a corner case where the conditional invokes the irq code path
> instead of the irqfd code path:
>
> static void virtio_blk_stop_ioeventfd(VirtIODevice *vdev)
> {
> ...
> /*
> * Set ->ioeventfd_started to false before draining so that host
> notifiers
> * are not detached/attached anymore.
> */
> s->ioeventfd_started = false;
>
> /* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */
> blk_drain(s->conf.conf.blk);
>
> During blk_drain() the conditional produces the wrong result because
> ioeventfd_started is false.
>
> Use qemu_in_iothread() instead of checking the ioeventfd state.
>
> Buglink: https://issues.redhat.com/browse/RHEL-15394
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
Ping?
> Based-on:
> https://repo.or.cz/qemu/kevin.git/shortlog/c14962c3ea6f0998d028142ed14affcb9dfccf28
>
> Stable backport notes: dataplane_started is being renamed to
> ioeventfd_started in the next block pull request. This patch can be
> safely applied to -stable although the variable name has changed and
> git-am will complain.
>
> hw/block/virtio-blk.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 227d83569f..287c31ee3c 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -64,7 +64,7 @@ static void virtio_blk_req_complete(VirtIOBlockReq *req,
> unsigned char status)
> iov_discard_undo(&req->inhdr_undo);
> iov_discard_undo(&req->outhdr_undo);
> virtqueue_push(req->vq, &req->elem, req->in_len);
> - if (s->ioeventfd_started && !s->ioeventfd_disabled) {
> + if (qemu_in_iothread()) {
> virtio_notify_irqfd(vdev, req->vq);
> } else {
> virtio_notify(vdev, req->vq);
> --
> 2.43.0
>
>
