Apologies for mixing up patches last time. This looks good from a
vhost-user-blk perspective, but I worry that some of these changes
could impact other vhost device types.
I agree with adding notifiers_set to struct vhost_dev, and setting it in
vhost_dev_enable/disable notifiers, but is there any reason notifiers_set
can’t be checked inside vhost-user-blk?
On Thu, Apr 30, 2020 at 9:55 AM Dima Stepanov <dimas...@yandex-team.ru> wrote:
>
> In case of the vhost-user devices the daemon can be killed at any
> moment. Since QEMU supports the reconnet functionality the guest
> notifiers should be reset and disabled after "disconnect" event. The
> most issues were found if the "disconnect" event happened during vhost
> device initialization step.
> The disconnect event leads to the call of the vhost_dev_cleanup()
> routine. Which memset to 0 a vhost device structure. Because of this, if
> device was not started (dev.started == false) and the connection is
> broken, then the set_guest_notifier method will produce assertion error.
> Also connection can be broken after the dev.started field is set to
> true.
> A new notifiers_set field is added to the vhost_dev structure to track
> the state of the guest notifiers during the initialization process.
>
>From what I can tell this patch does two things:
(1)
In vhost.c you’re adding checks to abort early, while still returning
successfully, from
vhost_dev_drop_guest_notifiers() and vhost_dev_disable_notifiers() if
notifiers have
not been enabled. This new logic will affect all existing vhost devices.
(2)
For vhost-user-blk backend disconnect, you are ensuring that notifiers
are dropped and
disabled if and only if the notifiers are currently enabled.
I completely agree with (2), but I don't think we need all of what
you've done for
(1) to accomplish (2).
Either way, please clarify in your commit message.
> Signed-off-by: Dima Stepanov <dimas...@yandex-team.ru>
> ---
> hw/block/vhost-user-blk.c | 8 ++++----
> hw/virtio/vhost.c | 11 +++++++++++
> include/hw/virtio/vhost.h | 1 +
> 3 files changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 70d7842..5a3de0f 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -175,7 +175,9 @@ static void vhost_user_blk_stop(VirtIODevice *vdev)
> return;
> }
>
> - vhost_dev_stop(&s->dev, vdev);
> + if (s->dev.started) {
> + vhost_dev_stop(&s->dev, vdev);
> + }
>
Couldn't we check if s->dev.notifiers_set here before calling
vhost_dev_drop_guest_notifiers()?
> ret = vhost_dev_drop_guest_notifiers(&s->dev, vdev, s->dev.nvqs);
> if (ret < 0) {
> @@ -337,9 +339,7 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
> }
> s->connected = false;
>
> - if (s->dev.started) {
> - vhost_user_blk_stop(vdev);
> - }
> + vhost_user_blk_stop(vdev);
>
> vhost_dev_cleanup(&s->dev);
> }
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index fa3da9c..ddbdc53 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1380,6 +1380,7 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev,
> VirtIODevice *vdev)
> goto fail_vq;
> }
> }
> + hdev->notifiers_set = true;
>
> return 0;
> fail_vq:
> @@ -1407,6 +1408,10 @@ void vhost_dev_disable_notifiers(struct vhost_dev
> *hdev, VirtIODevice *vdev)
> BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
> int i, r;
>
I’m a little weary of short circuiting logic like this without at
least propagating an
error up. Couldn’t we leave it to the backends to check notifiers_set
before they
call vhost_dev_disable_notifiers() or vhost_dev_drop_guest_notifiers()?
Then, if anything, maybe make this check an assert?
> + if (!hdev->notifiers_set) {
> + return;
> + }
> +
> for (i = 0; i < hdev->nvqs; ++i) {
> r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index +
> i,
> false);
> @@ -1417,6 +1422,8 @@ void vhost_dev_disable_notifiers(struct vhost_dev
> *hdev, VirtIODevice *vdev)
> virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index +
> i);
> }
> virtio_device_release_ioeventfd(vdev);
> +
> + hdev->notifiers_set = false;
> }
>
> /*
> @@ -1449,6 +1456,10 @@ int vhost_dev_drop_guest_notifiers(struct vhost_dev
> *hdev,
> VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
> int ret;
>
Same comment as above - I’d prefer vhost-user-blk (and other backends
supporting reconnect)
check before calling the function instead of changing existing API
behavior for other vhost devices.
> + if (!hdev->notifiers_set) {
> + return 0;
> + }
> +
> ret = k->set_guest_notifiers(qbus->parent, nvqs, false);
> if (ret < 0) {
> error_report("Error reset guest notifier: %d", -ret);
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 4d0d2e2..e3711a7 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -90,6 +90,7 @@ struct vhost_dev {
> QLIST_HEAD(, vhost_iommu) iommu_list;
> IOMMUNotifier n;
> const VhostDevConfigOps *config_ops;
> + bool notifiers_set;
> };
>
> int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
> --
> 2.7.4
>
>
