[PATCH v2 3/5] vhost-user-blk: add mechanism to track the guest notifiers init state

[Dima Stepanov <dimastep@yandex-team.ru>]

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.

Signed-off-by: Dima Stepanov <dimastep@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);
+    }
 
     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;
 
+    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;
 
+    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