virtio-scsi: don't process IO on fenced dataplane

If virtio_scsi_dataplane_start fails, there is a small window when it drops the
aio lock (in aio_wait_bh_oneshot) and the dataplane's AIO handler can
still run during that window.

This is done after the dataplane was marked as fenced, thus we use this flag
to avoid it doing any IO.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201217150040.906961-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/scsi/virtio-scsi-dataplane.c

@@ -52,12 +52,14 @@ void virtio_scsi_dataplane_setup(VirtIOSCSI *s, Error **errp)
 static bool virtio_scsi_data_plane_handle_cmd(VirtIODevice *vdev,
                                               VirtQueue *vq)
 {
-    bool progress;
+    bool progress = false;
     VirtIOSCSI *s = VIRTIO_SCSI(vdev);
 
     virtio_scsi_acquire(s);
-    assert(s->ctx && s->dataplane_started);
-    progress = virtio_scsi_handle_cmd_vq(s, vq);
+    if (!s->dataplane_fenced) {
+        assert(s->ctx && s->dataplane_started);
+        progress = virtio_scsi_handle_cmd_vq(s, vq);
+    }
     virtio_scsi_release(s);
     return progress;
 }
@@ -65,12 +67,14 @@ static bool virtio_scsi_data_plane_handle_cmd(VirtIODevice *vdev,
 static bool virtio_scsi_data_plane_handle_ctrl(VirtIODevice *vdev,
                                                VirtQueue *vq)
 {
-    bool progress;
+    bool progress = false;
     VirtIOSCSI *s = VIRTIO_SCSI(vdev);
 
     virtio_scsi_acquire(s);
-    assert(s->ctx && s->dataplane_started);
-    progress = virtio_scsi_handle_ctrl_vq(s, vq);
+    if (!s->dataplane_fenced) {
+        assert(s->ctx && s->dataplane_started);
+        progress = virtio_scsi_handle_ctrl_vq(s, vq);
+    }
     virtio_scsi_release(s);
     return progress;
 }
@@ -78,12 +82,14 @@ static bool virtio_scsi_data_plane_handle_ctrl(VirtIODevice *vdev,
 static bool virtio_scsi_data_plane_handle_event(VirtIODevice *vdev,
                                                 VirtQueue *vq)
 {
-    bool progress;
+    bool progress = false;
     VirtIOSCSI *s = VIRTIO_SCSI(vdev);
 
     virtio_scsi_acquire(s);
-    assert(s->ctx && s->dataplane_started);
-    progress = virtio_scsi_handle_event_vq(s, vq);
+    if (!s->dataplane_fenced) {
+        assert(s->ctx && s->dataplane_started);
+        progress = virtio_scsi_handle_event_vq(s, vq);
+    }
     virtio_scsi_release(s);
     return progress;
 }