[Qemu-devel] [PATCH 1/9] virtio-dataplane: pass assign=true to virtio_queue_aio_set_host_notifier_handler

[Paolo Bonzini <pbonzini@redhat.com>]

There is no need to run the handler one last time; the device is
being reset and it is okay to drop requests that are pending in
the virtqueue.  Even in the case of migration, the requests would
be processed when ioeventfd is re-enabled on the destination
side: virtio_queue_set_host_notifier_fd_handler will call
virtio_queue_host_notifier_read, which will start dataplane; the host
notifier is then connected to the I/O thread and event_notifier_set is
called to start processing it.

By omitting this call, we dodge a possible cause of races between the
dataplane thread on one side and the main/vCPU threads on the other.

The virtio_queue_aio_set_host_notifier_handler function is now
only ever called with assign=true, but for now this is left as is
because the function parameters will change soon anyway.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 2 +-
 hw/scsi/virtio-scsi-dataplane.c | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index e666dd4..fddd3ab 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -262,7 +262,7 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
     aio_context_acquire(s->ctx);
 
     /* Stop notifications for new requests from guest */
-    virtio_queue_aio_set_host_notifier_handler(s->vq, s->ctx, false, false);
+    virtio_queue_aio_set_host_notifier_handler(s->vq, s->ctx, true, false);
 
     /* Drain and switch bs back to the QEMU main loop */
     blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context());
diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index b44ac5d..21d5bfd 100644
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -70,10 +70,10 @@ static void virtio_scsi_clear_aio(VirtIOSCSI *s)
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);
     int i;
 
-    virtio_queue_aio_set_host_notifier_handler(vs->ctrl_vq, s->ctx, false, false);
-    virtio_queue_aio_set_host_notifier_handler(vs->event_vq, s->ctx, false, false);
+    virtio_queue_aio_set_host_notifier_handler(vs->ctrl_vq, s->ctx, true, false);
+    virtio_queue_aio_set_host_notifier_handler(vs->event_vq, s->ctx, true, false);
     for (i = 0; i < vs->conf.num_queues; i++) {
-        virtio_queue_aio_set_host_notifier_handler(vs->cmd_vqs[i], s->ctx, false, false);
+        virtio_queue_aio_set_host_notifier_handler(vs->cmd_vqs[i], s->ctx, true, false);
     }
 }
 
-- 
1.8.3.1