[Qemu-devel] [PATCH] virtio: revert host notifiers to old semantics

[Cornelia Huck]

The host notifier rework tried both to unify host notifiers across
transports and plug a possible hole during host notifier
re-assignment. Unfortunately, this meant a change in semantics that
breaks vhost and iSCSI+dataplane.

As the minimal fix, keep the common host notifier code but revert
to the old semantics so that we have time to figure out the proper
fix.

Fixes: 6798e245a3 ("virtio-bus: common ioeventfd infrastructure")
Reported-by: Peter Lieven <address@hidden>
Reported-by: Jason Wang <address@hidden>
Reported-by: Marc-André Lureau <address@hidden>
Signed-off-by: Cornelia Huck <address@hidden>
---
 hw/virtio/virtio-bus.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index 1313760..a85b7c8 100644
--- a/hw/virtio/virtio-bus.c
+++ b/hw/virtio/virtio-bus.c
@@ -176,8 +176,8 @@ static int set_host_notifier_internal(DeviceState *proxy, 
VirtioBusState *bus,
             return r;
         }
     } else {
-        virtio_queue_set_host_notifier_fd_handler(vq, false, false);
         k->ioeventfd_assign(proxy, notifier, n, assign);
+        virtio_queue_set_host_notifier_fd_handler(vq, false, false);
         event_notifier_cleanup(notifier);
     }
     return r;
@@ -251,31 +251,25 @@ int virtio_bus_set_host_notifier(VirtioBusState *bus, int 
n, bool assign)
 {
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
     DeviceState *proxy = DEVICE(BUS(bus)->parent);
-    VirtIODevice *vdev = virtio_bus_get_device(bus);
-    VirtQueue *vq = virtio_get_queue(vdev, n);
 
     if (!k->ioeventfd_started) {
         return -ENOSYS;
     }
+    k->ioeventfd_set_disabled(proxy, assign);
     if (assign) {
         /*
          * Stop using the generic ioeventfd, we are doing eventfd handling
          * ourselves below
+         *
+         * FIXME: We should just switch the handler and not deassign the
+         * ioeventfd.
+         * Otherwise, there's a window where we don't have an
+         * ioeventfd and we may end up with a notification where
+         * we don't expect one.
          */
-        k->ioeventfd_set_disabled(proxy, true);
-    }
-    /*
-     * Just switch the handler, don't deassign the ioeventfd.
-     * Otherwise, there's a window where we don't have an
-     * ioeventfd and we may end up with a notification where
-     * we don't expect one.
-     */
-    virtio_queue_set_host_notifier_fd_handler(vq, assign, !assign);
-    if (!assign) {
-        /* Use generic ioeventfd handler again. */
-        k->ioeventfd_set_disabled(proxy, false);
+        virtio_bus_stop_ioeventfd(bus);
     }
-    return 0;
+    return set_host_notifier_internal(proxy, bus, n, assign, false);
 }
 
 static char *virtio_bus_get_dev_path(DeviceState *dev)
-- 
2.6.6