virtio_queue_aio_attach_host_notifier() does not require the AioContext
lock. Stop taking the lock and remember add an explicit smp_wmb()
because we were relying on the implicit barrier in the AioContext lock
before.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/scsi/virtio-scsi-dataplane.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index 1e684beebe..135e23fe54 100644
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -149,23 +149,17 @@ int virtio_scsi_dataplane_start(VirtIODevice *vdev)
 
     memory_region_transaction_commit();
 
-    /*
-     * These fields are visible to the IOThread so we rely on implicit barriers
-     * in aio_context_acquire() on the write side and aio_notify_accept() on
-     * the read side.
-     */
     s->dataplane_starting = false;
     s->dataplane_started = true;
+    smp_wmb(); /* paired with aio_notify_accept() */
 
     if (s->bus.drain_count == 0) {
-        aio_context_acquire(s->ctx);
         virtio_queue_aio_attach_host_notifier(vs->ctrl_vq, s->ctx);
         virtio_queue_aio_attach_host_notifier_no_poll(vs->event_vq, s->ctx);
 
         for (i = 0; i < vs->conf.num_queues; i++) {
             virtio_queue_aio_attach_host_notifier(vs->cmd_vqs[i], s->ctx);
         }
-        aio_context_release(s->ctx);
     }
     return 0;
 
-- 
2.42.0

Am 23.11.2023 um 20:49 hat Stefan Hajnoczi geschrieben:
> virtio_queue_aio_attach_host_notifier() does not require the AioContext
> lock. Stop taking the lock and remember add an explicit smp_wmb()
> because we were relying on the implicit barrier in the AioContext lock
> before.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

On Thu, Nov 23, 2023 at 02:49:29PM -0500, Stefan Hajnoczi wrote:
> virtio_queue_aio_attach_host_notifier() does not require the AioContext
> lock. Stop taking the lock and remember add an explicit smp_wmb()

s/remember// ?

> because we were relying on the implicit barrier in the AioContext lock
> before.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  hw/scsi/virtio-scsi-dataplane.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org

On Mon, Nov 27, 2023 at 09:21:08AM -0600, Eric Blake wrote:
> On Thu, Nov 23, 2023 at 02:49:29PM -0500, Stefan Hajnoczi wrote:
> > virtio_queue_aio_attach_host_notifier() does not require the AioContext
> > lock. Stop taking the lock and remember add an explicit smp_wmb()
> 
> s/remember// ?

Will fix, thanks!

Stefan