virtio/ringtest: virtio_ring: fix up need_event math

last kicked event index must be updated unconditionally:
even if we don't need to kick, we do not want to re-check
the same entry for events.

Reported-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>

diff --git a/tools/virtio/ringtest/virtio_ring_0_9.c b/tools/virtio/ringtest/virtio_ring_0_9.c
index bbc3043b2fb169aa4764922a786e9cbfc34761ed..5fd3fbcb9e575b50f13fd5bc14505967a2755a31 100644 (file)
--- a/tools/virtio/ringtest/virtio_ring_0_9.c
+++ b/tools/virtio/ringtest/virtio_ring_0_9.c
@@ -225,16 +225,18 @@ bool enable_call()
 
 void kick_available(void)
 {
+       bool need;
+
        /* Flush in previous flags write */
        /* Barrier C (for pairing) */
        smp_mb();
-       if (!vring_need_event(vring_avail_event(&ring),
-                             guest.avail_idx,
-                             guest.kicked_avail_idx))
-               return;
+       need = vring_need_event(vring_avail_event(&ring),
+                               guest.avail_idx,
+                               guest.kicked_avail_idx);
 
        guest.kicked_avail_idx = guest.avail_idx;
-       kick();
+       if (need)
+               kick();
 }
 
 /* host side */
@@ -316,14 +318,16 @@ bool use_buf(unsigned *lenp, void **bufp)
 
 void call_used(void)
 {
+       bool need;
+
        /* Flush in previous flags write */
        /* Barrier D (for pairing) */
        smp_mb();
-       if (!vring_need_event(vring_used_event(&ring),
-                             host.used_idx,
-                             host.called_used_idx))
-               return;
+       need = vring_need_event(vring_used_event(&ring),
+                               host.used_idx,
+                               host.called_used_idx);
 
        host.called_used_idx = host.used_idx;
-       call();
+       if (need)
+               call();
 }