---

yaml
---
r: 284241
b: refs/heads/master
c: ee7cd89
h: refs/heads/master
i:
  284239: b8de77c
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 3b720b8c865098c49c1570b6b5c7832bcfa6e6c2
+refs/heads/master: ee7cd8981e15bcb365fc762afe3fc47b8242f630

trunk/drivers/virtio/virtio_ring.c

@@ -251,9 +251,20 @@ int virtqueue_add_buf(struct virtqueue *_vq,
 
 	/* Put entry in available array (but don't update avail->idx until they
 	 * do sync). */
-	avail = ((vq->vring.avail->idx + vq->num_added++) & (vq->vring.num-1));
+	avail = (vq->vring.avail->idx & (vq->vring.num-1));
 	vq->vring.avail->ring[avail] = head;
 
+	/* Descriptors and available array need to be set before we expose the
+	 * new available array entries. */
+	virtio_wmb(vq);
+	vq->vring.avail->idx++;
+	vq->num_added++;
+
+	/* This is very unlikely, but theoretically possible.  Kick
+	 * just in case. */
+	if (unlikely(vq->num_added == (1 << 16) - 1))
+		virtqueue_kick(_vq);
+
 	pr_debug("Added buffer head %i to %p\n", head, vq);
 	END_USE(vq);
 
@@ -283,13 +294,10 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq)
 	 * new available array entries. */
 	virtio_wmb(vq);
 
-	old = vq->vring.avail->idx;
-	new = vq->vring.avail->idx = old + vq->num_added;
+	old = vq->vring.avail->idx - vq->num_added;
+	new = vq->vring.avail->idx;
 	vq->num_added = 0;
 
-	/* Need to update avail index before checking if we should notify */
-	virtio_mb(vq);
-
 	if (vq->event) {
 		needs_kick = vring_need_event(vring_avail_event(&vq->vring),
 					      new, old);