virtio: order used ring after used index read

Commit Message

Michael S. Tsirkin Oct. 25, 2009, 12:22 p.m. UTC

None

Patch

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index f536005..4c4df3e 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -285,6 +285,9 @@  static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len)
 		return NULL;
 	}
 
+        /* Only get used array entries after they have been exposed by host. */
+	rmb();
+
 	i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
 	*len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;