net/virtio: fix read barriers on packed Tx cleanup

Read barrier must be implied between reading descriptor flags
and descriptor id. Otherwise, in case of reordering, we could
read wrong descriptor id.

For the reference, similar barrier for split rings is the read
barrier between VIRTQUEUE_NUSED (reading the used->idx) and
the call to the virtio_xmit_cleanup().

Additionally removed double update of 'used_idx'. It's enough
to set it in the end of the loop.

Fixes: 892dc798fa9c ("net/virtio: implement Tx path for packed queues")
Cc: stable@dpdk.org
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index cc476b8985a39a2c19e528d57f077b7155d6b4c2..63e4370e4ab3fde1dc5f934e26e74a8f707ef6ed 100644 (file)
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -234,7 +234,7 @@ virtio_xmit_cleanup_packed(struct virtqueue *vq, int num)
 
        used_idx = vq->vq_used_cons_idx;
        while (num-- && desc_is_used(&desc[used_idx], vq)) {
-               used_idx = vq->vq_used_cons_idx;
+               virtio_rmb(vq->hw->weak_barriers);
                id = desc[used_idx].id;
                dxp = &vq->vq_descx[id];
                vq->vq_used_cons_idx += dxp->ndescs;
@@ -1940,7 +1940,6 @@ virtio_xmit_pkts_packed(void *tx_queue, struct rte_mbuf **tx_pkts,
 
                /* Positive value indicates it need free vring descriptors */
                if (unlikely(need > 0)) {
-                       virtio_rmb(hw->weak_barriers);
                        need = RTE_MIN(need, (int)nb_pkts);
                        virtio_xmit_cleanup_packed(vq, need);
                        need = slots - vq->vq_free_cnt;