1 files changed, 41 insertions, 4 deletions

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index c8e162c9d1df..16ff976a86e3 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -557,6 +557,8 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	struct virtio_vsock_sock *vvs = vsk->trans;
 	size_t bytes, total = 0;
 	struct sk_buff *skb;
+	u32 fwd_cnt_delta;
+	bool low_rx_bytes;
 	int err = -EFAULT;
 	u32 free_space;
 
@@ -600,7 +602,10 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 		}
 	}
 
-	free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);
+	fwd_cnt_delta = vvs->fwd_cnt - vvs->last_fwd_cnt;
+	free_space = vvs->buf_alloc - fwd_cnt_delta;
+	low_rx_bytes = (vvs->rx_bytes <
+			sock_rcvlowat(sk_vsock(vsk), 0, INT_MAX));
 
 	spin_unlock_bh(&vvs->rx_lock);
 
@@ -610,9 +615,11 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	 * too high causes extra messages. Too low causes transmitter
 	 * stalls. As stalls are in theory more expensive than extra
 	 * messages, we set the limit to a high value. TODO: experiment
-	 * with different values.
+	 * with different values. Also send credit update message when
+	 * number of bytes in rx queue is not enough to wake up reader.
 	 */
-	if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
+	if (fwd_cnt_delta &&
+	    (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE || low_rx_bytes))
 		virtio_transport_send_credit_update(vsk);
 
 	return total;
@@ -843,7 +850,7 @@ static s64 virtio_transport_has_space(struct vsock_sock *vsk)
 	struct virtio_vsock_sock *vvs = vsk->trans;
 	s64 bytes;
 
-	bytes = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);
+	bytes = (s64)vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);
 	if (bytes < 0)
 		bytes = 0;
 
@@ -1683,6 +1690,36 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
 }
 EXPORT_SYMBOL_GPL(virtio_transport_read_skb);
 
+int virtio_transport_notify_set_rcvlowat(struct vsock_sock *vsk, int val)
+{
+	struct virtio_vsock_sock *vvs = vsk->trans;
+	bool send_update;
+
+	spin_lock_bh(&vvs->rx_lock);
+
+	/* If number of available bytes is less than new SO_RCVLOWAT value,
+	 * kick sender to send more data, because sender may sleep in its
+	 * 'send()' syscall waiting for enough space at our side. Also
+	 * don't send credit update when peer already knows actual value -
+	 * such transmission will be useless.
+	 */
+	send_update = (vvs->rx_bytes < val) &&
+		      (vvs->fwd_cnt != vvs->last_fwd_cnt);
+
+	spin_unlock_bh(&vvs->rx_lock);
+
+	if (send_update) {
+		int err;
+
+		err = virtio_transport_send_credit_update(vsk);
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(virtio_transport_notify_set_rcvlowat);
+
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Asias He");
 MODULE_DESCRIPTION("common code for virtio vsock");