virtio_vsock_skb_rx_put() only calls skb_put() if the length in the
packet header is not zero even though skb_put() handles this case
gracefully.

Remove the functionally redundant check from virtio_vsock_skb_rx_put()
and, on the assumption that this is a worthwhile optimisation for
handling credit messages, augment the existing length checks in
virtio_transport_rx_work() to elide the call for zero-length payloads.
Note that the vhost code already has similar logic in
vhost_vsock_alloc_skb().

Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/virtio_vsock.h     | 4 +---
 net/vmw_vsock/virtio_transport.c | 4 +++-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 36fb3edfa403..eb6980aa19fd 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h

@@ -52,9 +52,7 @@ static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb)
 	u32 len;
 
 	len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
-
-	if (len > 0)
-		skb_put(skb, len);
+	skb_put(skb, len);
 }
 
 static inline struct sk_buff *virtio_vsock_alloc_skb(unsigned int size, gfp_t mask)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index bd2c6aaa1a93..488e6ddc6ffa 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c

@@ -656,7 +656,9 @@ static void virtio_transport_rx_work(struct work_struct *work)
 				continue;
 			}
 
-			virtio_vsock_skb_rx_put(skb);
+			if (payload_len)
+				virtio_vsock_skb_rx_put(skb);
+
 			virtio_transport_deliver_tap_pkt(skb);
 			virtio_transport_recv_pkt(&virtio_transport, skb);
 		}

-- 
2.50.0.727.gbf7dc18ff4-goog