gve: fix gve_get_stats()

gve_get_stats() can report wrong numbers if/when u64_stats_fetch_retry()
returns true.

What is needed here is to sample values in temporary variables,
and only use them after each loop is ended.

Fixes: f5cedc8 ("gve: Add transmit and receive support")
Signed-off-by: Eric Dumazet <[email protected]>
Cc: Catherine Sullivan <[email protected]>
Cc: Sagi Shahar <[email protected]>
Cc: Jon Olson <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Cc: Luigi Rizzo <[email protected]>
Cc: Jeroen de Borst <[email protected]>
Cc: Tao Liu <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: edumazet

drivers/net/ethernet/google/gve/gve_main.c

@@ -41,28 +41,33 @@ static void gve_get_stats(struct net_device *dev, struct rtnl_link_stats64 *s)
 {
 	struct gve_priv *priv = netdev_priv(dev);
 	unsigned int start;
+	u64 packets, bytes;
 	int ring;
 
 	if (priv->rx) {
 		for (ring = 0; ring < priv->rx_cfg.num_queues; ring++) {
 			do {
 				start =
 				  u64_stats_fetch_begin(&priv->rx[ring].statss);
-				s->rx_packets += priv->rx[ring].rpackets;
-				s->rx_bytes += priv->rx[ring].rbytes;
+				packets = priv->rx[ring].rpackets;
+				bytes = priv->rx[ring].rbytes;
 			} while (u64_stats_fetch_retry(&priv->rx[ring].statss,
 						       start));
+			s->rx_packets += packets;
+			s->rx_bytes += bytes;
 		}
 	}
 	if (priv->tx) {
 		for (ring = 0; ring < priv->tx_cfg.num_queues; ring++) {
 			do {
 				start =
 				  u64_stats_fetch_begin(&priv->tx[ring].statss);
-				s->tx_packets += priv->tx[ring].pkt_done;
-				s->tx_bytes += priv->tx[ring].bytes_done;
+				packets = priv->tx[ring].pkt_done;
+				bytes = priv->tx[ring].bytes_done;
 			} while (u64_stats_fetch_retry(&priv->tx[ring].statss,
 						       start));
+			s->tx_packets += packets;
+			s->tx_bytes += bytes;
 		}
 	}
 }