net/ena: refactor ena_get_stats64 to be atomic context safe

BugLink: http://bugs.launchpad.net/bugs/1664312

ndo_get_stat64() can be called from atomic context, but the current
implementation sends an admin command to retrieve the statistics from
the device. This admin command can sleep.

This patch re-factors the implementation of ena_get_stats64() to use
the {rx,tx}bytes/count from the driver's inner counters, and to obtain
the rx drop counter from the asynchronous keep alive (heart bit)
event.
Signed-off-by: Netanel Belgazal <netanel@annapurnalabs.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[kamal: backport from commit d81db240 (context)]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/net/ethernet/amazon/ena/ena_admin_defs.h

@@ -873,6 +873,14 @@ struct ena_admin_aenq_link_change_desc {
 	u32 flags;
 };
 
+struct ena_admin_aenq_keep_alive_desc {
+	struct ena_admin_aenq_common_desc aenq_common_desc;
+
+	u32 rx_drops_low;
+
+	u32 rx_drops_high;
+};
+
 struct ena_admin_ena_mmio_req_read_less_resp {
 	u16 req_id;
 

drivers/net/ethernet/amazon/ena/ena_netdev.c

@@ -2176,28 +2176,46 @@ static struct rtnl_link_stats64 *ena_get_stats64(struct net_device *netdev,
 						 struct rtnl_link_stats64 *stats)
 {
 	struct ena_adapter *adapter = netdev_priv(netdev);
-	struct ena_admin_basic_stats ena_stats;
-	int rc;
+	struct ena_ring *rx_ring, *tx_ring;
+	unsigned int start;
+	u64 rx_drops;
+	int i;
 
 	if (!test_bit(ENA_FLAG_DEV_UP, &adapter->flags))
 		return NULL;
 
-	rc = ena_com_get_dev_basic_stats(adapter->ena_dev, &ena_stats);
-	if (rc)
-		return NULL;
+	for (i = 0; i < adapter->num_queues; i++) {
+		u64 bytes, packets;
+
+		tx_ring = &adapter->tx_ring[i];
+
+		do {
+			start = u64_stats_fetch_begin_irq(&tx_ring->syncp);
+			packets = tx_ring->tx_stats.cnt;
+			bytes = tx_ring->tx_stats.bytes;
+		} while (u64_stats_fetch_retry_irq(&tx_ring->syncp, start));
+
+		stats->tx_packets += packets;
+		stats->tx_bytes += bytes;
+
+		rx_ring = &adapter->rx_ring[i];
 
-	stats->tx_bytes = ((u64)ena_stats.tx_bytes_high << 32) |
-		ena_stats.tx_bytes_low;
-	stats->rx_bytes = ((u64)ena_stats.rx_bytes_high << 32) |
-		ena_stats.rx_bytes_low;
+		do {
+			start = u64_stats_fetch_begin_irq(&rx_ring->syncp);
+			packets = rx_ring->rx_stats.cnt;
+			bytes = rx_ring->rx_stats.bytes;
+		} while (u64_stats_fetch_retry_irq(&rx_ring->syncp, start));
+
+		stats->rx_packets += packets;
+		stats->rx_bytes += bytes;
+	}
 
-	stats->rx_packets = ((u64)ena_stats.rx_pkts_high << 32) |
-		ena_stats.rx_pkts_low;
-	stats->tx_packets = ((u64)ena_stats.tx_pkts_high << 32) |
-		ena_stats.tx_pkts_low;
+	do {
+		start = u64_stats_fetch_begin_irq(&adapter->syncp);
+		rx_drops = adapter->dev_stats.rx_drops;
+	} while (u64_stats_fetch_retry_irq(&adapter->syncp, start));
 
-	stats->rx_dropped = ((u64)ena_stats.rx_drops_high << 32) |
-		ena_stats.rx_drops_low;
+	stats->rx_dropped = rx_drops;
 
 	stats->multicast = 0;
 	stats->collisions = 0;

drivers/net/ethernet/amazon/ena/ena_netdev.h

@@ -241,6 +241,7 @@ struct ena_stats_dev {
 	u64 interface_up;
 	u64 interface_down;
 	u64 admin_q_pause;
+	u64 rx_drops;
 };
 
 enum ena_flags_t {