ice: safer stats processing

The driver was zeroing live stats that could be fetched by
ndo_get_stats64 at any time. This could result in inconsistent
statistics, and the telltale sign was when reading stats frequently from
/proc/net/dev, the stats would go backwards.

Fix by collecting stats into a local, and delaying when we write to the
structure so it's not incremental.

Fixes: fcea6f3d ("ice: Add stats and ethtool support")
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/ice/ice_main.c

@@ -5930,14 +5930,15 @@ ice_fetch_u64_stats_per_ring(struct u64_stats_sync *syncp, struct ice_q_stats st
 /**
  * ice_update_vsi_tx_ring_stats - Update VSI Tx ring stats counters
  * @vsi: the VSI to be updated
+ * @vsi_stats: the stats struct to be updated
  * @rings: rings to work on
  * @count: number of rings
  */
 static void
-ice_update_vsi_tx_ring_stats(struct ice_vsi *vsi, struct ice_tx_ring **rings,
-			     u16 count)
+ice_update_vsi_tx_ring_stats(struct ice_vsi *vsi,
+			     struct rtnl_link_stats64 *vsi_stats,
+			     struct ice_tx_ring **rings, u16 count)
 {
-	struct rtnl_link_stats64 *vsi_stats = &vsi->net_stats;
 	u16 i;
 
 	for (i = 0; i < count; i++) {
@@ -5961,15 +5962,13 @@ ice_update_vsi_tx_ring_stats(struct ice_vsi *vsi, struct ice_tx_ring **rings,
  */
 static void ice_update_vsi_ring_stats(struct ice_vsi *vsi)
 {
-	struct rtnl_link_stats64 *vsi_stats = &vsi->net_stats;
+	struct rtnl_link_stats64 *vsi_stats;
 	u64 pkts, bytes;
 	int i;
 
-	/* reset netdev stats */
-	vsi_stats->tx_packets = 0;
-	vsi_stats->tx_bytes = 0;
-	vsi_stats->rx_packets = 0;
-	vsi_stats->rx_bytes = 0;
+	vsi_stats = kzalloc(sizeof(*vsi_stats), GFP_ATOMIC);
+	if (!vsi_stats)
+		return;
 
 	/* reset non-netdev (extended) stats */
 	vsi->tx_restart = 0;
@@ -5981,7 +5980,8 @@ static void ice_update_vsi_ring_stats(struct ice_vsi *vsi)
 	rcu_read_lock();
 
 	/* update Tx rings counters */
-	ice_update_vsi_tx_ring_stats(vsi, vsi->tx_rings, vsi->num_txq);
+	ice_update_vsi_tx_ring_stats(vsi, vsi_stats, vsi->tx_rings,
+				     vsi->num_txq);
 
 	/* update Rx rings counters */
 	ice_for_each_rxq(vsi, i) {
@@ -5996,10 +5996,17 @@ static void ice_update_vsi_ring_stats(struct ice_vsi *vsi)
 
 	/* update XDP Tx rings counters */
 	if (ice_is_xdp_ena_vsi(vsi))
-		ice_update_vsi_tx_ring_stats(vsi, vsi->xdp_rings,
+		ice_update_vsi_tx_ring_stats(vsi, vsi_stats, vsi->xdp_rings,
 					     vsi->num_xdp_txq);
 
 	rcu_read_unlock();
+
+	vsi->net_stats.tx_packets = vsi_stats->tx_packets;
+	vsi->net_stats.tx_bytes = vsi_stats->tx_bytes;
+	vsi->net_stats.rx_packets = vsi_stats->rx_packets;
+	vsi->net_stats.rx_bytes = vsi_stats->rx_bytes;
+
+	kfree(vsi_stats);
 }
 
 /**