i40e: protect ring accesses with READ- and WRITE_ONCE

READ_ONCE should be used when reading rings prior to accessing the
statistics pointer. Introduce this as well as the corresponding WRITE_ONCE
usage when allocating and freeing the rings, to ensure protected access.
Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -439,11 +439,15 @@ static void i40e_get_netdev_stats_struct(struct net_device *netdev,
 		i40e_get_netdev_stats_struct_tx(ring, stats);
 
 		if (i40e_enabled_xdp_vsi(vsi)) {
-			ring++;
+			ring = READ_ONCE(vsi->xdp_rings[i]);
+			if (!ring)
+				continue;
 			i40e_get_netdev_stats_struct_tx(ring, stats);
 		}
 
-		ring++;
+		ring = READ_ONCE(vsi->rx_rings[i]);
+		if (!ring)
+			continue;
 		do {
 			start   = u64_stats_fetch_begin_irq(&ring->syncp);
 			packets = ring->stats.packets;
@@ -787,6 +791,8 @@ static void i40e_update_vsi_stats(struct i40e_vsi *vsi)
 	for (q = 0; q < vsi->num_queue_pairs; q++) {
 		/* locate Tx ring */
 		p = READ_ONCE(vsi->tx_rings[q]);
+		if (!p)
+			continue;
 
 		do {
 			start = u64_stats_fetch_begin_irq(&p->syncp);
@@ -800,8 +806,11 @@ static void i40e_update_vsi_stats(struct i40e_vsi *vsi)
 		tx_linearize += p->tx_stats.tx_linearize;
 		tx_force_wb += p->tx_stats.tx_force_wb;
 
-		/* Rx queue is part of the same block as Tx queue */
-		p = &p[1];
+		/* locate Rx ring */
+		p = READ_ONCE(vsi->rx_rings[q]);
+		if (!p)
+			continue;
+
 		do {
 			start = u64_stats_fetch_begin_irq(&p->syncp);
 			packets = p->stats.packets;
@@ -10824,10 +10833,10 @@ static void i40e_vsi_clear_rings(struct i40e_vsi *vsi)
 	if (vsi->tx_rings && vsi->tx_rings[0]) {
 		for (i = 0; i < vsi->alloc_queue_pairs; i++) {
 			kfree_rcu(vsi->tx_rings[i], rcu);
-			vsi->tx_rings[i] = NULL;
-			vsi->rx_rings[i] = NULL;
+			WRITE_ONCE(vsi->tx_rings[i], NULL);
+			WRITE_ONCE(vsi->rx_rings[i], NULL);
 			if (vsi->xdp_rings)
-				vsi->xdp_rings[i] = NULL;
+				WRITE_ONCE(vsi->xdp_rings[i], NULL);
 		}
 	}
 }
@@ -10861,7 +10870,7 @@ static int i40e_alloc_rings(struct i40e_vsi *vsi)
 		if (vsi->back->hw_features & I40E_HW_WB_ON_ITR_CAPABLE)
 			ring->flags = I40E_TXR_FLAGS_WB_ON_ITR;
 		ring->itr_setting = pf->tx_itr_default;
-		vsi->tx_rings[i] = ring++;
+		WRITE_ONCE(vsi->tx_rings[i], ring++);
 
 		if (!i40e_enabled_xdp_vsi(vsi))
 			goto setup_rx;
@@ -10879,7 +10888,7 @@ static int i40e_alloc_rings(struct i40e_vsi *vsi)
 			ring->flags = I40E_TXR_FLAGS_WB_ON_ITR;
 		set_ring_xdp(ring);
 		ring->itr_setting = pf->tx_itr_default;
-		vsi->xdp_rings[i] = ring++;
+		WRITE_ONCE(vsi->xdp_rings[i], ring++);
 
 setup_rx:
 		ring->queue_index = i;
@@ -10892,7 +10901,7 @@ static int i40e_alloc_rings(struct i40e_vsi *vsi)
 		ring->size = 0;
 		ring->dcb_tc = 0;
 		ring->itr_setting = pf->rx_itr_default;
-		vsi->rx_rings[i] = ring;
+		WRITE_ONCE(vsi->rx_rings[i], ring);
 	}
 
 	return 0;