net/mlx5e: Use READ_ONCE/WRITE_ONCE for DCBX trust state

trust_state can be written while mlx5e_select_queue() is reading it. To
avoid inconsistencies, use READ_ONCE and WRITE_ONCE for access and
updates, and touch the variable only once per operation.
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/en/selq.c

@@ -113,7 +113,7 @@ static int mlx5e_get_dscp_up(struct mlx5e_priv *priv, struct sk_buff *skb)
 static int mlx5e_get_up(struct mlx5e_priv *priv, struct sk_buff *skb)
 {
 #ifdef CONFIG_MLX5_CORE_EN_DCB
-	if (priv->dcbx_dp.trust_state == MLX5_QPTS_TRUST_DSCP)
+	if (READ_ONCE(priv->dcbx_dp.trust_state) == MLX5_QPTS_TRUST_DSCP)
 		return mlx5e_get_dscp_up(priv, skb);
 #endif
 	if (skb_vlan_tag_present(skb))

drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c

@@ -1142,7 +1142,7 @@ static int mlx5e_update_trust_state_hw(struct mlx5e_priv *priv, void *context)
 	err = mlx5_set_trust_state(priv->mdev, *trust_state);
 	if (err)
 		return err;
-	priv->dcbx_dp.trust_state = *trust_state;
+	WRITE_ONCE(priv->dcbx_dp.trust_state, *trust_state);
 
 	return 0;
 }
@@ -1187,16 +1187,18 @@ static int mlx5e_set_dscp2prio(struct mlx5e_priv *priv, u8 dscp, u8 prio)
 static int mlx5e_trust_initialize(struct mlx5e_priv *priv)
 {
 	struct mlx5_core_dev *mdev = priv->mdev;
+	u8 trust_state;
 	int err;
 
-	priv->dcbx_dp.trust_state = MLX5_QPTS_TRUST_PCP;
-
-	if (!MLX5_DSCP_SUPPORTED(mdev))
+	if (!MLX5_DSCP_SUPPORTED(mdev)) {
+		WRITE_ONCE(priv->dcbx_dp.trust_state, MLX5_QPTS_TRUST_PCP);
 		return 0;
+	}
 
-	err = mlx5_query_trust_state(priv->mdev, &priv->dcbx_dp.trust_state);
+	err = mlx5_query_trust_state(priv->mdev, &trust_state);
 	if (err)
 		return err;
+	WRITE_ONCE(priv->dcbx_dp.trust_state, trust_state);
 
 	mlx5e_params_calc_trust_tx_min_inline_mode(priv->mdev, &priv->channels.params,
 						   priv->dcbx_dp.trust_state);