net/mlx5e: Don't modify CQ before it was created

BugLink: http://bugs.launchpad.net/bugs/1557950

Calling mlx5e_set_coalesce while the interface is down will result in
modifying CQs that don't exist.

Fixes: f62b8bb8 ('net/mlx5: Extend mlx5_core to support ConnectX-4
Ethernet functionality')
Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from linux-next commit 2fcb92fb)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

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

@@ -422,11 +422,15 @@ static int mlx5e_set_coalesce(struct net_device *netdev,
 	if (!MLX5_CAP_GEN(mdev, cq_moderation))
 		return -ENOTSUPP;
 
+	mutex_lock(&priv->state_lock);
 	priv->params.tx_cq_moderation_usec = coal->tx_coalesce_usecs;
 	priv->params.tx_cq_moderation_pkts = coal->tx_max_coalesced_frames;
 	priv->params.rx_cq_moderation_usec = coal->rx_coalesce_usecs;
 	priv->params.rx_cq_moderation_pkts = coal->rx_max_coalesced_frames;
 
+	if (!test_bit(MLX5E_STATE_OPENED, &priv->state))
+		goto out;
+
 	for (i = 0; i < priv->params.num_channels; ++i) {
 		c = priv->channel[i];
 
@@ -442,6 +446,8 @@ static int mlx5e_set_coalesce(struct net_device *netdev,
 					       coal->rx_max_coalesced_frames);
 	}
 
+out:
+	mutex_unlock(&priv->state_lock);
 	return 0;
 }