net/mlx4_en: Issue the dump eth statistics command under lock

Performing the DUMP_ETH_STATS firmware command outside the lock leads to kernel
panic when data structures such as RX/TX rings are freed in parallel, e.g when
one changes the mtu or ring sizes.
Signed-off-by: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_netdev.c

@@ -977,12 +977,12 @@ static void mlx4_en_do_get_stats(struct work_struct *work)
 	struct mlx4_en_dev *mdev = priv->mdev;
 	int err;
 
+	mutex_lock(&mdev->state_lock);
+	if (mdev->device_up) {
 		err = mlx4_en_DUMP_ETH_STATS(mdev, priv->port, 0);
 		if (err)
 			en_dbg(HW, priv, "Could not update stats\n");
 
-	mutex_lock(&mdev->state_lock);
-	if (mdev->device_up) {
 		if (priv->port_up)
 			mlx4_en_auto_moderation(priv);