fixed a bug in l2 grad clip

    """Efficient L2 norm gradient clipping."""

    overflow_buf = torch.zeros(1, dtype=torch.int, device='cuda')

    # Make sure we have an iterable.

    if isinstance(parameters, torch.Tensor):

        parameters = [parameters]

    mp_rank_is_zero = (get_model_parallel_rank() == 0)

    parameters = list(filter(lambda p: (p.grad is not None) and

                             (p.model_parallel or mp_rank_is_zero),

                             parameters))

    # Filter parameters with gradients.

    parameters_with_grads = list(filter(

        lambda p: p.grad is not None, parameters))

    # Filter parameters for norm calculations.

    parameters_for_norm = list(filter(

        lambda p: p.model_parallel or mp_rank_is_zero, parameters_with_grads))

    # Calculate L2 norm.

    norm, _ = multi_tensor_applier(

        amp_C.multi_tensor_l2norm,

        overflow_buf,

        [parameters],

        [parameters_for_norm],

        False # no per-parameter norm

    )

    # Sum across all model parallel GPUs.

                                 op=torch.distributed.ReduceOp.SUM,

                                 group=get_model_parallel_group())

    total_norm = norm_2.item() ** 0.5

    clip_coef = max_norm / (total_norm + 1e-6)

    grads = [p.grad for p in parameters]

    if clip_coef < 1:

    # Scale to get max_norm.

    clip_coef = float(max_norm) / (total_norm + 1.0e-6)

    grads = [p.grad for p in parameters_with_grads]

    if clip_coef < 1.0:

        multi_tensor_applier(

            amp_C.multi_tensor_scale,

            overflow_buf,