Re: [PATCH] [v2] mlx5: reduce stack usage in mlx5_setup_tc

[Jacob Keller]

On 1/17/2023 1:01 PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> Clang warns about excessive stack usage on 32-bit targets:
> 
> drivers/net/ethernet/mellanox/mlx5/core/en_main.c:3597:12: error: stack frame size (1184) exceeds limit (1024) in 'mlx5e_setup_tc' [-Werror,-Wframe-larger-than]
> static int mlx5e_setup_tc(struct net_device *dev, enum tc_setup_type type,
> 
> It turns out that both the mlx5e_setup_tc_mqprio_dcb() function and
> the mlx5e_safe_switch_params() function it calls have a copy of
> 'struct mlx5e_params' on the stack, and this structure is fairly
> large.
> 
> Use dynamic allocation for the inner one.
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> v2: simplify the patch
> ---

This simpler version that focuses on fixing the stack frame issue looks
good to me.

Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>

Thanks,
Jake

>  .../net/ethernet/mellanox/mlx5/core/en_main.c   | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index 6bb0fdaa5efa..b0b872728653 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -2998,32 +2998,37 @@ int mlx5e_safe_switch_params(struct mlx5e_priv *priv,
>  			     mlx5e_fp_preactivate preactivate,
>  			     void *context, bool reset)
>  {
> -	struct mlx5e_channels new_chs = {};
> +	struct mlx5e_channels *new_chs;
>  	int err;
>  
>  	reset &= test_bit(MLX5E_STATE_OPENED, &priv->state);
>  	if (!reset)
>  		return mlx5e_switch_priv_params(priv, params, preactivate, context);
>  
> -	new_chs.params = *params;
> +	new_chs = kzalloc(sizeof(*new_chs), GFP_KERNEL);
> +	if (!new_chs)
> +		return -ENOMEM;
> +	new_chs->params = *params;
>  
> -	mlx5e_selq_prepare_params(&priv->selq, &new_chs.params);
> +	mlx5e_selq_prepare_params(&priv->selq, &new_chs->params);
>  
> -	err = mlx5e_open_channels(priv, &new_chs);
> +	err = mlx5e_open_channels(priv, new_chs);
>  	if (err)
>  		goto err_cancel_selq;
>  
> -	err = mlx5e_switch_priv_channels(priv, &new_chs, preactivate, context);
> +	err = mlx5e_switch_priv_channels(priv, new_chs, preactivate, context);
>  	if (err)
>  		goto err_close;
>  
> +	kfree(new_chs);
>  	return 0;
>  
>  err_close:
> -	mlx5e_close_channels(&new_chs);
> +	mlx5e_close_channels(new_chs);
>  
>  err_cancel_selq:
>  	mlx5e_selq_cancel(&priv->selq);
> +	kfree(new_chs);
>  	return err;
>  }
>