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

[Nick Desaulniers]

On Tue, Jan 17, 2023 at 9:28 AM Arnd Bergmann <arnd@xxxxxxxxxx> 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.

The logic changes LGTM, but were the noinline_for_stack left behind
from earlier local revisions? Do we still need those if these structs
have been moved from the stack?

>
> Use dynamic allocation for both.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  .../net/ethernet/mellanox/mlx5/core/en_main.c | 36 ++++++++++++-------
>  1 file changed, 23 insertions(+), 13 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..e5198c26e383 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -2993,37 +2993,42 @@ static int mlx5e_switch_priv_channels(struct mlx5e_priv *priv,
>         return err;
>  }
>
> -int mlx5e_safe_switch_params(struct mlx5e_priv *priv,
> +noinline_for_stack int mlx5e_safe_switch_params(struct mlx5e_priv *priv,
>                              struct mlx5e_params *params,
>                              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;
>  }
>
> @@ -3419,10 +3424,10 @@ static void mlx5e_params_mqprio_reset(struct mlx5e_params *params)
>         mlx5e_params_mqprio_dcb_set(params, 1);
>  }
>
> -static int mlx5e_setup_tc_mqprio_dcb(struct mlx5e_priv *priv,
> +static noinline_for_stack int mlx5e_setup_tc_mqprio_dcb(struct mlx5e_priv *priv,
>                                      struct tc_mqprio_qopt *mqprio)
>  {
> -       struct mlx5e_params new_params;
> +       struct mlx5e_params *new_params;
>         u8 tc = mqprio->num_tc;
>         int err;
>
> @@ -3431,10 +3436,13 @@ static int mlx5e_setup_tc_mqprio_dcb(struct mlx5e_priv *priv,
>         if (tc && tc != MLX5E_MAX_NUM_TC)
>                 return -EINVAL;
>
> -       new_params = priv->channels.params;
> -       mlx5e_params_mqprio_dcb_set(&new_params, tc ? tc : 1);
> +       new_params = kmemdup(&priv->channels.params,
> +                            sizeof(priv->channels.params), GFP_KERNEL);
> +       if (!new_params)
> +               return -ENOMEM;
> +       mlx5e_params_mqprio_dcb_set(new_params, tc ? tc : 1);
>
> -       err = mlx5e_safe_switch_params(priv, &new_params,
> +       err = mlx5e_safe_switch_params(priv, new_params,
>                                        mlx5e_num_channels_changed_ctx, NULL, true);
>
>         if (!err && priv->mqprio_rl) {
> @@ -3445,6 +3453,8 @@ static int mlx5e_setup_tc_mqprio_dcb(struct mlx5e_priv *priv,
>
>         priv->max_opened_tc = max_t(u8, priv->max_opened_tc,
>                                     mlx5e_get_dcb_num_tc(&priv->channels.params));
> +
> +       kfree(new_params);
>         return err;
>  }
>
> @@ -3533,7 +3543,7 @@ static struct mlx5e_mqprio_rl *mlx5e_mqprio_rl_create(struct mlx5_core_dev *mdev
>         return rl;
>  }
>
> -static int mlx5e_setup_tc_mqprio_channel(struct mlx5e_priv *priv,
> +static noinline_for_stack int mlx5e_setup_tc_mqprio_channel(struct mlx5e_priv *priv,
>                                          struct tc_mqprio_qopt_offload *mqprio)
>  {
>         mlx5e_fp_preactivate preactivate;
> --
> 2.39.0
>


-- 
Thanks,
~Nick Desaulniers