Re: [PATCH] net/mlx5: reduce stack usage in qp_read_field

[Saeed Mahameed]

On Tue, 2020-04-28 at 23:23 +0200, Arnd Bergmann wrote:
> Moving the mlx5_ifc_query_qp_out_bits structure on the stack was a
> bit
> excessive and now causes the compiler to complain on 32-bit
> architectures:
> 
> drivers/net/ethernet/mellanox/mlx5/core/debugfs.c: In function
> 'qp_read_field':
> drivers/net/ethernet/mellanox/mlx5/core/debugfs.c:274:1: error: the
> frame size of 1104 bytes is larger than 1024 bytes [-Werror=frame-
> larger-than=]
> 
> Revert the previous patch partially to use dynamically allocation as
> the code did before. Unfortunately there is no good error handling
> in case the allocation fails.
> 

I don't really mind this, since this is only for debugfs and 0 is not a
valid value anyway.

Acked-by: Saeed Mahameed <saeedm@xxxxxxxxxxxx> 

this should go to mlx5-next, i will let Leon decide and pick this up.

> Fixes: 57a6c5e992f5 ("net/mlx5: Replace hand written QP context
> struct with automatic getters")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/debugfs.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/debugfs.c
> b/drivers/net/ethernet/mellanox/mlx5/core/debugfs.c
> index 6409090b3ec5..d2d57213511b 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/debugfs.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/debugfs.c
> @@ -202,18 +202,23 @@ void mlx5_cq_debugfs_cleanup(struct
> mlx5_core_dev *dev)
>  static u64 qp_read_field(struct mlx5_core_dev *dev, struct
> mlx5_core_qp *qp,
>  			 int index, int *is_str)
>  {
> -	u32 out[MLX5_ST_SZ_BYTES(query_qp_out)] = {};
> +	int outlen = MLX5_ST_SZ_BYTES(query_qp_out);
>  	u32 in[MLX5_ST_SZ_DW(query_qp_in)] = {};
>  	u64 param = 0;
> +	u32 *out;
>  	int state;
>  	u32 *qpc;
>  	int err;
>  
> +	out = kzalloc(outlen, GFP_KERNEL);
> +	if (!out)
> +		return 0;
> +
>  	MLX5_SET(query_qp_in, in, opcode, MLX5_CMD_OP_QUERY_QP);
>  	MLX5_SET(query_qp_in, in, qpn, qp->qpn);
>  	err = mlx5_cmd_exec_inout(dev, query_qp, in, out);
>  	if (err)
> -		return 0;
> +		goto out;
>  
>  	*is_str = 0;
>  
> @@ -269,7 +274,8 @@ static u64 qp_read_field(struct mlx5_core_dev
> *dev, struct mlx5_core_qp *qp,
>  		param = MLX5_GET(qpc, qpc, remote_qpn);
>  		break;
>  	}
> -
> +out:
> +	kfree(out);
>  	return param;
>  }
>