netdev - Re: [net-next V3 13/15] net/mlx5: DR, Change SWS usage to debug fs seq

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Date: Sun, 4 Feb 2024 14:24:48 +0000
From: Simon Horman <horms@...nel.org>
To: Saeed Mahameed <saeed@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Saeed Mahameed <saeedm@...dia.com>, netdev@...r.kernel.org,
	Tariq Toukan <tariqt@...dia.com>, Gal Pressman <gal@...dia.com>,
	Leon Romanovsky <leonro@...dia.com>,
	Hamdan Igbaria <hamdani@...dia.com>,
	Yevgeny Kliteynik <kliteyn@...dia.com>
Subject: Re: [net-next V3 13/15] net/mlx5: DR, Change SWS usage to debug fs
 seq_file interface

On Fri, Feb 02, 2024 at 11:08:52AM -0800, Saeed Mahameed wrote:
> From: Hamdan Igbaria <hamdani@...dia.com>
> 
> In current SWS debug dump mechanism we implement the seq_file interface,
> but we only implement the 'show' callback to dump the whole steering DB
> with a single call to this callback.
> 
> However, for large data size the seq_printf function will fail to
> allocate a buffer with the adequate capacity to hold such data.
> 
> This patch solves this problem by utilizing the seq_file interface
> mechanism in the following way:
>  - when the user triggers a dump procedure, we will allocate a list of
>    buffers that hold the whole data dump (in the start callback)
>  - using the start, next, show and stop callbacks of the seq_file
>    API we iterate through the list and dump the whole data
> 
> Signed-off-by: Hamdan Igbaria <hamdani@...dia.com>
> Reviewed-by: Yevgeny Kliteynik <kliteyn@...dia.com>
> Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
> ---
>  .../mellanox/mlx5/core/steering/dr_dbg.c      | 735 ++++++++++++++----
>  .../mellanox/mlx5/core/steering/dr_dbg.h      |  20 +
>  2 files changed, 620 insertions(+), 135 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c

...

> +static struct mlx5dr_dbg_dump_data *
> +mlx5dr_dbg_create_dump_data(void)
> +{
> +	struct mlx5dr_dbg_dump_data *dump_data;
> +
> +	dump_data = kzalloc(sizeof(*dump_data), GFP_KERNEL);
> +	if (!dump_data)
> +		return NULL;
> +
> +	INIT_LIST_HEAD(&dump_data->buff_list);
> +
> +	if (!mlx5dr_dbg_dump_data_init_new_buff(dump_data))
> +		kfree(dump_data);

Hi Hamdan and Saeed,

dump_data may be freed above.
But it is returned unconditionally below.
This seems a little odd.

Flagged by Smatch and Coccinelle.

> +
> +	return dump_data;
> +}

...