Subject: Re: [PATCH v6 net-next 8/9] net: ethtool: use the tracking array for get_rxfh on custom RSS contexts

From: Simon Horman <[email-masked]>
Date: Thu, 20 Jun 2024 20:42:14 +0100

On Thu, Jun 20, 2024 at 06:47:11AM +0100, [email-masked] wrote:
> From: Edward Cree <[email-masked]>
> 
> On 'ethtool -x' with rss_context != 0, instead of calling the driver to
>  read the RSS settings for the context, just get the settings from the
>  rss_ctx xarray, and return them to the user with no driver involvement.
> 
> Signed-off-by: Edward Cree <[email-masked]>
> ---
>  net/ethtool/ioctl.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
> index 9d2d677770db..ac562ee3662e 100644
> --- a/net/ethtool/ioctl.c
> +++ b/net/ethtool/ioctl.c
> @@ -1199,6 +1199,7 @@ static noinline_for_stack int ethtool_get_rxfh(struct net_device *dev,
>  	const struct ethtool_ops *ops = dev->ethtool_ops;
>  	struct ethtool_rxfh_param rxfh_dev = {};
>  	u32 user_indir_size, user_key_size;
> +	struct ethtool_rxfh_context *ctx;
>  	struct ethtool_rxfh rxfh;
>  	u32 indir_bytes;
>  	u8 *rss_config;
> @@ -1246,11 +1247,25 @@ static noinline_for_stack int ethtool_get_rxfh(struct net_device *dev,
>  	if (user_key_size)
>  		rxfh_dev.key = rss_config + indir_bytes;
>  
> -	rxfh_dev.rss_context = rxfh.rss_context;
> -
> -	ret = dev->ethtool_ops->get_rxfh(dev, &rxfh_dev);
> -	if (ret)
> -		goto out;
> +	if (rxfh.rss_context) {
> +		ctx = xa_load(&dev->ethtool->rss_ctx, rxfh.rss_context);
> +		if (!ctx) {
> +			ret = -ENOENT;
> +			goto out;
> +		}
> +		if (rxfh_dev.indir)
> +			memcpy(rxfh_dev.indir, ethtool_rxfh_context_indir(ctx),
> +			       indir_bytes);
> +		if (rxfh_dev.key)
> +			memcpy(rxfh_dev.key, ethtool_rxfh_context_key(ctx),
> +			       user_key_size);
> +		rxfh_dev.hfunc = ctx->hfunc;
> +		rxfh_dev.input_xfrm = ctx->input_xfrm;

Hi Edward,

The last line of this function is:

	return ret;

With this patch applied, Smatch complains that ret may be used there
when unintialised.

I think that occurs when the code reaches the line where this
commentary has been placed in this email.

> +	} else {
> +		ret = dev->ethtool_ops->get_rxfh(dev, &rxfh_dev);
> +		if (ret)
> +			goto out;
> +	}
>  
>  	if (copy_to_user(useraddr + offsetof(struct ethtool_rxfh, hfunc),
>  			 &rxfh_dev.hfunc, sizeof(rxfh.hfunc))) {
>