netdev - Re: [PATCH net] net: qualcomm: rmnet: Allow configuration updates to existing devices

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Date:   Tue, 31 Mar 2020 19:06:14 -0500
From:   Alex Elder <elder@...aro.org>
To:     Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        ap420073@...il.com, davem@...emloft.net, netdev@...r.kernel.org
Cc:     Sean Tranchetti <stranche@...eaurora.org>
Subject: Re: [PATCH net] net: qualcomm: rmnet: Allow configuration updates to
 existing devices

On 3/31/20 5:43 PM, Subash Abhinov Kasiviswanathan wrote:
> This allows the changelink operation to succeed if the mux_id was
> specified as an argument. Note that the mux_id must match the
> existing mux_id of the rmnet device or should be an unused mux_id.
> 
> Fixes: 1dc49e9d164c ("net: rmnet: do not allow to change mux id if mux id is duplicated")
> Reported-by: Alex Elder <elder@...aro.org>
> Signed-off-by: Sean Tranchetti <stranche@...eaurora.org>
> Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>

This was a regression in 5.6, and got back-ported to 5.5.11 and
possibly further back.  Please be sure the fix gets applied to
stable branches if appropriate.

If you happen to post a second version of this I have a suggestion,
below.  But the patch looks OK to me as-is.

Thanks.

Tested-by: Alex Elder <elder@...aro.org>

> ---
>  .../ethernet/qualcomm/rmnet/rmnet_config.c    | 21 ++++++++++++-------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
> index fbf4cbcf1a65..06332984399d 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
> @@ -294,19 +294,24 @@ static int rmnet_changelink(struct net_device *dev, struct nlattr *tb[],
>  
>  	if (data[IFLA_RMNET_MUX_ID]) {
>  		mux_id = nla_get_u16(data[IFLA_RMNET_MUX_ID]);
> -		if (rmnet_get_endpoint(port, mux_id)) {
> -			NL_SET_ERR_MSG_MOD(extack, "MUX ID already exists");
> -			return -EINVAL;
> -		}

My suggestion is this:  Since the endpoint pointer isn't used
outside the "if (mux_id != priv->mux_id)" block, you could
do the lookup inside that block.

>  		ep = rmnet_get_endpoint(port, priv->mux_id);
>  		if (!ep)
>  			return -ENODEV;
>  
> -		hlist_del_init_rcu(&ep->hlnode);
> -		hlist_add_head_rcu(&ep->hlnode, &port->muxed_ep[mux_id]);
> +		if (mux_id != priv->mux_id) {
> +			if (rmnet_get_endpoint(port, mux_id)) {
> +				NL_SET_ERR_MSG_MOD(extack,
> +						   "MUX ID already exists");
> +				return -EINVAL;
> +			}
>  
> -		ep->mux_id = mux_id;
> -		priv->mux_id = mux_id;
> +			hlist_del_init_rcu(&ep->hlnode);
> +			hlist_add_head_rcu(&ep->hlnode,
> +					   &port->muxed_ep[mux_id]);
> +
> +			ep->mux_id = mux_id;
> +			priv->mux_id = mux_id;
> +		}
>  	}
>  
>  	if (data[IFLA_RMNET_FLAGS]) {
>