netdev - Re: [PATCH net 2/2] netdev: Enforce index cap in netdev_get_tx

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Date:   Mon, 20 Mar 2023 21:49:46 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Nick Child <nnac123@...ux.ibm.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net 2/2] netdev: Enforce index cap in
 netdev_get_tx_queue

On Fri, 17 Mar 2023 13:19:41 -0500 Nick Child wrote:
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 23b0d7eaaadd..fe88b1a7393d 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2482,6 +2482,13 @@ static inline
>  struct netdev_queue *netdev_get_tx_queue(const struct net_device *dev,
>  					 unsigned int index)
>  {
> +	if (unlikely(index >= dev->num_tx_queues)) {
> +		net_warn_ratelimited("%s selects TX queue %d, but number of TX queues is %d\n",
> +				     dev->name, index,
> +				     dev->num_tx_queues);
> +		return &dev->_tx[0];
> +	}
> +

Should we maybe do DEBUG_NET_WARN_ON_ONCE() instead?
It will likely run multiple times per each Tx packet,
so I wonder if we really want to add a branch for what's
effectively defensive programming...