Subject: Re: [PATCH] check the return value of ndo_select_queue()

From: Eric Dumazet <[email-masked]>
Date: Mon, 09 Nov 2009 10:50:41 +0100

Changli Gao a écrit :
> check the return value of ndo_select_queue()
> 
> Check the return value of ndo_select_queue(). If the value isn't smaller
> than the real_num_tx_queues, print a warning message, and reset it to zero.
> 
> Signed-off-by: Changli Gao <[email-masked]>
> ----
> net/core/dev.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index b8f74cf..0a6bf2e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1794,10 +1794,17 @@ static struct netdev_queue *dev_pick_tx(struct net_device *dev,
>  	const struct net_device_ops *ops = dev->netdev_ops;
>  	u16 queue_index = 0;
>  
> -	if (ops->ndo_select_queue)
> +	if (ops->ndo_select_queue) {
>  		queue_index = ops->ndo_select_queue(dev, skb);
> -	else if (dev->real_num_tx_queues > 1)
> +		if (queue_index >= dev->real_num_tx_queues) {
> +			WARN(1, "%s selects TX queue %d, "
> +			     "but real number of TX queues is %d\n",
> +			     dev->name, queue_index, dev->real_num_tx_queues);
> +			queue_index = 0;
> +		}
> +	} else if (dev->real_num_tx_queues > 1) {
>  		queue_index = skb_tx_hash(dev, skb);
> +	}
>  
>  	skb_set_queue_mapping(skb, queue_index);
>  	return netdev_get_tx_queue(dev, queue_index);

Yes, but this is a _very_ unlikely condition (a bug IMHO), so you could use :

if (unlikely(queue_index >= dev->real_num_tx_queues)) {
	...
}

(This unlikely() clause is implied in WARN... macros)