netdev - Re: [PATCH] bonding: reset queue mapping prior to transmission to physical device (v3)

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Date:	Fri, 03 Jun 2011 18:59:38 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	netdev@...r.kernel.org, Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] bonding: reset queue mapping prior to transmission to
 physical device (v3)

On Fri, 2011-06-03 at 13:32 -0400, Neil Horman wrote:
> The bonding driver is multiqueue enabled, in which each queue represents a slave
> to enable optional steering of output frames to given slaves against the default
> output policy.  However, it needs to reset the skb->queue_mapping prior to
> queuing to the physical device or the physical slave (if it is multiqueue) could
> wind up transmitting on an unintended tx queue
> 
> Change Notes:
> v2) Based on first pass review, updated the patch to restore the origional queue
> mapping that was found in bond_select_queue, rather than simply resetting to
> zero.  This preserves the value of queue_mapping when it was set on receive in
> the forwarding case which is desireable.
> 
> v3) Fixed spelling an casting error in skb->cb
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> CC: Jay Vosburgh <fubar@...ibm.com>
> CC: Andy Gospodarek <andy@...yhouse.net>
> CC: "David S. Miller" <davem@...emloft.net>
> ---
>  drivers/net/bonding/bond_main.c |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 17b4dd9..dbb1048 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -400,6 +400,11 @@ int bond_dev_queue_xmit(struct bonding *bond, struct sk_buff *skb,
>  {
>  	skb->dev = slave_dev;
>  	skb->priority = 1;
> +	/*
> +	 *restore the origional mapping
> +	 */
> +	skb_set_queue_mapping(skb, ((u16 *)skb->cb)[0]);
> +
>  	if (unlikely(netpoll_tx_running(slave_dev)))
>  		bond_netpoll_send_skb(bond_get_slave_by_dev(bond, slave_dev), skb);
>  	else
> @@ -4216,6 +4221,11 @@ static u16 bond_select_queue(struct net_device *dev, struct sk_buff *skb)
>  	 */
>  	u16 txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) : 0;
>  
> +	/*
> + 	 * Save the original txq to restore before passing to the driver
> + 	 */
> +	((u16 *)skb->cb)[0] = txq;
> +
>  	if (unlikely(txq >= dev->real_num_tx_queues)) {
>  		do {
>  			txq -= dev->real_num_tx_queues;

I should have read this more thoroughly before - I'm afraid this is
still not quite right as skb_get_rx_queue() will subtract 1.  You need
to save skb_get_queue_mapping() rather than txq.

But skb_{get,set}_queue_mapping() seem to be meant to deal with TX queue
numbers so maybe it's better to save and restore skb->queue_mapping
directly.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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