netdev - Re: [PATCH] net: fix problem in dequeuing from input_pkt

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Date:	Thu, 20 May 2010 07:45:42 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net: fix problem in dequeuing from input_pkt_queue

On Thu, May 20, 2010 at 5:47 AM, Tom Herbert <therbert@...gle.com> wrote:
> Fix some issues introduced in batch skb dequeuing for input_pkt_queue.
> The primary issue it that the queue head must be incremented only
> after a packet has been processed, that is only after
> __netif_receive_skb has been called.  This is needed for the mechanism
> to prevent OOO packet in RFS.  Also when flushing the input_pkt_queue
> and process_queue, the process queue should be done first to prevent
> OOO packets.
>
> Because the input_pkt_queue has been effectively split into two queues,
> the calculation of the tail ptr is no longer correct.  The correct value
> would be head+input_pkt_queue->len+process_queue->len.  To avoid
> this calculation we added an explict input_queue_tail in softnet_data.
> The tail value is simply incremented when queuing to input_pkt_queue.
>
> In process_backlog the processing of the packet queue can be done
> without irq's being disabled.
>
>  static int napi_gro_complete(struct sk_buff *skb)
> @@ -3320,26 +3319,24 @@ static int process_backlog(struct napi_struct *napi, int quota)
>        }
>  #endif
>        napi->weight = weight_p;
> -       local_irq_disable();
>        while (work < quota) {
>                struct sk_buff *skb;
>                unsigned int qlen;
>
>                while ((skb = __skb_dequeue(&sd->process_queue))) {
> -                       local_irq_enable();

we need to keep local irq disabled. If not, flush_backlog may be
called, and it will access sd->process_queue.


-- 
Regards，
Changli Gao(xiaosuo@...il.com)
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