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Commit 76cc8b13 authored by Tom Herbert's avatar Tom Herbert Committed by David S. Miller
Browse files

net: fix problem in dequeuing from input_pkt_queue 



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.

Signed-off-by: default avatarTom Herbert <therbert@google.com>
Acked-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1f01bfd2

include/linux/netdevice.h

+11 −3
Original line number Diff line number Diff line
@@ -1407,17 +1407,25 @@ struct softnet_data { 
	struct softnet_data	*rps_ipi_next;

	unsigned int		cpu;

	unsigned int		input_queue_head;

	unsigned int		input_queue_tail;

#endif

	unsigned		dropped;

	struct sk_buff_head	input_pkt_queue;

	struct napi_struct	backlog;

};



static inline void input_queue_head_add(struct softnet_data *sd,

					unsigned int len)

static inline void input_queue_head_incr(struct softnet_data *sd)

{

#ifdef CONFIG_RPS

	sd->input_queue_head += len;

	sd->input_queue_head++;

#endif

}



static inline void input_queue_tail_incr_save(struct softnet_data *sd,

					      unsigned int *qtail)

{

#ifdef CONFIG_RPS

	*qtail = ++sd->input_queue_tail;

#endif

}

net/core/dev.c

+15 −13
Original line number Diff line number Diff line
@@ -2426,10 +2426,7 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu, 
		if (skb_queue_len(&sd->input_pkt_queue)) {

enqueue:

			__skb_queue_tail(&sd->input_pkt_queue, skb);

#ifdef CONFIG_RPS

			*qtail = sd->input_queue_head +

					skb_queue_len(&sd->input_pkt_queue);

#endif

			input_queue_tail_incr_save(sd, qtail);

			rps_unlock(sd);

			local_irq_restore(flags);

			return NET_RX_SUCCESS;
@@ -2964,7 +2961,7 @@ static void flush_backlog(void *arg) 
		if (skb->dev == dev) {

			__skb_unlink(skb, &sd->input_pkt_queue);

			kfree_skb(skb);

			input_queue_head_add(sd, 1);

			input_queue_head_incr(sd);

		}

	}

	rps_unlock(sd);
@@ -2973,6 +2970,7 @@ static void flush_backlog(void *arg) 
		if (skb->dev == dev) {

			__skb_unlink(skb, &sd->process_queue);

			kfree_skb(skb);

			input_queue_head_incr(sd);

		}

	}

}
@@ -3328,18 +3326,20 @@ static int process_backlog(struct napi_struct *napi, int quota) 
		while ((skb = __skb_dequeue(&sd->process_queue))) {

			local_irq_enable();

			__netif_receive_skb(skb);

			if (++work >= quota)

				return work;

			local_irq_disable();

			input_queue_head_incr(sd);

			if (++work >= quota) {

				local_irq_enable();

				return work;

			}

		}



		rps_lock(sd);

		qlen = skb_queue_len(&sd->input_pkt_queue);

		if (qlen) {

			input_queue_head_add(sd, qlen);

		if (qlen)

			skb_queue_splice_tail_init(&sd->input_pkt_queue,

						   &sd->process_queue);

		}



		if (qlen < quota - work) {

			/*

			 * Inline a custom version of __napi_complete().
@@ -5679,12 +5679,14 @@ static int dev_cpu_callback(struct notifier_block *nfb, 
	local_irq_enable();



	/* Process offline CPU's input_pkt_queue */

	while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {

	while ((skb = __skb_dequeue(&oldsd->process_queue))) {

		netif_rx(skb);

		input_queue_head_add(oldsd, 1);

		input_queue_head_incr(oldsd);

	}

	while ((skb = __skb_dequeue(&oldsd->process_queue)))

	while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {

		netif_rx(skb);

		input_queue_head_incr(oldsd);

	}



	return NOTIFY_OK;

}