Commit 8efa8854 authored May 23, 2011 by Eric Dumazet Committed by David S. Miller May 23, 2011

sch_sfq: avoid giving spurious NET_XMIT_CN signals



While chasing a possible net_sched bug, I found that IP fragments have
litle chance to pass a congestioned SFQ qdisc :

- Say SFQ qdisc is full because one flow is non responsive.
- ip_fragment() wants to send two fragments belonging to an idle flow.
- sfq_enqueue() queues first packet, but see queue limit reached :
- sfq_enqueue() drops one packet from 'big consumer', and returns
NET_XMIT_CN.
- ip_fragment() cancel remaining fragments.

This patch restores fairness, making sure we return NET_XMIT_CN only if
we dropped a packet from the same flow.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Jarek Poplawski <jarkao2@gmail.com>
CC: Jamal Hadi Salim <hadi@cyberus.ca>
CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent a4910b74

net/sched/sch_sfq.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -361,7 +361,7 @@ sfq_enqueue(struct sk_buff skb, struct Qdisc sch)
		{
		struct sfq_sched_data *q = qdisc_priv(sch);
		unsigned int hash;
		sfq_index x;
		sfq_index x, qlen;
		struct sfq_slot *slot;
		int uninitialized_var(ret);

		@@ -405,8 +405,12 @@ sfq_enqueue(struct sk_buff skb, struct Qdisc sch)
		if (++sch->q.qlen <= q->limit)
		return NET_XMIT_SUCCESS;

		qlen = slot->qlen;
		sfq_drop(sch);
		return NET_XMIT_CN;
		/* Return Congestion Notification only if we dropped a packet
		* from this flow.
		*/
		return (qlen != slot->qlen) ? NET_XMIT_CN : NET_XMIT_SUCCESS;
		}

		static struct sk_buff *

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