From 8efa885406359af300d46910642b50ca82c0fe47 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 23 May 2011 11:02:42 +0000 Subject: [PATCH] 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 CC: Patrick McHardy CC: Jarek Poplawski CC: Jamal Hadi Salim CC: Stephen Hemminger Signed-off-by: David S. Miller --- net/sched/sch_sfq.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c index 7ef87f9eb675..b1d00f8e09f8 100644 --- a/net/sched/sch_sfq.c +++ b/net/sched/sch_sfq.c @@ -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 * -- 2.20.1