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sch_sfq: avoid giving spurious NET_XMIT_CN signals

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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>
This commit is contained in:
Eric Dumazet 2011-05-23 11:02:42 +00:00 committed by David S. Miller
parent a4910b7444
commit 8efa885406
1 changed files with 6 additions and 2 deletions
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8
net/sched/sch_sfq.c
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@ -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 *