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Subject[ 078/109] netem: add limitation to reordered packets
Date
From: Greg KH <gregkh@linuxfoundation.org>

3.4-stable review patch. If anyone has any objections, please let me know.

------------------


From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 960fb66e520a405dde39ff883f17ff2669c13d85 ]

Fix two netem bugs :

1) When a frame was dropped by tfifo_enqueue(), drop counter
was incremented twice.

2) When reordering is triggered, we enqueue a packet without
checking queue limit. This can OOM pretty fast when this
is repeated enough, since skbs are orphaned, no socket limit
can help in this situation.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mark Gordon <msg@google.com>
Cc: Andreas Terzis <aterzis@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/sch_netem.c | 42 +++++++++++++++---------------------------
1 file changed, 15 insertions(+), 27 deletions(-)

--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -329,29 +329,22 @@ static psched_time_t packet_len_2_sched_
return PSCHED_NS2TICKS(ticks);
}

-static int tfifo_enqueue(struct sk_buff *nskb, struct Qdisc *sch)
+static void tfifo_enqueue(struct sk_buff *nskb, struct Qdisc *sch)
{
struct sk_buff_head *list = &sch->q;
psched_time_t tnext = netem_skb_cb(nskb)->time_to_send;
- struct sk_buff *skb;
+ struct sk_buff *skb = skb_peek_tail(list);

- if (likely(skb_queue_len(list) < sch->limit)) {
- skb = skb_peek_tail(list);
- /* Optimize for add at tail */
- if (likely(!skb || tnext >= netem_skb_cb(skb)->time_to_send))
- return qdisc_enqueue_tail(nskb, sch);
-
- skb_queue_reverse_walk(list, skb) {
- if (tnext >= netem_skb_cb(skb)->time_to_send)
- break;
- }
+ /* Optimize for add at tail */
+ if (likely(!skb || tnext >= netem_skb_cb(skb)->time_to_send))
+ return __skb_queue_tail(list, nskb);

- __skb_queue_after(list, skb, nskb);
- sch->qstats.backlog += qdisc_pkt_len(nskb);
- return NET_XMIT_SUCCESS;
+ skb_queue_reverse_walk(list, skb) {
+ if (tnext >= netem_skb_cb(skb)->time_to_send)
+ break;
}

- return qdisc_reshape_fail(nskb, sch);
+ __skb_queue_after(list, skb, nskb);
}

/*
@@ -366,7 +359,6 @@ static int netem_enqueue(struct sk_buff
/* We don't fill cb now as skb_unshare() may invalidate it */
struct netem_skb_cb *cb;
struct sk_buff *skb2;
- int ret;
int count = 1;

/* Random duplication */
@@ -414,6 +406,11 @@ static int netem_enqueue(struct sk_buff
skb->data[net_random() % skb_headlen(skb)] ^= 1<<(net_random() % 8);
}

+ if (unlikely(skb_queue_len(&sch->q) >= sch->limit))
+ return qdisc_reshape_fail(skb, sch);
+
+ sch->qstats.backlog += qdisc_pkt_len(skb);
+
cb = netem_skb_cb(skb);
if (q->gap == 0 || /* not doing reordering */
q->counter < q->gap - 1 || /* inside last reordering gap */
@@ -445,7 +442,7 @@ static int netem_enqueue(struct sk_buff

cb->time_to_send = now + delay;
++q->counter;
- ret = tfifo_enqueue(skb, sch);
+ tfifo_enqueue(skb, sch);
} else {
/*
* Do re-ordering by putting one out of N packets at the front
@@ -455,16 +452,7 @@ static int netem_enqueue(struct sk_buff
q->counter = 0;

__skb_queue_head(&sch->q, skb);
- sch->qstats.backlog += qdisc_pkt_len(skb);
sch->qstats.requeues++;
- ret = NET_XMIT_SUCCESS;
- }
-
- if (ret != NET_XMIT_SUCCESS) {
- if (net_xmit_drop_count(ret)) {
- sch->qstats.drops++;
- return ret;
- }
}

return NET_XMIT_SUCCESS;



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