[PKT_SCHED]: netem: reinsert for duplication

Handle duplication of packets in netem by re-inserting at top of qdisc tree.
This avoid problems with qlen accounting with nested qdisc. This recursion
requires no additional locking but will potentially increase stack depth.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 29 insertions, 24 deletions

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index e0c9fbe73b15..5c0f0c209a4c 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -203,42 +203,47 @@ static int netem_run(struct Qdisc *sch)
         return 0;
 }
 
+/*
+ * Insert one skb into qdisc.
+ * Note: parent depends on return value to account for queue length.
+ *      NET_XMIT_DROP: queue length didn't change.
+ *      NET_XMIT_SUCCESS: one skb was queued.
+ */
 static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 {
         struct netem_sched_data *q = qdisc_priv(sch);
+        struct sk_buff *skb2;
         int ret;
+        int count = 1;
 
         pr_debug("netem_enqueue skb=%p\n", skb);
 
+        /* Random duplication */
+        if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor))
+                ++count;
+
         /* Random packet drop 0 => none, ~0 => all */
-        if (q->loss && q->loss >= get_crandom(&q->loss_cor)) {
-                pr_debug("netem_enqueue: random loss\n");
+        if (q->loss && q->loss >= get_crandom(&q->loss_cor))
+                --count;
+
+        if (count == 0) {
                 sch->qstats.drops++;
                 kfree_skb(skb);
-                return 0;       /* lie about loss so TCP doesn't know */
+                return NET_XMIT_DROP;
         }
 
-        /* Random duplication */
-        if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor)) {
-                struct sk_buff *skb2;
-
-                skb2 = skb_clone(skb, GFP_ATOMIC);
-                if (skb2 && netem_delay(sch, skb2) == NET_XMIT_SUCCESS) {
-                        struct Qdisc *qp;
-
-                        /* Since one packet can generate two packets in the
-                         * queue, the parent's qlen accounting gets confused,
-                         * so fix it.
-                         */
-                        qp = qdisc_lookup(sch->dev, TC_H_MAJ(sch->parent));
-                        if (qp)
-                                qp->q.qlen++;
-
-                        sch->q.qlen++;
-                        sch->bstats.bytes += skb2->len;
-                        sch->bstats.packets++;
-                } else
-                        sch->qstats.drops++;
+        /*
+         * If we need to duplicate packet, then re-insert at top of the
+         * qdisc tree, since parent queuer expects that only one
+         * skb will be queued.
+         */
+        if (count > 1 && (skb2 = skb_clone(skb, GFP_ATOMIC)) != NULL) {
+                struct Qdisc *rootq = sch->dev->qdisc;
+                u32 dupsave = q->duplicate; /* prevent duplicating a dup... */
+                q->duplicate = 0;
+
+                rootq->enqueue(skb2, rootq);
+                q->duplicate = dupsave;
         }
 
         /* If doing simple delay then gap == 0 so all packets