net: sch_netem: Fix an inconsistency in ingress netem timestamps.

Alex Sidorenko reported:

"while experimenting with 'netem' we have found some strange behaviour. It
seemed that ingress delay as measured by 'ping' command shows up on some
hosts but not on others.

After some investigation I have found that the problem is that skbuff->tstamp
field value depends on whether there are any packet sniffers enabled. That
is:

- if any ptype_all handler is registered, the tstamp field is as expected
- if there are no ptype_all handlers, the tstamp field does not show the delay"

This patch prevents unnecessary update of tstamp in dev_queue_xmit_nit()
on ingress path (with act_mirred) adding a check, so minimal overhead on
the fast path, but only when sniffers etc. are active.

Since netem at ingress seems to logically emulate a network before a host,
tstamp is zeroed to trigger the update and pretend delays are from the
outside.

Reported-by: Alex Sidorenko <alexandre.sidorenko@hp.com>
Tested-by: Alex Sidorenko <alexandre.sidorenko@hp.com>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 343883f65ea70a24f6548560e3358aac0f5335cf..dcc357e4f91e565a962b4f4aea4a83aac704752d 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1336,7 +1336,12 @@ static void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
 {
        struct packet_type *ptype;
 
+#ifdef CONFIG_NET_CLS_ACT
+       if (!(skb->tstamp.tv64 && (G_TC_FROM(skb->tc_verd) & AT_INGRESS)))
+               net_timestamp(skb);
+#else
        net_timestamp(skb);
+#endif
 
        rcu_read_lock();
        list_for_each_entry_rcu(ptype, &ptype_all, list) {

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index d876b873484852d0a1da004e51fc4198d65627de..2b88295cb7b7133f13e68b5e9e644c2d7fa888ab 100644 (file)
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -280,6 +280,14 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
                        if (unlikely(!skb))
                                return NULL;
 
+#ifdef CONFIG_NET_CLS_ACT
+                       /*
+                        * If it's at ingress let's pretend the delay is
+                        * from the network (tstamp will be updated).
+                        */
+                       if (G_TC_FROM(skb->tc_verd) & AT_INGRESS)
+                               skb->tstamp.tv64 = 0;
+#endif
                        pr_debug("netem_dequeue: return skb=%p\n", skb);
                        sch->q.qlen--;
                        return skb;