[LARTC] netem with prio hangs on duplicate

[Patrick McHardy]

js si wrote:
> hi
> 
> i tried the example given on the examples page to
> duplicate selected traffic like
> 
> tc qdisc add dev eth0 root handle 1: prio
> tc qdisc add dev eth0 parent 1:3 handle 3: netem
> duplicate 40% 
> tc filter add dev eth0 protocol ip parent 1:0 prio 3
> u32 match ip dst 11.0.2.2 flowid 1:3
> 
> when i ping from 11.0.2.2 to this interface my machine
> hangs. the same thing works for drop or delay. 
> 
> i would appreciate if someone can tell me what i am
> doing wrong.

Using netem with an upper qdisc screws up the upper qdisc's
q.qlen counter and qdisc_run() tries to dequeue it indefinitely.
I don't know whether netem is intended to be useable only as
top-level qdisc, if so it should make sure that it really is
used this way to avoid hanging the system.

Regards
Patrick