Re: DCCP_BUG called

[Eugen Dedu <Eugen.Dedu@pu-pm.univ-fcomte.fr>]

On 20/08/10 07:15, Gerrit Renker wrote:
>>    sudo $TC qdisc add dev $IF root handle 1: htb default 10
>>    sudo $TC class add dev $IF parent 1: classid 1:10 htb rate $up_rate
>>    sudo $TC filter add dev $IF protocol ip parent 1:0 prio 1 u32 match ip
>> dst $dest flowid 1:10
>>    sudo $TC qdisc add dev $IF parent 1:10 handle 40: sfq perturb 10 limit 2
>>
>> taken from http://lartc.org/howto/, we receive many errors like this:
>>
>> [27799.691275] BUG: err=1 after ccid_hc_tx_packet_sent at
>> /build/buildd/linux-2.6.32/net/dccp/output.c:307/dccp_write_xmit()
>> [27799.691288]<IRQ>   [<ffffffffa0441db5>] dccp_write_xmit+0x165/0x310
>> [dccp]
>> [27799.691308]  [<ffffffffa0443ac0>] ? dccp_write_xmit_timer+0x0/0x80 [dccp]
>> [27799.691315]  [<ffffffffa0443b3a>] dccp_write_xmit_timer+0x7a/0x80 [dccp]
>>
>> We found that they are triggered by the following code in net/dccp/output.c:
>> 306   err = dccp_transmit_skb(sk, skb);
>> 307   ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, 0, len);
>> 308   if (err)
>> 309     DCCP_BUG("err=%d after ccid_hc_tx_packet_sent",
>> 310              err);
>>
>> Is there a way to fix to workaround that?
>
> The 'err = 1' is triggered because the qdisc can refuse to take a packet, so that
>
>   #define NET_XMIT_DROP           0x01    /* skb dropped                  */
>
> is returned. Thus what you are seeing is not a real bug, but rather a misplaced
> BUG statement.
>
> I haven't verified this, but I am almost sure that the problem is rectified in the
> DCCP test tree which I would like to encourage you to use for all testing, since it

Thank you for your answer.  I have not yet tested with DCCP test tree 
indeed, but I see that the code involved is there too, i.e.:

  306  err = dccp_transmit_skb(sk, skb);
  307  ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, 0, len);
  308  if (err)
  309    DCCP_BUG("err=%d after ccid_hc_tx_packet_sent",
  310             err);

and in dccp_transmit_skb():

  139                 err = icsk->icsk_af_ops->queue_xmit(skb);
  140                 return net_xmit_eval(err);

-- 
Eugen