netdev - Re: CBQ(but probably u32 filter bug), kernel "freeze", at least from 3.2.0

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Date:	Thu, 06 Sep 2012 16:47:34 +0300
From:	Denys Fedoryshchenko <denys@...p.net.lb>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	<netdev@...r.kernel.org>
Subject: Re: CBQ(but probably u32 filter bug), kernel "freeze", at least
 from 3.2.0

On 2012-09-06 11:40, Eric Dumazet wrote:
> On Tue, 2012-08-28 at 03:59 -0700, Eric Dumazet wrote:
>> On Tue, 2012-08-28 at 07:50 +0300, Denys Fedoryshchenko wrote:
>> > Hi
>> >
>> > Got information from friend, confirmed that it crashed at least 
>> two my
>> > boxes also :)
>> > 3.0.5-rc1 is working fine, 3.4.1 , 3.2.0 from ubuntu  - crashing
>> > No watchdog fired, and didn't got yet significant debugging
>> > information.
>> >
>> > Very easy to reproduce:
>> > 1)run the script
>> > 2)ping 192.168.3.234
>> >
>> > script:
>> > DEV_OUT=eth0
>> > ICMP="match ip protocol 1 0xff"
>> > U32="protocol ip u32"
>> > DST="match ip dst"
>> > tc qdisc add dev $DEV_OUT root handle 1: cbq avpkt 1000 bandwidth
>> > 100mbit
>> > tc class add dev $DEV_OUT parent 1: classid 1:1 cbq rate 512kbit 
>> allot
>> > 1500 prio 5 bounded isolated
>> > tc filter add dev $DEV_OUT parent 1:              prio 3 $U32 
>> $ICMP
>> > $DST 192.168.3.234 flowid 1:
>> > tc qdisc add dev $DEV_OUT parent 1:1 sfq perturb 10
>>
>> Not sure what your friend expected from this buggy configuration.
>>
>> It probably never worked at all.
>>
>> CBQ needs at least one child class and one leaf class.
>>
>> This scripts creates a loop inside CBQ, so cpu is probably looping 
>> in
>> cbq_enqueue() (or more exactly cbq_classify()), as instructed by the
>> sysadmin ;)
>>
>> u32 (or sfq) seems ok.
>>
>> Could you try the following patch ?
>>
>> Thanks !
>>
>> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
>> index 6aabd77..564b9fc 100644
>> --- a/net/sched/sch_cbq.c
>> +++ b/net/sched/sch_cbq.c
>> @@ -250,10 +250,11 @@ cbq_classify(struct sk_buff *skb, struct Qdisc 
>> *sch, int *qerr)
>>  			else if ((cl = defmap[res.classid & TC_PRIO_MAX]) == NULL)
>>  				cl = defmap[TC_PRIO_BESTEFFORT];
>>
>> -			if (cl == NULL || cl->level >= head->level)
>> +			if (cl == NULL)
>>  				goto fallback;
>>  		}
>> -
>> +		if (cl->level >= head->level)
>> +			goto fallback;
>>  #ifdef CONFIG_NET_CLS_ACT
>>  		switch (result) {
>>  		case TC_ACT_QUEUED:
>>
>
> Hi Denys
>
> Any feedback on the suggested patch ?
>
> Thanks !
Dear Eric

Very sorry for delay, most of time in desert, without decent internet.
I will try to test today or tomorrow.

---
Denys Fedoryshchenko, Network Engineer, Virtual ISP S.A.L.
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