hard hang through qdisc

hard hang through qdisc

[Andi Kleen]

I just managed to hang a 2.6.24 (+ some non network patches) kernel 
with the following (non sensical) command

tc qdisc add dev eth0 root tbf rate 1000 burst 10 limit 100

No oops or anything just hangs. While I understand root can
do bad things just hanging like this seems a little extreme.

-Andi

Re: hard hang through qdisc

[jamal]

On Thu, 2008-31-01 at 13:21 +0100, Andi Kleen wrote:
> 
> I just managed to hang a 2.6.24 (+ some non network patches) kernel 
> with the following (non sensical) command
> 
> tc qdisc add dev eth0 root tbf rate 1000 burst 10 limit 100
> 
> No oops or anything just hangs. While I understand root can
> do bad things just hanging like this seems a little extreme.
> 

---------
lilsol:~# tc qdisc add dev eth0 root tbf rate 1000 burst 10 limit 100
lilsol:~# uname -a
Linux lilsol 2.6.24 #1 PREEMPT Sun Jan 27 09:22:00 EST 2008 i686
GNU/Linux
lilsol:~# tc qdisc ls dev eth0
qdisc tbf 8001: root rate 1000bit burst 10b lat 737.3ms
lilsol:~#
-------

What do your patches do?

cheers,
jamal

Re: hard hang through qdisc II

[Andi Kleen]

On Thursday 31 January 2008 13:21:00 Andi Kleen wrote:
> 
> I just managed to hang a 2.6.24 (+ some non network patches) kernel 
> with the following (non sensical) command

Correction: the kernel was actually a git linus kernel with David's 
recent merge included.

I found it's pretty easy to hang the kernel with various tbf parameters.

-Andi

> tc qdisc add dev eth0 root tbf rate 1000 burst 10 limit 100
> 
> No oops or anything just hangs. While I understand root can
> do bad things just hanging like this seems a little extreme.
> 
> -Andi
> 

Re: hard hang through qdisc

[Andi Kleen]

> ---------
> lilsol:~# tc qdisc add dev eth0 root tbf rate 1000 burst 10 limit 100
> lilsol:~# uname -a
> Linux lilsol 2.6.24 #1 PREEMPT Sun Jan 27 09:22:00 EST 2008 i686

Can you try it again with current git mainline?

> GNU/Linux
> lilsol:~# tc qdisc ls dev eth0
> qdisc tbf 8001: root rate 1000bit burst 10b lat 737.3ms
> lilsol:~#
> -------
> 
> What do your patches do?

Nothing really related to qdiscs.  I suspect it came from the git mainline patch
I had (but forgot to mention in the first email) 

-Andi

Re: hard hang through qdisc

[Patrick McHardy]

Andi Kleen wrote:
>> ---------
>> lilsol:~# tc qdisc add dev eth0 root tbf rate 1000 burst 10 limit 100
>> lilsol:~# uname -a
>> Linux lilsol 2.6.24 #1 PREEMPT Sun Jan 27 09:22:00 EST 2008 i686
> 
> Can you try it again with current git mainline?


I'll look into it.

Re: hard hang through qdisc

[Patrick McHardy]

Patrick McHardy wrote:
> Andi Kleen wrote:
>>> ---------
>>> lilsol:~# tc qdisc add dev eth0 root tbf rate 1000 burst 10 limit 100
>>> lilsol:~# uname -a
>>> Linux lilsol 2.6.24 #1 PREEMPT Sun Jan 27 09:22:00 EST 2008 i686
>>
>> Can you try it again with current git mainline?
> 
> 
> I'll look into it.


Works for me:

qdisc tbf 8001: root rate 1000bit burst 10b/8 mpu 0b lat 720.0ms
  Sent 0 bytes 0 pkt (dropped 9, overlimits 0 requeues 0)
  rate 0bit 0pps backlog 0b 0p requeues 0

Packets are dropped as expected.

Re: hard hang through qdisc

[Andi Kleen]

> Works for me:
>
> qdisc tbf 8001: root rate 1000bit burst 10b/8 mpu 0b lat 720.0ms
>   Sent 0 bytes 0 pkt (dropped 9, overlimits 0 requeues 0)
>   rate 0bit 0pps backlog 0b 0p requeues 0
>
> Packets are dropped as expected.

I can still reproduce it on 64bit with http://halobates.de/config-qdisc
(all qdiscs etc. compiled in for testing) 
with latest git tip (8af03e782cae1e0a0f530ddd22301cdd12cf9dc0)

The command line above causes an instant hang. Also tried it with
newer iproute2 (the original one was quite old), but it didn't make
a difference.

Perhaps it's related to what qdiscs are enabled? Can you please
try with the above config?

If everything fails I can do a bisect later.

-Andi

Re: hard hang through qdisc

[Patrick McHardy]

Andi Kleen wrote:
>> Works for me:
>>
>> qdisc tbf 8001: root rate 1000bit burst 10b/8 mpu 0b lat 720.0ms
>>   Sent 0 bytes 0 pkt (dropped 9, overlimits 0 requeues 0)
>>   rate 0bit 0pps backlog 0b 0p requeues 0
>>
>> Packets are dropped as expected.
> 
> I can still reproduce it on 64bit with http://halobates.de/config-qdisc
> (all qdiscs etc. compiled in for testing) 
> with latest git tip (8af03e782cae1e0a0f530ddd22301cdd12cf9dc0)
> 
> The command line above causes an instant hang. Also tried it with
> newer iproute2 (the original one was quite old), but it didn't make
> a difference.
> 
> Perhaps it's related to what qdiscs are enabled?


I'm also testing on 64 bit, with all qdiscs enabled as modules.

> Can you please try with the above config?


I'll give it a try later.

Re: hard hang through qdisc

[Patrick McHardy]

Patrick McHardy wrote:
> Andi Kleen wrote:
>
>> Can you please try with the above config?
> 
> 
> I'll give it a try later.


I took all options from that config that seemed possibly
related (qdiscs, no hrtimers, no nohz, slab, ...), but
still can't reproduce it.

Does it also crash if you use more reasonable parameters?

Re: hard hang through qdisc

[Andi Kleen]

On Thu, Jan 31, 2008 at 07:46:02PM +0100, Patrick McHardy wrote:
> Patrick McHardy wrote:
>> Andi Kleen wrote:
>>
>>> Can you please try with the above config?
>> I'll give it a try later.
>
>
> I took all options from that config that seemed possibly
> related (qdiscs, no hrtimers, no nohz, slab, ...), but
> still can't reproduce it.

Ok I'll do bisect then later (not today anymore likely) 

> Does it also crash if you use more reasonable parameters?

I managed to make it crash with different parameters too,
but with good parameters it did set a qdisc successfully
and appeared to work.

-Andi