Re: [Qemu-devel] slirp-related crash

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-02-13 20:35, Jan Kiszka wrote:
> On 2012-02-13 16:27, Zhi Yong Wu wrote:
>> On Mon, Feb 13, 2012 at 4:24 AM, Jan Kiszka <jan.kiszka@web.de> wrote:
>>> On 2012-02-12 19:34, Michael S. Tsirkin wrote:
>>>> It seems somewhat easy to crash qemu with slirp if we queue multiple packets.
>>>> I didn't investigate further yet so I don't know if this
>>>> is a regression. Anyone knowledgeable about slirp wants to take a look?
>>>>
>>>> /home/mst/qemu-test/bin/qemu-system-x86_64  -enable-kvm -m 1G -drive
>>>> file=/home/mst/rhel6.qcow2 -netdev user,id=bar -net
>>>> nic,netdev=bar,model=e1000,macaddr=52:54:00:12:34:57  -redir
>>>> tcp:8022::22  -vnc :1 -monitor stdio
>>>>
>>>> While guest is booting, quickly do this
>>>>
>>>> ssh localhost -p 8022
>>>> CTRL-C
>>>> ssh localhost -p 8022
>>>> CTRL-C
>>>> ssh localhost -p 8022
>>>> CTRL-C
>>>> ssh localhost -p 8022
>>>> CTRL-C
>>>
>>> Confirmed. A single canceled connection prior the interface setup is
>>> enough. Possibly something is not properly removed / cleaned up here.
>>> Will see if I find some time to debug, can't promise.
>> Interesting thing, pls give me some time, and i am trying to debug this issue.
> 
> I had a look today, but haven't found a fix yet. The problem is related
> to our requeuing of packets if the target MAC is not yet known.
> Something goes terribly wrong once it gets resolved (mbuf use after
> release?). Maybe it was always wrong and the requeuing just surfaced the
> bug, dunno.
> 
> After starring at the code for a while, I got the bad feeling of
> "unfixable with reasonable effort". The queuing code is horrible (well,
> like most of slirp), and the requeuing just made it worse. But maybe I'm
> just missing some trick now - yet another one that would make the code
> even more unreadable...
> 
> I'm inclined to suggest a slirp rewrite (base support, not all features
> at once) as a GSOC project. QEMU really deserves something better.
> 

Despite my grumbling, I would welcome any patch that fixes the bug, of
course!

Jan

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