netdev - Re: [BUG] Bug in netprio_cgroup and netcls

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Date:	Mon, 21 Jan 2013 10:27:25 +0100
From:	Daniel Wagner <wagi@...om.org>
To:	Li Zefan <lizefan@...wei.com>
CC:	John Fastabend <john.r.fastabend@...el.com>,
	Neil Horman <nhorman@...driver.com>,
	Daniel Wagner <daniel.wagner@...-carit.de>,
	LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [BUG] Bug in netprio_cgroup and netcls_cgroup ?

On 21.01.2013 10:01, Li Zefan wrote:
> On 2013/1/21 16:50, Daniel Wagner wrote:
>> Hi Li,
>>
>> On 21.01.2013 07:08, Li Zefan wrote:
>>> I'm not a network developer, so correct me if I'm wrong.
>>>
>>> Since commit 7955490f732c2b8
>>> ("net: netprio_cgroup: rework update socket logic"), sock->sk->sk_cgrp_prioidx
>>> is set when the socket is created, and won't be updated unless the task is
>>> moved to another cgroup.
>>>
>>> Now the problem is, a socket can be _shared_ by multiple processes (fork, SCM_RIGHT).
>>> If we place those processes in different cgroups, and each cgroup has
>>> different configs, but all of the processes will send data via this socket
>>> with the same network priority.
>>
>> Wouldn't that be addressed by 48a87cc26c13b68f6cce4e9d769fcb17a6b3e4b8
>>
>>     net: netprio: fd passed in SCM_RIGHTS datagram not set correctly
>>
>>      A socket fd passed in a SCM_RIGHTS datagram was not getting
>>      updated with the new tasks cgrp prioidx. This leaves IO on
>>      the socket tagged with the old tasks priority.
>>
>>      To fix this add a check in the scm recvmsg path to update the
>>      sock cgrp prioidx with the new tasks value.
>>
>> As I read this this should work for net_prio.
>>
> 
> But after process A passed the socket fd to B, both A and B can use the
> same socket to send data, right? Then if A and B were placed in different
> cgroups with differnt configs, A's config won't take effect anymore.
> 
> Am I missing something?

I don't know. I guess at one point the socket resources are shared and then
one configuration is taking preference. As you can see I am far away of
being
an expert in this field. Hopefully someone who understands this bits
can chip in.

BTW, isn't this a similar to what should happen with the block io cgroup?
What is the behavior with a fd writing to a file in the scenario you
describe above?

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