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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