[Ocfs2-devel] [RFC] make ocfs2/o2net reliable

[Changwei Ge]

Hi Gang

On 2017/11/17 10:24, Gang He wrote:
> 
> 
> 
>>>>
>> On 2017/11/16 18:05, Gang He wrote:
>>> Hello Changwei,
>>>
>>> Base on your description, it looks make sense.
>>> Since I uses fs/dlm kernel module, it looks stable.
>>> Do you compare both dlm implementation? maybe can learn from each other.
> Do you have a detailed steps to reproduce this problem? I think the problem should exist,

I assume you have four hosts: A, B, C, D.

ocfs2 cluster includes A, B, C.(total 3 nodes)
A.IP = 172.20.50.1
B.IP = 172.20.50.2
C.IP = 172.20.50.3

Let cluster begin to work and generate some workload into all nodes of them.

Configure node D IP address to 172.20.50.3.

ping node A from node D.


> Maybe the idea can be referenced by both dlm modules.
> Second, if you add this message-id and red-black tree mechanism, you also need to
> add a monitor kernel-thread, to see if these messages in red-black tree will become more and more bigger (this will lead to memory leak).

This is a good idea! I will take it into account.

Thanks,
Changwei

> 
> Thanks
> Gang
> 
> 
>>>
>>>
>>> Thanks
>>> Gang
>>
>> Hi Gang,
>> Actually , I have studied some code of fs/dlm and I don't think it can
>> handle such a exception scenario. But I don't have a test environment
>> with fs/dlm applied. Can you take some tests like configuring a
>> duplicated IP address to a host.
>> I think it is easy to reproduce.
>>
>> Thanks,
>> Changwei
>>
>>>
>>>
>>>>>>
>>>> Hi all,
>>>> As far as we know, ocfs2/o2net is not a reliable message mechanism.
>>>> Messages might get lost due to a sudden TCP socket connection shutdown.
>>>> And the only customer of o2net is ocfs2/dlm, so this may cause ocfs2/dlm
>>>> hang(missing AST and ASSERT MASTER). Sometimes it also causes
>>>> ocfs2/dlm's infinite wait for accomplishment of DLM recovery. But that
>>>> won't happen since target node is still heartbeating and no dlm recovery
>>>> procedure will be launched.
>>>>
>>>> So I think above cases drive us to improve current ocfs2/o2net making it
>>>> more reliable. I already have a draft design for it. And we indeed need
>>>> to change o2net behavior.
>>>>
>>>> To accomplish this goal, we tag each o2net message with a sequence
>>>> ::msg_seq to let receiver tell if the newly coming message is a
>>>> duplicated one or not and ::msg_seq will work as a key value for
>>>> searching a following key structure in a red-black tree.
>>>>
>>>> A brandy new structure is added to o2net named as *Message Holder*, it
>>>> is responsible for _handle_status_ storing.
>>>>
>>>> When TCP has to shutdown or reset due to unknown reason, although we
>>>> lose the packets in send or receive buffer, o2net still manages those
>>>> messages. This gives a chance to o2net to re-send the messages once TCP
>>>> connection is established again.
>>>>
>>>> Below diagram demonstrates how it works:
>>>>
>>>> SEND					RECV
>>>> send message				
>>>> tag message header with ::msg_seq	
>>>> 					search for Message Holder with
>>>> 					  ::msg_seq
>>>> 					NOT FOUND - insert one
>>>> 					(FOUND - means a duplicated one)
>>>> 					handle message
>>>> 					store status into Message Holder
>>>> 					send back status
>>>> instruct RECV to remove MH
>>>> 					notify SEND that MH is already
>>>> 					  removed
>>>> return to caller
>>>>
>>>> I am expecting your comments especially from @Mark, @Joseph and @Junxiao.
>>>>
>>>> Thanks,
>>>> Changwei.
>>>>
>>>> _______________________________________________
>>>> Ocfs2-devel mailing list
>>>> Ocfs2-devel at oss.oracle.com
>>>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
>>>
>>>
> 
>