netdev - Re: [PATCH] sctp: fix the check for path failure detection

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Message-ID: <4A924734.6000702@cn.fujitsu.com>
Date:	Mon, 24 Aug 2009 15:54:28 +0800
From:	Wei Yongjun <yjwei@...fujitsu.com>
To:	Luo Chunbo <chunbo.luo@...driver.com>
CC:	Vlad Yasevich <vladislav.yasevich@...com>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sctp: fix the check for path failure detection

Luo Chunbo 写道:
> On Fri, 2009-08-21 at 17:47 -0400, Vlad Yasevich wrote:
>   
>> Chunbo Luo wrote:
>>     
>>> The transport is marked DOWN immediately after sending the max+1 HB,
>>> which is equal to not sending the max+1 HB at all. We should wait
>>> a next period and make sure the last HB is not acknowledged.
>>>
>>>       
>> I don't think this code does what you want either...
>>
>> Let's say path_max_rxt = 2.  What we'll get is:
>> 	timeout:
>> 		err++ (1)
>> 		if (err > 2) false
>> 		send HB
>> 		reset timer
>> 	timeout:
>> 		err++ (2)
>> 		if (err > 2) false
>> 		send HB
>> 		reset timer
>> 	timeout:
>> 		err++ (3)
>> 		if (err > 2)
>> 			set transport DOWN
>> 		send HB
>> 		reset timer.
>>
>> We only had 2 unacknowledged HB when we should have had 3.
>>     
>
> The error count is increment after the HB was sent, and the error count
> check is before sending HB.
>
> Let's say path_max_rxt =2 . What we really get is:
>
> timeout:
> 	if( err > 2) false
> 	send HB
> 	err++ (1)
> 	reset timer
> timeout:
> 	if( err > 2) false
> 	send HB
> 	err++ (2)
> 	reset timer
> timeout:
> 	if( err > 2) false
> 	send HB
> 	err++ (3)
> 	reset timer
> timeout:
> 	if( err > 2)
> 		set transport DOWN
> 	send HB
> 	reset timer
>
> Here We had 3 unacknowledged HBs


But with Vlad's advice, you just need to do little change to the kernel
codes, may be two lines's patch, and it can do the same thing.



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