netdev - Re: [PATCH 2/2] sctp: fix heartbeat count of path failure

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Date:	Thu, 20 Aug 2009 10:10:17 -0400
From:	Vlad Yasevich <vladislav.yasevich@...com>
To:	Luo Chunbo <chunbo.luo@...driver.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH 2/2] sctp: fix heartbeat count of path failure

Luo Chunbo wrote:
> On Wed, 2009-08-19 at 10:48 -0400, Vlad Yasevich wrote:
>> Chunbo Luo wrote:
>>> RFC4960 Section 8.2 defined that the transport should enter INACTIVE
>>> state only when the value in the error counter exceeds the protocol 
>>> parameter 'Path.Max.Retrans' of that destination address. This means 
>>> that the transport should enter INACTIVE state after pathmaxrxt+1
>>> heartbeats are not acknowledged.
>>>
>>>
>>> Signed-off-by: Chunbo Luo <chunbo.luo@...driver.com>
>> NAK.  This patch seems to resurface periodically and I have to keep
>> explaining that it's wrong.
>>
>> Every time we send a HB, we tick up the error count and clear it when
>> the HB-ACK is received.  Each HB is separate and not a retransmission,
>> so we once we reach the pathmaxrxt, we've already sent max+1 HB, so we
>> have time out.  Walk through the code with some values and you'll see
>> what I mean.
> 
> Although we've already sent max+1 HB, but the code set the transport to
> INACTIVE state immediately, which is equal to not sending the max+1 HB
> at all.  We should wait for a next period and make sure the max+1 HB was
> not acknowledged.

Ok, I just re-read the section, and although we don't quite wait long
enough to mark the transport DOWN, this patch will cause us to send an
extra HB chunk, thus exceeding pathmaxrxt by 2.

What the spec really says is that an error is incremented when an
outstanding HB is not acknowledged.

So this code needs a bit of a rework.  This patch is still NAKed.

-vlad

> 
> Chunbo 
> 
>> -vlad
>>
>>> ---
>>>  net/sctp/sm_sideeffect.c |    2 +-
>>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
>>> index 86426aa..0e2e269 100644
>>> --- a/net/sctp/sm_sideeffect.c
>>> +++ b/net/sctp/sm_sideeffect.c
>>> @@ -447,7 +447,7 @@ static void sctp_do_8_2_transport_strike(struct sctp_association *asoc,
>>>  		asoc->overall_error_count++;
>>>  
>>>  	if (transport->state != SCTP_INACTIVE &&
>>> -	    (transport->error_count++ >= transport->pathmaxrxt)) {
>>> +	    (transport->error_count++ > transport->pathmaxrxt)) {
>>>  		SCTP_DEBUG_PRINTK_IPADDR("transport_strike:association %p",
>>>  					 " transport IP: port:%d failed.\n",
>>>  					 asoc,
> 

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