netdev - Re: [PATCH] sctp: Enforce maximum retransmissions during shutdown

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Date:	Thu, 30 Jun 2011 12:17:03 -0400
From:	Thomas Graf <tgraf@...radead.org>
To:	Vladislav Yasevich <vladislav.yasevich@...com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	Wei Yongjun <yjwei@...fujitsu.com>,
	Sridhar Samudrala <sri@...ibm.com>, linux-sctp@...r.kernel.org
Subject: Re: [PATCH] sctp: Enforce maximum retransmissions during shutdown

On Thu, Jun 30, 2011 at 10:08:40AM -0400, Vladislav Yasevich wrote:
> How about this.  If we in SHUTDOWN_PENDING state, let the errors accumulate upto
> max_retrans.  After that, start SHUTDOWN_GUARD timer to let the association live a
> bit longer just on the off-chance the receive comes back.  When SHUTDOWN_GUARD
> expires it will abort the association.
> 
> When we are in this state, SACK processing will have to reset SHUTDOWN_GUARD when
> the SACK is actually acknowledging something.

Good idea. I'll update my patch.

> > 
> > What sideeffects are you worried about resulting from my proposal?
> > 
> 
> There is a potential that the sender may abort prematurely.  The issue is that
> the sender has no way of knowing if the remote process somehow terminated and
> will never consume data, or if it is just extremely busy with something else and
> will come back.  Since this is a reliable protocol, we given the receive the benefit
> of the doubt and try our hardest to get the data across.

Understood although we are talking 10 * RTO here without an actual SACK.

> My suggestion above is still a bit of a hack that one could argue still violates the
> protocol, but the time period tries to remove as much doubt from the sender as possible
> the the receiver is really out-to-lunch.

Assuming that by 'shutdown sequence' the spec is only referring to the
SHUTDOWN / SHUTDOWN ACK exchange it would still violate the protocol
but I don't see how to avoid having association hang around forever without
violating the spec. This really looks like a hole in the spec to me.
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