netdev - Re: [PATCH] net: sctp: Potentially-Failed state should not be reached from unconfirmed state

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Date:	Thu, 20 Feb 2014 12:58:43 -0500
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@....com>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: sctp: Potentially-Failed state should not be reached
 from unconfirmed state

On 02/20/2014 08:13 AM, Matija Glavinic Pecotic wrote:
> In current implementation it is possible to reach PF state from unconfirmed.
> We can interpret sctp-failover-02 in a way that PF state is meant to be reached
> only from active state, in the end, this is when entering PF state makes sense.
> Here are few quotes from sctp-failover-02, but regardless of these, same
> understanding can be reached from whole section 5:
> 
> Section 5.1, quickfailover guide:
>     "The PF state is an intermediate state between Active and Failed states."
> 
>     "Each time the T3-rtx timer expires on an active or idle
>     destination, the error counter of that destination address will 
>     be incremented.  When the value in the error counter exceeds
>     PFMR, the endpoint should mark the destination transport address as PF."
> 
> There are several concrete reasons for such interpretation. For start, rfc4960
> does not take into concern quickfailover algorithm. Therefore, quickfailover
> must comply to 4960. Point where this compliance can be argued is following
> behavior:
> When PF is entered, association overall error counter is incremented for each
> missed HB. This is contradictory to rfc4960, as address, while in unconfirmed
> state, is subjected to probing, and while it is probed, it should not increment
> association overall error counter. This has as a consequence that we might end
> up in situation in which we drop association due path failure on unconfirmed
> address, in case we have wrong configuration in a way:
> Association.Max.Retrans == Path.Max.Retrans.
> 
> Another reason is that entering PF from unconfirmed will cause a loss of address
> confirmed event when address is once (if) confirmed. This is fine from failover
> guide point of view, but it is not consistent with behavior preceding failover
> implementation and recommendation from 4960:
> 
> 5.4.  Path Verification
>    Whenever a path is confirmed, an indication MAY be given to the upper
>    layer.
> 
> Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@....com>

Acked-by: Vlad Yasevich <vyasevich@...il.com>

Thanks
-vlad

> 
> --- net-next.orig/net/sctp/sm_sideeffect.c
> +++ net-next/net/sctp/sm_sideeffect.c
> @@ -495,11 +495,12 @@ static void sctp_do_8_2_transport_strike
>  	}
>  
>  	/* If the transport error count is greater than the pf_retrans
> -	 * threshold, and less than pathmaxrtx, then mark this transport
> -	 * as Partially Failed, ee SCTP Quick Failover Draft, secon 5.1,
> -	 * point 1
> +	 * threshold, and less than pathmaxrtx, and if the current state
> +	 * is not SCTP_UNCONFIRMED, then mark this transport as Partially
> +	 * Failed, see SCTP Quick Failover Draft, section 5.1
>  	 */
>  	if ((transport->state != SCTP_PF) &&
> +	   (transport->state != SCTP_UNCONFIRMED) &&
>  	   (asoc->pf_retrans < transport->pathmaxrxt) &&
>  	   (transport->error_count > asoc->pf_retrans)) {
>  
> --
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