From: Jon Maloy <jon.ma...@ericsson.com>
Date: Tue, 13 Oct 2015 12:41:51 -0400
> In commit 6e498158a827 ("tipc: move link synch and failover to link
> aggregation level")
> we introduced a new mechanism for performing link failover and
> synchronization. We have now detected a bug in this mechanism.
>
> During link synchronization we use the arrival of any packet on
> the tunnel link to trig a check for whether it has reached the
> synchronization point or not. This has turned out to be too
> permissive, since it may cause an arriving non-last SYNCH packet to
> end the synch state, just to see the next SYNCH packet initiate a
> new synch state with a new, higher synch point. This is not fatal,
> but should be avoided, because it may significantly extend the
> synchronization period, while at the same time we are not allowed
> to send NACKs if packets are lost. In the worst case, a low-traffic
> user may see its traffic stall until a LINK_PROTOCOL state message
> trigs the link to leave synchronization state.
>
> At the same time, LINK_PROTOCOL packets which happen to have a (non-
> valid) sequence number lower than the tunnel link's rcv_nxt value will
> be consistently dropped, and will never be able to resolve the situation
> described above.
>
> We fix this by exempting LINK_PROTOCOL packets from the sequence number
> check, as they should be. We also reduce (but don't completely
> eliminate) the risk of entering multiple synchronization states by only
> allowing the (logically) first SYNCH packet to initiate a synchronization
> state. This works independently of actual packet arrival order.
>
> Fixes: commit 6e498158a827 ("tipc: move link synch and failover to link
> aggregation level")
>
> Signed-off-by: Jon Maloy <jon.ma...@ericsson.com>
> Acked-by: Ying Xue <ying....@windriver.com>
Applied, thanks.
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