Re: [net] tipc: fix issues with early FAILOVER_MSG from peer

[David Miller <davem@davemloft.net>]

From: Tuong Lien <tuong.t.lien@dektech.com.au>
Date: Mon, 17 Jun 2019 11:56:12 +0700

> It appears that a FAILOVER_MSG can come from peer even when the failure
> link is resetting (i.e. just after the 'node_write_unlock()'...). This
> means the failover procedure on the node has not been started yet.
> The situation is as follows:
 ...
> Once this happens, the link failover procedure will be triggered
> wrongly on the receiving node since the node isn't in FAILINGOVER state
> but then another link failover will be carried out.
> The consequences are:
> 
> 1) A peer might get stuck in FAILINGOVER state because the 'sync_point'
> was set, reset and set incorrectly, the criteria to end the failover
> would not be met, it could keep waiting for a message that has already
> received.
> 
> 2) The early FAILOVER_MSG(s) could be queued in the link failover
> deferdq but would be purged or not pulled out because the 'drop_point'
> was not set correctly.
> 
> 3) The early FAILOVER_MSG(s) could be dropped too.
> 
> 4) The dummy FAILOVER_MSG could make the peer leaving FAILINGOVER state
> shortly, but later on it would be restarted.
> 
> The same situation can also happen when the link is in PEER_RESET state
> and a FAILOVER_MSG arrives.
> 
> The commit resolves the issues by forcing the link down immediately, so
> the failover procedure will be started normally (which is the same as
> when receiving a FAILOVER_MSG and the link is in up state).
> 
> Also, the function "tipc_node_link_failover()" is toughen to avoid such
> a situation from happening.
> 
> Acked-by: Jon Maloy <jon.maloy@ericsson.se>
> Signed-off-by: Tuong Lien <tuong.t.lien@dektech.com.au>

Applied, thank you.