Re: [B.A.T.M.A.N.] [PATCHv2 7/7] batman-adv: handle race condition for claims between gateways

[Simon Wunderlich <sw@simonwunderlich.de>]

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Hi Andreas,

On Friday 26 February 2016 14:19:50 Andreas Pape wrote:
> Consider the following situation which has been found in a test setup:
> Gateway B has claimed client C and gateway A has the same backbone
> network as B. C sends a broad- or multicast to B and directly after
> this packet decides to send another packet to A due to a better TQ
> value. B will forward the broad-/multicast into the backbone as it is
> the responsible gw and after that A will claim C as it has been
> chosen by C as the new gateway. If it now happens that A claims C
> before it has received the broad-/multicast forwarded by B (due to
> backbone topology or due to some delay in B when forwarding the
> packet) we get a critical situation: in the current code A will
> immediately unclaim C when receiving the multicast due to the
> roaming client scenario although the position of C has not changed
> in the mesh. If this happens the multi-/broadcast forwarded by B
> will be sent back into the mesh by A and we have looping packets
> until one of the gateways claims C again.
> In order to prevent this, unclaiming of a client due to the roaming
> client scenario is only done after a certain time is expired after
> the last claim of the client. 100 ms are used here, which should be
> slow enough for big backbones and slow gateways but fast enough not
> to break the roaming client use case.

That's an interesting solution. My original idea was to make clients "race" 
for clients, which wasn't ever implemented because in the scenarios I tested 
this was not a problem (Check batadv_bla_rx(), there is a note on a possible 
optimization).

I believe your solutions looks valid, let's implement that.

Acked-by: Simon Wunderlich <sw@simonwunderlich.de>

Thanks,
     Simon

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