Re: [B.A.T.M.A.N.] [PATCH] batman-adv: fix delayed foreign originator recognition

[Marek Lindner <mareklindner@neomailbox.ch>]

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On Thursday 30 October 2014 06:23:40 Linus Lüssing wrote:
> Currently it can happen that the reception of an OGM from a new
> originator is not being accepted. More precisely it can happen that
> an originator struct gets allocated and initialized
> (batadv_orig_node_new()), even the TQ gets calculated and set correctly
> (batadv_iv_ogm_calc_tq()) but still the periodic orig_node purging
> thread will decide to delete it if it has a chance to jump between
> these two function calls.
> 
> This is because batadv_orig_node_new() initializes the last_seen value
> to zero and its caller (batadv_iv_ogm_orig_get()) makes it visible to
> other threads by adding it to the hash table already.
> batadv_iv_ogm_calc_tq() will set the last_seen variable to the correct,
> current time a few lines later but if the purging thread jumps in between
> that it will think that the orig_node timed out and will wrongly
> schedule it for deletion already.
> 
> If the purging interval is the same as the originator interval (which is
> the default: 1 second), then this game can continue for several rounds
> until the random OGM jitter added enough difference between these
> two (in tests, two to about four rounds seemed common).
> 
> Fixing this by initializing the last_seen variable of an orig_node
> to the current time before adding it to the hash table.
> 
> Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
> ---
>  originator.c |    1 +
>  1 file changed, 1 insertion(+)

You're definitely contending for this year's highest code to commit message 
ratio. Kudos to you for this well documented fix!

Applied in revision  8a2ad52.

Thanks,
Marek

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