Re: [B.A.T.M.A.N.] [PATCH v2 2/2] batman-adv: Simple (re)broadcast avoidance

[Sven Eckelmann <sven@narfation.org>]

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On Donnerstag, 4. August 2016 01:43:29 CEST Linus Lüssing wrote:
[...]
> So the regular purging routines will break the cycle in the end
> when they reduce the refcount of the hardif_neigh_node to zero.

Ok, lets go through it with following idea:

1. the cycle exists (including the missing batadv_orig_node::ifinfo_list
   in my earlier example graph)
2. batadv_purge_orig is called via the worker (for some reason with a large delay)
3. _batadv_purge_orig goes through all entries in the orig hashtable
4. batadv_purge_orig_node is called
5. batadv_has_timed_out returns "hey, you are old - go away"
6. batadv_purge_orig_node now only does for this orig_entry:
   - batadv_gw_node_delete(bat_priv, orig_node);
   - hlist_del_rcu(&orig_node->hash_entry);
   - batadv_tt_global_del_orig(orig_node->bat_priv,
							  orig_node, -1,
							  "originator timed out");
   - batadv_orig_node_put(orig_node);

So the most cleanup work (batadv_orig_node_release) is only done when
the orig_node refcnt reaches zero.

The batadv_purge_orig_ifinfo, batadv_purge_orig_neighbors and the
rest from batadv_purge_orig_node is only done when the originator
has not yet reached its timeout. I would therefore guess it working
because you are lucky and your batadv_purge_orig_neighbors and
batadv_purge_orig_ifinfo sometimes(tm) solve this problem for you.

Kind regards,
	Sven

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digraph {
	
edge [fontname="Helvetica",fontsize="10",labelfontname="Helvetica",labelfontsize="10"];
node [fontname="Helvetica",fontsize="10",shape=record];

	"batadv_orig_node" -> "batadv_orig_ifinfo" [label=" last_bonding_candidate", style="dashed",color="green"];
"batadv_orig_node" -> "batadv_orig_ifinfo" [label=" ifinfo_list", style="dashed",color="green"];
"batadv_hardif_neigh_node" -> "batadv_orig_node" [label=" orig_node", style="dashed",color="blue"];
"batadv_orig_ifinfo" -> "batadv_neigh_node" [label=" router", style="dashed",color="green"];
"batadv_neigh_node" -> "batadv_hardif_neigh_node" [label=" hardif_neigh", style="dashed",color="green"];
"batadv_orig_node" -> "batadv_neigh_node" [label=" neigh_list", style="dashed",color="green"]
}

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