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batman-adv: Avoid recursive call_rcu for batadv_bla_claim 

The batadv_claim_free_ref function uses call_rcu to delay the free of the
batadv_bla_claim object until no (already started) rcu_read_lock is enabled
anymore. This makes sure that no context is still trying to access the
object which should be removed. But batadv_bla_claim also contains a
reference to backbone_gw which must be removed.

The reference drop of backbone_gw was done in the call_rcu function
batadv_claim_free_rcu but should actually be done in the
batadv_claim_release function to avoid nested call_rcus. This is important
because rcu_barrier (e.g. batadv_softif_free or batadv_exit) will not
detect the inner call_rcu as relevant for its execution. Otherwise this
barrier will most likely be inserted in the queue before the callback of
the first call_rcu was executed. The caller of rcu_barrier will therefore
continue to run before the inner call_rcu callback finished.

Fixes: 23721387c4 ("batman-adv: add basic bridge loop avoidance code")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Acked-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
This commit is contained in:
Sven Eckelmann 2016-01-14 15:28:19 +01:00 committed by Antonio Quartulli
parent 6c3f5aef11
commit 63b3992722
1 changed files with 3 additions and 7 deletions
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10
net/batman-adv/bridge_loop_avoidance.c
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@ -127,21 +127,17 @@ batadv_backbone_gw_free_ref(struct batadv_bla_backbone_gw *backbone_gw)
}
/* finally deinitialize the claim */
static void batadv_claim_free_rcu(struct rcu_head *rcu)
static void batadv_claim_release(struct batadv_bla_claim *claim)
{
struct batadv_bla_claim *claim;
claim = container_of(rcu, struct batadv_bla_claim, rcu);
batadv_backbone_gw_free_ref(claim->backbone_gw);
kfree(claim);
kfree_rcu(claim, rcu);
}
/* free a claim, call claim_free_rcu if its the last reference */
static void batadv_claim_free_ref(struct batadv_bla_claim *claim)
{
if (atomic_dec_and_test(&claim->refcount))
call_rcu(&claim->rcu, batadv_claim_free_rcu);
batadv_claim_release(claim);
}
/**