On Sat, Mar 06, 2010 at 02:56:55PM +0800, Herbert Xu wrote:
quoted text
>
> > In contrast, rcu_barrier_bh() is guaranteed not to return until all
> > pending RCU-bh callbacks have executed.
> 
> You're absolutely right.  I'll send a patch to fix this.

bridge: Fix RCU race in br_multicast_stop

Thanks to Paul McKenny for pointing out that it is incorrect to use 
synchronize_rcu_bh to ensure that pending callbacks have completed.
Instead we should use rcu_barrier_bh.

Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 2559fb5..48f3b00 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1135,7 +1135,7 @@ void br_multicast_stop(struct net_bridge *br)
 
 	if (mdb->old) {
 		spin_unlock_bh(&br->multicast_lock);
-		synchronize_rcu_bh();
+		rcu_barrier_bh();
 		spin_lock_bh(&br->multicast_lock);
 		WARN_ON(mdb->old);
 	}

Cheers,
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Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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