From: Eric Dumazet Date: Mon, 13 Sep 2010 12:24:54 +0000 (+0000) Subject: net: use rcu_barrier() in rollback_registered_many X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=ef885afbf8a37689afc1d9d545e2f3e7a8276c17;p=openwrt%2Fstaging%2Fblogic.git net: use rcu_barrier() in rollback_registered_many netdev_wait_allrefs() waits that all references to a device vanishes. It currently uses a _very_ pessimistic 250 ms delay between each probe. Some users reported that no more than 4 devices can be dismantled per second, this is a pretty serious problem for some setups. Most of the time, a refcount is about to be released by an RCU callback, that is still in flight because rollback_registered_many() uses a synchronize_rcu() call instead of rcu_barrier(). Problem is visible if number of online cpus is one, because synchronize_rcu() is then a no op. time to remove 50 ipip tunnels on a UP machine : before patch : real 11.910s after patch : real 1.250s Reported-by: Nicolas Dichtel Reported-by: Octavian Purdila Reported-by: Benjamin LaHaise Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- diff --git a/net/core/dev.c b/net/core/dev.c index b9b22a3c4c8f..660dd41aaaa6 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4845,7 +4845,7 @@ static void rollback_registered_many(struct list_head *head) dev = list_first_entry(head, struct net_device, unreg_list); call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev); - synchronize_net(); + rcu_barrier(); list_for_each_entry(dev, head, unreg_list) dev_put(dev);