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Commit ef885afb authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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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: default avatarNicolas Dichtel <nicolas.dichtel@6wind.com>
Reported-by: default avatarOctavian Purdila <opurdila@ixiacom.com>
Reported-by: default avatarBenjamin LaHaise <bcrl@kvack.org>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ab12811c

net/core/dev.c

+1 −1
Original line number Diff line number Diff line
@@ -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);