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Commit f0b07bb1 authored by Kirill Tkhai's avatar Kirill Tkhai Committed by David S. Miller
Browse files

net: Introduce net_rwsem to protect net_namespace_list 



rtnl_lock() is used everywhere, and contention is very high.
When someone wants to iterate over alive net namespaces,
he/she has no a possibility to do that without exclusive lock.
But the exclusive rtnl_lock() in such places is overkill,
and it just increases the contention. Yes, there is already
for_each_net_rcu() in kernel, but it requires rcu_read_lock(),
and this can't be sleepable. Also, sometimes it may be need
really prevent net_namespace_list growth, so for_each_net_rcu()
is not fit there.

This patch introduces new rw_semaphore, which will be used
instead of rtnl_mutex to protect net_namespace_list. It is
sleepable and allows not-exclusive iterations over net
namespaces list. It allows to stop using rtnl_lock()
in several places (what is made in next patches) and makes
less the time, we keep rtnl_mutex. Here we just add new lock,
while the explanation of we can remove rtnl_lock() there are
in next patches.

Fine grained locks generally are better, then one big lock,
so let's do that with net_namespace_list, while the situation
allows that.

Signed-off-by: default avatarKirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 906edee9

drivers/infiniband/core/roce_gid_mgmt.c

+2 −0
Original line number Diff line number Diff line
@@ -403,10 +403,12 @@ static void enum_all_gids_of_dev_cb(struct ib_device *ib_dev, 
	 * our feet

	 */

	rtnl_lock();

	down_read(&net_rwsem);

	for_each_net(net)

		for_each_netdev(net, ndev)

			if (is_eth_port_of_netdev(ib_dev, port, rdma_ndev, ndev))

				add_netdev_ips(ib_dev, port, rdma_ndev, ndev);

	up_read(&net_rwsem);

	rtnl_unlock();

}

include/linux/rtnetlink.h

+1 −0
Original line number Diff line number Diff line
@@ -37,6 +37,7 @@ extern int rtnl_lock_killable(void); 


extern wait_queue_head_t netdev_unregistering_wq;

extern struct rw_semaphore pernet_ops_rwsem;

extern struct rw_semaphore net_rwsem;



#ifdef CONFIG_PROVE_LOCKING

extern bool lockdep_rtnl_is_held(void);

include/net/net_namespace.h

+1 −0
Original line number Diff line number Diff line
@@ -291,6 +291,7 @@ static inline struct net *read_pnet(const possible_net_t *pnet) 
#endif

}



/* Protected by net_rwsem */

#define for_each_net(VAR)				\

	list_for_each_entry(VAR, &net_namespace_list, list)

net/core/dev.c

+5 −0
Original line number Diff line number Diff line
@@ -1629,6 +1629,7 @@ int register_netdevice_notifier(struct notifier_block *nb) 
		goto unlock;

	if (dev_boot_phase)

		goto unlock;

	down_read(&net_rwsem);

	for_each_net(net) {

		for_each_netdev(net, dev) {

			err = call_netdevice_notifier(nb, NETDEV_REGISTER, dev);
@@ -1642,6 +1643,7 @@ int register_netdevice_notifier(struct notifier_block *nb) 
			call_netdevice_notifier(nb, NETDEV_UP, dev);

		}

	}

	up_read(&net_rwsem);



unlock:

	rtnl_unlock();
@@ -1664,6 +1666,7 @@ int register_netdevice_notifier(struct notifier_block *nb) 
	}



outroll:

	up_read(&net_rwsem);

	raw_notifier_chain_unregister(&netdev_chain, nb);

	goto unlock;

}
@@ -1694,6 +1697,7 @@ int unregister_netdevice_notifier(struct notifier_block *nb) 
	if (err)

		goto unlock;



	down_read(&net_rwsem);

	for_each_net(net) {

		for_each_netdev(net, dev) {

			if (dev->flags & IFF_UP) {
@@ -1704,6 +1708,7 @@ int unregister_netdevice_notifier(struct notifier_block *nb) 
			call_netdevice_notifier(nb, NETDEV_UNREGISTER, dev);

		}

	}

	up_read(&net_rwsem);

unlock:

	rtnl_unlock();

	return err;

net/core/fib_notifier.c

+2 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ static unsigned int fib_seq_sum(void) 
	struct net *net;



	rtnl_lock();

	down_read(&net_rwsem);

	for_each_net(net) {

		rcu_read_lock();

		list_for_each_entry_rcu(ops, &net->fib_notifier_ops, list) {
@@ -43,6 +44,7 @@ static unsigned int fib_seq_sum(void) 
		}

		rcu_read_unlock();

	}

	up_read(&net_rwsem);

	rtnl_unlock();



	return fib_seq;