Commit 72c9528b authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: Introduce dev_get_by_name_rcu() 



Some workloads hit dev_base_lock rwlock pretty hard.
We can use RCU lookups to avoid touching this rwlock
(and avoid touching netdevice refcount)

netdevices are already freed after a RCU grace period, so this patch
adds no penalty at device dismantle time.

However, it adds a synchronize_rcu() call in dev_change_name()

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 68d8287c

include/linux/netdevice.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -1115,6 +1115,7 @@ extern void __dev_remove_pack(struct packet_type *pt); 
extern struct net_device	*dev_get_by_flags(struct net *net, unsigned short flags,

extern struct net_device	*dev_get_by_flags(struct net *net, unsigned short flags,

						  unsigned short mask);

						  unsigned short mask);

extern struct net_device	*dev_get_by_name(struct net *net, const char *name);

extern struct net_device	*dev_get_by_name(struct net *net, const char *name);

extern struct net_device	*dev_get_by_name_rcu(struct net *net, const char *name);

extern struct net_device	*__dev_get_by_name(struct net *net, const char *name);

extern struct net_device	*__dev_get_by_name(struct net *net, const char *name);

extern int		dev_alloc_name(struct net_device *dev, const char *name);

extern int		dev_alloc_name(struct net_device *dev, const char *name);

extern int		dev_open(struct net_device *dev);

extern int		dev_open(struct net_device *dev);

net/core/dev.c

+40 −9
Original line number Original line Diff line number Diff line
@@ -213,7 +213,7 @@ static int list_netdevice(struct net_device *dev) 




	write_lock_bh(&dev_base_lock);

	write_lock_bh(&dev_base_lock);

	list_add_tail(&dev->dev_list, &net->dev_base_head);

	list_add_tail(&dev->dev_list, &net->dev_base_head);

	hlist_add_head(&dev->name_hlist, dev_name_hash(net, dev->name));

	hlist_add_head_rcu(&dev->name_hlist, dev_name_hash(net, dev->name));

	hlist_add_head_rcu(&dev->index_hlist,

	hlist_add_head_rcu(&dev->index_hlist,

			   dev_index_hash(net, dev->ifindex));

			   dev_index_hash(net, dev->ifindex));

	write_unlock_bh(&dev_base_lock);

	write_unlock_bh(&dev_base_lock);
@@ -230,7 +230,7 @@ static void unlist_netdevice(struct net_device *dev) 
	/* Unlink dev from the device chain */

	/* Unlink dev from the device chain */

	write_lock_bh(&dev_base_lock);

	write_lock_bh(&dev_base_lock);

	list_del(&dev->dev_list);

	list_del(&dev->dev_list);

	hlist_del(&dev->name_hlist);

	hlist_del_rcu(&dev->name_hlist);

	hlist_del_rcu(&dev->index_hlist);

	hlist_del_rcu(&dev->index_hlist);

	write_unlock_bh(&dev_base_lock);

	write_unlock_bh(&dev_base_lock);

}

}
@@ -598,6 +598,32 @@ struct net_device *__dev_get_by_name(struct net *net, const char *name) 
}

}

EXPORT_SYMBOL(__dev_get_by_name);

EXPORT_SYMBOL(__dev_get_by_name);





/**

 *	dev_get_by_name_rcu	- find a device by its name

 *	@net: the applicable net namespace

 *	@name: name to find

 *

 *	Find an interface by name.

 *	If the name is found a pointer to the device is returned.

 * 	If the name is not found then %NULL is returned.

 *	The reference counters are not incremented so the caller must be

 *	careful with locks. The caller must hold RCU lock.

 */



struct net_device *dev_get_by_name_rcu(struct net *net, const char *name)

{

	struct hlist_node *p;

	struct net_device *dev;

	struct hlist_head *head = dev_name_hash(net, name);



	hlist_for_each_entry_rcu(dev, p, head, name_hlist)

		if (!strncmp(dev->name, name, IFNAMSIZ))

			return dev;



	return NULL;

}

EXPORT_SYMBOL(dev_get_by_name_rcu);



/**

/**

 *	dev_get_by_name		- find a device by its name

 *	dev_get_by_name		- find a device by its name

 *	@net: the applicable net namespace

 *	@net: the applicable net namespace
@@ -614,11 +640,11 @@ struct net_device *dev_get_by_name(struct net *net, const char *name) 
{

{

	struct net_device *dev;

	struct net_device *dev;





	read_lock(&dev_base_lock);

	rcu_read_lock();

	dev = __dev_get_by_name(net, name);

	dev = dev_get_by_name_rcu(net, name);

	if (dev)

	if (dev)

		dev_hold(dev);

		dev_hold(dev);

	read_unlock(&dev_base_lock);

	rcu_read_unlock();

	return dev;

	return dev;

}

}

EXPORT_SYMBOL(dev_get_by_name);

EXPORT_SYMBOL(dev_get_by_name);
@@ -960,7 +986,12 @@ rollback: 




	write_lock_bh(&dev_base_lock);

	write_lock_bh(&dev_base_lock);

	hlist_del(&dev->name_hlist);

	hlist_del(&dev->name_hlist);

	hlist_add_head(&dev->name_hlist, dev_name_hash(net, dev->name));

	write_unlock_bh(&dev_base_lock);



	synchronize_rcu();



	write_lock_bh(&dev_base_lock);

	hlist_add_head_rcu(&dev->name_hlist, dev_name_hash(net, dev->name));

	write_unlock_bh(&dev_base_lock);

	write_unlock_bh(&dev_base_lock);





	ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);

	ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
@@ -1062,9 +1093,9 @@ void dev_load(struct net *net, const char *name) 
{

{

	struct net_device *dev;

	struct net_device *dev;





	read_lock(&dev_base_lock);

	rcu_read_lock();

	dev = __dev_get_by_name(net, name);

	dev = dev_get_by_name_rcu(net, name);

	read_unlock(&dev_base_lock);

	rcu_read_unlock();





	if (!dev && capable(CAP_NET_ADMIN))

	if (!dev && capable(CAP_NET_ADMIN))

		request_module("%s", name);

		request_module("%s", name);

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