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Commit fb699dfd authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: Introduce dev_get_by_index_rcu() 



Some workloads hit dev_base_lock rwlock pretty hard.
We can use RCU lookups to avoid touching this rwlock.

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

dev_ifname() converted to dev_get_by_index_rcu()

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e0c5567d

include/linux/netdevice.h

+1 −0
Original line number Diff line number Diff line
@@ -1139,6 +1139,7 @@ extern void netdev_resync_ops(struct net_device *dev); 
extern int call_netdevice_notifiers(unsigned long val, struct net_device *dev);

extern struct net_device	*dev_get_by_index(struct net *net, int ifindex);

extern struct net_device	*__dev_get_by_index(struct net *net, int ifindex);

extern struct net_device	*dev_get_by_index_rcu(struct net *net, int ifindex);

extern int		dev_restart(struct net_device *dev);

#ifdef CONFIG_NETPOLL_TRAP

extern int		netpoll_trap(void);

net/core/dev.c

+38 −10
Original line number Diff line number Diff line
@@ -214,12 +214,15 @@ static int list_netdevice(struct net_device *dev) 
	write_lock_bh(&dev_base_lock);

	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(&dev->index_hlist, dev_index_hash(net, dev->ifindex));

	hlist_add_head_rcu(&dev->index_hlist,

			   dev_index_hash(net, dev->ifindex));

	write_unlock_bh(&dev_base_lock);

	return 0;

}



/* Device list removal */

/* Device list removal

 * caller must respect a RCU grace period before freeing/reusing dev

 */

static void unlist_netdevice(struct net_device *dev)

{

	ASSERT_RTNL();
@@ -228,7 +231,7 @@ static void unlist_netdevice(struct net_device *dev) 
	write_lock_bh(&dev_base_lock);

	list_del(&dev->dev_list);

	hlist_del(&dev->name_hlist);

	hlist_del(&dev->index_hlist);

	hlist_del_rcu(&dev->index_hlist);

	write_unlock_bh(&dev_base_lock);

}
@@ -646,6 +649,31 @@ struct net_device *__dev_get_by_index(struct net *net, int ifindex) 
}

EXPORT_SYMBOL(__dev_get_by_index);



/**

 *	dev_get_by_index_rcu - find a device by its ifindex

 *	@net: the applicable net namespace

 *	@ifindex: index of device

 *

 *	Search for an interface by index. Returns %NULL if the device

 *	is not found or a pointer to the device. The device has not

 *	had its reference counter increased so the caller must be careful

 *	about locking. The caller must hold RCU lock.

 */



struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex)

{

	struct hlist_node *p;

	struct net_device *dev;

	struct hlist_head *head = dev_index_hash(net, ifindex);



	hlist_for_each_entry_rcu(dev, p, head, index_hlist)

		if (dev->ifindex == ifindex)

			return dev;



	return NULL;

}

EXPORT_SYMBOL(dev_get_by_index_rcu);





/**

 *	dev_get_by_index - find a device by its ifindex
@@ -662,11 +690,11 @@ struct net_device *dev_get_by_index(struct net *net, int ifindex) 
{

	struct net_device *dev;



	read_lock(&dev_base_lock);

	dev = __dev_get_by_index(net, ifindex);

	rcu_read_lock();

	dev = dev_get_by_index_rcu(net, ifindex);

	if (dev)

		dev_hold(dev);

	read_unlock(&dev_base_lock);

	rcu_read_unlock();

	return dev;

}

EXPORT_SYMBOL(dev_get_by_index);
@@ -2939,15 +2967,15 @@ static int dev_ifname(struct net *net, struct ifreq __user *arg) 
	if (copy_from_user(&ifr, arg, sizeof(struct ifreq)))

		return -EFAULT;



	read_lock(&dev_base_lock);

	dev = __dev_get_by_index(net, ifr.ifr_ifindex);

	rcu_read_lock();

	dev = dev_get_by_index_rcu(net, ifr.ifr_ifindex);

	if (!dev) {

		read_unlock(&dev_base_lock);

		rcu_read_unlock();

		return -ENODEV;

	}



	strcpy(ifr.ifr_name, dev->name);

	read_unlock(&dev_base_lock);

	rcu_read_unlock();



	if (copy_to_user(arg, &ifr, sizeof(struct ifreq)))

		return -EFAULT;