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net: Introduce dev_get_by_name_rcu()

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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: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2009-10-30 07:11:27 +00:00 • committed by David S. Miller
commit 72c9528bab
2 changed files with 41 additions and 9 deletions
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1
include/linux/netdevice.h
View file

@ -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,
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_rcu(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_open(struct net_device *dev);

49
net/core/dev.c
View file

@ -213,7 +213,7 @@ 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_rcu(&dev->name_hlist, dev_name_hash(net, dev->name));
hlist_add_head_rcu(&dev->index_hlist,
dev_index_hash(net, dev->ifindex));
write_unlock_bh(&dev_base_lock);
@ -230,7 +230,7 @@ static void unlist_netdevice(struct net_device *dev)
/* Unlink dev from the device chain */
write_lock_bh(&dev_base_lock);
list_del(&dev->dev_list);
hlist_del(&dev->name_hlist);
hlist_del_rcu(&dev->name_hlist);
hlist_del_rcu(&dev->index_hlist);
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);
/**
* 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
* @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;
read_lock(&dev_base_lock);
dev = __dev_get_by_name(net, name);
rcu_read_lock();
dev = dev_get_by_name_rcu(net, name);
if (dev)
dev_hold(dev);
read_unlock(&dev_base_lock);
rcu_read_unlock();
return dev;
}
EXPORT_SYMBOL(dev_get_by_name);
@ -960,7 +986,12 @@ rollback:
write_lock_bh(&dev_base_lock);
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);
ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
@ -1062,9 +1093,9 @@ void dev_load(struct net *net, const char *name)
{
struct net_device *dev;
read_lock(&dev_base_lock);
dev = __dev_get_by_name(net, name);
read_unlock(&dev_base_lock);
rcu_read_lock();
dev = dev_get_by_name_rcu(net, name);
rcu_read_unlock();
if (!dev && capable(CAP_NET_ADMIN))
request_module("%s", name);