From fb699dfd426a189fe33b91586c15176a75c8aed0 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 19 Oct 2009 19:18:49 +0000 Subject: 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: Eric Dumazet Signed-off-by: David S. Miller --- net/core/dev.c | 48 ++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 38 insertions(+), 10 deletions(-) (limited to 'net/core') diff --git a/net/core/dev.c b/net/core/dev.c index 09551cc143a..68a1bb68b5a 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -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; -- cgit v1.2.3