net: Introduce for_each_netdev_rcu() iterator

Adds RCU management to the list of netdevices.

Convert some for_each_netdev() users to RCU version, if
it can avoid read_lock-ing dev_base_lock

Ie:
	read_lock(&dev_base_loack);
	for_each_netdev(net, dev)
		some_action();
	read_unlock(&dev_base_lock);

becomes :

	rcu_read_lock();
	for_each_netdev_rcu(net, dev)
		some_action();
	rcu_read_unlock();


Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

11 files changed, 68 insertions, 77 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index bcf1083857fc..5077de028317 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1081,6 +1081,8 @@ extern rwlock_t				dev_base_lock;		/* Device list lock */
 
 #define for_each_netdev(net, d)         \
                 list_for_each_entry(d, &(net)->dev_base_head, dev_list)
+#define for_each_netdev_rcu(net, d)             \
+                list_for_each_entry_rcu(d, &(net)->dev_base_head, dev_list)
 #define for_each_netdev_safe(net, d, n) \
                 list_for_each_entry_safe(d, n, &(net)->dev_base_head, dev_list)
 #define for_each_netdev_continue(net, d)                \
diff --git a/net/core/dev.c b/net/core/dev.c
index 76a1502efe67..bf629ac08b87 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -175,7 +175,7 @@ static struct list_head ptype_all __read_mostly;	/* Taps */
  * The @dev_base_head list is protected by @dev_base_lock and the rtnl
  * semaphore.
  *
- * Pure readers hold dev_base_lock for reading.
+ * Pure readers hold dev_base_lock for reading, or rcu_read_lock()
  *
  * Writers must hold the rtnl semaphore while they loop through the
  * dev_base_head list, and hold dev_base_lock for writing when they do the
@@ -212,7 +212,7 @@ static int list_netdevice(struct net_device *dev)
         ASSERT_RTNL();
 
         write_lock_bh(&dev_base_lock);
-        list_add_tail(&dev->dev_list, &net->dev_base_head);
+        list_add_tail_rcu(&dev->dev_list, &net->dev_base_head);
         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));
@@ -229,7 +229,7 @@ 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);
+        list_del_rcu(&dev->dev_list);
         hlist_del_rcu(&dev->name_hlist);
         hlist_del_rcu(&dev->index_hlist);
         write_unlock_bh(&dev_base_lock);
@@ -799,15 +799,15 @@ struct net_device *dev_get_by_flags(struct net *net, unsigned short if_flags,
         struct net_device *dev, *ret;
 
         ret = NULL;
-        read_lock(&dev_base_lock);
-        for_each_netdev(net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(net, dev) {
                 if (((dev->flags ^ if_flags) & mask) == 0) {
                         dev_hold(dev);
                         ret = dev;
                         break;
                 }
         }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
         return ret;
 }
 EXPORT_SYMBOL(dev_get_by_flags);
@@ -3077,18 +3077,18 @@ static int dev_ifconf(struct net *net, char __user *arg)
  *      in detail.
  */
 void *dev_seq_start(struct seq_file *seq, loff_t *pos)
-        __acquires(dev_base_lock)
+        __acquires(RCU)
 {
         struct net *net = seq_file_net(seq);
         loff_t off;
         struct net_device *dev;
 
-        read_lock(&dev_base_lock);
+        rcu_read_lock();
         if (!*pos)
                 return SEQ_START_TOKEN;
 
         off = 1;
-        for_each_netdev(net, dev)
+        for_each_netdev_rcu(net, dev)
                 if (off++ == *pos)
                         return dev;
 
@@ -3097,16 +3097,18 @@ void *dev_seq_start(struct seq_file *seq, loff_t *pos)
 
 void *dev_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-        struct net *net = seq_file_net(seq);
+        struct net_device *dev = (v == SEQ_START_TOKEN) ?
+                                  first_net_device(seq_file_net(seq)) :
+                                  next_net_device((struct net_device *)v);
+
         ++*pos;
-        return v == SEQ_START_TOKEN ?
-                first_net_device(net) : next_net_device((struct net_device *)v);
+        return rcu_dereference(dev);
 }
 
 void dev_seq_stop(struct seq_file *seq, void *v)
-        __releases(dev_base_lock)
+        __releases(RCU)
 {
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 }
 
 static void dev_seq_printf_stats(struct seq_file *seq, struct net_device *dev)
diff --git a/net/decnet/af_decnet.c b/net/decnet/af_decnet.c
index 664965c87e16..2e355841ca99 100644
--- a/net/decnet/af_decnet.c
+++ b/net/decnet/af_decnet.c
@@ -749,9 +749,9 @@ static int dn_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 
         if (!(saddr->sdn_flags & SDF_WILD)) {
                 if (le16_to_cpu(saddr->sdn_nodeaddrl)) {
-                        read_lock(&dev_base_lock);
+                        rcu_read_lock();
                         ldev = NULL;
-                        for_each_netdev(&init_net, dev) {
+                        for_each_netdev_rcu(&init_net, dev) {
                                 if (!dev->dn_ptr)
                                         continue;
                                 if (dn_dev_islocal(dev, dn_saddr2dn(saddr))) {
@@ -759,7 +759,7 @@ static int dn_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
                                         break;
                                 }
                         }
-                        read_unlock(&dev_base_lock);
+                        rcu_read_unlock();
                         if (ldev == NULL)
                                 return -EADDRNOTAVAIL;
                 }
diff --git a/net/decnet/dn_fib.c b/net/decnet/dn_fib.c
index 27ea2e9b080a..fd641f65e092 100644
--- a/net/decnet/dn_fib.c
+++ b/net/decnet/dn_fib.c
@@ -607,8 +607,8 @@ static void dn_fib_del_ifaddr(struct dn_ifaddr *ifa)
         ASSERT_RTNL();
 
         /* Scan device list */
-        read_lock(&dev_base_lock);
-        for_each_netdev(&init_net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(&init_net, dev) {
                 dn_db = dev->dn_ptr;
                 if (dn_db == NULL)
                         continue;
@@ -619,7 +619,7 @@ static void dn_fib_del_ifaddr(struct dn_ifaddr *ifa)
                         }
                 }
         }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 
         if (found_it == 0) {
                 fib_magic(RTM_DELROUTE, RTN_LOCAL, ifa->ifa_local, 16, ifa);
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index 57662cabaf9b..860286a3921b 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -908,8 +908,8 @@ static int dn_route_output_slow(struct dst_entry **pprt, const struct flowi *old
                         dev_put(dev_out);
                         goto out;
                 }
-                read_lock(&dev_base_lock);
-                for_each_netdev(&init_net, dev) {
+                rcu_read_lock();
+                for_each_netdev_rcu(&init_net, dev) {
                         if (!dev->dn_ptr)
                                 continue;
                         if (!dn_dev_islocal(dev, oldflp->fld_src))
@@ -922,7 +922,7 @@ static int dn_route_output_slow(struct dst_entry **pprt, const struct flowi *old
                         dev_out = dev;
                         break;
                 }
-                read_unlock(&dev_base_lock);
+                rcu_read_unlock();
                 if (dev_out == NULL)
                         goto out;
                 dev_hold(dev_out);
diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index ccccaae50b20..8aa7a134c1f1 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -876,19 +876,16 @@ __be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope)
                 if (!addr)
                         addr = ifa->ifa_local;
         } endfor_ifa(in_dev);
-no_in_dev:
-        rcu_read_unlock();
 
+no_in_dev:
         if (addr)
-                goto out;
+                goto out_unlock;
 
         /* Not loopback addresses on loopback should be preferred
            in this case. It is importnat that lo is the first interface
            in dev_base list.
          */
-        read_lock(&dev_base_lock);
-        rcu_read_lock();
-        for_each_netdev(net, dev) {
+        for_each_netdev_rcu(net, dev) {
                 if ((in_dev = __in_dev_get_rcu(dev)) == NULL)
                         continue;
 
@@ -896,12 +893,11 @@ no_in_dev:
                         if (ifa->ifa_scope != RT_SCOPE_LINK &&
                             ifa->ifa_scope <= scope) {
                                 addr = ifa->ifa_local;
-                                goto out_unlock_both;
+                                goto out_unlock;
                         }
                 } endfor_ifa(in_dev);
         }
-out_unlock_both:
-        read_unlock(&dev_base_lock);
+out_unlock:
         rcu_read_unlock();
 out:
         return addr;
@@ -962,9 +958,8 @@ __be32 inet_confirm_addr(struct in_device *in_dev,
                 return confirm_addr_indev(in_dev, dst, local, scope);
 
         net = dev_net(in_dev->dev);
-        read_lock(&dev_base_lock);
         rcu_read_lock();
-        for_each_netdev(net, dev) {
+        for_each_netdev_rcu(net, dev) {
                 if ((in_dev = __in_dev_get_rcu(dev))) {
                         addr = confirm_addr_indev(in_dev, dst, local, scope);
                         if (addr)
@@ -972,7 +967,6 @@ __be32 inet_confirm_addr(struct in_device *in_dev,
                 }
         }
         rcu_read_unlock();
-        read_unlock(&dev_base_lock);
 
         return addr;
 }
@@ -1240,18 +1234,18 @@ static void devinet_copy_dflt_conf(struct net *net, int i)
 {
         struct net_device *dev;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(net, dev) {
                 struct in_device *in_dev;
-                rcu_read_lock();
+
                 in_dev = __in_dev_get_rcu(dev);
                 if (in_dev && !test_bit(i, in_dev->cnf.state))
                         in_dev->cnf.data[i] = net->ipv4.devconf_dflt->data[i];
-                rcu_read_unlock();
         }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 }
 
+/* called with RTNL locked */
 static void inet_forward_change(struct net *net)
 {
         struct net_device *dev;
@@ -1260,7 +1254,6 @@ static void inet_forward_change(struct net *net)
         IPV4_DEVCONF_ALL(net, ACCEPT_REDIRECTS) = !on;
         IPV4_DEVCONF_DFLT(net, FORWARDING) = on;
 
-        read_lock(&dev_base_lock);
         for_each_netdev(net, dev) {
                 struct in_device *in_dev;
                 if (on)
@@ -1271,7 +1264,6 @@ static void inet_forward_change(struct net *net)
                         IN_DEV_CONF_SET(in_dev, FORWARDING, on);
                 rcu_read_unlock();
         }
-        read_unlock(&dev_base_lock);
 }
 
 static int devinet_conf_proc(ctl_table *ctl, int write,
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 918648409612..024bba30de21 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -481,9 +481,8 @@ static void addrconf_forward_change(struct net *net, __s32 newf)
         struct net_device *dev;
         struct inet6_dev *idev;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(net, dev) {
-                rcu_read_lock();
+        rcu_read_lock();
+        for_each_netdev_rcu(net, dev) {
                 idev = __in6_dev_get(dev);
                 if (idev) {
                         int changed = (!idev->cnf.forwarding) ^ (!newf);
@@ -491,9 +490,8 @@ static void addrconf_forward_change(struct net *net, __s32 newf)
                         if (changed)
                                 dev_forward_change(idev);
                 }
-                rcu_read_unlock();
         }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 }
 
 static int addrconf_fixup_forwarding(struct ctl_table *table, int *p, int old)
@@ -1137,10 +1135,9 @@ int ipv6_dev_get_saddr(struct net *net, struct net_device *dst_dev,
         hiscore->rule = -1;
         hiscore->ifa = NULL;
 
-        read_lock(&dev_base_lock);
         rcu_read_lock();
 
-        for_each_netdev(net, dev) {
+        for_each_netdev_rcu(net, dev) {
                 struct inet6_dev *idev;
 
                 /* Candidate Source Address (section 4)
@@ -1235,7 +1232,6 @@ try_nextdev:
                 read_unlock_bh(&idev->lock);
         }
         rcu_read_unlock();
-        read_unlock(&dev_base_lock);
 
         if (!hiscore->ifa)
                 return -EADDRNOTAVAIL;
@@ -4052,9 +4048,8 @@ static void addrconf_disable_change(struct net *net, __s32 newf)
         struct net_device *dev;
         struct inet6_dev *idev;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(net, dev) {
-                rcu_read_lock();
+        rcu_read_lock();
+        for_each_netdev_rcu(net, dev) {
                 idev = __in6_dev_get(dev);
                 if (idev) {
                         int changed = (!idev->cnf.disable_ipv6) ^ (!newf);
@@ -4062,9 +4057,8 @@ static void addrconf_disable_change(struct net *net, __s32 newf)
                         if (changed)
                                 dev_disable_change(idev);
                 }
-                rcu_read_unlock();
         }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 }
 
 static int addrconf_disable_ipv6(struct ctl_table *table, int *p, int old)
diff --git a/net/ipv6/anycast.c b/net/ipv6/anycast.c
index 1ae58bec1de0..2f00ca83f049 100644
--- a/net/ipv6/anycast.c
+++ b/net/ipv6/anycast.c
@@ -404,13 +404,13 @@ int ipv6_chk_acast_addr(struct net *net, struct net_device *dev,
 
         if (dev)
                 return ipv6_chk_acast_dev(dev, addr);
-        read_lock(&dev_base_lock);
-        for_each_netdev(net, dev)
+        rcu_read_lock();
+        for_each_netdev_rcu(net, dev)
                 if (ipv6_chk_acast_dev(dev, addr)) {
                         found = 1;
                         break;
                 }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
         return found;
 }
 
diff --git a/net/netrom/nr_route.c b/net/netrom/nr_route.c
index 4eb1ac9a7679..aacba76070fc 100644
--- a/net/netrom/nr_route.c
+++ b/net/netrom/nr_route.c
@@ -597,15 +597,15 @@ struct net_device *nr_dev_first(void)
 {
         struct net_device *dev, *first = NULL;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(&init_net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(&init_net, dev) {
                 if ((dev->flags & IFF_UP) && dev->type == ARPHRD_NETROM)
                         if (first == NULL || strncmp(dev->name, first->name, 3) < 0)
                                 first = dev;
         }
         if (first)
                 dev_hold(first);
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 
         return first;
 }
@@ -617,16 +617,17 @@ struct net_device *nr_dev_get(ax25_address *addr)
 {
         struct net_device *dev;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(&init_net, dev) {
-                if ((dev->flags & IFF_UP) && dev->type == ARPHRD_NETROM && ax25cmp(addr, (ax25_address *)dev->dev_addr) == 0) {
+        rcu_read_lock();
+        for_each_netdev_rcu(&init_net, dev) {
+                if ((dev->flags & IFF_UP) && dev->type == ARPHRD_NETROM &&
+                    ax25cmp(addr, (ax25_address *)dev->dev_addr) == 0) {
                         dev_hold(dev);
                         goto out;
                 }
         }
         dev = NULL;
 out:
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
         return dev;
 }
 
diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
index 9478d9b3d977..d936226916f2 100644
--- a/net/rose/rose_route.c
+++ b/net/rose/rose_route.c
@@ -600,13 +600,13 @@ struct net_device *rose_dev_first(void)
 {
         struct net_device *dev, *first = NULL;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(&init_net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(&init_net, dev) {
                 if ((dev->flags & IFF_UP) && dev->type == ARPHRD_ROSE)
                         if (first == NULL || strncmp(dev->name, first->name, 3) < 0)
                                 first = dev;
         }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 
         return first;
 }
@@ -618,8 +618,8 @@ struct net_device *rose_dev_get(rose_address *addr)
 {
         struct net_device *dev;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(&init_net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(&init_net, dev) {
                 if ((dev->flags & IFF_UP) && dev->type == ARPHRD_ROSE && rosecmp(addr, (rose_address *)dev->dev_addr) == 0) {
                         dev_hold(dev);
                         goto out;
@@ -627,7 +627,7 @@ struct net_device *rose_dev_get(rose_address *addr)
         }
         dev = NULL;
 out:
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
         return dev;
 }
 
@@ -635,14 +635,14 @@ static int rose_dev_exists(rose_address *addr)
 {
         struct net_device *dev;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(&init_net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(&init_net, dev) {
                 if ((dev->flags & IFF_UP) && dev->type == ARPHRD_ROSE && rosecmp(addr, (rose_address *)dev->dev_addr) == 0)
                         goto out;
         }
         dev = NULL;
 out:
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
         return dev != NULL;
 }
 
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index d9f4cc2c7869..fe44c57101de 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -205,14 +205,14 @@ static void sctp_get_local_addr_list(void)
         struct list_head *pos;
         struct sctp_af *af;
 
-        read_lock(&dev_base_lock);
-        for_each_netdev(&init_net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(&init_net, dev) {
                 __list_for_each(pos, &sctp_address_families) {
                         af = list_entry(pos, struct sctp_af, list);
                         af->copy_addrlist(&sctp_local_addr_list, dev);
                 }
         }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 }
 
 /* Free the existing local addresses.  */