net: dont hold rtnl mutex during netlink dump callbacks

Four years ago, Patrick made a change to hold rtnl mutex during netlink
dump callbacks.

I believe it was a wrong move. This slows down concurrent dumps, making
good old /proc/net/ files faster than rtnetlink in some situations.

This occurred to me because one "ip link show dev ..." was _very_ slow
on a workload adding/removing network devices in background.

All dump callbacks are able to use RCU locking now, so this patch does
roughly a revert of commits :

1c2d670f366 : [RTNETLINK]: Hold rtnl_mutex during netlink dump callbacks
6313c1e0992 : [RTNETLINK]: Remove unnecessary locking in dump callbacks

This let writers fight for rtnl mutex and readers going full speed.

It also takes care of phonet : phonet_route_get() is now called from rcu
read section. I renamed it to phonet_route_get_rcu()

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Remi Denis-Courmont <remi.denis-courmont@nokia.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

7 files changed, 24 insertions, 22 deletions

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 134a2ff6b98b..ffb0dc4cc0e8 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -120,8 +120,9 @@ static int br_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
         int idx;
 
         idx = 0;
-        for_each_netdev(net, dev) {
-                struct net_bridge_port *port = br_port_get_rtnl(dev);
+        rcu_read_lock();
+        for_each_netdev_rcu(net, dev) {
+                struct net_bridge_port *port = br_port_get_rcu(dev);
 
                 /* not a bridge port */
                 if (!port || idx < cb->args[0])
@@ -135,7 +136,7 @@ static int br_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 skip:
                 ++idx;
         }
-
+        rcu_read_unlock();
         cb->args[0] = idx;
 
         return skb->len;
diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index 8248ebb5891d..3911586e12e4 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -590,7 +590,8 @@ static int dump_rules(struct sk_buff *skb, struct netlink_callback *cb,
         int idx = 0;
         struct fib_rule *rule;
 
-        list_for_each_entry(rule, &ops->rules_list, list) {
+        rcu_read_lock();
+        list_for_each_entry_rcu(rule, &ops->rules_list, list) {
                 if (idx < cb->args[1])
                         goto skip;
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index d7c4bb4b1820..296331257195 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1007,10 +1007,11 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
         s_h = cb->args[0];
         s_idx = cb->args[1];
 
+        rcu_read_lock();
         for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
                 idx = 0;
                 head = &net->dev_index_head[h];
-                hlist_for_each_entry(dev, node, head, index_hlist) {
+                hlist_for_each_entry_rcu(dev, node, head, index_hlist) {
                         if (idx < s_idx)
                                 goto cont;
                         if (rtnl_fill_ifinfo(skb, dev, RTM_NEWLINK,
@@ -1023,6 +1024,7 @@ cont:
                 }
         }
 out:
+        rcu_read_unlock();
         cb->args[1] = idx;
         cb->args[0] = h;
 
@@ -1879,7 +1881,6 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
         int min_len;
         int family;
         int type;
-        int err;
 
         type = nlh->nlmsg_type;
         if (type > RTM_MAX)
@@ -1906,11 +1907,8 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
                 if (dumpit == NULL)
                         return -EOPNOTSUPP;
 
-                __rtnl_unlock();
                 rtnl = net->rtnl;
-                err = netlink_dump_start(rtnl, skb, nlh, dumpit, NULL);
-                rtnl_lock();
-                return err;
+                return netlink_dump_start(rtnl, skb, nlh, dumpit, NULL);
         }
 
         memset(rta_buf, 0, (rtattr_max * sizeof(struct rtattr *)));
@@ -1980,7 +1978,7 @@ static int __net_init rtnetlink_net_init(struct net *net)
 {
         struct sock *sk;
         sk = netlink_kernel_create(net, NETLINK_ROUTE, RTNLGRP_MAX,
-                                   rtnetlink_rcv, &rtnl_mutex, THIS_MODULE);
+                                   rtnetlink_rcv, NULL, THIS_MODULE);
         if (!sk)
                 return -ENOMEM;
         net->rtnl = sk;
diff --git a/net/decnet/dn_dev.c b/net/decnet/dn_dev.c
index 0dcaa903e00e..404fa1591027 100644
--- a/net/decnet/dn_dev.c
+++ b/net/decnet/dn_dev.c
@@ -752,7 +752,8 @@ static int dn_nl_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
         skip_naddr = cb->args[1];
 
         idx = 0;
-        for_each_netdev(&init_net, dev) {
+        rcu_read_lock();
+        for_each_netdev_rcu(&init_net, dev) {
                 if (idx < skip_ndevs)
                         goto cont;
                 else if (idx > skip_ndevs) {
@@ -761,11 +762,11 @@ static int dn_nl_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
                         skip_naddr = 0;
                 }
 
-                if ((dn_db = rtnl_dereference(dev->dn_ptr)) == NULL)
+                if ((dn_db = rcu_dereference(dev->dn_ptr)) == NULL)
                         goto cont;
 
-                for (ifa = rtnl_dereference(dn_db->ifa_list), dn_idx = 0; ifa;
-                     ifa = rtnl_dereference(ifa->ifa_next), dn_idx++) {
+                for (ifa = rcu_dereference(dn_db->ifa_list), dn_idx = 0; ifa;
+                     ifa = rcu_dereference(ifa->ifa_next), dn_idx++) {
                         if (dn_idx < skip_naddr)
                                 continue;
 
@@ -778,6 +779,7 @@ cont:
                 idx++;
         }
 done:
+        rcu_read_unlock();
         cb->args[0] = idx;
         cb->args[1] = dn_idx;
 
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index dd88df0a5d7f..4076a0b14b20 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -394,10 +394,11 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
         arg.net = net;
         w->args = &arg;
 
+        rcu_read_lock();
         for (h = s_h; h < FIB6_TABLE_HASHSZ; h++, s_e = 0) {
                 e = 0;
                 head = &net->ipv6.fib_table_hash[h];
-                hlist_for_each_entry(tb, node, head, tb6_hlist) {
+                hlist_for_each_entry_rcu(tb, node, head, tb6_hlist) {
                         if (e < s_e)
                                 goto next;
                         res = fib6_dump_table(tb, skb, cb);
@@ -408,6 +409,7 @@ next:
                 }
         }
 out:
+        rcu_read_unlock();
         cb->args[1] = e;
         cb->args[0] = h;
 
diff --git a/net/phonet/pn_dev.c b/net/phonet/pn_dev.c
index 947038ddd04c..47b3452675b6 100644
--- a/net/phonet/pn_dev.c
+++ b/net/phonet/pn_dev.c
@@ -426,18 +426,14 @@ int phonet_route_del(struct net_device *dev, u8 daddr)
         return 0;
 }
 
-struct net_device *phonet_route_get(struct net *net, u8 daddr)
+struct net_device *phonet_route_get_rcu(struct net *net, u8 daddr)
 {
         struct phonet_net *pnn = phonet_pernet(net);
         struct phonet_routes *routes = &pnn->routes;
         struct net_device *dev;
 
-        ASSERT_RTNL(); /* no need to hold the device */
-
         daddr >>= 2;
-        rcu_read_lock();
         dev = rcu_dereference(routes->table[daddr]);
-        rcu_read_unlock();
         return dev;
 }
 
diff --git a/net/phonet/pn_netlink.c b/net/phonet/pn_netlink.c
index 58b3b1f991ed..438accb7a5a8 100644
--- a/net/phonet/pn_netlink.c
+++ b/net/phonet/pn_netlink.c
@@ -264,10 +264,11 @@ static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
         struct net *net = sock_net(skb->sk);
         u8 addr, addr_idx = 0, addr_start_idx = cb->args[0];
 
+        rcu_read_lock();
         for (addr = 0; addr < 64; addr++) {
                 struct net_device *dev;
 
-                dev = phonet_route_get(net, addr << 2);
+                dev = phonet_route_get_rcu(net, addr << 2);
                 if (!dev)
                         continue;
 
@@ -279,6 +280,7 @@ static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
         }
 
 out:
+        rcu_read_unlock();
         cb->args[0] = addr_idx;
         cb->args[1] = 0;