ipv6: give an IPv6 dev to blackhole_netdev

IPv6 addrconf notifiers wants the loopback device to
be the last device being dismantled at netns deletion.

This caused many limitations and work arounds.

Back in linux-5.3, Mahesh added a per host blackhole_netdev
that can be used whenever we need to make sure objects no longer
refer to a disappearing device.

If we attach to blackhole_netdev an ip6_ptr (allocate an idev),
then we can use this special device (which is never freed)
in place of the loopback_dev (which can be freed).

This will permit improvements in netdev_run_todo() and other parts
of the stack where had steps to make sure loopback_dev was
the last device to disappear.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 4f402bc38f056e08f3761e63a7bc7a51e54e9384..02d31d4fcab3b3d529c4fe3260216ecee1108e82 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -372,7 +372,7 @@ static struct inet6_dev *ipv6_add_dev(struct net_device *dev)
 
        ASSERT_RTNL();
 
-       if (dev->mtu < IPV6_MIN_MTU)
+       if (dev->mtu < IPV6_MIN_MTU && dev != blackhole_netdev)
                return ERR_PTR(-EINVAL);
 
        ndev = kzalloc(sizeof(struct inet6_dev), GFP_KERNEL);
@@ -400,21 +400,22 @@ static struct inet6_dev *ipv6_add_dev(struct net_device *dev)
        /* We refer to the device */
        dev_hold_track(dev, &ndev->dev_tracker, GFP_KERNEL);
 
-       if (snmp6_alloc_dev(ndev) < 0) {
-               netdev_dbg(dev, "%s: cannot allocate memory for statistics\n",
-                          __func__);
-               neigh_parms_release(&nd_tbl, ndev->nd_parms);
-               dev_put_track(dev, &ndev->dev_tracker);
-               kfree(ndev);
-               return ERR_PTR(err);
-       }
+       if (dev != blackhole_netdev) {
+               if (snmp6_alloc_dev(ndev) < 0) {
+                       netdev_dbg(dev, "%s: cannot allocate memory for statistics\n",
+                                  __func__);
+                       neigh_parms_release(&nd_tbl, ndev->nd_parms);
+                       dev_put_track(dev, &ndev->dev_tracker);
+                       kfree(ndev);
+                       return ERR_PTR(err);
+               }
 
-       if (snmp6_register_dev(ndev) < 0) {
-               netdev_dbg(dev, "%s: cannot create /proc/net/dev_snmp6/%s\n",
-                          __func__, dev->name);
-               goto err_release;
+               if (snmp6_register_dev(ndev) < 0) {
+                       netdev_dbg(dev, "%s: cannot create /proc/net/dev_snmp6/%s\n",
+                                  __func__, dev->name);
+                       goto err_release;
+               }
        }
-
        /* One reference from device. */
        refcount_set(&ndev->refcnt, 1);
 
@@ -445,25 +446,28 @@ static struct inet6_dev *ipv6_add_dev(struct net_device *dev)
 
        ipv6_mc_init_dev(ndev);
        ndev->tstamp = jiffies;
-       err = addrconf_sysctl_register(ndev);
-       if (err) {
-               ipv6_mc_destroy_dev(ndev);
-               snmp6_unregister_dev(ndev);
-               goto err_release;
+       if (dev != blackhole_netdev) {
+               err = addrconf_sysctl_register(ndev);
+               if (err) {
+                       ipv6_mc_destroy_dev(ndev);
+                       snmp6_unregister_dev(ndev);
+                       goto err_release;
+               }
        }
        /* protected by rtnl_lock */
        rcu_assign_pointer(dev->ip6_ptr, ndev);
 
-       /* Join interface-local all-node multicast group */
-       ipv6_dev_mc_inc(dev, &in6addr_interfacelocal_allnodes);
+       if (dev != blackhole_netdev) {
+               /* Join interface-local all-node multicast group */
+               ipv6_dev_mc_inc(dev, &in6addr_interfacelocal_allnodes);
 
-       /* Join all-node multicast group */
-       ipv6_dev_mc_inc(dev, &in6addr_linklocal_allnodes);
-
-       /* Join all-router multicast group if forwarding is set */
-       if (ndev->cnf.forwarding && (dev->flags & IFF_MULTICAST))
-               ipv6_dev_mc_inc(dev, &in6addr_linklocal_allrouters);
+               /* Join all-node multicast group */
+               ipv6_dev_mc_inc(dev, &in6addr_linklocal_allnodes);
 
+               /* Join all-router multicast group if forwarding is set */
+               if (ndev->cnf.forwarding && (dev->flags & IFF_MULTICAST))
+                       ipv6_dev_mc_inc(dev, &in6addr_linklocal_allrouters);
+       }
        return ndev;
 
 err_release:
@@ -7233,26 +7237,8 @@ int __init addrconf_init(void)
                goto out_nowq;
        }
 
-       /* The addrconf netdev notifier requires that loopback_dev
-        * has it's ipv6 private information allocated and setup
-        * before it can bring up and give link-local addresses
-        * to other devices which are up.
-        *
-        * Unfortunately, loopback_dev is not necessarily the first
-        * entry in the global dev_base list of net devices.  In fact,
-        * it is likely to be the very last entry on that list.
-        * So this causes the notifier registry below to try and
-        * give link-local addresses to all devices besides loopback_dev
-        * first, then loopback_dev, which cases all the non-loopback_dev
-        * devices to fail to get a link-local address.
-        *
-        * So, as a temporary fix, allocate the ipv6 structure for
-        * loopback_dev first by hand.
-        * Longer term, all of the dependencies ipv6 has upon the loopback
-        * device and it being up should be removed.
-        */
        rtnl_lock();
-       idev = ipv6_add_dev(init_net.loopback_dev);
+       idev = ipv6_add_dev(blackhole_netdev);
        rtnl_unlock();
        if (IS_ERR(idev)) {
                err = PTR_ERR(idev);

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index ccdfa5aa808dce90dc86abf496d38f46848cc36d..b04aaf13e41eb962975c025c78aac77e950ae796 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -156,14 +156,10 @@ void rt6_uncached_list_del(struct rt6_info *rt)
        }
 }
 
-static void rt6_uncached_list_flush_dev(struct net *net, struct net_device *dev)
+static void rt6_uncached_list_flush_dev(struct net_device *dev)
 {
-       struct net_device *loopback_dev = net->loopback_dev;
        int cpu;
 
-       if (dev == loopback_dev)
-               return;
-
        for_each_possible_cpu(cpu) {
                struct uncached_list *ul = per_cpu_ptr(&rt6_uncached_list, cpu);
                struct rt6_info *rt;
@@ -174,7 +170,7 @@ static void rt6_uncached_list_flush_dev(struct net *net, struct net_device *dev)
                        struct net_device *rt_dev = rt->dst.dev;
 
                        if (rt_idev->dev == dev) {
-                               rt->rt6i_idev = in6_dev_get(loopback_dev);
+                               rt->rt6i_idev = in6_dev_get(blackhole_netdev);
                                in6_dev_put(rt_idev);
                        }
 
@@ -371,13 +367,12 @@ static void ip6_dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 {
        struct rt6_info *rt = (struct rt6_info *)dst;
        struct inet6_dev *idev = rt->rt6i_idev;
-       struct net_device *loopback_dev =
-               dev_net(dev)->loopback_dev;
 
-       if (idev && idev->dev != loopback_dev) {
-               struct inet6_dev *loopback_idev = in6_dev_get(loopback_dev);
-               if (loopback_idev) {
-                       rt->rt6i_idev = loopback_idev;
+       if (idev && idev->dev != blackhole_netdev) {
+               struct inet6_dev *blackhole_idev = in6_dev_get(blackhole_netdev);
+
+               if (blackhole_idev) {
+                       rt->rt6i_idev = blackhole_idev;
                        in6_dev_put(idev);
                }
        }
@@ -4892,7 +4887,7 @@ void rt6_sync_down_dev(struct net_device *dev, unsigned long event)
 void rt6_disable_ip(struct net_device *dev, unsigned long event)
 {
        rt6_sync_down_dev(dev, event);
-       rt6_uncached_list_flush_dev(dev_net(dev), dev);
+       rt6_uncached_list_flush_dev(dev);
        neigh_ifdown(&nd_tbl, dev);
 }