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ipv6: give an IPv6 dev to blackhole_netdev
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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 <[email protected]>
Cc: Mahesh Bandewar <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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@davem330
Eric Dumazet authored and davem330 committed Feb 11, 2022
1 parent 2d4feb2 commit e5f80fc
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Showing 2 changed files with 40 additions and 59 deletions.
78 changes: 32 additions & 46 deletions net/ipv6/addrconf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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:
Expand Down Expand Up @@ -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);
Expand Down
21 changes: 8 additions & 13 deletions net/ipv6/route.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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);
}

Expand Down Expand Up @@ -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);
}
}
Expand Down Expand Up @@ -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);
}

Expand Down

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