why does there need to lock?

[杨硕 <shanqn@gmail.com>]

Hi, i'm confused about why does "rcu_assign_pointer(dev->ip_ptr,
in_dev);" need to rcu lock?

TIA :)

static struct in_device *inetdev_init(struct net_device *dev)
{
	struct in_device *in_dev;

	ASSERT_RTNL();

	in_dev = kzalloc(sizeof(*in_dev), GFP_KERNEL);
	if (!in_dev)
		goto out;
	memcpy(&in_dev->cnf, dev_net(dev)->ipv4.devconf_dflt,
			sizeof(in_dev->cnf));
	in_dev->cnf.sysctl = NULL;
	in_dev->dev = dev;
	if ((in_dev->arp_parms = neigh_parms_alloc(dev, &arp_tbl)) == NULL)
		goto out_kfree;
	if (IPV4_DEVCONF(in_dev->cnf, FORWARDING))
		dev_disable_lro(dev);
	/* Reference in_dev->dev */
	dev_hold(dev);
	/* Account for reference dev->ip_ptr (below) */
	in_dev_hold(in_dev);

	devinet_sysctl_register(in_dev);
	ip_mc_init_dev(in_dev);
	if (dev->flags & IFF_UP)
		ip_mc_up(in_dev);

	/* we can receive as soon as ip_ptr is set -- do this last */
	rcu_assign_pointer(dev->ip_ptr, in_dev);
out:
	return in_dev;
out_kfree:
	kfree(in_dev);
	in_dev = NULL;
	goto out;
}