tuntap: attach queue 0 before registering netdevice

We attach queue 0 after registering netdevice currently. This leads to call
netif_set_real_num_{tx|rx}_queues() after registering the netdevice. Since we
allow tun/tap has a maximum of 1024 queues, this may lead a huge number of
uevents to be injected to userspace since we create 2048 kobjects and then
remove 2046. Solve this problem by attaching queue 0 and set the real number of
queues before registering netdevice.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Tested-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -493,9 +493,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
 
  tun_set_real_num_queues(tun);
 
- if (tun->numqueues == 1)
- netif_carrier_on(tun->dev);
-
  /* device is allowed to go away first, so no need to hold extra
  * refcnt.
  */
@@ -1612,6 +1609,10 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
  TUN_USER_FEATURES;
  dev->features = dev->hw_features;
 
+ err = tun_attach(tun, file);
+ if (err < 0)
+ goto err_free_dev;
+
  err = register_netdevice(tun->dev);
  if (err < 0)
  goto err_free_dev;
@@ -1621,9 +1622,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
  device_create_file(&tun->dev->dev, &dev_attr_group))
  pr_err("Failed to create tun sysfs files\n");
 
- err = tun_attach(tun, file);
- if (err < 0)
- goto err_free_dev;
+ netif_carrier_on(tun->dev);
  }
 
  tun_debug(KERN_INFO, tun, "tun_set_iff\n");