fou: implement FOU_CMD_GET

Hello WANG Cong,

The patch 7a6c8c34e5b7: "fou: implement FOU_CMD_GET" from Apr 10, 2015, leads to the following static checker warning:

	net/ipv4/fou.c:720 fou_nl_dump()
	warn: 'mutex:&fn->fou_lock' is sometimes locked here and sometimes unlocked.

net/ipv4/fou.c
699 static int fou_nl_dump(struct sk_buff *skb, struct netlink_callback *cb) 700 {

   701          struct net *net = sock_net(skb->sk);
   702          struct fou_net *fn = net_generic(net, fou_net_id);
   703          struct fou *fout;
   704          int idx = 0, ret;

705
706 mutex_lock(&fn->fou_lock);
707 list_for_each_entry(fout, &fn->fou_list, list) {
708 if (idx++ < cb->args[0])
709 continue;
710 ret = fou_dump_info(fout, NETLINK_CB(cb->skb).portid,
711 cb->nlh->nlmsg_seq, NLM_F_MULTI,
712 skb, FOU_CMD_GET);
713 if (ret)
714 goto done;
715 }
716 mutex_unlock(&fn->fou_lock);
717
718 done:

Probably the unlock should happen after the label.

   719          cb->args[0] = idx;
   720          return skb->len;
   721  }

regards,
dan carpenter