[SCTP] ipv6: inconsistent lock state ipv6_add_addr/sctp_v6_copy_addrlist

lockdep found that dev->lock taken from softirq in ipv6_add_addr
is also taken in sctp_v6_copy_addrlist with softirqs enabled, so
lockup is possible.
Noticed-by: Simon Arlott <simon@arlott.org>
Signed-off-by: Jarek Poplawski <jarkao2@o2.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/ipv6.c

@@ -360,7 +360,7 @@ static void sctp_v6_copy_addrlist(struct list_head *addrlist,
 		return;
 	}
 
-	read_lock(&in6_dev->lock);
+	read_lock_bh(&in6_dev->lock);
 	for (ifp = in6_dev->addr_list; ifp; ifp = ifp->if_next) {
 		/* Add the address to the local list.  */
 		addr = t_new(struct sctp_sockaddr_entry, GFP_ATOMIC);
@@ -374,7 +374,7 @@ static void sctp_v6_copy_addrlist(struct list_head *addrlist,
 		}
 	}
 
-	read_unlock(&in6_dev->lock);
+	read_unlock_bh(&in6_dev->lock);
 	rcu_read_unlock();
 }