There is no undefined behavior, only sparse that might be confused a little.
I do not think we can express in sparse the fact that
inet_csk_find_open_port() acquires head->lock
(head being the return value of this function...)
The following does not help.
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index aeebe881668996057d1495c84eee0f0b644b7ad0..ed7b3993316cd1ba0b2859b0bd3f447e066bd3b5
100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -323,6 +323,7 @@ static struct inet_bind_hashbucket *
inet_csk_find_open_port(const struct sock *sk, struct
inet_bind_bucket **tb_ret,
struct inet_bind2_bucket **tb2_ret,
struct inet_bind_hashbucket **head2_ret, int *port_ret)
+ __acquires(head->lock)
{
struct inet_hashinfo *hinfo = tcp_or_dccp_get_hashinfo(sk);
int i, low, high, attempt_half, port, l3mdev;