net: __sock_gen_cookie() cleanup

Adopt atomic64_try_cmpxchg() and remove the loop,
to make the intent more obvious.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock_diag.c

@@ -25,14 +25,14 @@ DEFINE_COOKIE(sock_cookie);
 
 u64 __sock_gen_cookie(struct sock *sk)
 {
-	while (1) {
-		u64 res = atomic64_read(&sk->sk_cookie);
+	u64 res = atomic64_read(&sk->sk_cookie);
 
-		if (res)
-			return res;
-		res = gen_cookie_next(&sock_cookie);
-		atomic64_cmpxchg(&sk->sk_cookie, 0, res);
+	if (!res) {
+		u64 new = gen_cookie_next(&sock_cookie);
+
+		atomic64_try_cmpxchg(&sk->sk_cookie, &res, new);
 	}
+	return res;
 }
 
 int sock_diag_check_cookie(struct sock *sk, const __u32 *cookie)