net: introduce lockdep_is_held and update various places to use it

The socket is either locked if we hold the slock spin_lock for
lock_sock_fast and unlock_sock_fast or we own the lock (sk_lock.owned
!= 0). Check for this and at the same time improve that the current
thread/cpu is really holding the lock.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/socket.c b/net/socket.c
index 979d314..afa3c34 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1046,7 +1046,7 @@
 		return -EINVAL;
 
 	lock_sock(sk);
-	wq = rcu_dereference_protected(sock->wq, sock_owned_by_user(sk));
+	wq = rcu_dereference_protected(sock->wq, lockdep_sock_is_held(sk));
 	fasync_helper(fd, filp, on, &wq->fasync_list);
 
 	if (!wq->fasync_list)