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/include/net/sock.h b/include/net/sock.h
index 91cee51..eb2d7c3 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1360,6 +1360,14 @@
 	lockdep_init_map(&(sk)->sk_lock.dep_map, (name), (key), 0);	\
 } while (0)
 
+static bool lockdep_sock_is_held(const struct sock *csk)
+{
+	struct sock *sk = (struct sock *)csk;
+
+	return lockdep_is_held(&sk->sk_lock) ||
+	       lockdep_is_held(&sk->sk_lock.slock);
+}
+
 void lock_sock_nested(struct sock *sk, int subclass);
 
 static inline void lock_sock(struct sock *sk)
@@ -1598,8 +1606,8 @@
 static inline struct dst_entry *
 __sk_dst_get(struct sock *sk)
 {
-	return rcu_dereference_check(sk->sk_dst_cache, sock_owned_by_user(sk) ||
-						       lockdep_is_held(&sk->sk_lock.slock));
+	return rcu_dereference_check(sk->sk_dst_cache,
+				     lockdep_sock_is_held(sk));
 }
 
 static inline struct dst_entry *