sock: fix lockdep annotation in release_sock

During release_sock we use callbacks to finish the processing
of outstanding skbs on the socket. We actually are still locked,
sk_locked.owned == 1, but we already told lockdep that the mutex
is released. This could lead to false positives in lockdep for
lockdep_sock_is_held (we don't hold the slock spinlock during processing
the outstanding skbs).

I took over this patch from Eric Dumazet and tested it.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1333,7 +1333,12 @@ static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb)
 
 static inline void sock_release_ownership(struct sock *sk)
 {
-	sk->sk_lock.owned = 0;
+	if (sk->sk_lock.owned) {
+		sk->sk_lock.owned = 0;
+
+		/* The sk_lock has mutex_unlock() semantics: */
+		mutex_release(&sk->sk_lock.dep_map, 1, _RET_IP_);
+	}
 }
 
 /*

net/core/sock.c

@@ -2483,11 +2483,6 @@ EXPORT_SYMBOL(lock_sock_nested);
 
 void release_sock(struct sock *sk)
 {
-	/*
-	 * The sk_lock has mutex_unlock() semantics:
-	 */
-	mutex_release(&sk->sk_lock.dep_map, 1, _RET_IP_);
-
 	spin_lock_bh(&sk->sk_lock.slock);
 	if (sk->sk_backlog.tail)
 		__release_sock(sk);