[PATCH] lockdep: annotate af_unix locking

Teach special (recursive) locking code to the lock validator.  Also splits
af_unix's sk_receive_queue.lock class from the other networking skb-queue
locks.  Has no effect on non-lockdep kernels.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/net/af_unix.h

@@ -67,6 +67,9 @@ struct unix_skb_parms {
 #define unix_state_rlock(s)	spin_lock(&unix_sk(s)->lock)
 #define unix_state_runlock(s)	spin_unlock(&unix_sk(s)->lock)
 #define unix_state_wlock(s)	spin_lock(&unix_sk(s)->lock)
+#define unix_state_wlock_nested(s) \
+				spin_lock_nested(&unix_sk(s)->lock, \
+				SINGLE_DEPTH_NESTING)
 #define unix_state_wunlock(s)	spin_unlock(&unix_sk(s)->lock)
 
 #ifdef __KERNEL__

net/unix/af_unix.c

@@ -565,6 +565,14 @@ static struct proto unix_proto = {
 	.obj_size = sizeof(struct unix_sock),
 };
 
+/*
+ * AF_UNIX sockets do not interact with hardware, hence they
+ * dont trigger interrupts - so it's safe for them to have
+ * bh-unsafe locking for their sk_receive_queue.lock. Split off
+ * this special lock-class by reinitializing the spinlock key:
+ */
+static struct lock_class_key af_unix_sk_receive_queue_lock_key;
+
 static struct sock * unix_create1(struct socket *sock)
 {
 	struct sock *sk = NULL;
@@ -580,6 +588,8 @@ static struct sock * unix_create1(struct socket *sock)
 	atomic_inc(&unix_nr_socks);
 
 	sock_init_data(sock,sk);
+	lockdep_set_class(&sk->sk_receive_queue.lock,
+				&af_unix_sk_receive_queue_lock_key);
 
 	sk->sk_write_space	= unix_write_space;
 	sk->sk_max_ack_backlog	= sysctl_unix_max_dgram_qlen;
@@ -1045,7 +1055,7 @@ restart:
 		goto out_unlock;
 	}
 
-	unix_state_wlock(sk);
+	unix_state_wlock_nested(sk);
 
 	if (sk->sk_state != st) {
 		unix_state_wunlock(sk);