DLM: Save and restore socket callbacks properly

index dc9ae6d..00640e7 100644
@@ -124,7 +124,10 @@ struct connection {
 	struct connection *othercon;
 	struct work_struct rwork; /* Receive workqueue */
 	struct work_struct swork; /* Send workqueue */
-	void (*orig_error_report)(struct sock *sk);
+	void (*orig_error_report)(struct sock *);
+	void (*orig_data_ready)(struct sock *);
+	void (*orig_state_change)(struct sock *);
+	void (*orig_write_space)(struct sock *);
 };
 #define sock2con(x) ((struct connection *)(x)->sk_user_data)
 

@@ -467,10 +470,17 @@ int dlm_lowcomms_connect_node(int nodeid)
 
 static void lowcomms_error_report(struct sock *sk)
 {
-	struct connection *con = sock2con(sk);
+	struct connection *con;
 	struct sockaddr_storage saddr;
 	int buflen;
+	void (*orig_report)(struct sock *) = NULL;
 
+	read_lock_bh(&sk->sk_callback_lock);
+	con = sock2con(sk);
+	if (con == NULL)
+		goto out;
+
+	orig_report = con->orig_error_report;
 	if (con->sock == NULL ||
 	    kernel_getpeername(con->sock, (struct sockaddr *)&saddr, &buflen)) {
 		printk_ratelimited(KERN_ERR "dlm: node %d: socket error "

@@ -478,7 +488,6 @@ static void lowcomms_error_report(struct sock *sk)
 				   "sk_err=%d/%d\n", dlm_our_nodeid(),
 				   con->nodeid, dlm_config.ci_tcp_port,
 				   sk->sk_err, sk->sk_err_soft);
-		return;
 	} else if (saddr.ss_family == AF_INET) {
 		struct sockaddr_in *sin4 = (struct sockaddr_in *)&saddr;
 

@@ -501,22 +510,54 @@ static void lowcomms_error_report(struct sock *sk)
 				   dlm_config.ci_tcp_port, sk->sk_err,
 				   sk->sk_err_soft);
 	}
-	con->orig_error_report(sk);
+out:
+	read_unlock_bh(&sk->sk_callback_lock);
+	if (orig_report)
+		orig_report(sk);
+}
+
+/* Note: sk_callback_lock must be locked before calling this function. */
+static void save_callbacks(struct connection *con, struct sock *sk)
+{
+	lock_sock(sk);
+	con->orig_data_ready = sk->sk_data_ready;
+	con->orig_state_change = sk->sk_state_change;
+	con->orig_write_space = sk->sk_write_space;
+	con->orig_error_report = sk->sk_error_report;
+	release_sock(sk);
+}
+
+static void restore_callbacks(struct connection *con, struct sock *sk)
+{
+	write_lock_bh(&sk->sk_callback_lock);
+	lock_sock(sk);
+	sk->sk_user_data = NULL;
+	sk->sk_data_ready = con->orig_data_ready;
+	sk->sk_state_change = con->orig_state_change;
+	sk->sk_write_space = con->orig_write_space;
+	sk->sk_error_report = con->orig_error_report;
+	release_sock(sk);
+	write_unlock_bh(&sk->sk_callback_lock);
 }
 
 /* Make a socket active */
 static void add_sock(struct socket *sock, struct connection *con)
 {
+	struct sock *sk = sock->sk;
+
+	write_lock_bh(&sk->sk_callback_lock);
 	con->sock = sock;
 
+	sk->sk_user_data = con;
+	if (!test_bit(CF_IS_OTHERCON, &con->flags))
+		save_callbacks(con, sk);
 	/* Install a data_ready callback */
-	con->sock->sk->sk_data_ready = lowcomms_data_ready;
-	con->sock->sk->sk_write_space = lowcomms_write_space;
-	con->sock->sk->sk_state_change = lowcomms_state_change;
-	con->sock->sk->sk_user_data = con;
-	con->sock->sk->sk_allocation = GFP_NOFS;
-	con->orig_error_report = con->sock->sk->sk_error_report;
-	con->sock->sk->sk_error_report = lowcomms_error_report;
+	sk->sk_data_ready = lowcomms_data_ready;
+	sk->sk_write_space = lowcomms_write_space;
+	sk->sk_state_change = lowcomms_state_change;
+	sk->sk_allocation = GFP_NOFS;
+	sk->sk_error_report = lowcomms_error_report;
+	write_unlock_bh(&sk->sk_callback_lock);
 }
 
 /* Add the port number to an IPv6 or 4 sockaddr and return the address

@@ -551,6 +592,8 @@ static void close_connection(struct connection *con, bool and_other,
 
 	mutex_lock(&con->sock_mutex);
 	if (con->sock) {
+		if (!test_bit(CF_IS_OTHERCON, &con->flags))
+			restore_callbacks(con, con->sock->sk);
 		sock_release(con->sock);
 		con->sock = NULL;
 	}

@@ -1192,6 +1235,8 @@ static struct socket *tcp_create_listen_sock(struct connection *con,
 	if (result < 0) {
 		log_print("Failed to set SO_REUSEADDR on socket: %d", result);
 	}
+	sock->sk->sk_user_data = con;
+
 	con->rx_action = tcp_accept_from_sock;
 	con->connect_action = tcp_connect_to_sock;
 

@@ -1273,6 +1318,7 @@ static int sctp_listen_for_all(void)
 	if (result < 0)
 		log_print("Could not set SCTP NODELAY error %d\n", result);
 
+	write_lock_bh(&sock->sk->sk_callback_lock);
 	/* Init con struct */
 	sock->sk->sk_user_data = con;
 	con->sock = sock;

@@ -1280,6 +1326,8 @@ static int sctp_listen_for_all(void)
 	con->rx_action = sctp_accept_from_sock;
 	con->connect_action = sctp_connect_to_sock;
 
+	write_unlock_bh(&sock->sk->sk_callback_lock);
+
 	/* Bind to all addresses. */
 	if (sctp_bind_addrs(con, dlm_config.ci_tcp_port))
 		goto create_delsock;