[Cluster-devel] [DLM PATCH 5/6] DLM: Add locking to protect save callback assignments

[Bob Peterson <rpeterso@redhat.com>]

This patch adds write_lock_bh locking to several places in the code
that save and restore the socket callbacks.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
---
 fs/dlm/lowcomms.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index ec5087a..4e82285 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -467,10 +467,17 @@ 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 "
@@ -500,22 +507,29 @@ 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);
 }
 
 /* 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;
 
 	/* 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_user_data = con;
+	sk->sk_allocation = GFP_NOFS;
+	con->orig_error_report = sk->sk_error_report;
+	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
@@ -1274,6 +1288,7 @@ 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;
@@ -1281,6 +1296,8 @@ 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;
-- 
2.5.0