Commit bd7c5f98 authored by Sowmini Varadhan's avatar Sowmini Varadhan Committed by David S. Miller
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RDS: TCP: Synchronize accept() and connect() paths on t_conn_lock. 



An arbitration scheme for duelling SYNs is implemented as part of
commit 241b2719 ("RDS-TCP: Reset tcp callbacks if re-using an
outgoing socket in rds_tcp_accept_one()") which ensures that both nodes
involved will arrive at the same arbitration decision. However, this
needs to be synchronized with an outgoing SYN to be generated by
rds_tcp_conn_connect(). This commit achieves the synchronization
through the t_conn_lock mutex in struct rds_tcp_connection.

The rds_conn_state is checked in rds_tcp_conn_connect() after acquiring
the t_conn_lock mutex.  A SYN is sent out only if the RDS connection is
not already UP (an UP would indicate that rds_tcp_accept_one() has
completed 3WH, so no SYN needs to be generated).

Similarly, the rds_conn_state is checked in rds_tcp_accept_one() after
acquiring the t_conn_lock mutex. The only acceptable states (to
allow continuation of the arbitration logic) are UP (i.e., outgoing SYN
was SYN-ACKed by peer after it sent us the SYN) or CONNECTING (we sent
outgoing SYN before we saw incoming SYN).

Signed-off-by: default avatarSowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: default avatarSantosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent eb192840

net/rds/tcp.c

+1 −0
Original line number Diff line number Diff line
@@ -216,6 +216,7 @@ static int rds_tcp_conn_alloc(struct rds_connection *conn, gfp_t gfp) 
	if (!tc)

		return -ENOMEM;



	mutex_init(&tc->t_conn_lock);

	tc->t_sock = NULL;

	tc->t_tinc = NULL;

	tc->t_tinc_hdr_rem = sizeof(struct rds_header);

net/rds/tcp.h

+4 −0
Original line number Diff line number Diff line
@@ -12,6 +12,10 @@ struct rds_tcp_connection { 


	struct list_head	t_tcp_node;

	struct rds_connection   *conn;

	/* t_conn_lock synchronizes the connection establishment between

	 * rds_tcp_accept_one and rds_tcp_conn_connect

	 */

	struct mutex		t_conn_lock;

	struct socket		*t_sock;

	void			*t_orig_write_space;

	void			*t_orig_data_ready;

net/rds/tcp_connect.c

+8 −0
Original line number Diff line number Diff line
@@ -78,7 +78,14 @@ int rds_tcp_conn_connect(struct rds_connection *conn) 
	struct socket *sock = NULL;

	struct sockaddr_in src, dest;

	int ret;

	struct rds_tcp_connection *tc = conn->c_transport_data;



	mutex_lock(&tc->t_conn_lock);



	if (rds_conn_up(conn)) {

		mutex_unlock(&tc->t_conn_lock);

		return 0;

	}

	ret = sock_create_kern(rds_conn_net(conn), PF_INET,

			       SOCK_STREAM, IPPROTO_TCP, &sock);

	if (ret < 0)
@@ -120,6 +127,7 @@ int rds_tcp_conn_connect(struct rds_connection *conn) 
	}



out:

	mutex_unlock(&tc->t_conn_lock);

	if (sock)

		sock_release(sock);

	return ret;

net/rds/tcp_listen.c

+20 −10
Original line number Diff line number Diff line
@@ -76,7 +76,9 @@ int rds_tcp_accept_one(struct socket *sock) 
	struct rds_connection *conn;

	int ret;

	struct inet_sock *inet;

	struct rds_tcp_connection *rs_tcp;

	struct rds_tcp_connection *rs_tcp = NULL;

	int conn_state;

	struct sock *nsk;



	ret = sock_create_kern(sock_net(sock->sk), sock->sk->sk_family,

			       sock->sk->sk_type, sock->sk->sk_protocol,
@@ -116,6 +118,10 @@ int rds_tcp_accept_one(struct socket *sock) 
	 */

	rs_tcp = (struct rds_tcp_connection *)conn->c_transport_data;

	rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING);

	mutex_lock(&rs_tcp->t_conn_lock);

	conn_state = rds_conn_state(conn);

	if (conn_state != RDS_CONN_CONNECTING && conn_state != RDS_CONN_UP)

		goto rst_nsk;

	if (rs_tcp->t_sock) {

		/* Need to resolve a duelling SYN between peers.

		 * We have an outstanding SYN to this peer, which may
@@ -126,14 +132,7 @@ int rds_tcp_accept_one(struct socket *sock) 
		wait_event(conn->c_waitq,

			   !test_bit(RDS_IN_XMIT, &conn->c_flags));

		if (ntohl(inet->inet_saddr) < ntohl(inet->inet_daddr)) {

			struct sock *nsk = new_sock->sk;



			nsk->sk_user_data = NULL;

			nsk->sk_prot->disconnect(nsk, 0);

			tcp_done(nsk);

			new_sock = NULL;

			ret = 0;

			goto out;

			goto rst_nsk;

		} else if (rs_tcp->t_sock) {

			rds_tcp_restore_callbacks(rs_tcp->t_sock, rs_tcp);

			conn->c_outgoing = 0;
@@ -143,8 +142,19 @@ int rds_tcp_accept_one(struct socket *sock) 
	rds_connect_complete(conn); /* marks RDS_CONN_UP */

	new_sock = NULL;

	ret = 0;



	goto out;

rst_nsk:

	/* reset the newly returned accept sock and bail */

	nsk = new_sock->sk;

	rds_tcp_stats_inc(s_tcp_listen_closed_stale);

	nsk->sk_user_data = NULL;

	nsk->sk_prot->disconnect(nsk, 0);

	tcp_done(nsk);

	new_sock = NULL;

	ret = 0;

out:

	if (rs_tcp)

		mutex_unlock(&rs_tcp->t_conn_lock);

	if (new_sock)

		sock_release(new_sock);

	return ret;

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