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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 241b271952 ("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: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
4.6.x
Sowmini Varadhan 2016-05-02 11:24:52 -07:00 committed by David S. Miller
parent eb19284026
commit bd7c5f983f
4 changed files with 33 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
net/rds/tcp.c
View File

@ -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);

4
net/rds/tcp.h
View File

@ -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;

8
net/rds/tcp_connect.c
View File

@ -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;

30
net/rds/tcp_listen.c
View File

@ -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;