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RDS: Connection handling

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While arguably the fact that the underlying transport needs a
connection to convey RDS's datagrame reliably is not important
to rds proper, the transports implemented so far (IB and TCP)
have both been connection-oriented, and so the connection
state machine-related code is in the common rds code.

This patch also includes several work items, to handle connecting,
sending, receiving, and shutdown.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Andy Grover
2009-02-24 15:30:23 +00:00
committed by David S. Miller
parent a8c879a7ee
commit 00e0f34c61
2 changed files with 752 additions and 0 deletions
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265
net/rds/threads.c Normal file
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/*
* Copyright (c) 2006 Oracle. All rights reserved.
*
* This software is available to you under a choice of one of two
* licenses. You may choose to be licensed under the terms of the GNU
* General Public License (GPL) Version 2, available from the file
* COPYING in the main directory of this source tree, or the
* OpenIB.org BSD license below:
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials
* provided with the distribution.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
*/
#include <linux/kernel.h>
#include <linux/random.h>
#include "rds.h"
/*
* All of connection management is simplified by serializing it through
* work queues that execute in a connection managing thread.
*
* TCP wants to send acks through sendpage() in response to data_ready(),
* but it needs a process context to do so.
*
* The receive paths need to allocate but can't drop packets (!) so we have
* a thread around to block allocating if the receive fast path sees an
* allocation failure.
*/
/* Grand Unified Theory of connection life cycle:
* At any point in time, the connection can be in one of these states:
* DOWN, CONNECTING, UP, DISCONNECTING, ERROR
*
* The following transitions are possible:
* ANY -> ERROR
* UP -> DISCONNECTING
* ERROR -> DISCONNECTING
* DISCONNECTING -> DOWN
* DOWN -> CONNECTING
* CONNECTING -> UP
*
* Transition to state DISCONNECTING/DOWN:
* - Inside the shutdown worker; synchronizes with xmit path
* through c_send_lock, and with connection management callbacks
* via c_cm_lock.
*
* For receive callbacks, we rely on the underlying transport
* (TCP, IB/RDMA) to provide the necessary synchronisation.
*/
struct workqueue_struct *rds_wq;
void rds_connect_complete(struct rds_connection *conn)
{
if (!rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_UP)) {
printk(KERN_WARNING "%s: Cannot transition to state UP, "
"current state is %d\n",
__func__,
atomic_read(&conn->c_state));
atomic_set(&conn->c_state, RDS_CONN_ERROR);
queue_work(rds_wq, &conn->c_down_w);
return;
}
rdsdebug("conn %p for %pI4 to %pI4 complete\n",
conn, &conn->c_laddr, &conn->c_faddr);
conn->c_reconnect_jiffies = 0;
set_bit(0, &conn->c_map_queued);
queue_delayed_work(rds_wq, &conn->c_send_w, 0);
queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
}
/*
* This random exponential backoff is relied on to eventually resolve racing
* connects.
*
* If connect attempts race then both parties drop both connections and come
* here to wait for a random amount of time before trying again. Eventually
* the backoff range will be so much greater than the time it takes to
* establish a connection that one of the pair will establish the connection
* before the other's random delay fires.
*
* Connection attempts that arrive while a connection is already established
* are also considered to be racing connects. This lets a connection from
* a rebooted machine replace an existing stale connection before the transport
* notices that the connection has failed.
*
* We should *always* start with a random backoff; otherwise a broken connection
* will always take several iterations to be re-established.
*/
static void rds_queue_reconnect(struct rds_connection *conn)
{
unsigned long rand;
rdsdebug("conn %p for %pI4 to %pI4 reconnect jiffies %lu\n",
conn, &conn->c_laddr, &conn->c_faddr,
conn->c_reconnect_jiffies);
set_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
if (conn->c_reconnect_jiffies == 0) {
conn->c_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
return;
}
get_random_bytes(&rand, sizeof(rand));
rdsdebug("%lu delay %lu ceil conn %p for %pI4 -> %pI4\n",
rand % conn->c_reconnect_jiffies, conn->c_reconnect_jiffies,
conn, &conn->c_laddr, &conn->c_faddr);
queue_delayed_work(rds_wq, &conn->c_conn_w,
rand % conn->c_reconnect_jiffies);
conn->c_reconnect_jiffies = min(conn->c_reconnect_jiffies * 2,
rds_sysctl_reconnect_max_jiffies);
}
void rds_connect_worker(struct work_struct *work)
{
struct rds_connection *conn = container_of(work, struct rds_connection, c_conn_w.work);
int ret;
clear_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
if (rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) {
ret = conn->c_trans->conn_connect(conn);
rdsdebug("conn %p for %pI4 to %pI4 dispatched, ret %d\n",
conn, &conn->c_laddr, &conn->c_faddr, ret);
if (ret) {
if (rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_DOWN))
rds_queue_reconnect(conn);
else
rds_conn_error(conn, "RDS: connect failed\n");
}
}
}
void rds_shutdown_worker(struct work_struct *work)
{
struct rds_connection *conn = container_of(work, struct rds_connection, c_down_w);
/* shut it down unless it's down already */
if (!rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_DOWN)) {
/*
* Quiesce the connection mgmt handlers before we start tearing
* things down. We don't hold the mutex for the entire
* duration of the shutdown operation, else we may be
* deadlocking with the CM handler. Instead, the CM event
* handler is supposed to check for state DISCONNECTING
*/
mutex_lock(&conn->c_cm_lock);
if (!rds_conn_transition(conn, RDS_CONN_UP, RDS_CONN_DISCONNECTING)
&& !rds_conn_transition(conn, RDS_CONN_ERROR, RDS_CONN_DISCONNECTING)) {
rds_conn_error(conn, "shutdown called in state %d\n",
atomic_read(&conn->c_state));
mutex_unlock(&conn->c_cm_lock);
return;
}
mutex_unlock(&conn->c_cm_lock);
mutex_lock(&conn->c_send_lock);
conn->c_trans->conn_shutdown(conn);
rds_conn_reset(conn);
mutex_unlock(&conn->c_send_lock);
if (!rds_conn_transition(conn, RDS_CONN_DISCONNECTING, RDS_CONN_DOWN)) {
/* This can happen - eg when we're in the middle of tearing
* down the connection, and someone unloads the rds module.
* Quite reproduceable with loopback connections.
* Mostly harmless.
*/
rds_conn_error(conn,
"%s: failed to transition to state DOWN, "
"current state is %d\n",
__func__,
atomic_read(&conn->c_state));
return;
}
}
/* Then reconnect if it's still live.
* The passive side of an IB loopback connection is never added
* to the conn hash, so we never trigger a reconnect on this
* conn - the reconnect is always triggered by the active peer. */
cancel_delayed_work(&conn->c_conn_w);
if (!hlist_unhashed(&conn->c_hash_node))
rds_queue_reconnect(conn);
}
void rds_send_worker(struct work_struct *work)
{
struct rds_connection *conn = container_of(work, struct rds_connection, c_send_w.work);
int ret;
if (rds_conn_state(conn) == RDS_CONN_UP) {
ret = rds_send_xmit(conn);
rdsdebug("conn %p ret %d\n", conn, ret);
switch (ret) {
case -EAGAIN:
rds_stats_inc(s_send_immediate_retry);
queue_delayed_work(rds_wq, &conn->c_send_w, 0);
break;
case -ENOMEM:
rds_stats_inc(s_send_delayed_retry);
queue_delayed_work(rds_wq, &conn->c_send_w, 2);
default:
break;
}
}
}
void rds_recv_worker(struct work_struct *work)
{
struct rds_connection *conn = container_of(work, struct rds_connection, c_recv_w.work);
int ret;
if (rds_conn_state(conn) == RDS_CONN_UP) {
ret = conn->c_trans->recv(conn);
rdsdebug("conn %p ret %d\n", conn, ret);
switch (ret) {
case -EAGAIN:
rds_stats_inc(s_recv_immediate_retry);
queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
break;
case -ENOMEM:
rds_stats_inc(s_recv_delayed_retry);
queue_delayed_work(rds_wq, &conn->c_recv_w, 2);
default:
break;
}
}
}
void rds_threads_exit(void)
{
destroy_workqueue(rds_wq);
}
int __init rds_threads_init(void)
{
rds_wq = create_singlethread_workqueue("krdsd");
if (rds_wq == NULL)
return -ENOMEM;
return 0;
}