linux/net/rds/threads.c
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   1/*
   2 * Copyright (c) 2006 Oracle.  All rights reserved.
   3 *
   4 * This software is available to you under a choice of one of two
   5 * licenses.  You may choose to be licensed under the terms of the GNU
   6 * General Public License (GPL) Version 2, available from the file
   7 * COPYING in the main directory of this source tree, or the
   8 * OpenIB.org BSD license below:
   9 *
  10 *     Redistribution and use in source and binary forms, with or
  11 *     without modification, are permitted provided that the following
  12 *     conditions are met:
  13 *
  14 *      - Redistributions of source code must retain the above
  15 *        copyright notice, this list of conditions and the following
  16 *        disclaimer.
  17 *
  18 *      - Redistributions in binary form must reproduce the above
  19 *        copyright notice, this list of conditions and the following
  20 *        disclaimer in the documentation and/or other materials
  21 *        provided with the distribution.
  22 *
  23 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  24 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  25 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  26 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  27 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  28 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  29 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  30 * SOFTWARE.
  31 *
  32 */
  33#include <linux/kernel.h>
  34#include <linux/random.h>
  35#include <linux/export.h>
  36
  37#include "rds.h"
  38
  39/*
  40 * All of connection management is simplified by serializing it through
  41 * work queues that execute in a connection managing thread.
  42 *
  43 * TCP wants to send acks through sendpage() in response to data_ready(),
  44 * but it needs a process context to do so.
  45 *
  46 * The receive paths need to allocate but can't drop packets (!) so we have
  47 * a thread around to block allocating if the receive fast path sees an
  48 * allocation failure.
  49 */
  50
  51/* Grand Unified Theory of connection life cycle:
  52 * At any point in time, the connection can be in one of these states:
  53 * DOWN, CONNECTING, UP, DISCONNECTING, ERROR
  54 *
  55 * The following transitions are possible:
  56 *  ANY           -> ERROR
  57 *  UP            -> DISCONNECTING
  58 *  ERROR         -> DISCONNECTING
  59 *  DISCONNECTING -> DOWN
  60 *  DOWN          -> CONNECTING
  61 *  CONNECTING    -> UP
  62 *
  63 * Transition to state DISCONNECTING/DOWN:
  64 *  -   Inside the shutdown worker; synchronizes with xmit path
  65 *      through RDS_IN_XMIT, and with connection management callbacks
  66 *      via c_cm_lock.
  67 *
  68 *      For receive callbacks, we rely on the underlying transport
  69 *      (TCP, IB/RDMA) to provide the necessary synchronisation.
  70 */
  71struct workqueue_struct *rds_wq;
  72EXPORT_SYMBOL_GPL(rds_wq);
  73
  74void rds_connect_complete(struct rds_connection *conn)
  75{
  76        if (!rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_UP)) {
  77                printk(KERN_WARNING "%s: Cannot transition to state UP, "
  78                                "current state is %d\n",
  79                                __func__,
  80                                atomic_read(&conn->c_state));
  81                atomic_set(&conn->c_state, RDS_CONN_ERROR);
  82                queue_work(rds_wq, &conn->c_down_w);
  83                return;
  84        }
  85
  86        rdsdebug("conn %p for %pI4 to %pI4 complete\n",
  87          conn, &conn->c_laddr, &conn->c_faddr);
  88
  89        conn->c_reconnect_jiffies = 0;
  90        set_bit(0, &conn->c_map_queued);
  91        queue_delayed_work(rds_wq, &conn->c_send_w, 0);
  92        queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
  93}
  94EXPORT_SYMBOL_GPL(rds_connect_complete);
  95
  96/*
  97 * This random exponential backoff is relied on to eventually resolve racing
  98 * connects.
  99 *
 100 * If connect attempts race then both parties drop both connections and come
 101 * here to wait for a random amount of time before trying again.  Eventually
 102 * the backoff range will be so much greater than the time it takes to
 103 * establish a connection that one of the pair will establish the connection
 104 * before the other's random delay fires.
 105 *
 106 * Connection attempts that arrive while a connection is already established
 107 * are also considered to be racing connects.  This lets a connection from
 108 * a rebooted machine replace an existing stale connection before the transport
 109 * notices that the connection has failed.
 110 *
 111 * We should *always* start with a random backoff; otherwise a broken connection
 112 * will always take several iterations to be re-established.
 113 */
 114void rds_queue_reconnect(struct rds_connection *conn)
 115{
 116        unsigned long rand;
 117
 118        rdsdebug("conn %p for %pI4 to %pI4 reconnect jiffies %lu\n",
 119          conn, &conn->c_laddr, &conn->c_faddr,
 120          conn->c_reconnect_jiffies);
 121
 122        set_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
 123        if (conn->c_reconnect_jiffies == 0) {
 124                conn->c_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
 125                queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
 126                return;
 127        }
 128
 129        get_random_bytes(&rand, sizeof(rand));
 130        rdsdebug("%lu delay %lu ceil conn %p for %pI4 -> %pI4\n",
 131                 rand % conn->c_reconnect_jiffies, conn->c_reconnect_jiffies,
 132                 conn, &conn->c_laddr, &conn->c_faddr);
 133        queue_delayed_work(rds_wq, &conn->c_conn_w,
 134                           rand % conn->c_reconnect_jiffies);
 135
 136        conn->c_reconnect_jiffies = min(conn->c_reconnect_jiffies * 2,
 137                                        rds_sysctl_reconnect_max_jiffies);
 138}
 139
 140void rds_connect_worker(struct work_struct *work)
 141{
 142        struct rds_connection *conn = container_of(work, struct rds_connection, c_conn_w.work);
 143        int ret;
 144
 145        clear_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
 146        if (rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) {
 147                ret = conn->c_trans->conn_connect(conn);
 148                rdsdebug("conn %p for %pI4 to %pI4 dispatched, ret %d\n",
 149                        conn, &conn->c_laddr, &conn->c_faddr, ret);
 150
 151                if (ret) {
 152                        if (rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_DOWN))
 153                                rds_queue_reconnect(conn);
 154                        else
 155                                rds_conn_error(conn, "RDS: connect failed\n");
 156                }
 157        }
 158}
 159
 160void rds_send_worker(struct work_struct *work)
 161{
 162        struct rds_connection *conn = container_of(work, struct rds_connection, c_send_w.work);
 163        int ret;
 164
 165        if (rds_conn_state(conn) == RDS_CONN_UP) {
 166                ret = rds_send_xmit(conn);
 167                rdsdebug("conn %p ret %d\n", conn, ret);
 168                switch (ret) {
 169                case -EAGAIN:
 170                        rds_stats_inc(s_send_immediate_retry);
 171                        queue_delayed_work(rds_wq, &conn->c_send_w, 0);
 172                        break;
 173                case -ENOMEM:
 174                        rds_stats_inc(s_send_delayed_retry);
 175                        queue_delayed_work(rds_wq, &conn->c_send_w, 2);
 176                default:
 177                        break;
 178                }
 179        }
 180}
 181
 182void rds_recv_worker(struct work_struct *work)
 183{
 184        struct rds_connection *conn = container_of(work, struct rds_connection, c_recv_w.work);
 185        int ret;
 186
 187        if (rds_conn_state(conn) == RDS_CONN_UP) {
 188                ret = conn->c_trans->recv(conn);
 189                rdsdebug("conn %p ret %d\n", conn, ret);
 190                switch (ret) {
 191                case -EAGAIN:
 192                        rds_stats_inc(s_recv_immediate_retry);
 193                        queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
 194                        break;
 195                case -ENOMEM:
 196                        rds_stats_inc(s_recv_delayed_retry);
 197                        queue_delayed_work(rds_wq, &conn->c_recv_w, 2);
 198                default:
 199                        break;
 200                }
 201        }
 202}
 203
 204void rds_shutdown_worker(struct work_struct *work)
 205{
 206        struct rds_connection *conn = container_of(work, struct rds_connection, c_down_w);
 207
 208        rds_conn_shutdown(conn);
 209}
 210
 211void rds_threads_exit(void)
 212{
 213        destroy_workqueue(rds_wq);
 214}
 215
 216int rds_threads_init(void)
 217{
 218        rds_wq = create_singlethread_workqueue("krdsd");
 219        if (!rds_wq)
 220                return -ENOMEM;
 221
 222        return 0;
 223}
 224
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