net/rds/threads.c

   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
  36 #include "rds.h"
  37
  38 /*
  39  * All of connection management is simplified by serializing it through
  40  * work queues that execute in a connection managing thread.
  41  *
  42  * TCP wants to send acks through sendpage() in response to data_ready(),
  43  * but it needs a process context to do so.
  44  *
  45  * The receive paths need to allocate but can't drop packets (!) so we have
  46  * a thread around to block allocating if the receive fast path sees an
  47  * allocation failure.
  48  */
  49
  50 /* Grand Unified Theory of connection life cycle:
  51  * At any point in time, the connection can be in one of these states:
  52  * DOWN, CONNECTING, UP, DISCONNECTING, ERROR
  53  *
  54  * The following transitions are possible:
  55  *  ANY           -> ERROR
  56  *  UP            -> DISCONNECTING
  57  *  ERROR         -> DISCONNECTING
  58  *  DISCONNECTING -> DOWN
  59  *  DOWN          -> CONNECTING
  60  *  CONNECTING    -> UP
  61  *
  62  * Transition to state DISCONNECTING/DOWN:
  63  *  -   Inside the shutdown worker; synchronizes with xmit path
  64  *      through c_send_lock, and with connection management callbacks
  65  *      via c_cm_lock.
  66  *
  67  *      For receive callbacks, we rely on the underlying transport
  68  *      (TCP, IB/RDMA) to provide the necessary synchronisation.
  69  */
  70 struct workqueue_struct *rds_wq;
  71
  72 void rds_connect_complete(struct rds_connection *conn)
  73 {
  74         if (!rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_UP)) {
  75                 printk(KERN_WARNING "%s: Cannot transition to state UP, "
  76                                 "current state is %d\n",
  77                                 __func__,
  78                                 atomic_read(&conn->c_state));
  79                 atomic_set(&conn->c_state, RDS_CONN_ERROR);
  80                 queue_work(rds_wq, &conn->c_down_w);
  81                 return;
  82         }
  83
  84         rdsdebug("conn %p for %pI4 to %pI4 complete\n",
  85           conn, &conn->c_laddr, &conn->c_faddr);
  86
  87         conn->c_reconnect_jiffies = 0;
  88         set_bit(0, &conn->c_map_queued);
  89         queue_delayed_work(rds_wq, &conn->c_send_w, 0);
  90         queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
  91 }
  92
  93 /*
  94  * This random exponential backoff is relied on to eventually resolve racing
  95  * connects.
  96  *
  97  * If connect attempts race then both parties drop both connections and come
  98  * here to wait for a random amount of time before trying again.  Eventually
  99  * the backoff range will be so much greater than the time it takes to
 100  * establish a connection that one of the pair will establish the connection
 101  * before the other's random delay fires.
 102  *
 103  * Connection attempts that arrive while a connection is already established
 104  * are also considered to be racing connects.  This lets a connection from
 105  * a rebooted machine replace an existing stale connection before the transport
 106  * notices that the connection has failed.
 107  *
 108  * We should *always* start with a random backoff; otherwise a broken connection
 109  * will always take several iterations to be re-established.
 110  */
 111 static void rds_queue_reconnect(struct rds_connection *conn)
 112 {
 113         unsigned long rand;
 114
 115         rdsdebug("conn %p for %pI4 to %pI4 reconnect jiffies %lu\n",
 116           conn, &conn->c_laddr, &conn->c_faddr,
 117           conn->c_reconnect_jiffies);
 118
 119         set_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
 120         if (conn->c_reconnect_jiffies == 0) {
 121                 conn->c_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
 122                 queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
 123                 return;
 124         }
 125
 126         get_random_bytes(&rand, sizeof(rand));
 127         rdsdebug("%lu delay %lu ceil conn %p for %pI4 -> %pI4\n",
 128                  rand % conn->c_reconnect_jiffies, conn->c_reconnect_jiffies,
 129                  conn, &conn->c_laddr, &conn->c_faddr);
 130         queue_delayed_work(rds_wq, &conn->c_conn_w,
 131                            rand % conn->c_reconnect_jiffies);
 132
 133         conn->c_reconnect_jiffies = min(conn->c_reconnect_jiffies * 2,
 134                                         rds_sysctl_reconnect_max_jiffies);
 135 }
 136
 137 void rds_connect_worker(struct work_struct *work)
 138 {
 139         struct rds_connection *conn = container_of(work, struct rds_connection, c_conn_w.work);
 140         int ret;
 141
 142         clear_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
 143         if (rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) {
 144                 ret = conn->c_trans->conn_connect(conn);
 145                 rdsdebug("conn %p for %pI4 to %pI4 dispatched, ret %d\n",
 146                         conn, &conn->c_laddr, &conn->c_faddr, ret);
 147
 148                 if (ret) {
 149                         if (rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_DOWN))
 150                                 rds_queue_reconnect(conn);
 151                         else
 152                                 rds_conn_error(conn, "RDS: connect failed\n");
 153                 }
 154         }
 155 }
 156
 157 void rds_shutdown_worker(struct work_struct *work)
 158 {
 159         struct rds_connection *conn = container_of(work, struct rds_connection, c_down_w);
 160
 161         /* shut it down unless it's down already */
 162         if (!rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_DOWN)) {
 163                 /*
 164                  * Quiesce the connection mgmt handlers before we start tearing
 165                  * things down. We don't hold the mutex for the entire
 166                  * duration of the shutdown operation, else we may be
 167                  * deadlocking with the CM handler. Instead, the CM event
 168                  * handler is supposed to check for state DISCONNECTING
 169                  */
 170                 mutex_lock(&conn->c_cm_lock);
 171                 if (!rds_conn_transition(conn, RDS_CONN_UP, RDS_CONN_DISCONNECTING)
 172                  && !rds_conn_transition(conn, RDS_CONN_ERROR, RDS_CONN_DISCONNECTING)) {
 173                         rds_conn_error(conn, "shutdown called in state %d\n",
 174                                         atomic_read(&conn->c_state));
 175                         mutex_unlock(&conn->c_cm_lock);
 176                         return;
 177                 }
 178                 mutex_unlock(&conn->c_cm_lock);
 179
 180                 mutex_lock(&conn->c_send_lock);
 181                 conn->c_trans->conn_shutdown(conn);
 182                 rds_conn_reset(conn);
 183                 mutex_unlock(&conn->c_send_lock);
 184
 185                 if (!rds_conn_transition(conn, RDS_CONN_DISCONNECTING, RDS_CONN_DOWN)) {
 186                         /* This can happen - eg when we're in the middle of tearing
 187                          * down the connection, and someone unloads the rds module.
 188                          * Quite reproduceable with loopback connections.
 189                          * Mostly harmless.
 190                          */
 191                         rds_conn_error(conn,
 192                                 "%s: failed to transition to state DOWN, "
 193                                 "current state is %d\n",
 194                                 __func__,
 195                                 atomic_read(&conn->c_state));
 196                         return;
 197                 }
 198         }
 199
 200         /* Then reconnect if it's still live.
 201          * The passive side of an IB loopback connection is never added
 202          * to the conn hash, so we never trigger a reconnect on this
 203          * conn - the reconnect is always triggered by the active peer. */
 204         cancel_delayed_work(&conn->c_conn_w);
 205         if (!hlist_unhashed(&conn->c_hash_node))
 206                 rds_queue_reconnect(conn);
 207 }
 208
 209 void rds_send_worker(struct work_struct *work)
 210 {
 211         struct rds_connection *conn = container_of(work, struct rds_connection, c_send_w.work);
 212         int ret;
 213
 214         if (rds_conn_state(conn) == RDS_CONN_UP) {
 215                 ret = rds_send_xmit(conn);
 216                 rdsdebug("conn %p ret %d\n", conn, ret);
 217                 switch (ret) {
 218                 case -EAGAIN:
 219                         rds_stats_inc(s_send_immediate_retry);
 220                         queue_delayed_work(rds_wq, &conn->c_send_w, 0);
 221                         break;
 222                 case -ENOMEM:
 223                         rds_stats_inc(s_send_delayed_retry);
 224                         queue_delayed_work(rds_wq, &conn->c_send_w, 2);
 225                 default:
 226                         break;
 227                 }
 228         }
 229 }
 230
 231 void rds_recv_worker(struct work_struct *work)
 232 {
 233         struct rds_connection *conn = container_of(work, struct rds_connection, c_recv_w.work);
 234         int ret;
 235
 236         if (rds_conn_state(conn) == RDS_CONN_UP) {
 237                 ret = conn->c_trans->recv(conn);
 238                 rdsdebug("conn %p ret %d\n", conn, ret);
 239                 switch (ret) {
 240                 case -EAGAIN:
 241                         rds_stats_inc(s_recv_immediate_retry);
 242                         queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
 243                         break;
 244                 case -ENOMEM:
 245                         rds_stats_inc(s_recv_delayed_retry);
 246                         queue_delayed_work(rds_wq, &conn->c_recv_w, 2);
 247                 default:
 248                         break;
 249                 }
 250         }
 251 }
 252
 253 void rds_threads_exit(void)
 254 {
 255         destroy_workqueue(rds_wq);
 256 }
 257
 258 int __init rds_threads_init(void)
 259 {
 260         rds_wq = create_singlethread_workqueue("krdsd");
 261         if (rds_wq == NULL)
 262                 return -ENOMEM;
 263
 264         return 0;
 265 }