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 EXPORT_SYMBOL_GPL(rds_wq);
  72
  73 void rds_connect_complete(struct rds_connection *conn)
  74 {
  75         if (!rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_UP)) {
  76                 printk(KERN_WARNING "%s: Cannot transition to state UP, "
  77                                 "current state is %d\n",
  78                                 __func__,
  79                                 atomic_read(&conn->c_state));
  80                 atomic_set(&conn->c_state, RDS_CONN_ERROR);
  81                 queue_work(rds_wq, &conn->c_down_w);
  82                 return;
  83         }
  84
  85         rdsdebug("conn %p for %pI4 to %pI4 complete\n",
  86           conn, &conn->c_laddr, &conn->c_faddr);
  87
  88         conn->c_reconnect_jiffies = 0;
  89         set_bit(0, &conn->c_map_queued);
  90         queue_delayed_work(rds_wq, &conn->c_send_w, 0);
  91         queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
  92 }
  93 EXPORT_SYMBOL_GPL(rds_connect_complete);
  94
  95 /*
  96  * This random exponential backoff is relied on to eventually resolve racing
  97  * connects.
  98  *
  99  * If connect attempts race then both parties drop both connections and come
 100  * here to wait for a random amount of time before trying again.  Eventually
 101  * the backoff range will be so much greater than the time it takes to
 102  * establish a connection that one of the pair will establish the connection
 103  * before the other's random delay fires.
 104  *
 105  * Connection attempts that arrive while a connection is already established
 106  * are also considered to be racing connects.  This lets a connection from
 107  * a rebooted machine replace an existing stale connection before the transport
 108  * notices that the connection has failed.
 109  *
 110  * We should *always* start with a random backoff; otherwise a broken connection
 111  * will always take several iterations to be re-established.
 112  */
 113 static void rds_queue_reconnect(struct rds_connection *conn)
 114 {
 115         unsigned long rand;
 116
 117         rdsdebug("conn %p for %pI4 to %pI4 reconnect jiffies %lu\n",
 118           conn, &conn->c_laddr, &conn->c_faddr,
 119           conn->c_reconnect_jiffies);
 120
 121         set_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
 122         if (conn->c_reconnect_jiffies == 0) {
 123                 conn->c_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
 124                 queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
 125                 return;
 126         }
 127
 128         get_random_bytes(&rand, sizeof(rand));
 129         rdsdebug("%lu delay %lu ceil conn %p for %pI4 -> %pI4\n",
 130                  rand % conn->c_reconnect_jiffies, conn->c_reconnect_jiffies,
 131                  conn, &conn->c_laddr, &conn->c_faddr);
 132         queue_delayed_work(rds_wq, &conn->c_conn_w,
 133                            rand % conn->c_reconnect_jiffies);
 134
 135         conn->c_reconnect_jiffies = min(conn->c_reconnect_jiffies * 2,
 136                                         rds_sysctl_reconnect_max_jiffies);
 137 }
 138
 139 void rds_connect_worker(struct work_struct *work)
 140 {
 141         struct rds_connection *conn = container_of(work, struct rds_connection, c_conn_w.work);
 142         int ret;
 143
 144         clear_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
 145         if (rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) {
 146                 ret = conn->c_trans->conn_connect(conn);
 147                 rdsdebug("conn %p for %pI4 to %pI4 dispatched, ret %d\n",
 148                         conn, &conn->c_laddr, &conn->c_faddr, ret);
 149
 150                 if (ret) {
 151                         if (rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_DOWN))
 152                                 rds_queue_reconnect(conn);
 153                         else
 154                                 rds_conn_error(conn, "RDS: connect failed\n");
 155                 }
 156         }
 157 }
 158
 159 void rds_shutdown_worker(struct work_struct *work)
 160 {
 161         struct rds_connection *conn = container_of(work, struct rds_connection, c_down_w);
 162
 163         /* shut it down unless it's down already */
 164         if (!rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_DOWN)) {
 165                 /*
 166                  * Quiesce the connection mgmt handlers before we start tearing
 167                  * things down. We don't hold the mutex for the entire
 168                  * duration of the shutdown operation, else we may be
 169                  * deadlocking with the CM handler. Instead, the CM event
 170                  * handler is supposed to check for state DISCONNECTING
 171                  */
 172                 mutex_lock(&conn->c_cm_lock);
 173                 if (!rds_conn_transition(conn, RDS_CONN_UP, RDS_CONN_DISCONNECTING)
 174                  && !rds_conn_transition(conn, RDS_CONN_ERROR, RDS_CONN_DISCONNECTING)) {
 175                         rds_conn_error(conn, "shutdown called in state %d\n",
 176                                         atomic_read(&conn->c_state));
 177                         mutex_unlock(&conn->c_cm_lock);
 178                         return;
 179                 }
 180                 mutex_unlock(&conn->c_cm_lock);
 181
 182                 mutex_lock(&conn->c_send_lock);
 183                 conn->c_trans->conn_shutdown(conn);
 184                 rds_conn_reset(conn);
 185                 mutex_unlock(&conn->c_send_lock);
 186
 187                 if (!rds_conn_transition(conn, RDS_CONN_DISCONNECTING, RDS_CONN_DOWN)) {
 188                         /* This can happen - eg when we're in the middle of tearing
 189                          * down the connection, and someone unloads the rds module.
 190                          * Quite reproduceable with loopback connections.
 191                          * Mostly harmless.
 192                          */
 193                         rds_conn_error(conn,
 194                                 "%s: failed to transition to state DOWN, "
 195                                 "current state is %d\n",
 196                                 __func__,
 197                                 atomic_read(&conn->c_state));
 198                         return;
 199                 }
 200         }
 201
 202         /* Then reconnect if it's still live.
 203          * The passive side of an IB loopback connection is never added
 204          * to the conn hash, so we never trigger a reconnect on this
 205          * conn - the reconnect is always triggered by the active peer. */
 206         cancel_delayed_work(&conn->c_conn_w);
 207         if (!hlist_unhashed(&conn->c_hash_node))
 208                 rds_queue_reconnect(conn);
 209 }
 210
 211 void rds_send_worker(struct work_struct *work)
 212 {
 213         struct rds_connection *conn = container_of(work, struct rds_connection, c_send_w.work);
 214         int ret;
 215
 216         if (rds_conn_state(conn) == RDS_CONN_UP) {
 217                 ret = rds_send_xmit(conn);
 218                 rdsdebug("conn %p ret %d\n", conn, ret);
 219                 switch (ret) {
 220                 case -EAGAIN:
 221                         rds_stats_inc(s_send_immediate_retry);
 222                         queue_delayed_work(rds_wq, &conn->c_send_w, 0);
 223                         break;
 224                 case -ENOMEM:
 225                         rds_stats_inc(s_send_delayed_retry);
 226                         queue_delayed_work(rds_wq, &conn->c_send_w, 2);
 227                 default:
 228                         break;
 229                 }
 230         }
 231 }
 232
 233 void rds_recv_worker(struct work_struct *work)
 234 {
 235         struct rds_connection *conn = container_of(work, struct rds_connection, c_recv_w.work);
 236         int ret;
 237
 238         if (rds_conn_state(conn) == RDS_CONN_UP) {
 239                 ret = conn->c_trans->recv(conn);
 240                 rdsdebug("conn %p ret %d\n", conn, ret);
 241                 switch (ret) {
 242                 case -EAGAIN:
 243                         rds_stats_inc(s_recv_immediate_retry);
 244                         queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
 245                         break;
 246                 case -ENOMEM:
 247                         rds_stats_inc(s_recv_delayed_retry);
 248                         queue_delayed_work(rds_wq, &conn->c_recv_w, 2);
 249                 default:
 250                         break;
 251                 }
 252         }
 253 }
 254
 255 void rds_threads_exit(void)
 256 {
 257         destroy_workqueue(rds_wq);
 258 }
 259
 260 int __init rds_threads_init(void)
 261 {
 262         rds_wq = create_singlethread_workqueue("krdsd");
 263         if (rds_wq == NULL)
 264                 return -ENOMEM;
 265
 266         return 0;
 267 }