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 #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  */
  71 struct workqueue_struct *rds_wq;
  72 EXPORT_SYMBOL_GPL(rds_wq);
  73
  74 void rds_connect_path_complete(struct rds_conn_path *cp, int curr)
  75 {
  76         if (!rds_conn_path_transition(cp, curr, RDS_CONN_UP)) {
  77                 printk(KERN_WARNING "%s: Cannot transition to state UP, "
  78                                 "current state is %d\n",
  79                                 __func__,
  80                                 atomic_read(&cp->cp_state));
  81                 rds_conn_path_drop(cp);
  82                 return;
  83         }
  84
  85         rdsdebug("conn %p for %pI4 to %pI4 complete\n",
  86           cp->cp_conn, &cp->cp_conn->c_laddr, &cp->cp_conn->c_faddr);
  87
  88         cp->cp_reconnect_jiffies = 0;
  89         set_bit(0, &cp->cp_conn->c_map_queued);
  90         queue_delayed_work(rds_wq, &cp->cp_send_w, 0);
  91         queue_delayed_work(rds_wq, &cp->cp_recv_w, 0);
  92 }
  93 EXPORT_SYMBOL_GPL(rds_connect_path_complete);
  94
  95 void rds_connect_complete(struct rds_connection *conn)
  96 {
  97         rds_connect_path_complete(&conn->c_path[0], RDS_CONN_CONNECTING);
  98 }
  99 EXPORT_SYMBOL_GPL(rds_connect_complete);
 100
 101 /*
 102  * This random exponential backoff is relied on to eventually resolve racing
 103  * connects.
 104  *
 105  * If connect attempts race then both parties drop both connections and come
 106  * here to wait for a random amount of time before trying again.  Eventually
 107  * the backoff range will be so much greater than the time it takes to
 108  * establish a connection that one of the pair will establish the connection
 109  * before the other's random delay fires.
 110  *
 111  * Connection attempts that arrive while a connection is already established
 112  * are also considered to be racing connects.  This lets a connection from
 113  * a rebooted machine replace an existing stale connection before the transport
 114  * notices that the connection has failed.
 115  *
 116  * We should *always* start with a random backoff; otherwise a broken connection
 117  * will always take several iterations to be re-established.
 118  */
 119 void rds_queue_reconnect(struct rds_conn_path *cp)
 120 {
 121         unsigned long rand;
 122         struct rds_connection *conn = cp->cp_conn;
 123
 124         rdsdebug("conn %p for %pI4 to %pI4 reconnect jiffies %lu\n",
 125           conn, &conn->c_laddr, &conn->c_faddr,
 126           cp->cp_reconnect_jiffies);
 127
 128         /* let peer with smaller addr initiate reconnect, to avoid duels */
 129         if (conn->c_trans->t_type == RDS_TRANS_TCP &&
 130             conn->c_laddr > conn->c_faddr)
 131                 return;
 132
 133         set_bit(RDS_RECONNECT_PENDING, &cp->cp_flags);
 134         if (cp->cp_reconnect_jiffies == 0) {
 135                 cp->cp_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
 136                 queue_delayed_work(rds_wq, &cp->cp_conn_w, 0);
 137                 return;
 138         }
 139
 140         get_random_bytes(&rand, sizeof(rand));
 141         rdsdebug("%lu delay %lu ceil conn %p for %pI4 -> %pI4\n",
 142                  rand % cp->cp_reconnect_jiffies, cp->cp_reconnect_jiffies,
 143                  conn, &conn->c_laddr, &conn->c_faddr);
 144         queue_delayed_work(rds_wq, &cp->cp_conn_w,
 145                            rand % cp->cp_reconnect_jiffies);
 146
 147         cp->cp_reconnect_jiffies = min(cp->cp_reconnect_jiffies * 2,
 148                                         rds_sysctl_reconnect_max_jiffies);
 149 }
 150
 151 void rds_connect_worker(struct work_struct *work)
 152 {
 153         struct rds_conn_path *cp = container_of(work,
 154                                                 struct rds_conn_path,
 155                                                 cp_conn_w.work);
 156         struct rds_connection *conn = cp->cp_conn;
 157         int ret;
 158
 159         if (cp->cp_index > 0 && cp->cp_conn->c_laddr > cp->cp_conn->c_faddr)
 160                 return;
 161         clear_bit(RDS_RECONNECT_PENDING, &cp->cp_flags);
 162         ret = rds_conn_path_transition(cp, RDS_CONN_DOWN, RDS_CONN_CONNECTING);
 163         if (ret) {
 164                 ret = conn->c_trans->conn_path_connect(cp);
 165                 rdsdebug("conn %p for %pI4 to %pI4 dispatched, ret %d\n",
 166                         conn, &conn->c_laddr, &conn->c_faddr, ret);
 167
 168                 if (ret) {
 169                         if (rds_conn_path_transition(cp,
 170                                                      RDS_CONN_CONNECTING,
 171                                                      RDS_CONN_DOWN))
 172                                 rds_queue_reconnect(cp);
 173                         else
 174                                 rds_conn_path_error(cp, "connect failed\n");
 175                 }
 176         }
 177 }
 178
 179 void rds_send_worker(struct work_struct *work)
 180 {
 181         struct rds_conn_path *cp = container_of(work,
 182                                                 struct rds_conn_path,
 183                                                 cp_send_w.work);
 184         int ret;
 185
 186         if (rds_conn_path_state(cp) == RDS_CONN_UP) {
 187                 clear_bit(RDS_LL_SEND_FULL, &cp->cp_flags);
 188                 ret = rds_send_xmit(cp);
 189                 cond_resched();
 190                 rdsdebug("conn %p ret %d\n", cp->cp_conn, ret);
 191                 switch (ret) {
 192                 case -EAGAIN:
 193                         rds_stats_inc(s_send_immediate_retry);
 194                         queue_delayed_work(rds_wq, &cp->cp_send_w, 0);
 195                         break;
 196                 case -ENOMEM:
 197                         rds_stats_inc(s_send_delayed_retry);
 198                         queue_delayed_work(rds_wq, &cp->cp_send_w, 2);
 199                 default:
 200                         break;
 201                 }
 202         }
 203 }
 204
 205 void rds_recv_worker(struct work_struct *work)
 206 {
 207         struct rds_conn_path *cp = container_of(work,
 208                                                 struct rds_conn_path,
 209                                                 cp_recv_w.work);
 210         int ret;
 211
 212         if (rds_conn_path_state(cp) == RDS_CONN_UP) {
 213                 ret = cp->cp_conn->c_trans->recv_path(cp);
 214                 rdsdebug("conn %p ret %d\n", cp->cp_conn, ret);
 215                 switch (ret) {
 216                 case -EAGAIN:
 217                         rds_stats_inc(s_recv_immediate_retry);
 218                         queue_delayed_work(rds_wq, &cp->cp_recv_w, 0);
 219                         break;
 220                 case -ENOMEM:
 221                         rds_stats_inc(s_recv_delayed_retry);
 222                         queue_delayed_work(rds_wq, &cp->cp_recv_w, 2);
 223                 default:
 224                         break;
 225                 }
 226         }
 227 }
 228
 229 void rds_shutdown_worker(struct work_struct *work)
 230 {
 231         struct rds_conn_path *cp = container_of(work,
 232                                                 struct rds_conn_path,
 233                                                 cp_down_w);
 234
 235         rds_conn_shutdown(cp);
 236 }
 237
 238 void rds_threads_exit(void)
 239 {
 240         destroy_workqueue(rds_wq);
 241 }
 242
 243 int rds_threads_init(void)
 244 {
 245         rds_wq = create_singlethread_workqueue("krdsd");
 246         if (!rds_wq)
 247                 return -ENOMEM;
 248
 249         return 0;
 250 }