V4L/DVB (12081): gspca_ov519: Cleanup some sensor special cases
[linux-2.6] / 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 }