Root/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 */
70struct workqueue_struct *rds_wq;
71EXPORT_SYMBOL_GPL(rds_wq);
72
73void 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}
93EXPORT_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 */
113static 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
139void 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
159void 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
211void 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
233void 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
255void rds_threads_exit(void)
256{
257    destroy_workqueue(rds_wq);
258}
259
260int __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}
268

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