threads.c

Go to the documentation of this file.

/*
 * Copyright (c) 2006 Oracle.  All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */
#include <linux/kernel.h>
#include <linux/random.h>
#include <linux/export.h>

#include "rds.h"

/*
 * All of connection management is simplified by serializing it through
 * work queues that execute in a connection managing thread.
 *
 * TCP wants to send acks through sendpage() in response to data_ready(),
 * but it needs a process context to do so.
 *
 * The receive paths need to allocate but can't drop packets (!) so we have
 * a thread around to block allocating if the receive fast path sees an
 * allocation failure.
 */

/* Grand Unified Theory of connection life cycle:
 * At any point in time, the connection can be in one of these states:
 * DOWN, CONNECTING, UP, DISCONNECTING, ERROR
 *
 * The following transitions are possible:
 *  ANY       -> ERROR
 *  UP        -> DISCONNECTING
 *  ERROR     -> DISCONNECTING
 *  DISCONNECTING -> DOWN
 *  DOWN      -> CONNECTING
 *  CONNECTING    -> UP
 *
 * Transition to state DISCONNECTING/DOWN:
 *  -   Inside the shutdown worker; synchronizes with xmit path
 *  through RDS_IN_XMIT, and with connection management callbacks
 *  via c_cm_lock.
 *
 *  For receive callbacks, we rely on the underlying transport
 *  (TCP, IB/RDMA) to provide the necessary synchronisation.
 */
struct workqueue_struct *rds_wq;
EXPORT_SYMBOL_GPL(rds_wq);

void rds_connect_complete(struct rds_connection *conn)
{
    if (!rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_UP)) {
        printk(KERN_WARNING "%s: Cannot transition to state UP, "
                "current state is %d\n",
                __func__,
                atomic_read(&conn->c_state));
        atomic_set(&conn->c_state, RDS_CONN_ERROR);
        queue_work(rds_wq, &conn->c_down_w);
        return;
    }

    rdsdebug("conn %p for %pI4 to %pI4 complete\n",
      conn, &conn->c_laddr, &conn->c_faddr);

    conn->c_reconnect_jiffies = 0;
    set_bit(0, &conn->c_map_queued);
    queue_delayed_work(rds_wq, &conn->c_send_w, 0);
    queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
}
EXPORT_SYMBOL_GPL(rds_connect_complete);

/*
 * This random exponential backoff is relied on to eventually resolve racing
 * connects.
 *
 * If connect attempts race then both parties drop both connections and come
 * here to wait for a random amount of time before trying again.  Eventually
 * the backoff range will be so much greater than the time it takes to
 * establish a connection that one of the pair will establish the connection
 * before the other's random delay fires.
 *
 * Connection attempts that arrive while a connection is already established
 * are also considered to be racing connects.  This lets a connection from
 * a rebooted machine replace an existing stale connection before the transport
 * notices that the connection has failed.
 *
 * We should *always* start with a random backoff; otherwise a broken connection
 * will always take several iterations to be re-established.
 */
void rds_queue_reconnect(struct rds_connection *conn)
{
    unsigned long rand;

    rdsdebug("conn %p for %pI4 to %pI4 reconnect jiffies %lu\n",
      conn, &conn->c_laddr, &conn->c_faddr,
      conn->c_reconnect_jiffies);

    set_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
    if (conn->c_reconnect_jiffies == 0) {
        conn->c_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
        queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
        return;
    }

    get_random_bytes(&rand, sizeof(rand));
    rdsdebug("%lu delay %lu ceil conn %p for %pI4 -> %pI4\n",
         rand % conn->c_reconnect_jiffies, conn->c_reconnect_jiffies,
         conn, &conn->c_laddr, &conn->c_faddr);
    queue_delayed_work(rds_wq, &conn->c_conn_w,
               rand % conn->c_reconnect_jiffies);

    conn->c_reconnect_jiffies = min(conn->c_reconnect_jiffies * 2,
                    rds_sysctl_reconnect_max_jiffies);
}

void rds_connect_worker(struct work_struct *work)
{
    struct rds_connection *conn = container_of(work, struct rds_connection, c_conn_w.work);
    int ret;

    clear_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
    if (rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) {
        ret = conn->c_trans->conn_connect(conn);
        rdsdebug("conn %p for %pI4 to %pI4 dispatched, ret %d\n",
            conn, &conn->c_laddr, &conn->c_faddr, ret);

        if (ret) {
            if (rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_DOWN))
                rds_queue_reconnect(conn);
            else
                rds_conn_error(conn, "RDS: connect failed\n");
        }
    }
}

void rds_send_worker(struct work_struct *work)
{
    struct rds_connection *conn = container_of(work, struct rds_connection, c_send_w.work);
    int ret;

    if (rds_conn_state(conn) == RDS_CONN_UP) {
        ret = rds_send_xmit(conn);
        rdsdebug("conn %p ret %d\n", conn, ret);
        switch (ret) {
        case -EAGAIN:
            rds_stats_inc(s_send_immediate_retry);
            queue_delayed_work(rds_wq, &conn->c_send_w, 0);
            break;
        case -ENOMEM:
            rds_stats_inc(s_send_delayed_retry);
            queue_delayed_work(rds_wq, &conn->c_send_w, 2);
        default:
            break;
        }
    }
}

void rds_recv_worker(struct work_struct *work)
{
    struct rds_connection *conn = container_of(work, struct rds_connection, c_recv_w.work);
    int ret;

    if (rds_conn_state(conn) == RDS_CONN_UP) {
        ret = conn->c_trans->recv(conn);
        rdsdebug("conn %p ret %d\n", conn, ret);
        switch (ret) {
        case -EAGAIN:
            rds_stats_inc(s_recv_immediate_retry);
            queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
            break;
        case -ENOMEM:
            rds_stats_inc(s_recv_delayed_retry);
            queue_delayed_work(rds_wq, &conn->c_recv_w, 2);
        default:
            break;
        }
    }
}

void rds_shutdown_worker(struct work_struct *work)
{
    struct rds_connection *conn = container_of(work, struct rds_connection, c_down_w);

    rds_conn_shutdown(conn);
}

void rds_threads_exit(void)
{
    destroy_workqueue(rds_wq);
}

int rds_threads_init(void)
{
    rds_wq = create_singlethread_workqueue("krdsd");
    if (!rds_wq)
        return -ENOMEM;

    return 0;
}