RDS: Connection handling

While arguably the fact that the underlying transport needs a
connection to convey RDS's datagrame reliably is not important
to rds proper, the transports implemented so far (IB and TCP)
have both been connection-oriented, and so the connection
state machine-related code is in the common rds code.

This patch also includes several work items, to handle connecting,
sending, receiving, and shutdown.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 752 insertions, 0 deletions

diff --git a/net/rds/connection.c b/net/rds/connection.c
new file mode 100644
index 000000000000..273f064930a8
--- /dev/null
+++ b/net/rds/connection.c
@@ -0,0 +1,487 @@
+/*
+ * 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/list.h>
+#include <net/inet_hashtables.h>
+
+#include "rds.h"
+#include "loop.h"
+#include "rdma.h"
+
+#define RDS_CONNECTION_HASH_BITS 12
+#define RDS_CONNECTION_HASH_ENTRIES (1 << RDS_CONNECTION_HASH_BITS)
+#define RDS_CONNECTION_HASH_MASK (RDS_CONNECTION_HASH_ENTRIES - 1)
+
+/* converting this to RCU is a chore for another day.. */
+static DEFINE_SPINLOCK(rds_conn_lock);
+static unsigned long rds_conn_count;
+static struct hlist_head rds_conn_hash[RDS_CONNECTION_HASH_ENTRIES];
+static struct kmem_cache *rds_conn_slab;
+
+static struct hlist_head *rds_conn_bucket(__be32 laddr, __be32 faddr)
+{
+        /* Pass NULL, don't need struct net for hash */
+        unsigned long hash = inet_ehashfn(NULL,
+                                          be32_to_cpu(laddr), 0,
+                                          be32_to_cpu(faddr), 0);
+        return &rds_conn_hash[hash & RDS_CONNECTION_HASH_MASK];
+}
+
+#define rds_conn_info_set(var, test, suffix) do {               \
+        if (test)                                               \
+                var |= RDS_INFO_CONNECTION_FLAG_##suffix;       \
+} while (0)
+
+static inline int rds_conn_is_sending(struct rds_connection *conn)
+{
+        int ret = 0;
+
+        if (!mutex_trylock(&conn->c_send_lock))
+                ret = 1;
+        else
+                mutex_unlock(&conn->c_send_lock);
+
+        return ret;
+}
+
+static struct rds_connection *rds_conn_lookup(struct hlist_head *head,
+                                              __be32 laddr, __be32 faddr,
+                                              struct rds_transport *trans)
+{
+        struct rds_connection *conn, *ret = NULL;
+        struct hlist_node *pos;
+
+        hlist_for_each_entry(conn, pos, head, c_hash_node) {
+                if (conn->c_faddr == faddr && conn->c_laddr == laddr &&
+                                conn->c_trans == trans) {
+                        ret = conn;
+                        break;
+                }
+        }
+        rdsdebug("returning conn %p for %pI4 -> %pI4\n", ret,
+                 &laddr, &faddr);
+        return ret;
+}
+
+/*
+ * This is called by transports as they're bringing down a connection.
+ * It clears partial message state so that the transport can start sending
+ * and receiving over this connection again in the future.  It is up to
+ * the transport to have serialized this call with its send and recv.
+ */
+void rds_conn_reset(struct rds_connection *conn)
+{
+        rdsdebug("connection %pI4 to %pI4 reset\n",
+          &conn->c_laddr, &conn->c_faddr);
+
+        rds_stats_inc(s_conn_reset);
+        rds_send_reset(conn);
+        conn->c_flags = 0;
+
+        /* Do not clear next_rx_seq here, else we cannot distinguish
+         * retransmitted packets from new packets, and will hand all
+         * of them to the application. That is not consistent with the
+         * reliability guarantees of RDS. */
+}
+
+/*
+ * There is only every one 'conn' for a given pair of addresses in the
+ * system at a time.  They contain messages to be retransmitted and so
+ * span the lifetime of the actual underlying transport connections.
+ *
+ * For now they are not garbage collected once they're created.  They
+ * are torn down as the module is removed, if ever.
+ */
+static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr,
+                                       struct rds_transport *trans, gfp_t gfp,
+                                       int is_outgoing)
+{
+        struct rds_connection *conn, *tmp, *parent = NULL;
+        struct hlist_head *head = rds_conn_bucket(laddr, faddr);
+        unsigned long flags;
+        int ret;
+
+        spin_lock_irqsave(&rds_conn_lock, flags);
+        conn = rds_conn_lookup(head, laddr, faddr, trans);
+        if (conn
+         && conn->c_loopback
+         && conn->c_trans != &rds_loop_transport
+         && !is_outgoing) {
+                /* This is a looped back IB connection, and we're
+                 * called by the code handling the incoming connect.
+                 * We need a second connection object into which we
+                 * can stick the other QP. */
+                parent = conn;
+                conn = parent->c_passive;
+        }
+        spin_unlock_irqrestore(&rds_conn_lock, flags);
+        if (conn)
+                goto out;
+
+        conn = kmem_cache_alloc(rds_conn_slab, gfp);
+        if (conn == NULL) {
+                conn = ERR_PTR(-ENOMEM);
+                goto out;
+        }
+
+        memset(conn, 0, sizeof(*conn));
+
+        INIT_HLIST_NODE(&conn->c_hash_node);
+        conn->c_version = RDS_PROTOCOL_3_0;
+        conn->c_laddr = laddr;
+        conn->c_faddr = faddr;
+        spin_lock_init(&conn->c_lock);
+        conn->c_next_tx_seq = 1;
+
+        mutex_init(&conn->c_send_lock);
+        INIT_LIST_HEAD(&conn->c_send_queue);
+        INIT_LIST_HEAD(&conn->c_retrans);
+
+        ret = rds_cong_get_maps(conn);
+        if (ret) {
+                kmem_cache_free(rds_conn_slab, conn);
+                conn = ERR_PTR(ret);
+                goto out;
+        }
+
+        /*
+         * This is where a connection becomes loopback.  If *any* RDS sockets
+         * can bind to the destination address then we'd rather the messages
+         * flow through loopback rather than either transport.
+         */
+        if (rds_trans_get_preferred(faddr)) {
+                conn->c_loopback = 1;
+                if (is_outgoing && trans->t_prefer_loopback) {
+                        /* "outgoing" connection - and the transport
+                         * says it wants the connection handled by the
+                         * loopback transport. This is what TCP does.
+                         */
+                        trans = &rds_loop_transport;
+                }
+        }
+
+        conn->c_trans = trans;
+
+        ret = trans->conn_alloc(conn, gfp);
+        if (ret) {
+                kmem_cache_free(rds_conn_slab, conn);
+                conn = ERR_PTR(ret);
+                goto out;
+        }
+
+        atomic_set(&conn->c_state, RDS_CONN_DOWN);
+        conn->c_reconnect_jiffies = 0;
+        INIT_DELAYED_WORK(&conn->c_send_w, rds_send_worker);
+        INIT_DELAYED_WORK(&conn->c_recv_w, rds_recv_worker);
+        INIT_DELAYED_WORK(&conn->c_conn_w, rds_connect_worker);
+        INIT_WORK(&conn->c_down_w, rds_shutdown_worker);
+        mutex_init(&conn->c_cm_lock);
+        conn->c_flags = 0;
+
+        rdsdebug("allocated conn %p for %pI4 -> %pI4 over %s %s\n",
+          conn, &laddr, &faddr,
+          trans->t_name ? trans->t_name : "[unknown]",
+          is_outgoing ? "(outgoing)" : "");
+
+        spin_lock_irqsave(&rds_conn_lock, flags);
+        if (parent == NULL) {
+                tmp = rds_conn_lookup(head, laddr, faddr, trans);
+                if (tmp == NULL)
+                        hlist_add_head(&conn->c_hash_node, head);
+        } else {
+                tmp = parent->c_passive;
+                if (!tmp)
+                        parent->c_passive = conn;
+        }
+
+        if (tmp) {
+                trans->conn_free(conn->c_transport_data);
+                kmem_cache_free(rds_conn_slab, conn);
+                conn = tmp;
+        } else {
+                rds_cong_add_conn(conn);
+                rds_conn_count++;
+        }
+
+        spin_unlock_irqrestore(&rds_conn_lock, flags);
+
+out:
+        return conn;
+}
+
+struct rds_connection *rds_conn_create(__be32 laddr, __be32 faddr,
+                                       struct rds_transport *trans, gfp_t gfp)
+{
+        return __rds_conn_create(laddr, faddr, trans, gfp, 0);
+}
+
+struct rds_connection *rds_conn_create_outgoing(__be32 laddr, __be32 faddr,
+                                       struct rds_transport *trans, gfp_t gfp)
+{
+        return __rds_conn_create(laddr, faddr, trans, gfp, 1);
+}
+
+void rds_conn_destroy(struct rds_connection *conn)
+{
+        struct rds_message *rm, *rtmp;
+
+        rdsdebug("freeing conn %p for %pI4 -> "
+                 "%pI4\n", conn, &conn->c_laddr,
+                 &conn->c_faddr);
+
+        hlist_del_init(&conn->c_hash_node);
+
+        /* wait for the rds thread to shut it down */
+        atomic_set(&conn->c_state, RDS_CONN_ERROR);
+        cancel_delayed_work(&conn->c_conn_w);
+        queue_work(rds_wq, &conn->c_down_w);
+        flush_workqueue(rds_wq);
+
+        /* tear down queued messages */
+        list_for_each_entry_safe(rm, rtmp,
+                                 &conn->c_send_queue,
+                                 m_conn_item) {
+                list_del_init(&rm->m_conn_item);
+                BUG_ON(!list_empty(&rm->m_sock_item));
+                rds_message_put(rm);
+        }
+        if (conn->c_xmit_rm)
+                rds_message_put(conn->c_xmit_rm);
+
+        conn->c_trans->conn_free(conn->c_transport_data);
+
+        /*
+         * The congestion maps aren't freed up here.  They're
+         * freed by rds_cong_exit() after all the connections
+         * have been freed.
+         */
+        rds_cong_remove_conn(conn);
+
+        BUG_ON(!list_empty(&conn->c_retrans));
+        kmem_cache_free(rds_conn_slab, conn);
+
+        rds_conn_count--;
+}
+
+static void rds_conn_message_info(struct socket *sock, unsigned int len,
+                                  struct rds_info_iterator *iter,
+                                  struct rds_info_lengths *lens,
+                                  int want_send)
+{
+        struct hlist_head *head;
+        struct hlist_node *pos;
+        struct list_head *list;
+        struct rds_connection *conn;
+        struct rds_message *rm;
+        unsigned long flags;
+        unsigned int total = 0;
+        size_t i;
+
+        len /= sizeof(struct rds_info_message);
+
+        spin_lock_irqsave(&rds_conn_lock, flags);
+
+        for (i = 0, head = rds_conn_hash; i < ARRAY_SIZE(rds_conn_hash);
+             i++, head++) {
+                hlist_for_each_entry(conn, pos, head, c_hash_node) {
+                        if (want_send)
+                                list = &conn->c_send_queue;
+                        else
+                                list = &conn->c_retrans;
+
+                        spin_lock(&conn->c_lock);
+
+                        /* XXX too lazy to maintain counts.. */
+                        list_for_each_entry(rm, list, m_conn_item) {
+                                total++;
+                                if (total <= len)
+                                        rds_inc_info_copy(&rm->m_inc, iter,
+                                                          conn->c_laddr,
+                                                          conn->c_faddr, 0);
+                        }
+
+                        spin_unlock(&conn->c_lock);
+                }
+        }
+
+        spin_unlock_irqrestore(&rds_conn_lock, flags);
+
+        lens->nr = total;
+        lens->each = sizeof(struct rds_info_message);
+}
+
+static void rds_conn_message_info_send(struct socket *sock, unsigned int len,
+                                       struct rds_info_iterator *iter,
+                                       struct rds_info_lengths *lens)
+{
+        rds_conn_message_info(sock, len, iter, lens, 1);
+}
+
+static void rds_conn_message_info_retrans(struct socket *sock,
+                                          unsigned int len,
+                                          struct rds_info_iterator *iter,
+                                          struct rds_info_lengths *lens)
+{
+        rds_conn_message_info(sock, len, iter, lens, 0);
+}
+
+void rds_for_each_conn_info(struct socket *sock, unsigned int len,
+                          struct rds_info_iterator *iter,
+                          struct rds_info_lengths *lens,
+                          int (*visitor)(struct rds_connection *, void *),
+                          size_t item_len)
+{
+        uint64_t buffer[(item_len + 7) / 8];
+        struct hlist_head *head;
+        struct hlist_node *pos;
+        struct hlist_node *tmp;
+        struct rds_connection *conn;
+        unsigned long flags;
+        size_t i;
+
+        spin_lock_irqsave(&rds_conn_lock, flags);
+
+        lens->nr = 0;
+        lens->each = item_len;
+
+        for (i = 0, head = rds_conn_hash; i < ARRAY_SIZE(rds_conn_hash);
+             i++, head++) {
+                hlist_for_each_entry_safe(conn, pos, tmp, head, c_hash_node) {
+
+                        /* XXX no c_lock usage.. */
+                        if (!visitor(conn, buffer))
+                                continue;
+
+                        /* We copy as much as we can fit in the buffer,
+                         * but we count all items so that the caller
+                         * can resize the buffer. */
+                        if (len >= item_len) {
+                                rds_info_copy(iter, buffer, item_len);
+                                len -= item_len;
+                        }
+                        lens->nr++;
+                }
+        }
+
+        spin_unlock_irqrestore(&rds_conn_lock, flags);
+}
+
+static int rds_conn_info_visitor(struct rds_connection *conn,
+                                  void *buffer)
+{
+        struct rds_info_connection *cinfo = buffer;
+
+        cinfo->next_tx_seq = conn->c_next_tx_seq;
+        cinfo->next_rx_seq = conn->c_next_rx_seq;
+        cinfo->laddr = conn->c_laddr;
+        cinfo->faddr = conn->c_faddr;
+        strncpy(cinfo->transport, conn->c_trans->t_name,
+                sizeof(cinfo->transport));
+        cinfo->flags = 0;
+
+        rds_conn_info_set(cinfo->flags,
+                          rds_conn_is_sending(conn), SENDING);
+        /* XXX Future: return the state rather than these funky bits */
+        rds_conn_info_set(cinfo->flags,
+                          atomic_read(&conn->c_state) == RDS_CONN_CONNECTING,
+                          CONNECTING);
+        rds_conn_info_set(cinfo->flags,
+                          atomic_read(&conn->c_state) == RDS_CONN_UP,
+                          CONNECTED);
+        return 1;
+}
+
+static void rds_conn_info(struct socket *sock, unsigned int len,
+                          struct rds_info_iterator *iter,
+                          struct rds_info_lengths *lens)
+{
+        rds_for_each_conn_info(sock, len, iter, lens,
+                                rds_conn_info_visitor,
+                                sizeof(struct rds_info_connection));
+}
+
+int __init rds_conn_init(void)
+{
+        rds_conn_slab = kmem_cache_create("rds_connection",
+                                          sizeof(struct rds_connection),
+                                          0, 0, NULL);
+        if (rds_conn_slab == NULL)
+                return -ENOMEM;
+
+        rds_info_register_func(RDS_INFO_CONNECTIONS, rds_conn_info);
+        rds_info_register_func(RDS_INFO_SEND_MESSAGES,
+                               rds_conn_message_info_send);
+        rds_info_register_func(RDS_INFO_RETRANS_MESSAGES,
+                               rds_conn_message_info_retrans);
+
+        return 0;
+}
+
+void rds_conn_exit(void)
+{
+        rds_loop_exit();
+
+        WARN_ON(!hlist_empty(rds_conn_hash));
+
+        kmem_cache_destroy(rds_conn_slab);
+
+        rds_info_deregister_func(RDS_INFO_CONNECTIONS, rds_conn_info);
+        rds_info_deregister_func(RDS_INFO_SEND_MESSAGES,
+                                 rds_conn_message_info_send);
+        rds_info_deregister_func(RDS_INFO_RETRANS_MESSAGES,
+                                 rds_conn_message_info_retrans);
+}
+
+/*
+ * Force a disconnect
+ */
+void rds_conn_drop(struct rds_connection *conn)
+{
+        atomic_set(&conn->c_state, RDS_CONN_ERROR);
+        queue_work(rds_wq, &conn->c_down_w);
+}
+
+/*
+ * An error occurred on the connection
+ */
+void
+__rds_conn_error(struct rds_connection *conn, const char *fmt, ...)
+{
+        va_list ap;
+
+        va_start(ap, fmt);
+        vprintk(fmt, ap);
+        va_end(ap);
+
+        rds_conn_drop(conn);
+}
diff --git a/net/rds/threads.c b/net/rds/threads.c
new file mode 100644
index 000000000000..828a1bf9ea92
--- /dev/null
+++ b/net/rds/threads.c
@@ -0,0 +1,265 @@
+/*
+ * 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 "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 c_send_lock, 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;
+
+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);
+}
+
+/*
+ * 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.
+ */
+static 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_shutdown_worker(struct work_struct *work)
+{
+        struct rds_connection *conn = container_of(work, struct rds_connection, c_down_w);
+
+        /* shut it down unless it's down already */
+        if (!rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_DOWN)) {
+                /*
+                 * Quiesce the connection mgmt handlers before we start tearing
+                 * things down. We don't hold the mutex for the entire
+                 * duration of the shutdown operation, else we may be
+                 * deadlocking with the CM handler. Instead, the CM event
+                 * handler is supposed to check for state DISCONNECTING
+                 */
+                mutex_lock(&conn->c_cm_lock);
+                if (!rds_conn_transition(conn, RDS_CONN_UP, RDS_CONN_DISCONNECTING)
+                 && !rds_conn_transition(conn, RDS_CONN_ERROR, RDS_CONN_DISCONNECTING)) {
+                        rds_conn_error(conn, "shutdown called in state %d\n",
+                                        atomic_read(&conn->c_state));
+                        mutex_unlock(&conn->c_cm_lock);
+                        return;
+                }
+                mutex_unlock(&conn->c_cm_lock);
+
+                mutex_lock(&conn->c_send_lock);
+                conn->c_trans->conn_shutdown(conn);
+                rds_conn_reset(conn);
+                mutex_unlock(&conn->c_send_lock);
+
+                if (!rds_conn_transition(conn, RDS_CONN_DISCONNECTING, RDS_CONN_DOWN)) {
+                        /* This can happen - eg when we're in the middle of tearing
+                         * down the connection, and someone unloads the rds module.
+                         * Quite reproduceable with loopback connections.
+                         * Mostly harmless.
+                         */
+                        rds_conn_error(conn,
+                                "%s: failed to transition to state DOWN, "
+                                "current state is %d\n",
+                                __func__,
+                                atomic_read(&conn->c_state));
+                        return;
+                }
+        }
+
+        /* Then reconnect if it's still live.
+         * The passive side of an IB loopback connection is never added
+         * to the conn hash, so we never trigger a reconnect on this
+         * conn - the reconnect is always triggered by the active peer. */
+        cancel_delayed_work(&conn->c_conn_w);
+        if (!hlist_unhashed(&conn->c_hash_node))
+                rds_queue_reconnect(conn);
+}
+
+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_threads_exit(void)
+{
+        destroy_workqueue(rds_wq);
+}
+
+int __init rds_threads_init(void)
+{
+        rds_wq = create_singlethread_workqueue("krdsd");
+        if (rds_wq == NULL)
+                return -ENOMEM;
+
+        return 0;
+}