RDS: send.c

This is the code to send an RDS datagram.

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

1 files changed, 1003 insertions, 0 deletions

diff --git a/net/rds/send.c b/net/rds/send.c
new file mode 100644
index 000000000000..1b37364656f0
--- /dev/null
+++ b/net/rds/send.c
@@ -0,0 +1,1003 @@
+/*
+ * 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 <net/sock.h>
+#include <linux/in.h>
+#include <linux/list.h>
+
+#include "rds.h"
+#include "rdma.h"
+
+/* When transmitting messages in rds_send_xmit, we need to emerge from
+ * time to time and briefly release the CPU. Otherwise the softlock watchdog
+ * will kick our shin.
+ * Also, it seems fairer to not let one busy connection stall all the
+ * others.
+ *
+ * send_batch_count is the number of times we'll loop in send_xmit. Setting
+ * it to 0 will restore the old behavior (where we looped until we had
+ * drained the queue).
+ */
+static int send_batch_count = 64;
+module_param(send_batch_count, int, 0444);
+MODULE_PARM_DESC(send_batch_count, " batch factor when working the send queue");
+
+/*
+ * Reset the send state. Caller must hold c_send_lock when calling here.
+ */
+void rds_send_reset(struct rds_connection *conn)
+{
+        struct rds_message *rm, *tmp;
+        unsigned long flags;
+
+        if (conn->c_xmit_rm) {
+                /* Tell the user the RDMA op is no longer mapped by the
+                 * transport. This isn't entirely true (it's flushed out
+                 * independently) but as the connection is down, there's
+                 * no ongoing RDMA to/from that memory */
+                rds_message_unmapped(conn->c_xmit_rm);
+                rds_message_put(conn->c_xmit_rm);
+                conn->c_xmit_rm = NULL;
+        }
+        conn->c_xmit_sg = 0;
+        conn->c_xmit_hdr_off = 0;
+        conn->c_xmit_data_off = 0;
+        conn->c_xmit_rdma_sent = 0;
+
+        conn->c_map_queued = 0;
+
+        conn->c_unacked_packets = rds_sysctl_max_unacked_packets;
+        conn->c_unacked_bytes = rds_sysctl_max_unacked_bytes;
+
+        /* Mark messages as retransmissions, and move them to the send q */
+        spin_lock_irqsave(&conn->c_lock, flags);
+        list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
+                set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);
+                set_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags);
+        }
+        list_splice_init(&conn->c_retrans, &conn->c_send_queue);
+        spin_unlock_irqrestore(&conn->c_lock, flags);
+}
+
+/*
+ * We're making the concious trade-off here to only send one message
+ * down the connection at a time.
+ *   Pro:
+ *      - tx queueing is a simple fifo list
+ *      - reassembly is optional and easily done by transports per conn
+ *      - no per flow rx lookup at all, straight to the socket
+ *      - less per-frag memory and wire overhead
+ *   Con:
+ *      - queued acks can be delayed behind large messages
+ *   Depends:
+ *      - small message latency is higher behind queued large messages
+ *      - large message latency isn't starved by intervening small sends
+ */
+int rds_send_xmit(struct rds_connection *conn)
+{
+        struct rds_message *rm;
+        unsigned long flags;
+        unsigned int tmp;
+        unsigned int send_quota = send_batch_count;
+        struct scatterlist *sg;
+        int ret = 0;
+        int was_empty = 0;
+        LIST_HEAD(to_be_dropped);
+
+        /*
+         * sendmsg calls here after having queued its message on the send
+         * queue.  We only have one task feeding the connection at a time.  If
+         * another thread is already feeding the queue then we back off.  This
+         * avoids blocking the caller and trading per-connection data between
+         * caches per message.
+         *
+         * The sem holder will issue a retry if they notice that someone queued
+         * a message after they stopped walking the send queue but before they
+         * dropped the sem.
+         */
+        if (!mutex_trylock(&conn->c_send_lock)) {
+                rds_stats_inc(s_send_sem_contention);
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        if (conn->c_trans->xmit_prepare)
+                conn->c_trans->xmit_prepare(conn);
+
+        /*
+         * spin trying to push headers and data down the connection until
+         * the connection doens't make forward progress.
+         */
+        while (--send_quota) {
+                /*
+                 * See if need to send a congestion map update if we're
+                 * between sending messages.  The send_sem protects our sole
+                 * use of c_map_offset and _bytes.
+                 * Note this is used only by transports that define a special
+                 * xmit_cong_map function. For all others, we create allocate
+                 * a cong_map message and treat it just like any other send.
+                 */
+                if (conn->c_map_bytes) {
+                        ret = conn->c_trans->xmit_cong_map(conn, conn->c_lcong,
+                                                conn->c_map_offset);
+                        if (ret <= 0)
+                                break;
+
+                        conn->c_map_offset += ret;
+                        conn->c_map_bytes -= ret;
+                        if (conn->c_map_bytes)
+                                continue;
+                }
+
+                /* If we're done sending the current message, clear the
+                 * offset and S/G temporaries.
+                 */
+                rm = conn->c_xmit_rm;
+                if (rm != NULL &&
+                    conn->c_xmit_hdr_off == sizeof(struct rds_header) &&
+                    conn->c_xmit_sg == rm->m_nents) {
+                        conn->c_xmit_rm = NULL;
+                        conn->c_xmit_sg = 0;
+                        conn->c_xmit_hdr_off = 0;
+                        conn->c_xmit_data_off = 0;
+                        conn->c_xmit_rdma_sent = 0;
+
+                        /* Release the reference to the previous message. */
+                        rds_message_put(rm);
+                        rm = NULL;
+                }
+
+                /* If we're asked to send a cong map update, do so.
+                 */
+                if (rm == NULL && test_and_clear_bit(0, &conn->c_map_queued)) {
+                        if (conn->c_trans->xmit_cong_map != NULL) {
+                                conn->c_map_offset = 0;
+                                conn->c_map_bytes = sizeof(struct rds_header) +
+                                        RDS_CONG_MAP_BYTES;
+                                continue;
+                        }
+
+                        rm = rds_cong_update_alloc(conn);
+                        if (IS_ERR(rm)) {
+                                ret = PTR_ERR(rm);
+                                break;
+                        }
+
+                        conn->c_xmit_rm = rm;
+                }
+
+                /*
+                 * Grab the next message from the send queue, if there is one.
+                 *
+                 * c_xmit_rm holds a ref while we're sending this message down
+                 * the connction.  We can use this ref while holding the
+                 * send_sem.. rds_send_reset() is serialized with it.
+                 */
+                if (rm == NULL) {
+                        unsigned int len;
+
+                        spin_lock_irqsave(&conn->c_lock, flags);
+
+                        if (!list_empty(&conn->c_send_queue)) {
+                                rm = list_entry(conn->c_send_queue.next,
+                                                struct rds_message,
+                                                m_conn_item);
+                                rds_message_addref(rm);
+
+                                /*
+                                 * Move the message from the send queue to the retransmit
+                                 * list right away.
+                                 */
+                                list_move_tail(&rm->m_conn_item, &conn->c_retrans);
+                        }
+
+                        spin_unlock_irqrestore(&conn->c_lock, flags);
+
+                        if (rm == NULL) {
+                                was_empty = 1;
+                                break;
+                        }
+
+                        /* Unfortunately, the way Infiniband deals with
+                         * RDMA to a bad MR key is by moving the entire
+                         * queue pair to error state. We cold possibly
+                         * recover from that, but right now we drop the
+                         * connection.
+                         * Therefore, we never retransmit messages with RDMA ops.
+                         */
+                        if (rm->m_rdma_op
+                         && test_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags)) {
+                                spin_lock_irqsave(&conn->c_lock, flags);
+                                if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags))
+                                        list_move(&rm->m_conn_item, &to_be_dropped);
+                                spin_unlock_irqrestore(&conn->c_lock, flags);
+                                rds_message_put(rm);
+                                continue;
+                        }
+
+                        /* Require an ACK every once in a while */
+                        len = ntohl(rm->m_inc.i_hdr.h_len);
+                        if (conn->c_unacked_packets == 0
+                         || conn->c_unacked_bytes < len) {
+                                __set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);
+
+                                conn->c_unacked_packets = rds_sysctl_max_unacked_packets;
+                                conn->c_unacked_bytes = rds_sysctl_max_unacked_bytes;
+                                rds_stats_inc(s_send_ack_required);
+                        } else {
+                                conn->c_unacked_bytes -= len;
+                                conn->c_unacked_packets--;
+                        }
+
+                        conn->c_xmit_rm = rm;
+                }
+
+                /*
+                 * Try and send an rdma message.  Let's see if we can
+                 * keep this simple and require that the transport either
+                 * send the whole rdma or none of it.
+                 */
+                if (rm->m_rdma_op && !conn->c_xmit_rdma_sent) {
+                        ret = conn->c_trans->xmit_rdma(conn, rm->m_rdma_op);
+                        if (ret)
+                                break;
+                        conn->c_xmit_rdma_sent = 1;
+                        /* The transport owns the mapped memory for now.
+                         * You can't unmap it while it's on the send queue */
+                        set_bit(RDS_MSG_MAPPED, &rm->m_flags);
+                }
+
+                if (conn->c_xmit_hdr_off < sizeof(struct rds_header) ||
+                    conn->c_xmit_sg < rm->m_nents) {
+                        ret = conn->c_trans->xmit(conn, rm,
+                                                  conn->c_xmit_hdr_off,
+                                                  conn->c_xmit_sg,
+                                                  conn->c_xmit_data_off);
+                        if (ret <= 0)
+                                break;
+
+                        if (conn->c_xmit_hdr_off < sizeof(struct rds_header)) {
+                                tmp = min_t(int, ret,
+                                            sizeof(struct rds_header) -
+                                            conn->c_xmit_hdr_off);
+                                conn->c_xmit_hdr_off += tmp;
+                                ret -= tmp;
+                        }
+
+                        sg = &rm->m_sg[conn->c_xmit_sg];
+                        while (ret) {
+                                tmp = min_t(int, ret, sg->length -
+                                                      conn->c_xmit_data_off);
+                                conn->c_xmit_data_off += tmp;
+                                ret -= tmp;
+                                if (conn->c_xmit_data_off == sg->length) {
+                                        conn->c_xmit_data_off = 0;
+                                        sg++;
+                                        conn->c_xmit_sg++;
+                                        BUG_ON(ret != 0 &&
+                                               conn->c_xmit_sg == rm->m_nents);
+                                }
+                        }
+                }
+        }
+
+        /* Nuke any messages we decided not to retransmit. */
+        if (!list_empty(&to_be_dropped))
+                rds_send_remove_from_sock(&to_be_dropped, RDS_RDMA_DROPPED);
+
+        if (conn->c_trans->xmit_complete)
+                conn->c_trans->xmit_complete(conn);
+
+        /*
+         * We might be racing with another sender who queued a message but
+         * backed off on noticing that we held the c_send_lock.  If we check
+         * for queued messages after dropping the sem then either we'll
+         * see the queued message or the queuer will get the sem.  If we
+         * notice the queued message then we trigger an immediate retry.
+         *
+         * We need to be careful only to do this when we stopped processing
+         * the send queue because it was empty.  It's the only way we
+         * stop processing the loop when the transport hasn't taken
+         * responsibility for forward progress.
+         */
+        mutex_unlock(&conn->c_send_lock);
+
+        if (conn->c_map_bytes || (send_quota == 0 && !was_empty)) {
+                /* We exhausted the send quota, but there's work left to
+                 * do. Return and (re-)schedule the send worker.
+                 */
+                ret = -EAGAIN;
+        }
+
+        if (ret == 0 && was_empty) {
+                /* A simple bit test would be way faster than taking the
+                 * spin lock */
+                spin_lock_irqsave(&conn->c_lock, flags);
+                if (!list_empty(&conn->c_send_queue)) {
+                        rds_stats_inc(s_send_sem_queue_raced);
+                        ret = -EAGAIN;
+                }
+                spin_unlock_irqrestore(&conn->c_lock, flags);
+        }
+out:
+        return ret;
+}
+
+static void rds_send_sndbuf_remove(struct rds_sock *rs, struct rds_message *rm)
+{
+        u32 len = be32_to_cpu(rm->m_inc.i_hdr.h_len);
+
+        assert_spin_locked(&rs->rs_lock);
+
+        BUG_ON(rs->rs_snd_bytes < len);
+        rs->rs_snd_bytes -= len;
+
+        if (rs->rs_snd_bytes == 0)
+                rds_stats_inc(s_send_queue_empty);
+}
+
+static inline int rds_send_is_acked(struct rds_message *rm, u64 ack,
+                                    is_acked_func is_acked)
+{
+        if (is_acked)
+                return is_acked(rm, ack);
+        return be64_to_cpu(rm->m_inc.i_hdr.h_sequence) <= ack;
+}
+
+/*
+ * Returns true if there are no messages on the send and retransmit queues
+ * which have a sequence number greater than or equal to the given sequence
+ * number.
+ */
+int rds_send_acked_before(struct rds_connection *conn, u64 seq)
+{
+        struct rds_message *rm, *tmp;
+        int ret = 1;
+
+        spin_lock(&conn->c_lock);
+
+        list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
+                if (be64_to_cpu(rm->m_inc.i_hdr.h_sequence) < seq)
+                        ret = 0;
+                break;
+        }
+
+        list_for_each_entry_safe(rm, tmp, &conn->c_send_queue, m_conn_item) {
+                if (be64_to_cpu(rm->m_inc.i_hdr.h_sequence) < seq)
+                        ret = 0;
+                break;
+        }
+
+        spin_unlock(&conn->c_lock);
+
+        return ret;
+}
+
+/*
+ * This is pretty similar to what happens below in the ACK
+ * handling code - except that we call here as soon as we get
+ * the IB send completion on the RDMA op and the accompanying
+ * message.
+ */
+void rds_rdma_send_complete(struct rds_message *rm, int status)
+{
+        struct rds_sock *rs = NULL;
+        struct rds_rdma_op *ro;
+        struct rds_notifier *notifier;
+
+        spin_lock(&rm->m_rs_lock);
+
+        ro = rm->m_rdma_op;
+        if (test_bit(RDS_MSG_ON_SOCK, &rm->m_flags)
+         && ro && ro->r_notify && ro->r_notifier) {
+                notifier = ro->r_notifier;
+                rs = rm->m_rs;
+                sock_hold(rds_rs_to_sk(rs));
+
+                notifier->n_status = status;
+                spin_lock(&rs->rs_lock);
+                list_add_tail(&notifier->n_list, &rs->rs_notify_queue);
+                spin_unlock(&rs->rs_lock);
+
+                ro->r_notifier = NULL;
+        }
+
+        spin_unlock(&rm->m_rs_lock);
+
+        if (rs) {
+                rds_wake_sk_sleep(rs);
+                sock_put(rds_rs_to_sk(rs));
+        }
+}
+
+/*
+ * This is the same as rds_rdma_send_complete except we
+ * don't do any locking - we have all the ingredients (message,
+ * socket, socket lock) and can just move the notifier.
+ */
+static inline void
+__rds_rdma_send_complete(struct rds_sock *rs, struct rds_message *rm, int status)
+{
+        struct rds_rdma_op *ro;
+
+        ro = rm->m_rdma_op;
+        if (ro && ro->r_notify && ro->r_notifier) {
+                ro->r_notifier->n_status = status;
+                list_add_tail(&ro->r_notifier->n_list, &rs->rs_notify_queue);
+                ro->r_notifier = NULL;
+        }
+
+        /* No need to wake the app - caller does this */
+}
+
+/*
+ * This is called from the IB send completion when we detect
+ * a RDMA operation that failed with remote access error.
+ * So speed is not an issue here.
+ */
+struct rds_message *rds_send_get_message(struct rds_connection *conn,
+                                         struct rds_rdma_op *op)
+{
+        struct rds_message *rm, *tmp, *found = NULL;
+        unsigned long flags;
+
+        spin_lock_irqsave(&conn->c_lock, flags);
+
+        list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
+                if (rm->m_rdma_op == op) {
+                        atomic_inc(&rm->m_refcount);
+                        found = rm;
+                        goto out;
+                }
+        }
+
+        list_for_each_entry_safe(rm, tmp, &conn->c_send_queue, m_conn_item) {
+                if (rm->m_rdma_op == op) {
+                        atomic_inc(&rm->m_refcount);
+                        found = rm;
+                        break;
+                }
+        }
+
+out:
+        spin_unlock_irqrestore(&conn->c_lock, flags);
+
+        return found;
+}
+
+/*
+ * This removes messages from the socket's list if they're on it.  The list
+ * argument must be private to the caller, we must be able to modify it
+ * without locks.  The messages must have a reference held for their
+ * position on the list.  This function will drop that reference after
+ * removing the messages from the 'messages' list regardless of if it found
+ * the messages on the socket list or not.
+ */
+void rds_send_remove_from_sock(struct list_head *messages, int status)
+{
+        unsigned long flags = 0; /* silence gcc :P */
+        struct rds_sock *rs = NULL;
+        struct rds_message *rm;
+
+        local_irq_save(flags);
+        while (!list_empty(messages)) {
+                rm = list_entry(messages->next, struct rds_message,
+                                m_conn_item);
+                list_del_init(&rm->m_conn_item);
+
+                /*
+                 * If we see this flag cleared then we're *sure* that someone
+                 * else beat us to removing it from the sock.  If we race
+                 * with their flag update we'll get the lock and then really
+                 * see that the flag has been cleared.
+                 *
+                 * The message spinlock makes sure nobody clears rm->m_rs
+                 * while we're messing with it. It does not prevent the
+                 * message from being removed from the socket, though.
+                 */
+                spin_lock(&rm->m_rs_lock);
+                if (!test_bit(RDS_MSG_ON_SOCK, &rm->m_flags))
+                        goto unlock_and_drop;
+
+                if (rs != rm->m_rs) {
+                        if (rs) {
+                                spin_unlock(&rs->rs_lock);
+                                rds_wake_sk_sleep(rs);
+                                sock_put(rds_rs_to_sk(rs));
+                        }
+                        rs = rm->m_rs;
+                        spin_lock(&rs->rs_lock);
+                        sock_hold(rds_rs_to_sk(rs));
+                }
+
+                if (test_and_clear_bit(RDS_MSG_ON_SOCK, &rm->m_flags)) {
+                        struct rds_rdma_op *ro = rm->m_rdma_op;
+                        struct rds_notifier *notifier;
+
+                        list_del_init(&rm->m_sock_item);
+                        rds_send_sndbuf_remove(rs, rm);
+
+                        if (ro && ro->r_notifier
+                           && (status || ro->r_notify)) {
+                                notifier = ro->r_notifier;
+                                list_add_tail(&notifier->n_list,
+                                                &rs->rs_notify_queue);
+                                if (!notifier->n_status)
+                                        notifier->n_status = status;
+                                rm->m_rdma_op->r_notifier = NULL;
+                        }
+                        rds_message_put(rm);
+                        rm->m_rs = NULL;
+                }
+
+unlock_and_drop:
+                spin_unlock(&rm->m_rs_lock);
+                rds_message_put(rm);
+        }
+
+        if (rs) {
+                spin_unlock(&rs->rs_lock);
+                rds_wake_sk_sleep(rs);
+                sock_put(rds_rs_to_sk(rs));
+        }
+        local_irq_restore(flags);
+}
+
+/*
+ * Transports call here when they've determined that the receiver queued
+ * messages up to, and including, the given sequence number.  Messages are
+ * moved to the retrans queue when rds_send_xmit picks them off the send
+ * queue. This means that in the TCP case, the message may not have been
+ * assigned the m_ack_seq yet - but that's fine as long as tcp_is_acked
+ * checks the RDS_MSG_HAS_ACK_SEQ bit.
+ *
+ * XXX It's not clear to me how this is safely serialized with socket
+ * destruction.  Maybe it should bail if it sees SOCK_DEAD.
+ */
+void rds_send_drop_acked(struct rds_connection *conn, u64 ack,
+                         is_acked_func is_acked)
+{
+        struct rds_message *rm, *tmp;
+        unsigned long flags;
+        LIST_HEAD(list);
+
+        spin_lock_irqsave(&conn->c_lock, flags);
+
+        list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
+                if (!rds_send_is_acked(rm, ack, is_acked))
+                        break;
+
+                list_move(&rm->m_conn_item, &list);
+                clear_bit(RDS_MSG_ON_CONN, &rm->m_flags);
+        }
+
+        /* order flag updates with spin locks */
+        if (!list_empty(&list))
+                smp_mb__after_clear_bit();
+
+        spin_unlock_irqrestore(&conn->c_lock, flags);
+
+        /* now remove the messages from the sock list as needed */
+        rds_send_remove_from_sock(&list, RDS_RDMA_SUCCESS);
+}
+
+void rds_send_drop_to(struct rds_sock *rs, struct sockaddr_in *dest)
+{
+        struct rds_message *rm, *tmp;
+        struct rds_connection *conn;
+        unsigned long flags;
+        LIST_HEAD(list);
+        int wake = 0;
+
+        /* get all the messages we're dropping under the rs lock */
+        spin_lock_irqsave(&rs->rs_lock, flags);
+
+        list_for_each_entry_safe(rm, tmp, &rs->rs_send_queue, m_sock_item) {
+                if (dest && (dest->sin_addr.s_addr != rm->m_daddr ||
+                             dest->sin_port != rm->m_inc.i_hdr.h_dport))
+                        continue;
+
+                wake = 1;
+                list_move(&rm->m_sock_item, &list);
+                rds_send_sndbuf_remove(rs, rm);
+                clear_bit(RDS_MSG_ON_SOCK, &rm->m_flags);
+
+                /* If this is a RDMA operation, notify the app. */
+                __rds_rdma_send_complete(rs, rm, RDS_RDMA_CANCELED);
+        }
+
+        /* order flag updates with the rs lock */
+        if (wake)
+                smp_mb__after_clear_bit();
+
+        spin_unlock_irqrestore(&rs->rs_lock, flags);
+
+        if (wake)
+                rds_wake_sk_sleep(rs);
+
+        conn = NULL;
+
+        /* now remove the messages from the conn list as needed */
+        list_for_each_entry(rm, &list, m_sock_item) {
+                /* We do this here rather than in the loop above, so that
+                 * we don't have to nest m_rs_lock under rs->rs_lock */
+                spin_lock(&rm->m_rs_lock);
+                rm->m_rs = NULL;
+                spin_unlock(&rm->m_rs_lock);
+
+                /*
+                 * If we see this flag cleared then we're *sure* that someone
+                 * else beat us to removing it from the conn.  If we race
+                 * with their flag update we'll get the lock and then really
+                 * see that the flag has been cleared.
+                 */
+                if (!test_bit(RDS_MSG_ON_CONN, &rm->m_flags))
+                        continue;
+
+                if (conn != rm->m_inc.i_conn) {
+                        if (conn)
+                                spin_unlock_irqrestore(&conn->c_lock, flags);
+                        conn = rm->m_inc.i_conn;
+                        spin_lock_irqsave(&conn->c_lock, flags);
+                }
+
+                if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags)) {
+                        list_del_init(&rm->m_conn_item);
+                        rds_message_put(rm);
+                }
+        }
+
+        if (conn)
+                spin_unlock_irqrestore(&conn->c_lock, flags);
+
+        while (!list_empty(&list)) {
+                rm = list_entry(list.next, struct rds_message, m_sock_item);
+                list_del_init(&rm->m_sock_item);
+
+                rds_message_wait(rm);
+                rds_message_put(rm);
+        }
+}
+
+/*
+ * we only want this to fire once so we use the callers 'queued'.  It's
+ * possible that another thread can race with us and remove the
+ * message from the flow with RDS_CANCEL_SENT_TO.
+ */
+static int rds_send_queue_rm(struct rds_sock *rs, struct rds_connection *conn,
+                             struct rds_message *rm, __be16 sport,
+                             __be16 dport, int *queued)
+{
+        unsigned long flags;
+        u32 len;
+
+        if (*queued)
+                goto out;
+
+        len = be32_to_cpu(rm->m_inc.i_hdr.h_len);
+
+        /* this is the only place which holds both the socket's rs_lock
+         * and the connection's c_lock */
+        spin_lock_irqsave(&rs->rs_lock, flags);
+
+        /*
+         * If there is a little space in sndbuf, we don't queue anything,
+         * and userspace gets -EAGAIN. But poll() indicates there's send
+         * room. This can lead to bad behavior (spinning) if snd_bytes isn't
+         * freed up by incoming acks. So we check the *old* value of
+         * rs_snd_bytes here to allow the last msg to exceed the buffer,
+         * and poll() now knows no more data can be sent.
+         */
+        if (rs->rs_snd_bytes < rds_sk_sndbuf(rs)) {
+                rs->rs_snd_bytes += len;
+
+                /* let recv side know we are close to send space exhaustion.
+                 * This is probably not the optimal way to do it, as this
+                 * means we set the flag on *all* messages as soon as our
+                 * throughput hits a certain threshold.
+                 */
+                if (rs->rs_snd_bytes >= rds_sk_sndbuf(rs) / 2)
+                        __set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);
+
+                list_add_tail(&rm->m_sock_item, &rs->rs_send_queue);
+                set_bit(RDS_MSG_ON_SOCK, &rm->m_flags);
+                rds_message_addref(rm);
+                rm->m_rs = rs;
+
+                /* The code ordering is a little weird, but we're
+                   trying to minimize the time we hold c_lock */
+                rds_message_populate_header(&rm->m_inc.i_hdr, sport, dport, 0);
+                rm->m_inc.i_conn = conn;
+                rds_message_addref(rm);
+
+                spin_lock(&conn->c_lock);
+                rm->m_inc.i_hdr.h_sequence = cpu_to_be64(conn->c_next_tx_seq++);
+                list_add_tail(&rm->m_conn_item, &conn->c_send_queue);
+                set_bit(RDS_MSG_ON_CONN, &rm->m_flags);
+                spin_unlock(&conn->c_lock);
+
+                rdsdebug("queued msg %p len %d, rs %p bytes %d seq %llu\n",
+                         rm, len, rs, rs->rs_snd_bytes,
+                         (unsigned long long)be64_to_cpu(rm->m_inc.i_hdr.h_sequence));
+
+                *queued = 1;
+        }
+
+        spin_unlock_irqrestore(&rs->rs_lock, flags);
+out:
+        return *queued;
+}
+
+static int rds_cmsg_send(struct rds_sock *rs, struct rds_message *rm,
+                         struct msghdr *msg, int *allocated_mr)
+{
+        struct cmsghdr *cmsg;
+        int ret = 0;
+
+        for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg)) {
+                if (!CMSG_OK(msg, cmsg))
+                        return -EINVAL;
+
+                if (cmsg->cmsg_level != SOL_RDS)
+                        continue;
+
+                /* As a side effect, RDMA_DEST and RDMA_MAP will set
+                 * rm->m_rdma_cookie and rm->m_rdma_mr.
+                 */
+                switch (cmsg->cmsg_type) {
+                case RDS_CMSG_RDMA_ARGS:
+                        ret = rds_cmsg_rdma_args(rs, rm, cmsg);
+                        break;
+
+                case RDS_CMSG_RDMA_DEST:
+                        ret = rds_cmsg_rdma_dest(rs, rm, cmsg);
+                        break;
+
+                case RDS_CMSG_RDMA_MAP:
+                        ret = rds_cmsg_rdma_map(rs, rm, cmsg);
+                        if (!ret)
+                                *allocated_mr = 1;
+                        break;
+
+                default:
+                        return -EINVAL;
+                }
+
+                if (ret)
+                        break;
+        }
+
+        return ret;
+}
+
+int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
+                size_t payload_len)
+{
+        struct sock *sk = sock->sk;
+        struct rds_sock *rs = rds_sk_to_rs(sk);
+        struct sockaddr_in *usin = (struct sockaddr_in *)msg->msg_name;
+        __be32 daddr;
+        __be16 dport;
+        struct rds_message *rm = NULL;
+        struct rds_connection *conn;
+        int ret = 0;
+        int queued = 0, allocated_mr = 0;
+        int nonblock = msg->msg_flags & MSG_DONTWAIT;
+        long timeo = sock_rcvtimeo(sk, nonblock);
+
+        /* Mirror Linux UDP mirror of BSD error message compatibility */
+        /* XXX: Perhaps MSG_MORE someday */
+        if (msg->msg_flags & ~(MSG_DONTWAIT | MSG_CMSG_COMPAT)) {
+                printk(KERN_INFO "msg_flags 0x%08X\n", msg->msg_flags);
+                ret = -EOPNOTSUPP;
+                goto out;
+        }
+
+        if (msg->msg_namelen) {
+                /* XXX fail non-unicast destination IPs? */
+                if (msg->msg_namelen < sizeof(*usin) || usin->sin_family != AF_INET) {
+                        ret = -EINVAL;
+                        goto out;
+                }
+                daddr = usin->sin_addr.s_addr;
+                dport = usin->sin_port;
+        } else {
+                /* We only care about consistency with ->connect() */
+                lock_sock(sk);
+                daddr = rs->rs_conn_addr;
+                dport = rs->rs_conn_port;
+                release_sock(sk);
+        }
+
+        /* racing with another thread binding seems ok here */
+        if (daddr == 0 || rs->rs_bound_addr == 0) {
+                ret = -ENOTCONN; /* XXX not a great errno */
+                goto out;
+        }
+
+        rm = rds_message_copy_from_user(msg->msg_iov, payload_len);
+        if (IS_ERR(rm)) {
+                ret = PTR_ERR(rm);
+                rm = NULL;
+                goto out;
+        }
+
+        rm->m_daddr = daddr;
+
+        /* Parse any control messages the user may have included. */
+        ret = rds_cmsg_send(rs, rm, msg, &allocated_mr);
+        if (ret)
+                goto out;
+
+        /* rds_conn_create has a spinlock that runs with IRQ off.
+         * Caching the conn in the socket helps a lot. */
+        if (rs->rs_conn && rs->rs_conn->c_faddr == daddr)
+                conn = rs->rs_conn;
+        else {
+                conn = rds_conn_create_outgoing(rs->rs_bound_addr, daddr,
+                                        rs->rs_transport,
+                                        sock->sk->sk_allocation);
+                if (IS_ERR(conn)) {
+                        ret = PTR_ERR(conn);
+                        goto out;
+                }
+                rs->rs_conn = conn;
+        }
+
+        if ((rm->m_rdma_cookie || rm->m_rdma_op)
+         && conn->c_trans->xmit_rdma == NULL) {
+                if (printk_ratelimit())
+                        printk(KERN_NOTICE "rdma_op %p conn xmit_rdma %p\n",
+                                rm->m_rdma_op, conn->c_trans->xmit_rdma);
+                ret = -EOPNOTSUPP;
+                goto out;
+        }
+
+        /* If the connection is down, trigger a connect. We may
+         * have scheduled a delayed reconnect however - in this case
+         * we should not interfere.
+         */
+        if (rds_conn_state(conn) == RDS_CONN_DOWN
+         && !test_and_set_bit(RDS_RECONNECT_PENDING, &conn->c_flags))
+                queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
+
+        ret = rds_cong_wait(conn->c_fcong, dport, nonblock, rs);
+        if (ret)
+                goto out;
+
+        while (!rds_send_queue_rm(rs, conn, rm, rs->rs_bound_port,
+                                  dport, &queued)) {
+                rds_stats_inc(s_send_queue_full);
+                /* XXX make sure this is reasonable */
+                if (payload_len > rds_sk_sndbuf(rs)) {
+                        ret = -EMSGSIZE;
+                        goto out;
+                }
+                if (nonblock) {
+                        ret = -EAGAIN;
+                        goto out;
+                }
+
+                timeo = wait_event_interruptible_timeout(*sk->sk_sleep,
+                                        rds_send_queue_rm(rs, conn, rm,
+                                                          rs->rs_bound_port,
+                                                          dport,
+                                                          &queued),
+                                        timeo);
+                rdsdebug("sendmsg woke queued %d timeo %ld\n", queued, timeo);
+                if (timeo > 0 || timeo == MAX_SCHEDULE_TIMEOUT)
+                        continue;
+
+                ret = timeo;
+                if (ret == 0)
+                        ret = -ETIMEDOUT;
+                goto out;
+        }
+
+        /*
+         * By now we've committed to the send.  We reuse rds_send_worker()
+         * to retry sends in the rds thread if the transport asks us to.
+         */
+        rds_stats_inc(s_send_queued);
+
+        if (!test_bit(RDS_LL_SEND_FULL, &conn->c_flags))
+                rds_send_worker(&conn->c_send_w.work);
+
+        rds_message_put(rm);
+        return payload_len;
+
+out:
+        /* If the user included a RDMA_MAP cmsg, we allocated a MR on the fly.
+         * If the sendmsg goes through, we keep the MR. If it fails with EAGAIN
+         * or in any other way, we need to destroy the MR again */
+        if (allocated_mr)
+                rds_rdma_unuse(rs, rds_rdma_cookie_key(rm->m_rdma_cookie), 1);
+
+        if (rm)
+                rds_message_put(rm);
+        return ret;
+}
+
+/*
+ * Reply to a ping packet.
+ */
+int
+rds_send_pong(struct rds_connection *conn, __be16 dport)
+{
+        struct rds_message *rm;
+        unsigned long flags;
+        int ret = 0;
+
+        rm = rds_message_alloc(0, GFP_ATOMIC);
+        if (rm == NULL) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        rm->m_daddr = conn->c_faddr;
+
+        /* If the connection is down, trigger a connect. We may
+         * have scheduled a delayed reconnect however - in this case
+         * we should not interfere.
+         */
+        if (rds_conn_state(conn) == RDS_CONN_DOWN
+         && !test_and_set_bit(RDS_RECONNECT_PENDING, &conn->c_flags))
+                queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
+
+        ret = rds_cong_wait(conn->c_fcong, dport, 1, NULL);
+        if (ret)
+                goto out;
+
+        spin_lock_irqsave(&conn->c_lock, flags);
+        list_add_tail(&rm->m_conn_item, &conn->c_send_queue);
+        set_bit(RDS_MSG_ON_CONN, &rm->m_flags);
+        rds_message_addref(rm);
+        rm->m_inc.i_conn = conn;
+
+        rds_message_populate_header(&rm->m_inc.i_hdr, 0, dport,
+                                    conn->c_next_tx_seq);
+        conn->c_next_tx_seq++;
+        spin_unlock_irqrestore(&conn->c_lock, flags);
+
+        rds_stats_inc(s_send_queued);
+        rds_stats_inc(s_send_pong);
+
+        queue_delayed_work(rds_wq, &conn->c_send_w, 0);
+        rds_message_put(rm);
+        return 0;
+
+out:
+        if (rm)
+                rds_message_put(rm);
+        return ret;
+}