xprtrdma: Avoid Send Queue wrapping

[linux-2.6-microblaze.git] / net / sunrpc / xprtrdma / verbs.c

// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
/*
 * Copyright (c) 2014-2017 Oracle.  All rights reserved.
 * Copyright (c) 2003-2007 Network Appliance, Inc. 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 BSD-type
 * 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.
 *
 *      Neither the name of the Network Appliance, Inc. nor the names of
 *      its contributors may be used to endorse or promote products
 *      derived from this software without specific prior written
 *      permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * verbs.c
 *
 * Encapsulates the major functions managing:
 *  o adapters
 *  o endpoints
 *  o connections
 *  o buffer memory
 */

#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/sunrpc/addr.h>
#include <linux/sunrpc/svc_rdma.h>
#include <linux/log2.h>

#include <asm-generic/barrier.h>
#include <asm/bitops.h>

#include <rdma/ib_cm.h>

#include "xprt_rdma.h"
#include <trace/events/rpcrdma.h>

/*
 * Globals/Macros
 */

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY        RPCDBG_TRANS
#endif

/*
 * internal functions
 */
static int rpcrdma_sendctxs_create(struct rpcrdma_xprt *r_xprt);
static void rpcrdma_sendctxs_destroy(struct rpcrdma_xprt *r_xprt);
static void rpcrdma_sendctx_put_locked(struct rpcrdma_xprt *r_xprt,
                                       struct rpcrdma_sendctx *sc);
static int rpcrdma_reqs_setup(struct rpcrdma_xprt *r_xprt);
static void rpcrdma_reqs_reset(struct rpcrdma_xprt *r_xprt);
static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep);
static void rpcrdma_reps_unmap(struct rpcrdma_xprt *r_xprt);
static void rpcrdma_mrs_create(struct rpcrdma_xprt *r_xprt);
static void rpcrdma_mrs_destroy(struct rpcrdma_xprt *r_xprt);
static void rpcrdma_ep_get(struct rpcrdma_ep *ep);
static int rpcrdma_ep_put(struct rpcrdma_ep *ep);
static struct rpcrdma_regbuf *
rpcrdma_regbuf_alloc(size_t size, enum dma_data_direction direction,
                     gfp_t flags);
static void rpcrdma_regbuf_dma_unmap(struct rpcrdma_regbuf *rb);
static void rpcrdma_regbuf_free(struct rpcrdma_regbuf *rb);

/* Wait for outstanding transport work to finish. ib_drain_qp
 * handles the drains in the wrong order for us, so open code
 * them here.
 */
static void rpcrdma_xprt_drain(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_ep *ep = r_xprt->rx_ep;
        struct rdma_cm_id *id = ep->re_id;

        /* Wait for rpcrdma_post_recvs() to leave its critical
         * section.
         */
        if (atomic_inc_return(&ep->re_receiving) > 1)
                wait_for_completion(&ep->re_done);

        /* Flush Receives, then wait for deferred Reply work
         * to complete.
         */
        ib_drain_rq(id->qp);

        /* Deferred Reply processing might have scheduled
         * local invalidations.
         */
        ib_drain_sq(id->qp);

        rpcrdma_ep_put(ep);
}

/**
 * rpcrdma_qp_event_handler - Handle one QP event (error notification)
 * @event: details of the event
 * @context: ep that owns QP where event occurred
 *
 * Called from the RDMA provider (device driver) possibly in an interrupt
 * context. The QP is always destroyed before the ID, so the ID will be
 * reliably available when this handler is invoked.
 */
static void rpcrdma_qp_event_handler(struct ib_event *event, void *context)
{
        struct rpcrdma_ep *ep = context;

        trace_xprtrdma_qp_event(ep, event);
}

/* Ensure xprt_force_disconnect() is invoked exactly once when a
 * connection is closed or lost. (The important thing is it needs
 * to be invoked "at least" once).
 */
static void rpcrdma_force_disconnect(struct rpcrdma_ep *ep)
{
        if (atomic_add_unless(&ep->re_force_disconnect, 1, 1))
                xprt_force_disconnect(ep->re_xprt);
}

/**
 * rpcrdma_flush_disconnect - Disconnect on flushed completion
 * @r_xprt: transport to disconnect
 * @wc: work completion entry
 *
 * Must be called in process context.
 */
void rpcrdma_flush_disconnect(struct rpcrdma_xprt *r_xprt, struct ib_wc *wc)
{
        if (wc->status != IB_WC_SUCCESS)
                rpcrdma_force_disconnect(r_xprt->rx_ep);
}

/**
 * rpcrdma_wc_send - Invoked by RDMA provider for each polled Send WC
 * @cq: completion queue
 * @wc: WCE for a completed Send WR
 *
 */
static void rpcrdma_wc_send(struct ib_cq *cq, struct ib_wc *wc)
{
        struct ib_cqe *cqe = wc->wr_cqe;
        struct rpcrdma_sendctx *sc =
                container_of(cqe, struct rpcrdma_sendctx, sc_cqe);
        struct rpcrdma_xprt *r_xprt = cq->cq_context;

        /* WARNING: Only wr_cqe and status are reliable at this point */
        trace_xprtrdma_wc_send(wc, &sc->sc_cid);
        rpcrdma_sendctx_put_locked(r_xprt, sc);
        rpcrdma_flush_disconnect(r_xprt, wc);
}

/**
 * rpcrdma_wc_receive - Invoked by RDMA provider for each polled Receive WC
 * @cq: completion queue
 * @wc: WCE for a completed Receive WR
 *
 */
static void rpcrdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc)
{
        struct ib_cqe *cqe = wc->wr_cqe;
        struct rpcrdma_rep *rep = container_of(cqe, struct rpcrdma_rep,
                                               rr_cqe);
        struct rpcrdma_xprt *r_xprt = cq->cq_context;

        /* WARNING: Only wr_cqe and status are reliable at this point */
        trace_xprtrdma_wc_receive(wc, &rep->rr_cid);
        --r_xprt->rx_ep->re_receive_count;
        if (wc->status != IB_WC_SUCCESS)
                goto out_flushed;

        /* status == SUCCESS means all fields in wc are trustworthy */
        rpcrdma_set_xdrlen(&rep->rr_hdrbuf, wc->byte_len);
        rep->rr_wc_flags = wc->wc_flags;
        rep->rr_inv_rkey = wc->ex.invalidate_rkey;

        ib_dma_sync_single_for_cpu(rdmab_device(rep->rr_rdmabuf),
                                   rdmab_addr(rep->rr_rdmabuf),
                                   wc->byte_len, DMA_FROM_DEVICE);

        rpcrdma_reply_handler(rep);
        return;

out_flushed:
        rpcrdma_flush_disconnect(r_xprt, wc);
        rpcrdma_rep_put(&r_xprt->rx_buf, rep);
}

static void rpcrdma_update_cm_private(struct rpcrdma_ep *ep,
                                      struct rdma_conn_param *param)
{
        const struct rpcrdma_connect_private *pmsg = param->private_data;
        unsigned int rsize, wsize;

        /* Default settings for RPC-over-RDMA Version One */
        ep->re_implicit_roundup = xprt_rdma_pad_optimize;
        rsize = RPCRDMA_V1_DEF_INLINE_SIZE;
        wsize = RPCRDMA_V1_DEF_INLINE_SIZE;

        if (pmsg &&
            pmsg->cp_magic == rpcrdma_cmp_magic &&
            pmsg->cp_version == RPCRDMA_CMP_VERSION) {
                ep->re_implicit_roundup = true;
                rsize = rpcrdma_decode_buffer_size(pmsg->cp_send_size);
                wsize = rpcrdma_decode_buffer_size(pmsg->cp_recv_size);
        }

        if (rsize < ep->re_inline_recv)
                ep->re_inline_recv = rsize;
        if (wsize < ep->re_inline_send)
                ep->re_inline_send = wsize;

        rpcrdma_set_max_header_sizes(ep);
}

/**
 * rpcrdma_cm_event_handler - Handle RDMA CM events
 * @id: rdma_cm_id on which an event has occurred
 * @event: details of the event
 *
 * Called with @id's mutex held. Returns 1 if caller should
 * destroy @id, otherwise 0.
 */
static int
rpcrdma_cm_event_handler(struct rdma_cm_id *id, struct rdma_cm_event *event)
{
        struct sockaddr *sap = (struct sockaddr *)&id->route.addr.dst_addr;
        struct rpcrdma_ep *ep = id->context;

        might_sleep();

        switch (event->event) {
        case RDMA_CM_EVENT_ADDR_RESOLVED:
        case RDMA_CM_EVENT_ROUTE_RESOLVED:
                ep->re_async_rc = 0;
                complete(&ep->re_done);
                return 0;
        case RDMA_CM_EVENT_ADDR_ERROR:
                ep->re_async_rc = -EPROTO;
                complete(&ep->re_done);
                return 0;
        case RDMA_CM_EVENT_ROUTE_ERROR:
                ep->re_async_rc = -ENETUNREACH;
                complete(&ep->re_done);
                return 0;
        case RDMA_CM_EVENT_DEVICE_REMOVAL:
                pr_info("rpcrdma: removing device %s for %pISpc\n",
                        ep->re_id->device->name, sap);
                fallthrough;
        case RDMA_CM_EVENT_ADDR_CHANGE:
                ep->re_connect_status = -ENODEV;
                goto disconnected;
        case RDMA_CM_EVENT_ESTABLISHED:
                rpcrdma_ep_get(ep);
                ep->re_connect_status = 1;
                rpcrdma_update_cm_private(ep, &event->param.conn);
                trace_xprtrdma_inline_thresh(ep);
                wake_up_all(&ep->re_connect_wait);
                break;
        case RDMA_CM_EVENT_CONNECT_ERROR:
                ep->re_connect_status = -ENOTCONN;
                goto wake_connect_worker;
        case RDMA_CM_EVENT_UNREACHABLE:
                ep->re_connect_status = -ENETUNREACH;
                goto wake_connect_worker;
        case RDMA_CM_EVENT_REJECTED:
                dprintk("rpcrdma: connection to %pISpc rejected: %s\n",
                        sap, rdma_reject_msg(id, event->status));
                ep->re_connect_status = -ECONNREFUSED;
                if (event->status == IB_CM_REJ_STALE_CONN)
                        ep->re_connect_status = -ENOTCONN;
wake_connect_worker:
                wake_up_all(&ep->re_connect_wait);
                return 0;
        case RDMA_CM_EVENT_DISCONNECTED:
                ep->re_connect_status = -ECONNABORTED;
disconnected:
                rpcrdma_force_disconnect(ep);
                return rpcrdma_ep_put(ep);
        default:
                break;
        }

        dprintk("RPC:       %s: %pISpc on %s/frwr: %s\n", __func__, sap,
                ep->re_id->device->name, rdma_event_msg(event->event));
        return 0;
}

static struct rdma_cm_id *rpcrdma_create_id(struct rpcrdma_xprt *r_xprt,
                                            struct rpcrdma_ep *ep)
{
        unsigned long wtimeout = msecs_to_jiffies(RDMA_RESOLVE_TIMEOUT) + 1;
        struct rpc_xprt *xprt = &r_xprt->rx_xprt;
        struct rdma_cm_id *id;
        int rc;

        init_completion(&ep->re_done);

        id = rdma_create_id(xprt->xprt_net, rpcrdma_cm_event_handler, ep,
                            RDMA_PS_TCP, IB_QPT_RC);
        if (IS_ERR(id))
                return id;

        ep->re_async_rc = -ETIMEDOUT;
        rc = rdma_resolve_addr(id, NULL, (struct sockaddr *)&xprt->addr,
                               RDMA_RESOLVE_TIMEOUT);
        if (rc)
                goto out;
        rc = wait_for_completion_interruptible_timeout(&ep->re_done, wtimeout);
        if (rc < 0)
                goto out;

        rc = ep->re_async_rc;
        if (rc)
                goto out;

        ep->re_async_rc = -ETIMEDOUT;
        rc = rdma_resolve_route(id, RDMA_RESOLVE_TIMEOUT);
        if (rc)
                goto out;
        rc = wait_for_completion_interruptible_timeout(&ep->re_done, wtimeout);
        if (rc < 0)
                goto out;
        rc = ep->re_async_rc;
        if (rc)
                goto out;

        return id;

out:
        rdma_destroy_id(id);
        return ERR_PTR(rc);
}

static void rpcrdma_ep_destroy(struct kref *kref)
{
        struct rpcrdma_ep *ep = container_of(kref, struct rpcrdma_ep, re_kref);

        if (ep->re_id->qp) {
                rdma_destroy_qp(ep->re_id);
                ep->re_id->qp = NULL;
        }

        if (ep->re_attr.recv_cq)
                ib_free_cq(ep->re_attr.recv_cq);
        ep->re_attr.recv_cq = NULL;
        if (ep->re_attr.send_cq)
                ib_free_cq(ep->re_attr.send_cq);
        ep->re_attr.send_cq = NULL;

        if (ep->re_pd)
                ib_dealloc_pd(ep->re_pd);
        ep->re_pd = NULL;

        kfree(ep);
        module_put(THIS_MODULE);
}

static noinline void rpcrdma_ep_get(struct rpcrdma_ep *ep)
{
        kref_get(&ep->re_kref);
}

/* Returns:
 *     %0 if @ep still has a positive kref count, or
 *     %1 if @ep was destroyed successfully.
 */
static noinline int rpcrdma_ep_put(struct rpcrdma_ep *ep)
{
        return kref_put(&ep->re_kref, rpcrdma_ep_destroy);
}

static int rpcrdma_ep_create(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_connect_private *pmsg;
        struct ib_device *device;
        struct rdma_cm_id *id;
        struct rpcrdma_ep *ep;
        int rc;

        ep = kzalloc(sizeof(*ep), GFP_NOFS);
        if (!ep)
                return -ENOTCONN;
        ep->re_xprt = &r_xprt->rx_xprt;
        kref_init(&ep->re_kref);

        id = rpcrdma_create_id(r_xprt, ep);
        if (IS_ERR(id)) {
                kfree(ep);
                return PTR_ERR(id);
        }
        __module_get(THIS_MODULE);
        device = id->device;
        ep->re_id = id;
        reinit_completion(&ep->re_done);

        ep->re_max_requests = r_xprt->rx_xprt.max_reqs;
        ep->re_inline_send = xprt_rdma_max_inline_write;
        ep->re_inline_recv = xprt_rdma_max_inline_read;
        rc = frwr_query_device(ep, device);
        if (rc)
                goto out_destroy;

        r_xprt->rx_buf.rb_max_requests = cpu_to_be32(ep->re_max_requests);

        ep->re_attr.event_handler = rpcrdma_qp_event_handler;
        ep->re_attr.qp_context = ep;
        ep->re_attr.srq = NULL;
        ep->re_attr.cap.max_inline_data = 0;
        ep->re_attr.sq_sig_type = IB_SIGNAL_REQ_WR;
        ep->re_attr.qp_type = IB_QPT_RC;
        ep->re_attr.port_num = ~0;

        dprintk("RPC:       %s: requested max: dtos: send %d recv %d; "
                "iovs: send %d recv %d\n",
                __func__,
                ep->re_attr.cap.max_send_wr,
                ep->re_attr.cap.max_recv_wr,
                ep->re_attr.cap.max_send_sge,
                ep->re_attr.cap.max_recv_sge);

        ep->re_send_batch = ep->re_max_requests >> 3;
        ep->re_send_count = ep->re_send_batch;
        init_waitqueue_head(&ep->re_connect_wait);

        ep->re_attr.send_cq = ib_alloc_cq_any(device, r_xprt,
                                              ep->re_attr.cap.max_send_wr,
                                              IB_POLL_WORKQUEUE);
        if (IS_ERR(ep->re_attr.send_cq)) {
                rc = PTR_ERR(ep->re_attr.send_cq);
                goto out_destroy;
        }

        ep->re_attr.recv_cq = ib_alloc_cq_any(device, r_xprt,
                                              ep->re_attr.cap.max_recv_wr,
                                              IB_POLL_WORKQUEUE);
        if (IS_ERR(ep->re_attr.recv_cq)) {
                rc = PTR_ERR(ep->re_attr.recv_cq);
                goto out_destroy;
        }
        ep->re_receive_count = 0;

        /* Initialize cma parameters */
        memset(&ep->re_remote_cma, 0, sizeof(ep->re_remote_cma));

        /* Prepare RDMA-CM private message */
        pmsg = &ep->re_cm_private;
        pmsg->cp_magic = rpcrdma_cmp_magic;
        pmsg->cp_version = RPCRDMA_CMP_VERSION;
        pmsg->cp_flags |= RPCRDMA_CMP_F_SND_W_INV_OK;
        pmsg->cp_send_size = rpcrdma_encode_buffer_size(ep->re_inline_send);
        pmsg->cp_recv_size = rpcrdma_encode_buffer_size(ep->re_inline_recv);
        ep->re_remote_cma.private_data = pmsg;
        ep->re_remote_cma.private_data_len = sizeof(*pmsg);

        /* Client offers RDMA Read but does not initiate */
        ep->re_remote_cma.initiator_depth = 0;
        ep->re_remote_cma.responder_resources =
                min_t(int, U8_MAX, device->attrs.max_qp_rd_atom);

        /* Limit transport retries so client can detect server
         * GID changes quickly. RPC layer handles re-establishing
         * transport connection and retransmission.
         */
        ep->re_remote_cma.retry_count = 6;

        /* RPC-over-RDMA handles its own flow control. In addition,
         * make all RNR NAKs visible so we know that RPC-over-RDMA
         * flow control is working correctly (no NAKs should be seen).
         */
        ep->re_remote_cma.flow_control = 0;
        ep->re_remote_cma.rnr_retry_count = 0;

        ep->re_pd = ib_alloc_pd(device, 0);
        if (IS_ERR(ep->re_pd)) {
                rc = PTR_ERR(ep->re_pd);
                goto out_destroy;
        }

        rc = rdma_create_qp(id, ep->re_pd, &ep->re_attr);
        if (rc)
                goto out_destroy;

        r_xprt->rx_ep = ep;
        return 0;

out_destroy:
        rpcrdma_ep_put(ep);
        rdma_destroy_id(id);
        return rc;
}

/**
 * rpcrdma_xprt_connect - Connect an unconnected transport
 * @r_xprt: controlling transport instance
 *
 * Returns 0 on success or a negative errno.
 */
int rpcrdma_xprt_connect(struct rpcrdma_xprt *r_xprt)
{
        struct rpc_xprt *xprt = &r_xprt->rx_xprt;
        struct rpcrdma_ep *ep;
        int rc;

        rc = rpcrdma_ep_create(r_xprt);
        if (rc)
                return rc;
        ep = r_xprt->rx_ep;

        xprt_clear_connected(xprt);
        rpcrdma_reset_cwnd(r_xprt);

        /* Bump the ep's reference count while there are
         * outstanding Receives.
         */
        rpcrdma_ep_get(ep);
        rpcrdma_post_recvs(r_xprt, 1, true);

        rc = rdma_connect(ep->re_id, &ep->re_remote_cma);
        if (rc)
                goto out;

        if (xprt->reestablish_timeout < RPCRDMA_INIT_REEST_TO)
                xprt->reestablish_timeout = RPCRDMA_INIT_REEST_TO;
        wait_event_interruptible(ep->re_connect_wait,
                                 ep->re_connect_status != 0);
        if (ep->re_connect_status <= 0) {
                rc = ep->re_connect_status;
                goto out;
        }

        rc = rpcrdma_sendctxs_create(r_xprt);
        if (rc) {
                rc = -ENOTCONN;
                goto out;
        }

        rc = rpcrdma_reqs_setup(r_xprt);
        if (rc) {
                rc = -ENOTCONN;
                goto out;
        }
        rpcrdma_mrs_create(r_xprt);

out:
        trace_xprtrdma_connect(r_xprt, rc);
        return rc;
}

/**
 * rpcrdma_xprt_disconnect - Disconnect underlying transport
 * @r_xprt: controlling transport instance
 *
 * Caller serializes. Either the transport send lock is held,
 * or we're being called to destroy the transport.
 *
 * On return, @r_xprt is completely divested of all hardware
 * resources and prepared for the next ->connect operation.
 */
void rpcrdma_xprt_disconnect(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_ep *ep = r_xprt->rx_ep;
        struct rdma_cm_id *id;
        int rc;

        if (!ep)
                return;

        id = ep->re_id;
        rc = rdma_disconnect(id);
        trace_xprtrdma_disconnect(r_xprt, rc);

        rpcrdma_xprt_drain(r_xprt);
        rpcrdma_reps_unmap(r_xprt);
        rpcrdma_reqs_reset(r_xprt);
        rpcrdma_mrs_destroy(r_xprt);
        rpcrdma_sendctxs_destroy(r_xprt);

        if (rpcrdma_ep_put(ep))
                rdma_destroy_id(id);

        r_xprt->rx_ep = NULL;
}

/* Fixed-size circular FIFO queue. This implementation is wait-free and
 * lock-free.
 *
 * Consumer is the code path that posts Sends. This path dequeues a
 * sendctx for use by a Send operation. Multiple consumer threads
 * are serialized by the RPC transport lock, which allows only one
 * ->send_request call at a time.
 *
 * Producer is the code path that handles Send completions. This path
 * enqueues a sendctx that has been completed. Multiple producer
 * threads are serialized by the ib_poll_cq() function.
 */

/* rpcrdma_sendctxs_destroy() assumes caller has already quiesced
 * queue activity, and rpcrdma_xprt_drain has flushed all remaining
 * Send requests.
 */
static void rpcrdma_sendctxs_destroy(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        unsigned long i;

        if (!buf->rb_sc_ctxs)
                return;
        for (i = 0; i <= buf->rb_sc_last; i++)
                kfree(buf->rb_sc_ctxs[i]);
        kfree(buf->rb_sc_ctxs);
        buf->rb_sc_ctxs = NULL;
}

static struct rpcrdma_sendctx *rpcrdma_sendctx_create(struct rpcrdma_ep *ep)
{
        struct rpcrdma_sendctx *sc;

        sc = kzalloc(struct_size(sc, sc_sges, ep->re_attr.cap.max_send_sge),
                     GFP_KERNEL);
        if (!sc)
                return NULL;

        sc->sc_cqe.done = rpcrdma_wc_send;
        sc->sc_cid.ci_queue_id = ep->re_attr.send_cq->res.id;
        sc->sc_cid.ci_completion_id =
                atomic_inc_return(&ep->re_completion_ids);
        return sc;
}

static int rpcrdma_sendctxs_create(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_sendctx *sc;
        unsigned long i;

        /* Maximum number of concurrent outstanding Send WRs. Capping
         * the circular queue size stops Send Queue overflow by causing
         * the ->send_request call to fail temporarily before too many
         * Sends are posted.
         */
        i = r_xprt->rx_ep->re_max_requests + RPCRDMA_MAX_BC_REQUESTS;
        buf->rb_sc_ctxs = kcalloc(i, sizeof(sc), GFP_KERNEL);
        if (!buf->rb_sc_ctxs)
                return -ENOMEM;

        buf->rb_sc_last = i - 1;
        for (i = 0; i <= buf->rb_sc_last; i++) {
                sc = rpcrdma_sendctx_create(r_xprt->rx_ep);
                if (!sc)
                        return -ENOMEM;

                buf->rb_sc_ctxs[i] = sc;
        }

        buf->rb_sc_head = 0;
        buf->rb_sc_tail = 0;
        return 0;
}

/* The sendctx queue is not guaranteed to have a size that is a
 * power of two, thus the helpers in circ_buf.h cannot be used.
 * The other option is to use modulus (%), which can be expensive.
 */
static unsigned long rpcrdma_sendctx_next(struct rpcrdma_buffer *buf,
                                          unsigned long item)
{
        return likely(item < buf->rb_sc_last) ? item + 1 : 0;
}

/**
 * rpcrdma_sendctx_get_locked - Acquire a send context
 * @r_xprt: controlling transport instance
 *
 * Returns pointer to a free send completion context; or NULL if
 * the queue is empty.
 *
 * Usage: Called to acquire an SGE array before preparing a Send WR.
 *
 * The caller serializes calls to this function (per transport), and
 * provides an effective memory barrier that flushes the new value
 * of rb_sc_head.
 */
struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_sendctx *sc;
        unsigned long next_head;

        next_head = rpcrdma_sendctx_next(buf, buf->rb_sc_head);

        if (next_head == READ_ONCE(buf->rb_sc_tail))
                goto out_emptyq;

        /* ORDER: item must be accessed _before_ head is updated */
        sc = buf->rb_sc_ctxs[next_head];

        /* Releasing the lock in the caller acts as a memory
         * barrier that flushes rb_sc_head.
         */
        buf->rb_sc_head = next_head;

        return sc;

out_emptyq:
        /* The queue is "empty" if there have not been enough Send
         * completions recently. This is a sign the Send Queue is
         * backing up. Cause the caller to pause and try again.
         */
        xprt_wait_for_buffer_space(&r_xprt->rx_xprt);
        r_xprt->rx_stats.empty_sendctx_q++;
        return NULL;
}

/**
 * rpcrdma_sendctx_put_locked - Release a send context
 * @r_xprt: controlling transport instance
 * @sc: send context to release
 *
 * Usage: Called from Send completion to return a sendctxt
 * to the queue.
 *
 * The caller serializes calls to this function (per transport).
 */
static void rpcrdma_sendctx_put_locked(struct rpcrdma_xprt *r_xprt,
                                       struct rpcrdma_sendctx *sc)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        unsigned long next_tail;

        /* Unmap SGEs of previously completed but unsignaled
         * Sends by walking up the queue until @sc is found.
         */
        next_tail = buf->rb_sc_tail;
        do {
                next_tail = rpcrdma_sendctx_next(buf, next_tail);

                /* ORDER: item must be accessed _before_ tail is updated */
                rpcrdma_sendctx_unmap(buf->rb_sc_ctxs[next_tail]);

        } while (buf->rb_sc_ctxs[next_tail] != sc);

        /* Paired with READ_ONCE */
        smp_store_release(&buf->rb_sc_tail, next_tail);

        xprt_write_space(&r_xprt->rx_xprt);
}

static void
rpcrdma_mrs_create(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_ep *ep = r_xprt->rx_ep;
        unsigned int count;

        for (count = 0; count < ep->re_max_rdma_segs; count++) {
                struct rpcrdma_mr *mr;
                int rc;

                mr = kzalloc(sizeof(*mr), GFP_NOFS);
                if (!mr)
                        break;

                rc = frwr_mr_init(r_xprt, mr);
                if (rc) {
                        kfree(mr);
                        break;
                }

                spin_lock(&buf->rb_lock);
                rpcrdma_mr_push(mr, &buf->rb_mrs);
                list_add(&mr->mr_all, &buf->rb_all_mrs);
                spin_unlock(&buf->rb_lock);
        }

        r_xprt->rx_stats.mrs_allocated += count;
        trace_xprtrdma_createmrs(r_xprt, count);
}

static void
rpcrdma_mr_refresh_worker(struct work_struct *work)
{
        struct rpcrdma_buffer *buf = container_of(work, struct rpcrdma_buffer,
                                                  rb_refresh_worker);
        struct rpcrdma_xprt *r_xprt = container_of(buf, struct rpcrdma_xprt,
                                                   rx_buf);

        rpcrdma_mrs_create(r_xprt);
        xprt_write_space(&r_xprt->rx_xprt);
}

/**
 * rpcrdma_mrs_refresh - Wake the MR refresh worker
 * @r_xprt: controlling transport instance
 *
 */
void rpcrdma_mrs_refresh(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_ep *ep = r_xprt->rx_ep;

        /* If there is no underlying connection, it's no use
         * to wake the refresh worker.
         */
        if (ep->re_connect_status == 1) {
                /* The work is scheduled on a WQ_MEM_RECLAIM
                 * workqueue in order to prevent MR allocation
                 * from recursing into NFS during direct reclaim.
                 */
                queue_work(xprtiod_workqueue, &buf->rb_refresh_worker);
        }
}

/**
 * rpcrdma_req_create - Allocate an rpcrdma_req object
 * @r_xprt: controlling r_xprt
 * @size: initial size, in bytes, of send and receive buffers
 * @flags: GFP flags passed to memory allocators
 *
 * Returns an allocated and fully initialized rpcrdma_req or NULL.
 */
struct rpcrdma_req *rpcrdma_req_create(struct rpcrdma_xprt *r_xprt, size_t size,
                                       gfp_t flags)
{
        struct rpcrdma_buffer *buffer = &r_xprt->rx_buf;
        struct rpcrdma_req *req;

        req = kzalloc(sizeof(*req), flags);
        if (req == NULL)
                goto out1;

        req->rl_sendbuf = rpcrdma_regbuf_alloc(size, DMA_TO_DEVICE, flags);
        if (!req->rl_sendbuf)
                goto out2;

        req->rl_recvbuf = rpcrdma_regbuf_alloc(size, DMA_NONE, flags);
        if (!req->rl_recvbuf)
                goto out3;

        INIT_LIST_HEAD(&req->rl_free_mrs);
        INIT_LIST_HEAD(&req->rl_registered);
        spin_lock(&buffer->rb_lock);
        list_add(&req->rl_all, &buffer->rb_allreqs);
        spin_unlock(&buffer->rb_lock);
        return req;

out3:
        kfree(req->rl_sendbuf);
out2:
        kfree(req);
out1:
        return NULL;
}

/**
 * rpcrdma_req_setup - Per-connection instance setup of an rpcrdma_req object
 * @r_xprt: controlling transport instance
 * @req: rpcrdma_req object to set up
 *
 * Returns zero on success, and a negative errno on failure.
 */
int rpcrdma_req_setup(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
{
        struct rpcrdma_regbuf *rb;
        size_t maxhdrsize;

        /* Compute maximum header buffer size in bytes */
        maxhdrsize = rpcrdma_fixed_maxsz + 3 +
                     r_xprt->rx_ep->re_max_rdma_segs * rpcrdma_readchunk_maxsz;
        maxhdrsize *= sizeof(__be32);
        rb = rpcrdma_regbuf_alloc(__roundup_pow_of_two(maxhdrsize),
                                  DMA_TO_DEVICE, GFP_KERNEL);
        if (!rb)
                goto out;

        if (!__rpcrdma_regbuf_dma_map(r_xprt, rb))
                goto out_free;

        req->rl_rdmabuf = rb;
        xdr_buf_init(&req->rl_hdrbuf, rdmab_data(rb), rdmab_length(rb));
        return 0;

out_free:
        rpcrdma_regbuf_free(rb);
out:
        return -ENOMEM;
}

/* ASSUMPTION: the rb_allreqs list is stable for the duration,
 * and thus can be walked without holding rb_lock. Eg. the
 * caller is holding the transport send lock to exclude
 * device removal or disconnection.
 */
static int rpcrdma_reqs_setup(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_req *req;
        int rc;

        list_for_each_entry(req, &buf->rb_allreqs, rl_all) {
                rc = rpcrdma_req_setup(r_xprt, req);
                if (rc)
                        return rc;
        }
        return 0;
}

static void rpcrdma_req_reset(struct rpcrdma_req *req)
{
        /* Credits are valid for only one connection */
        req->rl_slot.rq_cong = 0;

        rpcrdma_regbuf_free(req->rl_rdmabuf);
        req->rl_rdmabuf = NULL;

        rpcrdma_regbuf_dma_unmap(req->rl_sendbuf);
        rpcrdma_regbuf_dma_unmap(req->rl_recvbuf);

        frwr_reset(req);
}

/* ASSUMPTION: the rb_allreqs list is stable for the duration,
 * and thus can be walked without holding rb_lock. Eg. the
 * caller is holding the transport send lock to exclude
 * device removal or disconnection.
 */
static void rpcrdma_reqs_reset(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_req *req;

        list_for_each_entry(req, &buf->rb_allreqs, rl_all)
                rpcrdma_req_reset(req);
}

static noinline
struct rpcrdma_rep *rpcrdma_rep_create(struct rpcrdma_xprt *r_xprt,
                                       bool temp)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_rep *rep;

        rep = kzalloc(sizeof(*rep), GFP_KERNEL);
        if (rep == NULL)
                goto out;

        rep->rr_rdmabuf = rpcrdma_regbuf_alloc(r_xprt->rx_ep->re_inline_recv,
                                               DMA_FROM_DEVICE, GFP_KERNEL);
        if (!rep->rr_rdmabuf)
                goto out_free;

        if (!rpcrdma_regbuf_dma_map(r_xprt, rep->rr_rdmabuf))
                goto out_free_regbuf;

        rep->rr_cid.ci_completion_id =
                atomic_inc_return(&r_xprt->rx_ep->re_completion_ids);

        xdr_buf_init(&rep->rr_hdrbuf, rdmab_data(rep->rr_rdmabuf),
                     rdmab_length(rep->rr_rdmabuf));
        rep->rr_cqe.done = rpcrdma_wc_receive;
        rep->rr_rxprt = r_xprt;
        rep->rr_recv_wr.next = NULL;
        rep->rr_recv_wr.wr_cqe = &rep->rr_cqe;
        rep->rr_recv_wr.sg_list = &rep->rr_rdmabuf->rg_iov;
        rep->rr_recv_wr.num_sge = 1;
        rep->rr_temp = temp;

        spin_lock(&buf->rb_lock);
        list_add(&rep->rr_all, &buf->rb_all_reps);
        spin_unlock(&buf->rb_lock);
        return rep;

out_free_regbuf:
        rpcrdma_regbuf_free(rep->rr_rdmabuf);
out_free:
        kfree(rep);
out:
        return NULL;
}

static void rpcrdma_rep_free(struct rpcrdma_rep *rep)
{
        rpcrdma_regbuf_free(rep->rr_rdmabuf);
        kfree(rep);
}

static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep)
{
        struct rpcrdma_buffer *buf = &rep->rr_rxprt->rx_buf;

        spin_lock(&buf->rb_lock);
        list_del(&rep->rr_all);
        spin_unlock(&buf->rb_lock);

        rpcrdma_rep_free(rep);
}

static struct rpcrdma_rep *rpcrdma_rep_get_locked(struct rpcrdma_buffer *buf)
{
        struct llist_node *node;

        /* Calls to llist_del_first are required to be serialized */
        node = llist_del_first(&buf->rb_free_reps);
        if (!node)
                return NULL;
        return llist_entry(node, struct rpcrdma_rep, rr_node);
}

/**
 * rpcrdma_rep_put - Release rpcrdma_rep back to free list
 * @buf: buffer pool
 * @rep: rep to release
 *
 */
void rpcrdma_rep_put(struct rpcrdma_buffer *buf, struct rpcrdma_rep *rep)
{
        llist_add(&rep->rr_node, &buf->rb_free_reps);
}

/* Caller must ensure the QP is quiescent (RQ is drained) before
 * invoking this function, to guarantee rb_all_reps is not
 * changing.
 */
static void rpcrdma_reps_unmap(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_rep *rep;

        list_for_each_entry(rep, &buf->rb_all_reps, rr_all) {
                rpcrdma_regbuf_dma_unmap(rep->rr_rdmabuf);
                rep->rr_temp = true;    /* Mark this rep for destruction */
        }
}

static void rpcrdma_reps_destroy(struct rpcrdma_buffer *buf)
{
        struct rpcrdma_rep *rep;

        spin_lock(&buf->rb_lock);
        while ((rep = list_first_entry_or_null(&buf->rb_all_reps,
                                               struct rpcrdma_rep,
                                               rr_all)) != NULL) {
                list_del(&rep->rr_all);
                spin_unlock(&buf->rb_lock);

                rpcrdma_rep_free(rep);

                spin_lock(&buf->rb_lock);
        }
        spin_unlock(&buf->rb_lock);
}

/**
 * rpcrdma_buffer_create - Create initial set of req/rep objects
 * @r_xprt: transport instance to (re)initialize
 *
 * Returns zero on success, otherwise a negative errno.
 */
int rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        int i, rc;

        buf->rb_bc_srv_max_requests = 0;
        spin_lock_init(&buf->rb_lock);
        INIT_LIST_HEAD(&buf->rb_mrs);
        INIT_LIST_HEAD(&buf->rb_all_mrs);
        INIT_WORK(&buf->rb_refresh_worker, rpcrdma_mr_refresh_worker);

        INIT_LIST_HEAD(&buf->rb_send_bufs);
        INIT_LIST_HEAD(&buf->rb_allreqs);
        INIT_LIST_HEAD(&buf->rb_all_reps);

        rc = -ENOMEM;
        for (i = 0; i < r_xprt->rx_xprt.max_reqs; i++) {
                struct rpcrdma_req *req;

                req = rpcrdma_req_create(r_xprt, RPCRDMA_V1_DEF_INLINE_SIZE * 2,
                                         GFP_KERNEL);
                if (!req)
                        goto out;
                list_add(&req->rl_list, &buf->rb_send_bufs);
        }

        init_llist_head(&buf->rb_free_reps);

        return 0;
out:
        rpcrdma_buffer_destroy(buf);
        return rc;
}

/**
 * rpcrdma_req_destroy - Destroy an rpcrdma_req object
 * @req: unused object to be destroyed
 *
 * Relies on caller holding the transport send lock to protect
 * removing req->rl_all from buf->rb_all_reqs safely.
 */
void rpcrdma_req_destroy(struct rpcrdma_req *req)
{
        struct rpcrdma_mr *mr;

        list_del(&req->rl_all);

        while ((mr = rpcrdma_mr_pop(&req->rl_free_mrs))) {
                struct rpcrdma_buffer *buf = &mr->mr_xprt->rx_buf;

                spin_lock(&buf->rb_lock);
                list_del(&mr->mr_all);
                spin_unlock(&buf->rb_lock);

                frwr_mr_release(mr);
        }

        rpcrdma_regbuf_free(req->rl_recvbuf);
        rpcrdma_regbuf_free(req->rl_sendbuf);
        rpcrdma_regbuf_free(req->rl_rdmabuf);
        kfree(req);
}

/**
 * rpcrdma_mrs_destroy - Release all of a transport's MRs
 * @r_xprt: controlling transport instance
 *
 * Relies on caller holding the transport send lock to protect
 * removing mr->mr_list from req->rl_free_mrs safely.
 */
static void rpcrdma_mrs_destroy(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_mr *mr;

        cancel_work_sync(&buf->rb_refresh_worker);

        spin_lock(&buf->rb_lock);
        while ((mr = list_first_entry_or_null(&buf->rb_all_mrs,
                                              struct rpcrdma_mr,
                                              mr_all)) != NULL) {
                list_del(&mr->mr_list);
                list_del(&mr->mr_all);
                spin_unlock(&buf->rb_lock);

                frwr_mr_release(mr);

                spin_lock(&buf->rb_lock);
        }
        spin_unlock(&buf->rb_lock);
}

/**
 * rpcrdma_buffer_destroy - Release all hw resources
 * @buf: root control block for resources
 *
 * ORDERING: relies on a prior rpcrdma_xprt_drain :
 * - No more Send or Receive completions can occur
 * - All MRs, reps, and reqs are returned to their free lists
 */
void
rpcrdma_buffer_destroy(struct rpcrdma_buffer *buf)
{
        rpcrdma_reps_destroy(buf);

        while (!list_empty(&buf->rb_send_bufs)) {
                struct rpcrdma_req *req;

                req = list_first_entry(&buf->rb_send_bufs,
                                       struct rpcrdma_req, rl_list);
                list_del(&req->rl_list);
                rpcrdma_req_destroy(req);
        }
}

/**
 * rpcrdma_mr_get - Allocate an rpcrdma_mr object
 * @r_xprt: controlling transport
 *
 * Returns an initialized rpcrdma_mr or NULL if no free
 * rpcrdma_mr objects are available.
 */
struct rpcrdma_mr *
rpcrdma_mr_get(struct rpcrdma_xprt *r_xprt)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_mr *mr;

        spin_lock(&buf->rb_lock);
        mr = rpcrdma_mr_pop(&buf->rb_mrs);
        spin_unlock(&buf->rb_lock);
        return mr;
}

/**
 * rpcrdma_buffer_get - Get a request buffer
 * @buffers: Buffer pool from which to obtain a buffer
 *
 * Returns a fresh rpcrdma_req, or NULL if none are available.
 */
struct rpcrdma_req *
rpcrdma_buffer_get(struct rpcrdma_buffer *buffers)
{
        struct rpcrdma_req *req;

        spin_lock(&buffers->rb_lock);
        req = list_first_entry_or_null(&buffers->rb_send_bufs,
                                       struct rpcrdma_req, rl_list);
        if (req)
                list_del_init(&req->rl_list);
        spin_unlock(&buffers->rb_lock);
        return req;
}

/**
 * rpcrdma_buffer_put - Put request/reply buffers back into pool
 * @buffers: buffer pool
 * @req: object to return
 *
 */
void rpcrdma_buffer_put(struct rpcrdma_buffer *buffers, struct rpcrdma_req *req)
{
        if (req->rl_reply)
                rpcrdma_rep_put(buffers, req->rl_reply);
        req->rl_reply = NULL;

        spin_lock(&buffers->rb_lock);
        list_add(&req->rl_list, &buffers->rb_send_bufs);
        spin_unlock(&buffers->rb_lock);
}

/* Returns a pointer to a rpcrdma_regbuf object, or NULL.
 *
 * xprtrdma uses a regbuf for posting an outgoing RDMA SEND, or for
 * receiving the payload of RDMA RECV operations. During Long Calls
 * or Replies they may be registered externally via frwr_map.
 */
static struct rpcrdma_regbuf *
rpcrdma_regbuf_alloc(size_t size, enum dma_data_direction direction,
                     gfp_t flags)
{
        struct rpcrdma_regbuf *rb;

        rb = kmalloc(sizeof(*rb), flags);
        if (!rb)
                return NULL;
        rb->rg_data = kmalloc(size, flags);
        if (!rb->rg_data) {
                kfree(rb);
                return NULL;
        }

        rb->rg_device = NULL;
        rb->rg_direction = direction;
        rb->rg_iov.length = size;
        return rb;
}

/**
 * rpcrdma_regbuf_realloc - re-allocate a SEND/RECV buffer
 * @rb: regbuf to reallocate
 * @size: size of buffer to be allocated, in bytes
 * @flags: GFP flags
 *
 * Returns true if reallocation was successful. If false is
 * returned, @rb is left untouched.
 */
bool rpcrdma_regbuf_realloc(struct rpcrdma_regbuf *rb, size_t size, gfp_t flags)
{
        void *buf;

        buf = kmalloc(size, flags);
        if (!buf)
                return false;

        rpcrdma_regbuf_dma_unmap(rb);
        kfree(rb->rg_data);

        rb->rg_data = buf;
        rb->rg_iov.length = size;
        return true;
}

/**
 * __rpcrdma_regbuf_dma_map - DMA-map a regbuf
 * @r_xprt: controlling transport instance
 * @rb: regbuf to be mapped
 *
 * Returns true if the buffer is now DMA mapped to @r_xprt's device
 */
bool __rpcrdma_regbuf_dma_map(struct rpcrdma_xprt *r_xprt,
                              struct rpcrdma_regbuf *rb)
{
        struct ib_device *device = r_xprt->rx_ep->re_id->device;

        if (rb->rg_direction == DMA_NONE)
                return false;

        rb->rg_iov.addr = ib_dma_map_single(device, rdmab_data(rb),
                                            rdmab_length(rb), rb->rg_direction);
        if (ib_dma_mapping_error(device, rdmab_addr(rb))) {
                trace_xprtrdma_dma_maperr(rdmab_addr(rb));
                return false;
        }

        rb->rg_device = device;
        rb->rg_iov.lkey = r_xprt->rx_ep->re_pd->local_dma_lkey;
        return true;
}

static void rpcrdma_regbuf_dma_unmap(struct rpcrdma_regbuf *rb)
{
        if (!rb)
                return;

        if (!rpcrdma_regbuf_is_mapped(rb))
                return;

        ib_dma_unmap_single(rb->rg_device, rdmab_addr(rb), rdmab_length(rb),
                            rb->rg_direction);
        rb->rg_device = NULL;
}

static void rpcrdma_regbuf_free(struct rpcrdma_regbuf *rb)
{
        rpcrdma_regbuf_dma_unmap(rb);
        if (rb)
                kfree(rb->rg_data);
        kfree(rb);
}

/**
 * rpcrdma_post_sends - Post WRs to a transport's Send Queue
 * @r_xprt: controlling transport instance
 * @req: rpcrdma_req containing the Send WR to post
 *
 * Returns 0 if the post was successful, otherwise -ENOTCONN
 * is returned.
 */
int rpcrdma_post_sends(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
{
        if (frwr_send(r_xprt, req))
                return -ENOTCONN;
        return 0;
}

/**
 * rpcrdma_post_recvs - Refill the Receive Queue
 * @r_xprt: controlling transport instance
 * @needed: current credit grant
 * @temp: mark Receive buffers to be deleted after one use
 *
 */
void rpcrdma_post_recvs(struct rpcrdma_xprt *r_xprt, int needed, bool temp)
{
        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
        struct rpcrdma_ep *ep = r_xprt->rx_ep;
        struct ib_recv_wr *wr, *bad_wr;
        struct rpcrdma_rep *rep;
        int count, rc;

        rc = 0;
        count = 0;

        if (likely(ep->re_receive_count > needed))
                goto out;
        needed -= ep->re_receive_count;
        if (!temp)
                needed += RPCRDMA_MAX_RECV_BATCH;

        if (atomic_inc_return(&ep->re_receiving) > 1)
                goto out;

        /* fast path: all needed reps can be found on the free list */
        wr = NULL;
        while (needed) {
                rep = rpcrdma_rep_get_locked(buf);
                if (rep && rep->rr_temp) {
                        rpcrdma_rep_destroy(rep);
                        continue;
                }
                if (!rep)
                        rep = rpcrdma_rep_create(r_xprt, temp);
                if (!rep)
                        break;

                rep->rr_cid.ci_queue_id = ep->re_attr.recv_cq->res.id;
                trace_xprtrdma_post_recv(rep);
                rep->rr_recv_wr.next = wr;
                wr = &rep->rr_recv_wr;
                --needed;
                ++count;
        }
        if (!wr)
                goto out;

        rc = ib_post_recv(ep->re_id->qp, wr,
                          (const struct ib_recv_wr **)&bad_wr);
        if (atomic_dec_return(&ep->re_receiving) > 0)
                complete(&ep->re_done);

out:
        trace_xprtrdma_post_recvs(r_xprt, count, rc);
        if (rc) {
                for (wr = bad_wr; wr;) {
                        struct rpcrdma_rep *rep;

                        rep = container_of(wr, struct rpcrdma_rep, rr_recv_wr);
                        wr = wr->next;
                        rpcrdma_rep_put(buf, rep);
                        --count;
                }
        }
        ep->re_receive_count += count;
        return;
}