// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * RDMA Transport Layer
 *
 * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
 * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
 * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
 */

#undef pr_fmt
#define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt

#include <linux/module.h>
#include <linux/rculist.h>
#include <linux/random.h>

#include "rtrs-clt.h"
#include "rtrs-log.h"

#define RTRS_CONNECT_TIMEOUT_MS 30000
/*
 * Wait a bit before trying to reconnect after a failure
 * in order to give server time to finish clean up which
 * leads to "false positives" failed reconnect attempts
 */
#define RTRS_RECONNECT_BACKOFF 1000
/*
 * Wait for additional random time between 0 and 8 seconds
 * before starting to reconnect to avoid clients reconnecting
 * all at once in case of a major network outage
 */
#define RTRS_RECONNECT_SEED 8

#define FIRST_CONN 0x01
/* limit to 128 * 4k = 512k max IO */
#define RTRS_MAX_SEGMENTS          128

MODULE_DESCRIPTION("RDMA Transport Client");
MODULE_LICENSE("GPL");

static const struct rtrs_rdma_dev_pd_ops dev_pd_ops;
static struct rtrs_rdma_dev_pd dev_pd = {
        .ops = &dev_pd_ops
};

static struct workqueue_struct *rtrs_wq;
static struct class *rtrs_clt_dev_class;

static inline bool rtrs_clt_is_connected(const struct rtrs_clt *clt)
{
        struct rtrs_clt_sess *sess;
        bool connected = false;

        rcu_read_lock();
        list_for_each_entry_rcu(sess, &clt->paths_list, s.entry)
                connected |= READ_ONCE(sess->state) == RTRS_CLT_CONNECTED;
        rcu_read_unlock();

        return connected;
}

static struct rtrs_permit *
__rtrs_get_permit(struct rtrs_clt *clt, enum rtrs_clt_con_type con_type)
{
        size_t max_depth = clt->queue_depth;
        struct rtrs_permit *permit;
        int bit;

        /*
         * Adapted from null_blk get_tag(). Callers from different cpus may
         * grab the same bit, since find_first_zero_bit is not atomic.
         * But then the test_and_set_bit_lock will fail for all the
         * callers but one, so that they will loop again.
         * This way an explicit spinlock is not required.
         */
        do {
                bit = find_first_zero_bit(clt->permits_map, max_depth);
                if (unlikely(bit >= max_depth))
                        return NULL;
        } while (unlikely(test_and_set_bit_lock(bit, clt->permits_map)));

        permit = get_permit(clt, bit);
        WARN_ON(permit->mem_id != bit);
        permit->cpu_id = raw_smp_processor_id();
        permit->con_type = con_type;

        return permit;
}

static inline void __rtrs_put_permit(struct rtrs_clt *clt,
                                      struct rtrs_permit *permit)
{
        clear_bit_unlock(permit->mem_id, clt->permits_map);
}

/**
 * rtrs_clt_get_permit() - allocates permit for future RDMA operation
 * @clt:        Current session
 * @con_type:   Type of connection to use with the permit
 * @can_wait:   Wait type
 *
 * Description:
 *    Allocates permit for the following RDMA operation.  Permit is used
 *    to preallocate all resources and to propagate memory pressure
 *    up earlier.
 *
 * Context:
 *    Can sleep if @wait == RTRS_PERMIT_WAIT
 */
struct rtrs_permit *rtrs_clt_get_permit(struct rtrs_clt *clt,
                                          enum rtrs_clt_con_type con_type,
                                          enum wait_type can_wait)
{
        struct rtrs_permit *permit;
        DEFINE_WAIT(wait);

        permit = __rtrs_get_permit(clt, con_type);
        if (likely(permit) || !can_wait)
                return permit;

        do {
                prepare_to_wait(&clt->permits_wait, &wait,
                                TASK_UNINTERRUPTIBLE);
                permit = __rtrs_get_permit(clt, con_type);
                if (likely(permit))
                        break;

                io_schedule();
        } while (1);

        finish_wait(&clt->permits_wait, &wait);

        return permit;
}
EXPORT_SYMBOL(rtrs_clt_get_permit);

/**
 * rtrs_clt_put_permit() - puts allocated permit
 * @clt:        Current session
 * @permit:     Permit to be freed
 *
 * Context:
 *    Does not matter
 */
void rtrs_clt_put_permit(struct rtrs_clt *clt, struct rtrs_permit *permit)
{
        if (WARN_ON(!test_bit(permit->mem_id, clt->permits_map)))
                return;

        __rtrs_put_permit(clt, permit);

        /*
         * rtrs_clt_get_permit() adds itself to the &clt->permits_wait list
         * before calling schedule(). So if rtrs_clt_get_permit() is sleeping
         * it must have added itself to &clt->permits_wait before
         * __rtrs_put_permit() finished.
         * Hence it is safe to guard wake_up() with a waitqueue_active() test.
         */
        if (waitqueue_active(&clt->permits_wait))
                wake_up(&clt->permits_wait);
}
EXPORT_SYMBOL(rtrs_clt_put_permit);

/**
 * rtrs_permit_to_clt_con() - returns RDMA connection pointer by the permit
 * @sess: client session pointer
 * @permit: permit for the allocation of the RDMA buffer
 * Note:
 *     IO connection starts from 1.
 *     0 connection is for user messages.
 */
static
struct rtrs_clt_con *rtrs_permit_to_clt_con(struct rtrs_clt_sess *sess,
                                            struct rtrs_permit *permit)
{
        int id = 0;

        if (likely(permit->con_type == RTRS_IO_CON))
                id = (permit->cpu_id % (sess->s.irq_con_num - 1)) + 1;

        return to_clt_con(sess->s.con[id]);
}

/**
 * rtrs_clt_change_state() - change the session state through session state
 * machine.
 *
 * @sess: client session to change the state of.
 * @new_state: state to change to.
 *
 * returns true if sess's state is changed to new state, otherwise return false.
 *
 * Locks:
 * state_wq lock must be hold.
 */
static bool rtrs_clt_change_state(struct rtrs_clt_sess *sess,
                                     enum rtrs_clt_state new_state)
{
        enum rtrs_clt_state old_state;
        bool changed = false;

        lockdep_assert_held(&sess->state_wq.lock);

        old_state = sess->state;
        switch (new_state) {
        case RTRS_CLT_CONNECTING:
                switch (old_state) {
                case RTRS_CLT_RECONNECTING:
                        changed = true;
                        fallthrough;
                default:
                        break;
                }
                break;
        case RTRS_CLT_RECONNECTING:
                switch (old_state) {
                case RTRS_CLT_CONNECTED:
                case RTRS_CLT_CONNECTING_ERR:
                case RTRS_CLT_CLOSED:
                        changed = true;
                        fallthrough;
                default:
                        break;
                }
                break;
        case RTRS_CLT_CONNECTED:
                switch (old_state) {
                case RTRS_CLT_CONNECTING:
                        changed = true;
                        fallthrough;
                default:
                        break;
                }
                break;
        case RTRS_CLT_CONNECTING_ERR:
                switch (old_state) {
                case RTRS_CLT_CONNECTING:
                        changed = true;
                        fallthrough;
                default:
                        break;
                }
                break;
        case RTRS_CLT_CLOSING:
                switch (old_state) {
                case RTRS_CLT_CONNECTING:
                case RTRS_CLT_CONNECTING_ERR:
                case RTRS_CLT_RECONNECTING:
                case RTRS_CLT_CONNECTED:
                        changed = true;
                        fallthrough;
                default:
                        break;
                }
                break;
        case RTRS_CLT_CLOSED:
                switch (old_state) {
                case RTRS_CLT_CLOSING:
                        changed = true;
                        fallthrough;
                default:
                        break;
                }
                break;
        case RTRS_CLT_DEAD:
                switch (old_state) {
                case RTRS_CLT_CLOSED:
                        changed = true;
                        fallthrough;
                default:
                        break;
                }
                break;
        default:
                break;
        }
        if (changed) {
                sess->state = new_state;
                wake_up_locked(&sess->state_wq);
        }

        return changed;
}

static bool rtrs_clt_change_state_from_to(struct rtrs_clt_sess *sess,
                                           enum rtrs_clt_state old_state,
                                           enum rtrs_clt_state new_state)
{
        bool changed = false;

        spin_lock_irq(&sess->state_wq.lock);
        if (sess->state == old_state)
                changed = rtrs_clt_change_state(sess, new_state);
        spin_unlock_irq(&sess->state_wq.lock);

        return changed;
}

static void rtrs_rdma_error_recovery(struct rtrs_clt_con *con)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);

        if (rtrs_clt_change_state_from_to(sess,
                                           RTRS_CLT_CONNECTED,
                                           RTRS_CLT_RECONNECTING)) {
                struct rtrs_clt *clt = sess->clt;
                unsigned int delay_ms;

                /*
                 * Normal scenario, reconnect if we were successfully connected
                 */
                delay_ms = clt->reconnect_delay_sec * 1000;
                queue_delayed_work(rtrs_wq, &sess->reconnect_dwork,
                                   msecs_to_jiffies(delay_ms +
                                                    prandom_u32() % RTRS_RECONNECT_SEED));
        } else {
                /*
                 * Error can happen just on establishing new connection,
                 * so notify waiter with error state, waiter is responsible
                 * for cleaning the rest and reconnect if needed.
                 */
                rtrs_clt_change_state_from_to(sess,
                                               RTRS_CLT_CONNECTING,
                                               RTRS_CLT_CONNECTING_ERR);
        }
}

static void rtrs_clt_fast_reg_done(struct ib_cq *cq, struct ib_wc *wc)
{
        struct rtrs_clt_con *con = to_clt_con(wc->qp->qp_context);

        if (unlikely(wc->status != IB_WC_SUCCESS)) {
                rtrs_err(con->c.sess, "Failed IB_WR_REG_MR: %s\n",
                          ib_wc_status_msg(wc->status));
                rtrs_rdma_error_recovery(con);
        }
}

static struct ib_cqe fast_reg_cqe = {
        .done = rtrs_clt_fast_reg_done
};

static void complete_rdma_req(struct rtrs_clt_io_req *req, int errno,
                              bool notify, bool can_wait);

static void rtrs_clt_inv_rkey_done(struct ib_cq *cq, struct ib_wc *wc)
{
        struct rtrs_clt_io_req *req =
                container_of(wc->wr_cqe, typeof(*req), inv_cqe);
        struct rtrs_clt_con *con = to_clt_con(wc->qp->qp_context);

        if (unlikely(wc->status != IB_WC_SUCCESS)) {
                rtrs_err(con->c.sess, "Failed IB_WR_LOCAL_INV: %s\n",
                          ib_wc_status_msg(wc->status));
                rtrs_rdma_error_recovery(con);
        }
        req->need_inv = false;
        if (likely(req->need_inv_comp))
                complete(&req->inv_comp);
        else
                /* Complete request from INV callback */
                complete_rdma_req(req, req->inv_errno, true, false);
}

static int rtrs_inv_rkey(struct rtrs_clt_io_req *req)
{
        struct rtrs_clt_con *con = req->con;
        struct ib_send_wr wr = {
                .opcode             = IB_WR_LOCAL_INV,
                .wr_cqe             = &req->inv_cqe,
                .send_flags         = IB_SEND_SIGNALED,
                .ex.invalidate_rkey = req->mr->rkey,
        };
        req->inv_cqe.done = rtrs_clt_inv_rkey_done;

        return ib_post_send(con->c.qp, &wr, NULL);
}

static void complete_rdma_req(struct rtrs_clt_io_req *req, int errno,
                              bool notify, bool can_wait)
{
        struct rtrs_clt_con *con = req->con;
        struct rtrs_clt_sess *sess;
        int err;

        if (WARN_ON(!req->in_use))
                return;
        if (WARN_ON(!req->con))
                return;
        sess = to_clt_sess(con->c.sess);

        if (req->sg_cnt) {
                if (unlikely(req->dir == DMA_FROM_DEVICE && req->need_inv)) {
                        /*
                         * We are here to invalidate read requests
                         * ourselves.  In normal scenario server should
                         * send INV for all read requests, but
                         * we are here, thus two things could happen:
                         *
                         *    1.  this is failover, when errno != 0
                         *        and can_wait == 1,
                         *
                         *    2.  something totally bad happened and
                         *        server forgot to send INV, so we
                         *        should do that ourselves.
                         */

                        if (likely(can_wait)) {
                                req->need_inv_comp = true;
                        } else {
                                /* This should be IO path, so always notify */
                                WARN_ON(!notify);
                                /* Save errno for INV callback */
                                req->inv_errno = errno;
                        }

                        refcount_inc(&req->ref);
                        err = rtrs_inv_rkey(req);
                        if (unlikely(err)) {
                                rtrs_err(con->c.sess, "Send INV WR key=%#x: %d\n",
                                          req->mr->rkey, err);
                        } else if (likely(can_wait)) {
                                wait_for_completion(&req->inv_comp);
                        } else {
                                /*
                                 * Something went wrong, so request will be
                                 * completed from INV callback.
                                 */
                                WARN_ON_ONCE(1);

                                return;
                        }
                        if (!refcount_dec_and_test(&req->ref))
                                return;
                }
                ib_dma_unmap_sg(sess->s.dev->ib_dev, req->sglist,
                                req->sg_cnt, req->dir);
        }
        if (!refcount_dec_and_test(&req->ref))
                return;
        if (sess->clt->mp_policy == MP_POLICY_MIN_INFLIGHT)
                atomic_dec(&sess->stats->inflight);

        req->in_use = false;
        req->con = NULL;

        if (errno) {
                rtrs_err_rl(con->c.sess, "IO request failed: error=%d path=%s [%s:%u] notify=%d\n",
                            errno, kobject_name(&sess->kobj), sess->hca_name,
                            sess->hca_port, notify);
        }

        if (notify)
                req->conf(req->priv, errno);
}

static int rtrs_post_send_rdma(struct rtrs_clt_con *con,
                                struct rtrs_clt_io_req *req,
                                struct rtrs_rbuf *rbuf, u32 off,
                                u32 imm, struct ib_send_wr *wr)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        enum ib_send_flags flags;
        struct ib_sge sge;

        if (unlikely(!req->sg_size)) {
                rtrs_wrn(con->c.sess,
                         "Doing RDMA Write failed, no data supplied\n");
                return -EINVAL;
        }

        /* user data and user message in the first list element */
        sge.addr   = req->iu->dma_addr;
        sge.length = req->sg_size;
        sge.lkey   = sess->s.dev->ib_pd->local_dma_lkey;

        /*
         * From time to time we have to post signalled sends,
         * or send queue will fill up and only QP reset can help.
         */
        flags = atomic_inc_return(&con->io_cnt) % sess->queue_depth ?
                        0 : IB_SEND_SIGNALED;

        ib_dma_sync_single_for_device(sess->s.dev->ib_dev, req->iu->dma_addr,
                                      req->sg_size, DMA_TO_DEVICE);

        return rtrs_iu_post_rdma_write_imm(&con->c, req->iu, &sge, 1,
                                            rbuf->rkey, rbuf->addr + off,
                                            imm, flags, wr, NULL);
}

static void process_io_rsp(struct rtrs_clt_sess *sess, u32 msg_id,
                           s16 errno, bool w_inval)
{
        struct rtrs_clt_io_req *req;

        if (WARN_ON(msg_id >= sess->queue_depth))
                return;

        req = &sess->reqs[msg_id];
        /* Drop need_inv if server responded with send with invalidation */
        req->need_inv &= !w_inval;
        complete_rdma_req(req, errno, true, false);
}

static void rtrs_clt_recv_done(struct rtrs_clt_con *con, struct ib_wc *wc)
{
        struct rtrs_iu *iu;
        int err;
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);

        WARN_ON((sess->flags & RTRS_MSG_NEW_RKEY_F) == 0);
        iu = container_of(wc->wr_cqe, struct rtrs_iu,
                          cqe);
        err = rtrs_iu_post_recv(&con->c, iu);
        if (unlikely(err)) {
                rtrs_err(con->c.sess, "post iu failed %d\n", err);
                rtrs_rdma_error_recovery(con);
        }
}

static void rtrs_clt_rkey_rsp_done(struct rtrs_clt_con *con, struct ib_wc *wc)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        struct rtrs_msg_rkey_rsp *msg;
        u32 imm_type, imm_payload;
        bool w_inval = false;
        struct rtrs_iu *iu;
        u32 buf_id;
        int err;

        WARN_ON((sess->flags & RTRS_MSG_NEW_RKEY_F) == 0);

        iu = container_of(wc->wr_cqe, struct rtrs_iu, cqe);

        if (unlikely(wc->byte_len < sizeof(*msg))) {
                rtrs_err(con->c.sess, "rkey response is malformed: size %d\n",
                          wc->byte_len);
                goto out;
        }
        ib_dma_sync_single_for_cpu(sess->s.dev->ib_dev, iu->dma_addr,
                                   iu->size, DMA_FROM_DEVICE);
        msg = iu->buf;
        if (unlikely(le16_to_cpu(msg->type) != RTRS_MSG_RKEY_RSP)) {
                rtrs_err(sess->clt, "rkey response is malformed: type %d\n",
                          le16_to_cpu(msg->type));
                goto out;
        }
        buf_id = le16_to_cpu(msg->buf_id);
        if (WARN_ON(buf_id >= sess->queue_depth))
                goto out;

        rtrs_from_imm(be32_to_cpu(wc->ex.imm_data), &imm_type, &imm_payload);
        if (likely(imm_type == RTRS_IO_RSP_IMM ||
                   imm_type == RTRS_IO_RSP_W_INV_IMM)) {
                u32 msg_id;

                w_inval = (imm_type == RTRS_IO_RSP_W_INV_IMM);
                rtrs_from_io_rsp_imm(imm_payload, &msg_id, &err);

                if (WARN_ON(buf_id != msg_id))
                        goto out;
                sess->rbufs[buf_id].rkey = le32_to_cpu(msg->rkey);
                process_io_rsp(sess, msg_id, err, w_inval);
        }
        ib_dma_sync_single_for_device(sess->s.dev->ib_dev, iu->dma_addr,
                                      iu->size, DMA_FROM_DEVICE);
        return rtrs_clt_recv_done(con, wc);
out:
        rtrs_rdma_error_recovery(con);
}

static void rtrs_clt_rdma_done(struct ib_cq *cq, struct ib_wc *wc);

static struct ib_cqe io_comp_cqe = {
        .done = rtrs_clt_rdma_done
};

/*
 * Post x2 empty WRs: first is for this RDMA with IMM,
 * second is for RECV with INV, which happened earlier.
 */
static int rtrs_post_recv_empty_x2(struct rtrs_con *con, struct ib_cqe *cqe)
{
        struct ib_recv_wr wr_arr[2], *wr;
        int i;

        memset(wr_arr, 0, sizeof(wr_arr));
        for (i = 0; i < ARRAY_SIZE(wr_arr); i++) {
                wr = &wr_arr[i];
                wr->wr_cqe  = cqe;
                if (i)
                        /* Chain backwards */
                        wr->next = &wr_arr[i - 1];
        }

        return ib_post_recv(con->qp, wr, NULL);
}

static void rtrs_clt_rdma_done(struct ib_cq *cq, struct ib_wc *wc)
{
        struct rtrs_clt_con *con = to_clt_con(wc->qp->qp_context);
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        u32 imm_type, imm_payload;
        bool w_inval = false;
        int err;

        if (unlikely(wc->status != IB_WC_SUCCESS)) {
                if (wc->status != IB_WC_WR_FLUSH_ERR) {
                        rtrs_err(sess->clt, "RDMA failed: %s\n",
                                  ib_wc_status_msg(wc->status));
                        rtrs_rdma_error_recovery(con);
                }
                return;
        }
        rtrs_clt_update_wc_stats(con);

        switch (wc->opcode) {
        case IB_WC_RECV_RDMA_WITH_IMM:
                /*
                 * post_recv() RDMA write completions of IO reqs (read/write)
                 * and hb
                 */
                if (WARN_ON(wc->wr_cqe->done != rtrs_clt_rdma_done))
                        return;
                rtrs_from_imm(be32_to_cpu(wc->ex.imm_data),
                               &imm_type, &imm_payload);
                if (likely(imm_type == RTRS_IO_RSP_IMM ||
                           imm_type == RTRS_IO_RSP_W_INV_IMM)) {
                        u32 msg_id;

                        w_inval = (imm_type == RTRS_IO_RSP_W_INV_IMM);
                        rtrs_from_io_rsp_imm(imm_payload, &msg_id, &err);

                        process_io_rsp(sess, msg_id, err, w_inval);
                } else if (imm_type == RTRS_HB_MSG_IMM) {
                        WARN_ON(con->c.cid);
                        rtrs_send_hb_ack(&sess->s);
                        if (sess->flags & RTRS_MSG_NEW_RKEY_F)
                                return  rtrs_clt_recv_done(con, wc);
                } else if (imm_type == RTRS_HB_ACK_IMM) {
                        WARN_ON(con->c.cid);
                        sess->s.hb_missed_cnt = 0;
                        sess->s.hb_cur_latency =
                                ktime_sub(ktime_get(), sess->s.hb_last_sent);
                        if (sess->flags & RTRS_MSG_NEW_RKEY_F)
                                return  rtrs_clt_recv_done(con, wc);
                } else {
                        rtrs_wrn(con->c.sess, "Unknown IMM type %u\n",
                                  imm_type);
                }
                if (w_inval)
                        /*
                         * Post x2 empty WRs: first is for this RDMA with IMM,
                         * second is for RECV with INV, which happened earlier.
                         */
                        err = rtrs_post_recv_empty_x2(&con->c, &io_comp_cqe);
                else
                        err = rtrs_post_recv_empty(&con->c, &io_comp_cqe);
                if (unlikely(err)) {
                        rtrs_err(con->c.sess, "rtrs_post_recv_empty(): %d\n",
                                  err);
                        rtrs_rdma_error_recovery(con);
                }
                break;
        case IB_WC_RECV:
                /*
                 * Key invalidations from server side
                 */
                WARN_ON(!(wc->wc_flags & IB_WC_WITH_INVALIDATE ||
                          wc->wc_flags & IB_WC_WITH_IMM));
                WARN_ON(wc->wr_cqe->done != rtrs_clt_rdma_done);
                if (sess->flags & RTRS_MSG_NEW_RKEY_F) {
                        if (wc->wc_flags & IB_WC_WITH_INVALIDATE)
                                return  rtrs_clt_recv_done(con, wc);

                        return  rtrs_clt_rkey_rsp_done(con, wc);
                }
                break;
        case IB_WC_RDMA_WRITE:
                /*
                 * post_send() RDMA write completions of IO reqs (read/write)
                 */
                break;

        default:
                rtrs_wrn(sess->clt, "Unexpected WC type: %d\n", wc->opcode);
                return;
        }
}

static int post_recv_io(struct rtrs_clt_con *con, size_t q_size)
{
        int err, i;
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);

        for (i = 0; i < q_size; i++) {
                if (sess->flags & RTRS_MSG_NEW_RKEY_F) {
                        struct rtrs_iu *iu = &con->rsp_ius[i];

                        err = rtrs_iu_post_recv(&con->c, iu);
                } else {
                        err = rtrs_post_recv_empty(&con->c, &io_comp_cqe);
                }
                if (unlikely(err))
                        return err;
        }

        return 0;
}

static int post_recv_sess(struct rtrs_clt_sess *sess)
{
        size_t q_size = 0;
        int err, cid;

        for (cid = 0; cid < sess->s.con_num; cid++) {
                if (cid == 0)
                        q_size = SERVICE_CON_QUEUE_DEPTH;
                else
                        q_size = sess->queue_depth;

                /*
                 * x2 for RDMA read responses + FR key invalidations,
                 * RDMA writes do not require any FR registrations.
                 */
                q_size *= 2;

                err = post_recv_io(to_clt_con(sess->s.con[cid]), q_size);
                if (unlikely(err)) {
                        rtrs_err(sess->clt, "post_recv_io(), err: %d\n", err);
                        return err;
                }
        }

        return 0;
}

struct path_it {
        int i;
        struct list_head skip_list;
        struct rtrs_clt *clt;
        struct rtrs_clt_sess *(*next_path)(struct path_it *it);
};

/**
 * list_next_or_null_rr_rcu - get next list element in round-robin fashion.
 * @head:       the head for the list.
 * @ptr:        the list head to take the next element from.
 * @type:       the type of the struct this is embedded in.
 * @memb:       the name of the list_head within the struct.
 *
 * Next element returned in round-robin fashion, i.e. head will be skipped,
 * but if list is observed as empty, NULL will be returned.
 *
 * This primitive may safely run concurrently with the _rcu list-mutation
 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
 */
#define list_next_or_null_rr_rcu(head, ptr, type, memb) \
({ \
        list_next_or_null_rcu(head, ptr, type, memb) ?: \
                list_next_or_null_rcu(head, READ_ONCE((ptr)->next), \
                                      type, memb); \
})

/**
 * get_next_path_rr() - Returns path in round-robin fashion.
 * @it: the path pointer
 *
 * Related to @MP_POLICY_RR
 *
 * Locks:
 *    rcu_read_lock() must be hold.
 */
static struct rtrs_clt_sess *get_next_path_rr(struct path_it *it)
{
        struct rtrs_clt_sess __rcu **ppcpu_path;
        struct rtrs_clt_sess *path;
        struct rtrs_clt *clt;

        clt = it->clt;

        /*
         * Here we use two RCU objects: @paths_list and @pcpu_path
         * pointer.  See rtrs_clt_remove_path_from_arr() for details
         * how that is handled.
         */

        ppcpu_path = this_cpu_ptr(clt->pcpu_path);
        path = rcu_dereference(*ppcpu_path);
        if (unlikely(!path))
                path = list_first_or_null_rcu(&clt->paths_list,
                                              typeof(*path), s.entry);
        else
                path = list_next_or_null_rr_rcu(&clt->paths_list,
                                                &path->s.entry,
                                                typeof(*path),
                                                s.entry);
        rcu_assign_pointer(*ppcpu_path, path);

        return path;
}

/**
 * get_next_path_min_inflight() - Returns path with minimal inflight count.
 * @it: the path pointer
 *
 * Related to @MP_POLICY_MIN_INFLIGHT
 *
 * Locks:
 *    rcu_read_lock() must be hold.
 */
static struct rtrs_clt_sess *get_next_path_min_inflight(struct path_it *it)
{
        struct rtrs_clt_sess *min_path = NULL;
        struct rtrs_clt *clt = it->clt;
        struct rtrs_clt_sess *sess;
        int min_inflight = INT_MAX;
        int inflight;

        list_for_each_entry_rcu(sess, &clt->paths_list, s.entry) {
                if (unlikely(READ_ONCE(sess->state) != RTRS_CLT_CONNECTED))
                        continue;

                if (unlikely(!list_empty(raw_cpu_ptr(sess->mp_skip_entry))))
                        continue;

                inflight = atomic_read(&sess->stats->inflight);

                if (inflight < min_inflight) {
                        min_inflight = inflight;
                        min_path = sess;
                }
        }

        /*
         * add the path to the skip list, so that next time we can get
         * a different one
         */
        if (min_path)
                list_add(raw_cpu_ptr(min_path->mp_skip_entry), &it->skip_list);

        return min_path;
}

/**
 * get_next_path_min_latency() - Returns path with minimal latency.
 * @it: the path pointer
 *
 * Return: a path with the lowest latency or NULL if all paths are tried
 *
 * Locks:
 *    rcu_read_lock() must be hold.
 *
 * Related to @MP_POLICY_MIN_LATENCY
 *
 * This DOES skip an already-tried path.
 * There is a skip-list to skip a path if the path has tried but failed.
 * It will try the minimum latency path and then the second minimum latency
 * path and so on. Finally it will return NULL if all paths are tried.
 * Therefore the caller MUST check the returned
 * path is NULL and trigger the IO error.
 */
static struct rtrs_clt_sess *get_next_path_min_latency(struct path_it *it)
{
        struct rtrs_clt_sess *min_path = NULL;
        struct rtrs_clt *clt = it->clt;
        struct rtrs_clt_sess *sess;
        ktime_t min_latency = INT_MAX;
        ktime_t latency;

        list_for_each_entry_rcu(sess, &clt->paths_list, s.entry) {
                if (unlikely(READ_ONCE(sess->state) != RTRS_CLT_CONNECTED))
                        continue;

                if (unlikely(!list_empty(raw_cpu_ptr(sess->mp_skip_entry))))
                        continue;

                latency = sess->s.hb_cur_latency;

                if (latency < min_latency) {
                        min_latency = latency;
                        min_path = sess;
                }
        }

        /*
         * add the path to the skip list, so that next time we can get
         * a different one
         */
        if (min_path)
                list_add(raw_cpu_ptr(min_path->mp_skip_entry), &it->skip_list);

        return min_path;
}

static inline void path_it_init(struct path_it *it, struct rtrs_clt *clt)
{
        INIT_LIST_HEAD(&it->skip_list);
        it->clt = clt;
        it->i = 0;

        if (clt->mp_policy == MP_POLICY_RR)
                it->next_path = get_next_path_rr;
        else if (clt->mp_policy == MP_POLICY_MIN_INFLIGHT)
                it->next_path = get_next_path_min_inflight;
        else
                it->next_path = get_next_path_min_latency;
}

static inline void path_it_deinit(struct path_it *it)
{
        struct list_head *skip, *tmp;
        /*
         * The skip_list is used only for the MIN_INFLIGHT policy.
         * We need to remove paths from it, so that next IO can insert
         * paths (->mp_skip_entry) into a skip_list again.
         */
        list_for_each_safe(skip, tmp, &it->skip_list)
                list_del_init(skip);
}

/**
 * rtrs_clt_init_req() - Initialize an rtrs_clt_io_req holding information
 * about an inflight IO.
 * The user buffer holding user control message (not data) is copied into
 * the corresponding buffer of rtrs_iu (req->iu->buf), which later on will
 * also hold the control message of rtrs.
 * @req: an io request holding information about IO.
 * @sess: client session
 * @conf: conformation callback function to notify upper layer.
 * @permit: permit for allocation of RDMA remote buffer
 * @priv: private pointer
 * @vec: kernel vector containing control message
 * @usr_len: length of the user message
 * @sg: scater list for IO data
 * @sg_cnt: number of scater list entries
 * @data_len: length of the IO data
 * @dir: direction of the IO.
 */
static void rtrs_clt_init_req(struct rtrs_clt_io_req *req,
                              struct rtrs_clt_sess *sess,
                              void (*conf)(void *priv, int errno),
                              struct rtrs_permit *permit, void *priv,
                              const struct kvec *vec, size_t usr_len,
                              struct scatterlist *sg, size_t sg_cnt,
                              size_t data_len, int dir)
{
        struct iov_iter iter;
        size_t len;

        req->permit = permit;
        req->in_use = true;
        req->usr_len = usr_len;
        req->data_len = data_len;
        req->sglist = sg;
        req->sg_cnt = sg_cnt;
        req->priv = priv;
        req->dir = dir;
        req->con = rtrs_permit_to_clt_con(sess, permit);
        req->conf = conf;
        req->need_inv = false;
        req->need_inv_comp = false;
        req->inv_errno = 0;
        refcount_set(&req->ref, 1);

        iov_iter_kvec(&iter, READ, vec, 1, usr_len);
        len = _copy_from_iter(req->iu->buf, usr_len, &iter);
        WARN_ON(len != usr_len);

        reinit_completion(&req->inv_comp);
}

static struct rtrs_clt_io_req *
rtrs_clt_get_req(struct rtrs_clt_sess *sess,
                 void (*conf)(void *priv, int errno),
                 struct rtrs_permit *permit, void *priv,
                 const struct kvec *vec, size_t usr_len,
                 struct scatterlist *sg, size_t sg_cnt,
                 size_t data_len, int dir)
{
        struct rtrs_clt_io_req *req;

        req = &sess->reqs[permit->mem_id];
        rtrs_clt_init_req(req, sess, conf, permit, priv, vec, usr_len,
                           sg, sg_cnt, data_len, dir);
        return req;
}

static struct rtrs_clt_io_req *
rtrs_clt_get_copy_req(struct rtrs_clt_sess *alive_sess,
                       struct rtrs_clt_io_req *fail_req)
{
        struct rtrs_clt_io_req *req;
        struct kvec vec = {
                .iov_base = fail_req->iu->buf,
                .iov_len  = fail_req->usr_len
        };

        req = &alive_sess->reqs[fail_req->permit->mem_id];

        rtrs_clt_init_req(req, alive_sess, fail_req->conf, fail_req->permit,
                           fail_req->priv, &vec, fail_req->usr_len,
                           fail_req->sglist, fail_req->sg_cnt,
                           fail_req->data_len, fail_req->dir);
        return req;
}

static int rtrs_post_rdma_write_sg(struct rtrs_clt_con *con,
                                   struct rtrs_clt_io_req *req,
                                   struct rtrs_rbuf *rbuf, bool fr_en,
                                   u32 size, u32 imm, struct ib_send_wr *wr,
                                   struct ib_send_wr *tail)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        struct ib_sge *sge = req->sge;
        enum ib_send_flags flags;
        struct scatterlist *sg;
        size_t num_sge;
        int i;
        struct ib_send_wr *ptail = NULL;

        if (fr_en) {
                i = 0;
                sge[i].addr   = req->mr->iova;
                sge[i].length = req->mr->length;
                sge[i].lkey   = req->mr->lkey;
                i++;
                num_sge = 2;
                ptail = tail;
        } else {
                for_each_sg(req->sglist, sg, req->sg_cnt, i) {
                        sge[i].addr   = sg_dma_address(sg);
                        sge[i].length = sg_dma_len(sg);
                        sge[i].lkey   = sess->s.dev->ib_pd->local_dma_lkey;
                }
                num_sge = 1 + req->sg_cnt;
        }
        sge[i].addr   = req->iu->dma_addr;
        sge[i].length = size;
        sge[i].lkey   = sess->s.dev->ib_pd->local_dma_lkey;

        /*
         * From time to time we have to post signalled sends,
         * or send queue will fill up and only QP reset can help.
         */
        flags = atomic_inc_return(&con->io_cnt) % sess->queue_depth ?
                        0 : IB_SEND_SIGNALED;

        ib_dma_sync_single_for_device(sess->s.dev->ib_dev, req->iu->dma_addr,
                                      size, DMA_TO_DEVICE);

        return rtrs_iu_post_rdma_write_imm(&con->c, req->iu, sge, num_sge,
                                            rbuf->rkey, rbuf->addr, imm,
                                            flags, wr, ptail);
}

static int rtrs_map_sg_fr(struct rtrs_clt_io_req *req, size_t count)
{
        int nr;

        /* Align the MR to a 4K page size to match the block virt boundary */
        nr = ib_map_mr_sg(req->mr, req->sglist, count, NULL, SZ_4K);
        if (nr < 0)
                return nr;
        if (unlikely(nr < req->sg_cnt))
                return -EINVAL;
        ib_update_fast_reg_key(req->mr, ib_inc_rkey(req->mr->rkey));

        return nr;
}

static int rtrs_clt_write_req(struct rtrs_clt_io_req *req)
{
        struct rtrs_clt_con *con = req->con;
        struct rtrs_sess *s = con->c.sess;
        struct rtrs_clt_sess *sess = to_clt_sess(s);
        struct rtrs_msg_rdma_write *msg;

        struct rtrs_rbuf *rbuf;
        int ret, count = 0;
        u32 imm, buf_id;
        struct ib_reg_wr rwr;
        struct ib_send_wr inv_wr;
        struct ib_send_wr *wr = NULL;
        bool fr_en = false;

        const size_t tsize = sizeof(*msg) + req->data_len + req->usr_len;

        if (unlikely(tsize > sess->chunk_size)) {
                rtrs_wrn(s, "Write request failed, size too big %zu > %d\n",
                          tsize, sess->chunk_size);
                return -EMSGSIZE;
        }
        if (req->sg_cnt) {
                count = ib_dma_map_sg(sess->s.dev->ib_dev, req->sglist,
                                      req->sg_cnt, req->dir);
                if (unlikely(!count)) {
                        rtrs_wrn(s, "Write request failed, map failed\n");
                        return -EINVAL;
                }
        }
        /* put rtrs msg after sg and user message */
        msg = req->iu->buf + req->usr_len;
        msg->type = cpu_to_le16(RTRS_MSG_WRITE);
        msg->usr_len = cpu_to_le16(req->usr_len);

        /* rtrs message on server side will be after user data and message */
        imm = req->permit->mem_off + req->data_len + req->usr_len;
        imm = rtrs_to_io_req_imm(imm);
        buf_id = req->permit->mem_id;
        req->sg_size = tsize;
        rbuf = &sess->rbufs[buf_id];

        if (count) {
                ret = rtrs_map_sg_fr(req, count);
                if (ret < 0) {
                        rtrs_err_rl(s,
                                    "Write request failed, failed to map fast reg. data, err: %d\n",
                                    ret);
                        ib_dma_unmap_sg(sess->s.dev->ib_dev, req->sglist,
                                        req->sg_cnt, req->dir);
                        return ret;
                }
                inv_wr = (struct ib_send_wr) {
                        .opcode             = IB_WR_LOCAL_INV,
                        .wr_cqe             = &req->inv_cqe,
                        .send_flags         = IB_SEND_SIGNALED,
                        .ex.invalidate_rkey = req->mr->rkey,
                };
                req->inv_cqe.done = rtrs_clt_inv_rkey_done;
                rwr = (struct ib_reg_wr) {
                        .wr.opcode = IB_WR_REG_MR,
                        .wr.wr_cqe = &fast_reg_cqe,
                        .mr = req->mr,
                        .key = req->mr->rkey,
                        .access = (IB_ACCESS_LOCAL_WRITE),
                };
                wr = &rwr.wr;
                fr_en = true;
                refcount_inc(&req->ref);
        }
        /*
         * Update stats now, after request is successfully sent it is not
         * safe anymore to touch it.
         */
        rtrs_clt_update_all_stats(req, WRITE);

        ret = rtrs_post_rdma_write_sg(req->con, req, rbuf, fr_en,
                                      req->usr_len + sizeof(*msg),
                                      imm, wr, &inv_wr);
        if (unlikely(ret)) {
                rtrs_err_rl(s,
                            "Write request failed: error=%d path=%s [%s:%u]\n",
                            ret, kobject_name(&sess->kobj), sess->hca_name,
                            sess->hca_port);
                if (sess->clt->mp_policy == MP_POLICY_MIN_INFLIGHT)
                        atomic_dec(&sess->stats->inflight);
                if (req->sg_cnt)
                        ib_dma_unmap_sg(sess->s.dev->ib_dev, req->sglist,
                                        req->sg_cnt, req->dir);
        }

        return ret;
}

static int rtrs_clt_read_req(struct rtrs_clt_io_req *req)
{
        struct rtrs_clt_con *con = req->con;
        struct rtrs_sess *s = con->c.sess;
        struct rtrs_clt_sess *sess = to_clt_sess(s);
        struct rtrs_msg_rdma_read *msg;
        struct rtrs_ib_dev *dev = sess->s.dev;

        struct ib_reg_wr rwr;
        struct ib_send_wr *wr = NULL;

        int ret, count = 0;
        u32 imm, buf_id;

        const size_t tsize = sizeof(*msg) + req->data_len + req->usr_len;

        if (unlikely(tsize > sess->chunk_size)) {
                rtrs_wrn(s,
                          "Read request failed, message size is %zu, bigger than CHUNK_SIZE %d\n",
                          tsize, sess->chunk_size);
                return -EMSGSIZE;
        }

        if (req->sg_cnt) {
                count = ib_dma_map_sg(dev->ib_dev, req->sglist, req->sg_cnt,
                                      req->dir);
                if (unlikely(!count)) {
                        rtrs_wrn(s,
                                  "Read request failed, dma map failed\n");
                        return -EINVAL;
                }
        }
        /* put our message into req->buf after user message*/
        msg = req->iu->buf + req->usr_len;
        msg->type = cpu_to_le16(RTRS_MSG_READ);
        msg->usr_len = cpu_to_le16(req->usr_len);

        if (count) {
                ret = rtrs_map_sg_fr(req, count);
                if (ret < 0) {
                        rtrs_err_rl(s,
                                     "Read request failed, failed to map  fast reg. data, err: %d\n",
                                     ret);
                        ib_dma_unmap_sg(dev->ib_dev, req->sglist, req->sg_cnt,
                                        req->dir);
                        return ret;
                }
                rwr = (struct ib_reg_wr) {
                        .wr.opcode = IB_WR_REG_MR,
                        .wr.wr_cqe = &fast_reg_cqe,
                        .mr = req->mr,
                        .key = req->mr->rkey,
                        .access = (IB_ACCESS_LOCAL_WRITE |
                                   IB_ACCESS_REMOTE_WRITE),
                };
                wr = &rwr.wr;

                msg->sg_cnt = cpu_to_le16(1);
                msg->flags = cpu_to_le16(RTRS_MSG_NEED_INVAL_F);

                msg->desc[0].addr = cpu_to_le64(req->mr->iova);
                msg->desc[0].key = cpu_to_le32(req->mr->rkey);
                msg->desc[0].len = cpu_to_le32(req->mr->length);

                /* Further invalidation is required */
                req->need_inv = !!RTRS_MSG_NEED_INVAL_F;

        } else {
                msg->sg_cnt = 0;
                msg->flags = 0;
        }
        /*
         * rtrs message will be after the space reserved for disk data and
         * user message
         */
        imm = req->permit->mem_off + req->data_len + req->usr_len;
        imm = rtrs_to_io_req_imm(imm);
        buf_id = req->permit->mem_id;

        req->sg_size  = sizeof(*msg);
        req->sg_size += le16_to_cpu(msg->sg_cnt) * sizeof(struct rtrs_sg_desc);
        req->sg_size += req->usr_len;

        /*
         * Update stats now, after request is successfully sent it is not
         * safe anymore to touch it.
         */
        rtrs_clt_update_all_stats(req, READ);

        ret = rtrs_post_send_rdma(req->con, req, &sess->rbufs[buf_id],
                                   req->data_len, imm, wr);
        if (unlikely(ret)) {
                rtrs_err_rl(s,
                            "Read request failed: error=%d path=%s [%s:%u]\n",
                            ret, kobject_name(&sess->kobj), sess->hca_name,
                            sess->hca_port);
                if (sess->clt->mp_policy == MP_POLICY_MIN_INFLIGHT)
                        atomic_dec(&sess->stats->inflight);
                req->need_inv = false;
                if (req->sg_cnt)
                        ib_dma_unmap_sg(dev->ib_dev, req->sglist,
                                        req->sg_cnt, req->dir);
        }

        return ret;
}

/**
 * rtrs_clt_failover_req() - Try to find an active path for a failed request
 * @clt: clt context
 * @fail_req: a failed io request.
 */
static int rtrs_clt_failover_req(struct rtrs_clt *clt,
                                 struct rtrs_clt_io_req *fail_req)
{
        struct rtrs_clt_sess *alive_sess;
        struct rtrs_clt_io_req *req;
        int err = -ECONNABORTED;
        struct path_it it;

        rcu_read_lock();
        for (path_it_init(&it, clt);
             (alive_sess = it.next_path(&it)) && it.i < it.clt->paths_num;
             it.i++) {
                if (unlikely(READ_ONCE(alive_sess->state) !=
                             RTRS_CLT_CONNECTED))
                        continue;
                req = rtrs_clt_get_copy_req(alive_sess, fail_req);
                if (req->dir == DMA_TO_DEVICE)
                        err = rtrs_clt_write_req(req);
                else
                        err = rtrs_clt_read_req(req);
                if (unlikely(err)) {
                        req->in_use = false;
                        continue;
                }
                /* Success path */
                rtrs_clt_inc_failover_cnt(alive_sess->stats);
                break;
        }
        path_it_deinit(&it);
        rcu_read_unlock();

        return err;
}

static void fail_all_outstanding_reqs(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt *clt = sess->clt;
        struct rtrs_clt_io_req *req;
        int i, err;

        if (!sess->reqs)
                return;
        for (i = 0; i < sess->queue_depth; ++i) {
                req = &sess->reqs[i];
                if (!req->in_use)
                        continue;

                /*
                 * Safely (without notification) complete failed request.
                 * After completion this request is still useble and can
                 * be failovered to another path.
                 */
                complete_rdma_req(req, -ECONNABORTED, false, true);

                err = rtrs_clt_failover_req(clt, req);
                if (unlikely(err))
                        /* Failover failed, notify anyway */
                        req->conf(req->priv, err);
        }
}

static void free_sess_reqs(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt_io_req *req;
        int i;

        if (!sess->reqs)
                return;
        for (i = 0; i < sess->queue_depth; ++i) {
                req = &sess->reqs[i];
                if (req->mr)
                        ib_dereg_mr(req->mr);
                kfree(req->sge);
                rtrs_iu_free(req->iu, sess->s.dev->ib_dev, 1);
        }
        kfree(sess->reqs);
        sess->reqs = NULL;
}

static int alloc_sess_reqs(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt_io_req *req;
        int i, err = -ENOMEM;

        sess->reqs = kcalloc(sess->queue_depth, sizeof(*sess->reqs),
                             GFP_KERNEL);
        if (!sess->reqs)
                return -ENOMEM;

        for (i = 0; i < sess->queue_depth; ++i) {
                req = &sess->reqs[i];
                req->iu = rtrs_iu_alloc(1, sess->max_hdr_size, GFP_KERNEL,
                                         sess->s.dev->ib_dev,
                                         DMA_TO_DEVICE,
                                         rtrs_clt_rdma_done);
                if (!req->iu)
                        goto out;

                req->sge = kcalloc(2, sizeof(*req->sge), GFP_KERNEL);
                if (!req->sge)
                        goto out;

                req->mr = ib_alloc_mr(sess->s.dev->ib_pd, IB_MR_TYPE_MEM_REG,
                                      sess->max_pages_per_mr);
                if (IS_ERR(req->mr)) {
                        err = PTR_ERR(req->mr);
                        req->mr = NULL;
                        pr_err("Failed to alloc sess->max_pages_per_mr %d\n",
                               sess->max_pages_per_mr);
                        goto out;
                }

                init_completion(&req->inv_comp);
        }

        return 0;

out:
        free_sess_reqs(sess);

        return err;
}

static int alloc_permits(struct rtrs_clt *clt)
{
        unsigned int chunk_bits;
        int err, i;

        clt->permits_map = kcalloc(BITS_TO_LONGS(clt->queue_depth),
                                   sizeof(long), GFP_KERNEL);
        if (!clt->permits_map) {
                err = -ENOMEM;
                goto out_err;
        }
        clt->permits = kcalloc(clt->queue_depth, permit_size(clt), GFP_KERNEL);
        if (!clt->permits) {
                err = -ENOMEM;
                goto err_map;
        }
        chunk_bits = ilog2(clt->queue_depth - 1) + 1;
        for (i = 0; i < clt->queue_depth; i++) {
                struct rtrs_permit *permit;

                permit = get_permit(clt, i);
                permit->mem_id = i;
                permit->mem_off = i << (MAX_IMM_PAYL_BITS - chunk_bits);
        }

        return 0;

err_map:
        kfree(clt->permits_map);
        clt->permits_map = NULL;
out_err:
        return err;
}

static void free_permits(struct rtrs_clt *clt)
{
        if (clt->permits_map) {
                size_t sz = clt->queue_depth;

                wait_event(clt->permits_wait,
                           find_first_bit(clt->permits_map, sz) >= sz);
        }
        kfree(clt->permits_map);
        clt->permits_map = NULL;
        kfree(clt->permits);
        clt->permits = NULL;
}

static void query_fast_reg_mode(struct rtrs_clt_sess *sess)
{
        struct ib_device *ib_dev;
        u64 max_pages_per_mr;
        int mr_page_shift;

        ib_dev = sess->s.dev->ib_dev;

        /*
         * Use the smallest page size supported by the HCA, down to a
         * minimum of 4096 bytes. We're unlikely to build large sglists
         * out of smaller entries.
         */
        mr_page_shift      = max(12, ffs(ib_dev->attrs.page_size_cap) - 1);
        max_pages_per_mr   = ib_dev->attrs.max_mr_size;
        do_div(max_pages_per_mr, (1ull << mr_page_shift));
        sess->max_pages_per_mr =
                min3(sess->max_pages_per_mr, (u32)max_pages_per_mr,
                     ib_dev->attrs.max_fast_reg_page_list_len);
        sess->clt->max_segments =
                min(sess->max_pages_per_mr, sess->clt->max_segments);
}

static bool rtrs_clt_change_state_get_old(struct rtrs_clt_sess *sess,
                                           enum rtrs_clt_state new_state,
                                           enum rtrs_clt_state *old_state)
{
        bool changed;

        spin_lock_irq(&sess->state_wq.lock);
        if (old_state)
                *old_state = sess->state;
        changed = rtrs_clt_change_state(sess, new_state);
        spin_unlock_irq(&sess->state_wq.lock);

        return changed;
}

static void rtrs_clt_hb_err_handler(struct rtrs_con *c)
{
        struct rtrs_clt_con *con = container_of(c, typeof(*con), c);

        rtrs_rdma_error_recovery(con);
}

static void rtrs_clt_init_hb(struct rtrs_clt_sess *sess)
{
        rtrs_init_hb(&sess->s, &io_comp_cqe,
                      RTRS_HB_INTERVAL_MS,
                      RTRS_HB_MISSED_MAX,
                      rtrs_clt_hb_err_handler,
                      rtrs_wq);
}

static void rtrs_clt_reconnect_work(struct work_struct *work);
static void rtrs_clt_close_work(struct work_struct *work);

static struct rtrs_clt_sess *alloc_sess(struct rtrs_clt *clt,
                                        const struct rtrs_addr *path,
                                        size_t con_num, u32 nr_poll_queues)
{
        struct rtrs_clt_sess *sess;
        int err = -ENOMEM;
        int cpu;
        size_t total_con;

        sess = kzalloc(sizeof(*sess), GFP_KERNEL);
        if (!sess)
                goto err;

        /*
         * irqmode and poll
         * +1: Extra connection for user messages
         */
        total_con = con_num + nr_poll_queues + 1;
        sess->s.con = kcalloc(total_con, sizeof(*sess->s.con), GFP_KERNEL);
        if (!sess->s.con)
                goto err_free_sess;

        sess->s.con_num = total_con;
        sess->s.irq_con_num = con_num + 1;

        sess->stats = kzalloc(sizeof(*sess->stats), GFP_KERNEL);
        if (!sess->stats)
                goto err_free_con;

        mutex_init(&sess->init_mutex);
        uuid_gen(&sess->s.uuid);
        memcpy(&sess->s.dst_addr, path->dst,
               rdma_addr_size((struct sockaddr *)path->dst));

        /*
         * rdma_resolve_addr() passes src_addr to cma_bind_addr, which
         * checks the sa_family to be non-zero. If user passed src_addr=NULL
         * the sess->src_addr will contain only zeros, which is then fine.
         */
        if (path->src)
                memcpy(&sess->s.src_addr, path->src,
                       rdma_addr_size((struct sockaddr *)path->src));
        strscpy(sess->s.sessname, clt->sessname, sizeof(sess->s.sessname));
        sess->clt = clt;
        sess->max_pages_per_mr = RTRS_MAX_SEGMENTS;
        init_waitqueue_head(&sess->state_wq);
        sess->state = RTRS_CLT_CONNECTING;
        atomic_set(&sess->connected_cnt, 0);
        INIT_WORK(&sess->close_work, rtrs_clt_close_work);
        INIT_DELAYED_WORK(&sess->reconnect_dwork, rtrs_clt_reconnect_work);
        rtrs_clt_init_hb(sess);

        sess->mp_skip_entry = alloc_percpu(typeof(*sess->mp_skip_entry));
        if (!sess->mp_skip_entry)
                goto err_free_stats;

        for_each_possible_cpu(cpu)
                INIT_LIST_HEAD(per_cpu_ptr(sess->mp_skip_entry, cpu));

        err = rtrs_clt_init_stats(sess->stats);
        if (err)
                goto err_free_percpu;

        return sess;

err_free_percpu:
        free_percpu(sess->mp_skip_entry);
err_free_stats:
        kfree(sess->stats);
err_free_con:
        kfree(sess->s.con);
err_free_sess:
        kfree(sess);
err:
        return ERR_PTR(err);
}

void free_sess(struct rtrs_clt_sess *sess)
{
        free_percpu(sess->mp_skip_entry);
        mutex_destroy(&sess->init_mutex);
        kfree(sess->s.con);
        kfree(sess->rbufs);
        kfree(sess);
}

static int create_con(struct rtrs_clt_sess *sess, unsigned int cid)
{
        struct rtrs_clt_con *con;

        con = kzalloc(sizeof(*con), GFP_KERNEL);
        if (!con)
                return -ENOMEM;

        /* Map first two connections to the first CPU */
        con->cpu  = (cid ? cid - 1 : 0) % nr_cpu_ids;
        con->c.cid = cid;
        con->c.sess = &sess->s;
        atomic_set(&con->io_cnt, 0);
        mutex_init(&con->con_mutex);

        sess->s.con[cid] = &con->c;

        return 0;
}

static void destroy_con(struct rtrs_clt_con *con)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);

        sess->s.con[con->c.cid] = NULL;
        mutex_destroy(&con->con_mutex);
        kfree(con);
}

static int create_con_cq_qp(struct rtrs_clt_con *con)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        u32 max_send_wr, max_recv_wr, cq_num, max_send_sge, wr_limit;
        int err, cq_vector;
        struct rtrs_msg_rkey_rsp *rsp;

        lockdep_assert_held(&con->con_mutex);
        if (con->c.cid == 0) {
                max_send_sge = 1;
                /* We must be the first here */
                if (WARN_ON(sess->s.dev))
                        return -EINVAL;

                /*
                 * The whole session uses device from user connection.
                 * Be careful not to close user connection before ib dev
                 * is gracefully put.
                 */
                sess->s.dev = rtrs_ib_dev_find_or_add(con->c.cm_id->device,
                                                       &dev_pd);
                if (!sess->s.dev) {
                        rtrs_wrn(sess->clt,
                                  "rtrs_ib_dev_find_get_or_add(): no memory\n");
                        return -ENOMEM;
                }
                sess->s.dev_ref = 1;
                query_fast_reg_mode(sess);
                wr_limit = sess->s.dev->ib_dev->attrs.max_qp_wr;
                /*
                 * Two (request + registration) completion for send
                 * Two for recv if always_invalidate is set on server
                 * or one for recv.
                 * + 2 for drain and heartbeat
                 * in case qp gets into error state.
                 */
                max_send_wr =
                        min_t(int, wr_limit, SERVICE_CON_QUEUE_DEPTH * 2 + 2);
                max_recv_wr = max_send_wr;
        } else {
                /*
                 * Here we assume that session members are correctly set.
                 * This is always true if user connection (cid == 0) is
                 * established first.
                 */
                if (WARN_ON(!sess->s.dev))
                        return -EINVAL;
                if (WARN_ON(!sess->queue_depth))
                        return -EINVAL;

                wr_limit = sess->s.dev->ib_dev->attrs.max_qp_wr;
                /* Shared between connections */
                sess->s.dev_ref++;
                max_send_wr = min_t(int, wr_limit,
                              /* QD * (REQ + RSP + FR REGS or INVS) + drain */
                              sess->queue_depth * 3 + 1);
                max_recv_wr = min_t(int, wr_limit,
                              sess->queue_depth * 3 + 1);
                max_send_sge = 2;
        }
        cq_num = max_send_wr + max_recv_wr;
        /* alloc iu to recv new rkey reply when server reports flags set */
        if (sess->flags & RTRS_MSG_NEW_RKEY_F || con->c.cid == 0) {
                con->rsp_ius = rtrs_iu_alloc(cq_num, sizeof(*rsp),
                                              GFP_KERNEL, sess->s.dev->ib_dev,
                                              DMA_FROM_DEVICE,
                                              rtrs_clt_rdma_done);
                if (!con->rsp_ius)
                        return -ENOMEM;
                con->queue_num = cq_num;
        }
        cq_num = max_send_wr + max_recv_wr;
        cq_vector = con->cpu % sess->s.dev->ib_dev->num_comp_vectors;
        if (con->c.cid >= sess->s.irq_con_num)
                err = rtrs_cq_qp_create(&sess->s, &con->c, max_send_sge,
                                        cq_vector, cq_num, max_send_wr,
                                        max_recv_wr, IB_POLL_DIRECT);
        else
                err = rtrs_cq_qp_create(&sess->s, &con->c, max_send_sge,
                                        cq_vector, cq_num, max_send_wr,
                                        max_recv_wr, IB_POLL_SOFTIRQ);
        /*
         * In case of error we do not bother to clean previous allocations,
         * since destroy_con_cq_qp() must be called.
         */
        return err;
}

static void destroy_con_cq_qp(struct rtrs_clt_con *con)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);

        /*
         * Be careful here: destroy_con_cq_qp() can be called even
         * create_con_cq_qp() failed, see comments there.
         */
        lockdep_assert_held(&con->con_mutex);
        rtrs_cq_qp_destroy(&con->c);
        if (con->rsp_ius) {
                rtrs_iu_free(con->rsp_ius, sess->s.dev->ib_dev, con->queue_num);
                con->rsp_ius = NULL;
                con->queue_num = 0;
        }
        if (sess->s.dev_ref && !--sess->s.dev_ref) {
                rtrs_ib_dev_put(sess->s.dev);
                sess->s.dev = NULL;
        }
}

static void stop_cm(struct rtrs_clt_con *con)
{
        rdma_disconnect(con->c.cm_id);
        if (con->c.qp)
                ib_drain_qp(con->c.qp);
}

static void destroy_cm(struct rtrs_clt_con *con)
{
        rdma_destroy_id(con->c.cm_id);
        con->c.cm_id = NULL;
}

static int rtrs_rdma_addr_resolved(struct rtrs_clt_con *con)
{
        struct rtrs_sess *s = con->c.sess;
        int err;

        mutex_lock(&con->con_mutex);
        err = create_con_cq_qp(con);
        mutex_unlock(&con->con_mutex);
        if (err) {
                rtrs_err(s, "create_con_cq_qp(), err: %d\n", err);
                return err;
        }
        err = rdma_resolve_route(con->c.cm_id, RTRS_CONNECT_TIMEOUT_MS);
        if (err)
                rtrs_err(s, "Resolving route failed, err: %d\n", err);

        return err;
}

static int rtrs_rdma_route_resolved(struct rtrs_clt_con *con)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        struct rtrs_clt *clt = sess->clt;
        struct rtrs_msg_conn_req msg;
        struct rdma_conn_param param;

        int err;

        param = (struct rdma_conn_param) {
                .retry_count = 7,
                .rnr_retry_count = 7,
                .private_data = &msg,
                .private_data_len = sizeof(msg),
        };

        msg = (struct rtrs_msg_conn_req) {
                .magic = cpu_to_le16(RTRS_MAGIC),
                .version = cpu_to_le16(RTRS_PROTO_VER),
                .cid = cpu_to_le16(con->c.cid),
                .cid_num = cpu_to_le16(sess->s.con_num),
                .recon_cnt = cpu_to_le16(sess->s.recon_cnt),
        };
        msg.first_conn = sess->for_new_clt ? FIRST_CONN : 0;
        uuid_copy(&msg.sess_uuid, &sess->s.uuid);
        uuid_copy(&msg.paths_uuid, &clt->paths_uuid);

        err = rdma_connect_locked(con->c.cm_id, &param);
        if (err)
                rtrs_err(clt, "rdma_connect_locked(): %d\n", err);

        return err;
}

static int rtrs_rdma_conn_established(struct rtrs_clt_con *con,
                                       struct rdma_cm_event *ev)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        struct rtrs_clt *clt = sess->clt;
        const struct rtrs_msg_conn_rsp *msg;
        u16 version, queue_depth;
        int errno;
        u8 len;

        msg = ev->param.conn.private_data;
        len = ev->param.conn.private_data_len;
        if (len < sizeof(*msg)) {
                rtrs_err(clt, "Invalid RTRS connection response\n");
                return -ECONNRESET;
        }
        if (le16_to_cpu(msg->magic) != RTRS_MAGIC) {
                rtrs_err(clt, "Invalid RTRS magic\n");
                return -ECONNRESET;
        }
        version = le16_to_cpu(msg->version);
        if (version >> 8 != RTRS_PROTO_VER_MAJOR) {
                rtrs_err(clt, "Unsupported major RTRS version: %d, expected %d\n",
                          version >> 8, RTRS_PROTO_VER_MAJOR);
                return -ECONNRESET;
        }
        errno = le16_to_cpu(msg->errno);
        if (errno) {
                rtrs_err(clt, "Invalid RTRS message: errno %d\n",
                          errno);
                return -ECONNRESET;
        }
        if (con->c.cid == 0) {
                queue_depth = le16_to_cpu(msg->queue_depth);

                if (sess->queue_depth > 0 && queue_depth != sess->queue_depth) {
                        rtrs_err(clt, "Error: queue depth changed\n");

                        /*
                         * Stop any more reconnection attempts
                         */
                        sess->reconnect_attempts = -1;
                        rtrs_err(clt,
                                "Disabling auto-reconnect. Trigger a manual reconnect after issue is resolved\n");
                        return -ECONNRESET;
                }

                if (!sess->rbufs) {
                        kfree(sess->rbufs);
                        sess->rbufs = kcalloc(queue_depth, sizeof(*sess->rbufs),
                                              GFP_KERNEL);
                        if (!sess->rbufs)
                                return -ENOMEM;
                }
                sess->queue_depth = queue_depth;
                sess->max_hdr_size = le32_to_cpu(msg->max_hdr_size);
                sess->max_io_size = le32_to_cpu(msg->max_io_size);
                sess->flags = le32_to_cpu(msg->flags);
                sess->chunk_size = sess->max_io_size + sess->max_hdr_size;

                /*
                 * Global IO size is always a minimum.
                 * If while a reconnection server sends us a value a bit
                 * higher - client does not care and uses cached minimum.
                 *
                 * Since we can have several sessions (paths) restablishing
                 * connections in parallel, use lock.
                 */
                mutex_lock(&clt->paths_mutex);
                clt->queue_depth = sess->queue_depth;
                clt->max_io_size = min_not_zero(sess->max_io_size,
                                                clt->max_io_size);
                mutex_unlock(&clt->paths_mutex);

                /*
                 * Cache the hca_port and hca_name for sysfs
                 */
                sess->hca_port = con->c.cm_id->port_num;
                scnprintf(sess->hca_name, sizeof(sess->hca_name),
                          sess->s.dev->ib_dev->name);
                sess->s.src_addr = con->c.cm_id->route.addr.src_addr;
                /* set for_new_clt, to allow future reconnect on any path */
                sess->for_new_clt = 1;
        }

        return 0;
}

static inline void flag_success_on_conn(struct rtrs_clt_con *con)
{
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);

        atomic_inc(&sess->connected_cnt);
        con->cm_err = 1;
}

static int rtrs_rdma_conn_rejected(struct rtrs_clt_con *con,
                                    struct rdma_cm_event *ev)
{
        struct rtrs_sess *s = con->c.sess;
        const struct rtrs_msg_conn_rsp *msg;
        const char *rej_msg;
        int status, errno;
        u8 data_len;

        status = ev->status;
        rej_msg = rdma_reject_msg(con->c.cm_id, status);
        msg = rdma_consumer_reject_data(con->c.cm_id, ev, &data_len);

        if (msg && data_len >= sizeof(*msg)) {
                errno = (int16_t)le16_to_cpu(msg->errno);
                if (errno == -EBUSY)
                        rtrs_err(s,
                                  "Previous session is still exists on the server, please reconnect later\n");
                else
                        rtrs_err(s,
                                  "Connect rejected: status %d (%s), rtrs errno %d\n",
                                  status, rej_msg, errno);
        } else {
                rtrs_err(s,
                          "Connect rejected but with malformed message: status %d (%s)\n",
                          status, rej_msg);
        }

        return -ECONNRESET;
}

void rtrs_clt_close_conns(struct rtrs_clt_sess *sess, bool wait)
{
        if (rtrs_clt_change_state_get_old(sess, RTRS_CLT_CLOSING, NULL))
                queue_work(rtrs_wq, &sess->close_work);
        if (wait)
                flush_work(&sess->close_work);
}

static inline void flag_error_on_conn(struct rtrs_clt_con *con, int cm_err)
{
        if (con->cm_err == 1) {
                struct rtrs_clt_sess *sess;

                sess = to_clt_sess(con->c.sess);
                if (atomic_dec_and_test(&sess->connected_cnt))

                        wake_up(&sess->state_wq);
        }
        con->cm_err = cm_err;
}

static int rtrs_clt_rdma_cm_handler(struct rdma_cm_id *cm_id,
                                     struct rdma_cm_event *ev)
{
        struct rtrs_clt_con *con = cm_id->context;
        struct rtrs_sess *s = con->c.sess;
        struct rtrs_clt_sess *sess = to_clt_sess(s);
        int cm_err = 0;

        switch (ev->event) {
        case RDMA_CM_EVENT_ADDR_RESOLVED:
                cm_err = rtrs_rdma_addr_resolved(con);
                break;
        case RDMA_CM_EVENT_ROUTE_RESOLVED:
                cm_err = rtrs_rdma_route_resolved(con);
                break;
        case RDMA_CM_EVENT_ESTABLISHED:
                cm_err = rtrs_rdma_conn_established(con, ev);
                if (likely(!cm_err)) {
                        /*
                         * Report success and wake up. Here we abuse state_wq,
                         * i.e. wake up without state change, but we set cm_err.
                         */
                        flag_success_on_conn(con);
                        wake_up(&sess->state_wq);
                        return 0;
                }
                break;
        case RDMA_CM_EVENT_REJECTED:
                cm_err = rtrs_rdma_conn_rejected(con, ev);
                break;
        case RDMA_CM_EVENT_DISCONNECTED:
                /* No message for disconnecting */
                cm_err = -ECONNRESET;
                break;
        case RDMA_CM_EVENT_CONNECT_ERROR:
        case RDMA_CM_EVENT_UNREACHABLE:
        case RDMA_CM_EVENT_ADDR_CHANGE:
        case RDMA_CM_EVENT_TIMEWAIT_EXIT:
                rtrs_wrn(s, "CM error (CM event: %s, err: %d)\n",
                         rdma_event_msg(ev->event), ev->status);
                cm_err = -ECONNRESET;
                break;
        case RDMA_CM_EVENT_ADDR_ERROR:
        case RDMA_CM_EVENT_ROUTE_ERROR:
                rtrs_wrn(s, "CM error (CM event: %s, err: %d)\n",
                         rdma_event_msg(ev->event), ev->status);
                cm_err = -EHOSTUNREACH;
                break;
        case RDMA_CM_EVENT_DEVICE_REMOVAL:
                /*
                 * Device removal is a special case.  Queue close and return 0.
                 */
                rtrs_clt_close_conns(sess, false);
                return 0;
        default:
                rtrs_err(s, "Unexpected RDMA CM error (CM event: %s, err: %d)\n",
                         rdma_event_msg(ev->event), ev->status);

                cm_err = -ECONNRESET;
                break;
        }

        if (cm_err) {
                /*
                 * cm error makes sense only on connection establishing,
                 * in other cases we rely on normal procedure of reconnecting.
                 */
                flag_error_on_conn(con, cm_err);
                rtrs_rdma_error_recovery(con);
        }

        return 0;
}

static int create_cm(struct rtrs_clt_con *con)
{
        struct rtrs_sess *s = con->c.sess;
        struct rtrs_clt_sess *sess = to_clt_sess(s);
        struct rdma_cm_id *cm_id;
        int err;

        cm_id = rdma_create_id(&init_net, rtrs_clt_rdma_cm_handler, con,
                               sess->s.dst_addr.ss_family == AF_IB ?
                               RDMA_PS_IB : RDMA_PS_TCP, IB_QPT_RC);
        if (IS_ERR(cm_id)) {
                err = PTR_ERR(cm_id);
                rtrs_err(s, "Failed to create CM ID, err: %d\n", err);

                return err;
        }
        con->c.cm_id = cm_id;
        con->cm_err = 0;
        /* allow the port to be reused */
        err = rdma_set_reuseaddr(cm_id, 1);
        if (err != 0) {
                rtrs_err(s, "Set address reuse failed, err: %d\n", err);
                goto destroy_cm;
        }
        err = rdma_resolve_addr(cm_id, (struct sockaddr *)&sess->s.src_addr,
                                (struct sockaddr *)&sess->s.dst_addr,
                                RTRS_CONNECT_TIMEOUT_MS);
        if (err) {
                rtrs_err(s, "Failed to resolve address, err: %d\n", err);
                goto destroy_cm;
        }
        /*
         * Combine connection status and session events. This is needed
         * for waiting two possible cases: cm_err has something meaningful
         * or session state was really changed to error by device removal.
         */
        err = wait_event_interruptible_timeout(
                        sess->state_wq,
                        con->cm_err || sess->state != RTRS_CLT_CONNECTING,
                        msecs_to_jiffies(RTRS_CONNECT_TIMEOUT_MS));
        if (err == 0 || err == -ERESTARTSYS) {
                if (err == 0)
                        err = -ETIMEDOUT;
                /* Timedout or interrupted */
                goto errr;
        }
        if (con->cm_err < 0) {
                err = con->cm_err;
                goto errr;
        }
        if (READ_ONCE(sess->state) != RTRS_CLT_CONNECTING) {
                /* Device removal */
                err = -ECONNABORTED;
                goto errr;
        }

        return 0;

errr:
        stop_cm(con);
        mutex_lock(&con->con_mutex);
        destroy_con_cq_qp(con);
        mutex_unlock(&con->con_mutex);
destroy_cm:
        destroy_cm(con);

        return err;
}

static void rtrs_clt_sess_up(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt *clt = sess->clt;
        int up;

        /*
         * We can fire RECONNECTED event only when all paths were
         * connected on rtrs_clt_open(), then each was disconnected
         * and the first one connected again.  That's why this nasty
         * game with counter value.
         */

        mutex_lock(&clt->paths_ev_mutex);
        up = ++clt->paths_up;
        /*
         * Here it is safe to access paths num directly since up counter
         * is greater than MAX_PATHS_NUM only while rtrs_clt_open() is
         * in progress, thus paths removals are impossible.
         */
        if (up > MAX_PATHS_NUM && up == MAX_PATHS_NUM + clt->paths_num)
                clt->paths_up = clt->paths_num;
        else if (up == 1)
                clt->link_ev(clt->priv, RTRS_CLT_LINK_EV_RECONNECTED);
        mutex_unlock(&clt->paths_ev_mutex);

        /* Mark session as established */
        sess->established = true;
        sess->reconnect_attempts = 0;
        sess->stats->reconnects.successful_cnt++;
}

static void rtrs_clt_sess_down(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt *clt = sess->clt;

        if (!sess->established)
                return;

        sess->established = false;
        mutex_lock(&clt->paths_ev_mutex);
        WARN_ON(!clt->paths_up);
        if (--clt->paths_up == 0)
                clt->link_ev(clt->priv, RTRS_CLT_LINK_EV_DISCONNECTED);
        mutex_unlock(&clt->paths_ev_mutex);
}

static void rtrs_clt_stop_and_destroy_conns(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt_con *con;
        unsigned int cid;

        WARN_ON(READ_ONCE(sess->state) == RTRS_CLT_CONNECTED);

        /*
         * Possible race with rtrs_clt_open(), when DEVICE_REMOVAL comes
         * exactly in between.  Start destroying after it finishes.
         */
        mutex_lock(&sess->init_mutex);
        mutex_unlock(&sess->init_mutex);

        /*
         * All IO paths must observe !CONNECTED state before we
         * free everything.
         */
        synchronize_rcu();

        rtrs_stop_hb(&sess->s);

        /*
         * The order it utterly crucial: firstly disconnect and complete all
         * rdma requests with error (thus set in_use=false for requests),
         * then fail outstanding requests checking in_use for each, and
         * eventually notify upper layer about session disconnection.
         */

        for (cid = 0; cid < sess->s.con_num; cid++) {
                if (!sess->s.con[cid])
                        break;
                con = to_clt_con(sess->s.con[cid]);
                stop_cm(con);
        }
        fail_all_outstanding_reqs(sess);
        free_sess_reqs(sess);
        rtrs_clt_sess_down(sess);

        /*
         * Wait for graceful shutdown, namely when peer side invokes
         * rdma_disconnect(). 'connected_cnt' is decremented only on
         * CM events, thus if other side had crashed and hb has detected
         * something is wrong, here we will stuck for exactly timeout ms,
         * since CM does not fire anything.  That is fine, we are not in
         * hurry.
         */
        wait_event_timeout(sess->state_wq, !atomic_read(&sess->connected_cnt),
                           msecs_to_jiffies(RTRS_CONNECT_TIMEOUT_MS));

        for (cid = 0; cid < sess->s.con_num; cid++) {
                if (!sess->s.con[cid])
                        break;
                con = to_clt_con(sess->s.con[cid]);
                mutex_lock(&con->con_mutex);
                destroy_con_cq_qp(con);
                mutex_unlock(&con->con_mutex);
                destroy_cm(con);
                destroy_con(con);
        }
}

static inline bool xchg_sessions(struct rtrs_clt_sess __rcu **rcu_ppcpu_path,
                                 struct rtrs_clt_sess *sess,
                                 struct rtrs_clt_sess *next)
{
        struct rtrs_clt_sess **ppcpu_path;

        /* Call cmpxchg() without sparse warnings */
        ppcpu_path = (typeof(ppcpu_path))rcu_ppcpu_path;
        return sess == cmpxchg(ppcpu_path, sess, next);
}

static void rtrs_clt_remove_path_from_arr(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt *clt = sess->clt;
        struct rtrs_clt_sess *next;
        bool wait_for_grace = false;
        int cpu;

        mutex_lock(&clt->paths_mutex);
        list_del_rcu(&sess->s.entry);

        /* Make sure everybody observes path removal. */
        synchronize_rcu();

        /*
         * At this point nobody sees @sess in the list, but still we have
         * dangling pointer @pcpu_path which _can_ point to @sess.  Since
         * nobody can observe @sess in the list, we guarantee that IO path
         * will not assign @sess to @pcpu_path, i.e. @pcpu_path can be equal
         * to @sess, but can never again become @sess.
         */

        /*
         * Decrement paths number only after grace period, because
         * caller of do_each_path() must firstly observe list without
         * path and only then decremented paths number.
         *
         * Otherwise there can be the following situation:
         *    o Two paths exist and IO is coming.
         *    o One path is removed:
         *      CPU#0                          CPU#1
         *      do_each_path():                rtrs_clt_remove_path_from_arr():
         *          path = get_next_path()
         *          ^^^                            list_del_rcu(path)
         *          [!CONNECTED path]              clt->paths_num--
         *                                              ^^^^^^^^^
         *          load clt->paths_num                 from 2 to 1
         *                    ^^^^^^^^^
         *                    sees 1
         *
         *      path is observed as !CONNECTED, but do_each_path() loop
         *      ends, because expression i < clt->paths_num is false.
         */
        clt->paths_num--;

        /*
         * Get @next connection from current @sess which is going to be
         * removed.  If @sess is the last element, then @next is NULL.
         */
        rcu_read_lock();
        next = list_next_or_null_rr_rcu(&clt->paths_list, &sess->s.entry,
                                        typeof(*next), s.entry);
        rcu_read_unlock();

        /*
         * @pcpu paths can still point to the path which is going to be
         * removed, so change the pointer manually.
         */
        for_each_possible_cpu(cpu) {
                struct rtrs_clt_sess __rcu **ppcpu_path;

                ppcpu_path = per_cpu_ptr(clt->pcpu_path, cpu);
                if (rcu_dereference_protected(*ppcpu_path,
                        lockdep_is_held(&clt->paths_mutex)) != sess)
                        /*
                         * synchronize_rcu() was called just after deleting
                         * entry from the list, thus IO code path cannot
                         * change pointer back to the pointer which is going
                         * to be removed, we are safe here.
                         */
                        continue;

                /*
                 * We race with IO code path, which also changes pointer,
                 * thus we have to be careful not to overwrite it.
                 */
                if (xchg_sessions(ppcpu_path, sess, next))
                        /*
                         * @ppcpu_path was successfully replaced with @next,
                         * that means that someone could also pick up the
                         * @sess and dereferencing it right now, so wait for
                         * a grace period is required.
                         */
                        wait_for_grace = true;
        }
        if (wait_for_grace)
                synchronize_rcu();

        mutex_unlock(&clt->paths_mutex);
}

static void rtrs_clt_add_path_to_arr(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt *clt = sess->clt;

        mutex_lock(&clt->paths_mutex);
        clt->paths_num++;

        list_add_tail_rcu(&sess->s.entry, &clt->paths_list);
        mutex_unlock(&clt->paths_mutex);
}

static void rtrs_clt_close_work(struct work_struct *work)
{
        struct rtrs_clt_sess *sess;

        sess = container_of(work, struct rtrs_clt_sess, close_work);

        cancel_delayed_work_sync(&sess->reconnect_dwork);
        rtrs_clt_stop_and_destroy_conns(sess);
        rtrs_clt_change_state_get_old(sess, RTRS_CLT_CLOSED, NULL);
}

static int init_conns(struct rtrs_clt_sess *sess)
{
        unsigned int cid;
        int err;

        /*
         * On every new session connections increase reconnect counter
         * to avoid clashes with previous sessions not yet closed
         * sessions on a server side.
         */
        sess->s.recon_cnt++;

        /* Establish all RDMA connections  */
        for (cid = 0; cid < sess->s.con_num; cid++) {
                err = create_con(sess, cid);
                if (err)
                        goto destroy;

                err = create_cm(to_clt_con(sess->s.con[cid]));
                if (err) {
                        destroy_con(to_clt_con(sess->s.con[cid]));
                        goto destroy;
                }
        }
        err = alloc_sess_reqs(sess);
        if (err)
                goto destroy;

        rtrs_start_hb(&sess->s);

        return 0;

destroy:
        while (cid--) {
                struct rtrs_clt_con *con = to_clt_con(sess->s.con[cid]);

                stop_cm(con);

                mutex_lock(&con->con_mutex);
                destroy_con_cq_qp(con);
                mutex_unlock(&con->con_mutex);
                destroy_cm(con);
                destroy_con(con);
        }
        /*
         * If we've never taken async path and got an error, say,
         * doing rdma_resolve_addr(), switch to CONNECTION_ERR state
         * manually to keep reconnecting.
         */
        rtrs_clt_change_state_get_old(sess, RTRS_CLT_CONNECTING_ERR, NULL);

        return err;
}

static void rtrs_clt_info_req_done(struct ib_cq *cq, struct ib_wc *wc)
{
        struct rtrs_clt_con *con = to_clt_con(wc->qp->qp_context);
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        struct rtrs_iu *iu;

        iu = container_of(wc->wr_cqe, struct rtrs_iu, cqe);
        rtrs_iu_free(iu, sess->s.dev->ib_dev, 1);

        if (unlikely(wc->status != IB_WC_SUCCESS)) {
                rtrs_err(sess->clt, "Sess info request send failed: %s\n",
                          ib_wc_status_msg(wc->status));
                rtrs_clt_change_state_get_old(sess, RTRS_CLT_CONNECTING_ERR, NULL);
                return;
        }

        rtrs_clt_update_wc_stats(con);
}

static int process_info_rsp(struct rtrs_clt_sess *sess,
                            const struct rtrs_msg_info_rsp *msg)
{
        unsigned int sg_cnt, total_len;
        int i, sgi;

        sg_cnt = le16_to_cpu(msg->sg_cnt);
        if (unlikely(!sg_cnt || (sess->queue_depth % sg_cnt))) {
                rtrs_err(sess->clt, "Incorrect sg_cnt %d, is not multiple\n",
                          sg_cnt);
                return -EINVAL;
        }

        /*
         * Check if IB immediate data size is enough to hold the mem_id and
         * the offset inside the memory chunk.
         */
        if (unlikely((ilog2(sg_cnt - 1) + 1) +
                     (ilog2(sess->chunk_size - 1) + 1) >
                     MAX_IMM_PAYL_BITS)) {
                rtrs_err(sess->clt,
                          "RDMA immediate size (%db) not enough to encode %d buffers of size %dB\n",
                          MAX_IMM_PAYL_BITS, sg_cnt, sess->chunk_size);
                return -EINVAL;
        }
        total_len = 0;
        for (sgi = 0, i = 0; sgi < sg_cnt && i < sess->queue_depth; sgi++) {
                const struct rtrs_sg_desc *desc = &msg->desc[sgi];
                u32 len, rkey;
                u64 addr;

                addr = le64_to_cpu(desc->addr);
                rkey = le32_to_cpu(desc->key);
                len  = le32_to_cpu(desc->len);

                total_len += len;

                if (unlikely(!len || (len % sess->chunk_size))) {
                        rtrs_err(sess->clt, "Incorrect [%d].len %d\n", sgi,
                                  len);
                        return -EINVAL;
                }
                for ( ; len && i < sess->queue_depth; i++) {
                        sess->rbufs[i].addr = addr;
                        sess->rbufs[i].rkey = rkey;

                        len  -= sess->chunk_size;
                        addr += sess->chunk_size;
                }
        }
        /* Sanity check */
        if (unlikely(sgi != sg_cnt || i != sess->queue_depth)) {
                rtrs_err(sess->clt, "Incorrect sg vector, not fully mapped\n");
                return -EINVAL;
        }
        if (unlikely(total_len != sess->chunk_size * sess->queue_depth)) {
                rtrs_err(sess->clt, "Incorrect total_len %d\n", total_len);
                return -EINVAL;
        }

        return 0;
}

static void rtrs_clt_info_rsp_done(struct ib_cq *cq, struct ib_wc *wc)
{
        struct rtrs_clt_con *con = to_clt_con(wc->qp->qp_context);
        struct rtrs_clt_sess *sess = to_clt_sess(con->c.sess);
        struct rtrs_msg_info_rsp *msg;
        enum rtrs_clt_state state;
        struct rtrs_iu *iu;
        size_t rx_sz;
        int err;

        state = RTRS_CLT_CONNECTING_ERR;

        WARN_ON(con->c.cid);
        iu = container_of(wc->wr_cqe, struct rtrs_iu, cqe);
        if (unlikely(wc->status != IB_WC_SUCCESS)) {
                rtrs_err(sess->clt, "Sess info response recv failed: %s\n",
                          ib_wc_status_msg(wc->status));
                goto out;
        }
        WARN_ON(wc->opcode != IB_WC_RECV);

        if (unlikely(wc->byte_len < sizeof(*msg))) {
                rtrs_err(sess->clt, "Sess info response is malformed: size %d\n",
                          wc->byte_len);
                goto out;
        }
        ib_dma_sync_single_for_cpu(sess->s.dev->ib_dev, iu->dma_addr,
                                   iu->size, DMA_FROM_DEVICE);
        msg = iu->buf;
        if (unlikely(le16_to_cpu(msg->type) != RTRS_MSG_INFO_RSP)) {
                rtrs_err(sess->clt, "Sess info response is malformed: type %d\n",
                          le16_to_cpu(msg->type));
                goto out;
        }
        rx_sz  = sizeof(*msg);
        rx_sz += sizeof(msg->desc[0]) * le16_to_cpu(msg->sg_cnt);
        if (unlikely(wc->byte_len < rx_sz)) {
                rtrs_err(sess->clt, "Sess info response is malformed: size %d\n",
                          wc->byte_len);
                goto out;
        }
        err = process_info_rsp(sess, msg);
        if (unlikely(err))
                goto out;

        err = post_recv_sess(sess);
        if (unlikely(err))
                goto out;

        state = RTRS_CLT_CONNECTED;

out:
        rtrs_clt_update_wc_stats(con);
        rtrs_iu_free(iu, sess->s.dev->ib_dev, 1);
        rtrs_clt_change_state_get_old(sess, state, NULL);
}

static int rtrs_send_sess_info(struct rtrs_clt_sess *sess)
{
        struct rtrs_clt_con *usr_con = to_clt_con(sess->s.con[0]);
        struct rtrs_msg_info_req *msg;
        struct rtrs_iu *tx_iu, *rx_iu;
        size_t rx_sz;
        int err;

        rx_sz  = sizeof(struct rtrs_msg_info_rsp);
        rx_sz += sizeof(struct rtrs_sg_desc) * sess->queue_depth;

        tx_iu = rtrs_iu_alloc(1, sizeof(struct rtrs_msg_info_req), GFP_KERNEL,
                               sess->s.dev->ib_dev, DMA_TO_DEVICE,
                               rtrs_clt_info_req_done);
        rx_iu = rtrs_iu_alloc(1, rx_sz, GFP_KERNEL, sess->s.dev->ib_dev,
                               DMA_FROM_DEVICE, rtrs_clt_info_rsp_done);
        if (unlikely(!tx_iu || !rx_iu)) {
                err = -ENOMEM;
                goto out;
        }
        /* Prepare for getting info response */
        err = rtrs_iu_post_recv(&usr_con->c, rx_iu);
        if (unlikely(err)) {
                rtrs_err(sess->clt, "rtrs_iu_post_recv(), err: %d\n", err);
                goto out;
        }
        rx_iu = NULL;

        msg = tx_iu->buf;
        msg->type = cpu_to_le16(RTRS_MSG_INFO_REQ);
        memcpy(msg->sessname, sess->s.sessname, sizeof(msg->sessname));

        ib_dma_sync_single_for_device(sess->s.dev->ib_dev, tx_iu->dma_addr,
                                      tx_iu->size, DMA_TO_DEVICE);

        /* Send info request */
        err = rtrs_iu_post_send(&usr_con->c, tx_iu, sizeof(*msg), NULL);
        if (unlikely(err)) {
                rtrs_err(sess->clt, "rtrs_iu_post_send(), err: %d\n", err);
                goto out;
        }
        tx_iu = NULL;

        /* Wait for state change */
        wait_event_interruptible_timeout(sess->state_wq,
                                         sess->state != RTRS_CLT_CONNECTING,
                                         msecs_to_jiffies(
                                                 RTRS_CONNECT_TIMEOUT_MS));
        if (unlikely(READ_ONCE(sess->state) != RTRS_CLT_CONNECTED)) {
                if (READ_ONCE(sess->state) == RTRS_CLT_CONNECTING_ERR)
                        err = -ECONNRESET;
                else
                        err = -ETIMEDOUT;
        }

out:
        if (tx_iu)
                rtrs_iu_free(tx_iu, sess->s.dev->ib_dev, 1);
        if (rx_iu)
                rtrs_iu_free(rx_iu, sess->s.dev->ib_dev, 1);
        if (unlikely(err))
                /* If we've never taken async path because of malloc problems */
                rtrs_clt_change_state_get_old(sess, RTRS_CLT_CONNECTING_ERR, NULL);

        return err;
}

/**
 * init_sess() - establishes all session connections and does handshake
 * @sess: client session.
 * In case of error full close or reconnect procedure should be taken,
 * because reconnect or close async works can be started.
 */
static int init_sess(struct rtrs_clt_sess *sess)
{
        int err;
        char str[NAME_MAX];
        struct rtrs_addr path = {
                .src = &sess->s.src_addr,
                .dst = &sess->s.dst_addr,
        };

        rtrs_addr_to_str(&path, str, sizeof(str));

        mutex_lock(&sess->init_mutex);
        err = init_conns(sess);
        if (err) {
                rtrs_err(sess->clt,
                         "init_conns() failed: err=%d path=%s [%s:%u]\n", err,
                         str, sess->hca_name, sess->hca_port);
                goto out;
        }
        err = rtrs_send_sess_info(sess);
        if (err) {
                rtrs_err(
                        sess->clt,
                        "rtrs_send_sess_info() failed: err=%d path=%s [%s:%u]\n",
                        err, str, sess->hca_name, sess->hca_port);
                goto out;
        }
        rtrs_clt_sess_up(sess);
out:
        mutex_unlock(&sess->init_mutex);

        return err;
}

static void rtrs_clt_reconnect_work(struct work_struct *work)
{
        struct rtrs_clt_sess *sess;
        struct rtrs_clt *clt;
        unsigned int delay_ms;
        int err;

        sess = container_of(to_delayed_work(work), struct rtrs_clt_sess,
                            reconnect_dwork);
        clt = sess->clt;

        if (READ_ONCE(sess->state) != RTRS_CLT_RECONNECTING)
                return;

        if (sess->reconnect_attempts >= clt->max_reconnect_attempts) {
                /* Close a session completely if max attempts is reached */
                rtrs_clt_close_conns(sess, false);
                return;
        }
        sess->reconnect_attempts++;

        /* Stop everything */
        rtrs_clt_stop_and_destroy_conns(sess);
        msleep(RTRS_RECONNECT_BACKOFF);
        if (rtrs_clt_change_state_get_old(sess, RTRS_CLT_CONNECTING, NULL)) {
                err = init_sess(sess);
                if (err)
                        goto reconnect_again;
        }

        return;

reconnect_again:
        if (rtrs_clt_change_state_get_old(sess, RTRS_CLT_RECONNECTING, NULL)) {
                sess->stats->reconnects.fail_cnt++;
                delay_ms = clt->reconnect_delay_sec * 1000;
                queue_delayed_work(rtrs_wq, &sess->reconnect_dwork,
                                   msecs_to_jiffies(delay_ms +
                                                    prandom_u32() %
                                                    RTRS_RECONNECT_SEED));
        }
}

static void rtrs_clt_dev_release(struct device *dev)
{
        struct rtrs_clt *clt = container_of(dev, struct rtrs_clt, dev);

        kfree(clt);
}

static struct rtrs_clt *alloc_clt(const char *sessname, size_t paths_num,
                                  u16 port, size_t pdu_sz, void *priv,
                                  void  (*link_ev)(void *priv,
                                                   enum rtrs_clt_link_ev ev),
                                  unsigned int reconnect_delay_sec,
                                  unsigned int max_reconnect_attempts)
{
        struct rtrs_clt *clt;
        int err;

        if (!paths_num || paths_num > MAX_PATHS_NUM)
                return ERR_PTR(-EINVAL);

        if (strlen(sessname) >= sizeof(clt->sessname))
                return ERR_PTR(-EINVAL);

        clt = kzalloc(sizeof(*clt), GFP_KERNEL);
        if (!clt)
                return ERR_PTR(-ENOMEM);

        clt->pcpu_path = alloc_percpu(typeof(*clt->pcpu_path));
        if (!clt->pcpu_path) {
                kfree(clt);
                return ERR_PTR(-ENOMEM);
        }

        uuid_gen(&clt->paths_uuid);
        INIT_LIST_HEAD_RCU(&clt->paths_list);
        clt->paths_num = paths_num;
        clt->paths_up = MAX_PATHS_NUM;
        clt->port = port;
        clt->pdu_sz = pdu_sz;
        clt->max_segments = RTRS_MAX_SEGMENTS;
        clt->reconnect_delay_sec = reconnect_delay_sec;
        clt->max_reconnect_attempts = max_reconnect_attempts;
        clt->priv = priv;
        clt->link_ev = link_ev;
        clt->mp_policy = MP_POLICY_MIN_INFLIGHT;
        strscpy(clt->sessname, sessname, sizeof(clt->sessname));
        init_waitqueue_head(&clt->permits_wait);
        mutex_init(&clt->paths_ev_mutex);
        mutex_init(&clt->paths_mutex);

        clt->dev.class = rtrs_clt_dev_class;
        clt->dev.release = rtrs_clt_dev_release;
        err = dev_set_name(&clt->dev, "%s", sessname);
        if (err)
                goto err;
        /*
         * Suppress user space notification until
         * sysfs files are created
         */
        dev_set_uevent_suppress(&clt->dev, true);
        err = device_register(&clt->dev);
        if (err) {
                put_device(&clt->dev);
                goto err;
        }

        clt->kobj_paths = kobject_create_and_add("paths", &clt->dev.kobj);
        if (!clt->kobj_paths) {
                err = -ENOMEM;
                goto err_dev;
        }
        err = rtrs_clt_create_sysfs_root_files(clt);
        if (err) {
                kobject_del(clt->kobj_paths);
                kobject_put(clt->kobj_paths);
                goto err_dev;
        }
        dev_set_uevent_suppress(&clt->dev, false);
        kobject_uevent(&clt->dev.kobj, KOBJ_ADD);

        return clt;
err_dev:
        device_unregister(&clt->dev);
err:
        free_percpu(clt->pcpu_path);
        kfree(clt);
        return ERR_PTR(err);
}

static void free_clt(struct rtrs_clt *clt)
{
        free_permits(clt);
        free_percpu(clt->pcpu_path);
        mutex_destroy(&clt->paths_ev_mutex);
        mutex_destroy(&clt->paths_mutex);
        /* release callback will free clt in last put */
        device_unregister(&clt->dev);
}

/**
 * rtrs_clt_open() - Open a session to an RTRS server
 * @ops: holds the link event callback and the private pointer.
 * @sessname: name of the session
 * @paths: Paths to be established defined by their src and dst addresses
 * @paths_num: Number of elements in the @paths array
 * @port: port to be used by the RTRS session
 * @pdu_sz: Size of extra payload which can be accessed after permit allocation.
 * @reconnect_delay_sec: time between reconnect tries
 * @max_reconnect_attempts: Number of times to reconnect on error before giving
 *                          up, 0 for * disabled, -1 for forever
 * @nr_poll_queues: number of polling mode connection using IB_POLL_DIRECT flag
 *
 * Starts session establishment with the rtrs_server. The function can block
 * up to ~2000ms before it returns.
 *
 * Return a valid pointer on success otherwise PTR_ERR.
 */
struct rtrs_clt *rtrs_clt_open(struct rtrs_clt_ops *ops,
                                 const char *sessname,
                                 const struct rtrs_addr *paths,
                                 size_t paths_num, u16 port,
                                 size_t pdu_sz, u8 reconnect_delay_sec,
                                 s16 max_reconnect_attempts, u32 nr_poll_queues)
{
        struct rtrs_clt_sess *sess, *tmp;
        struct rtrs_clt *clt;
        int err, i;

        clt = alloc_clt(sessname, paths_num, port, pdu_sz, ops->priv,
                        ops->link_ev,
                        reconnect_delay_sec,
                        max_reconnect_attempts);
        if (IS_ERR(clt)) {
                err = PTR_ERR(clt);
                goto out;
        }
        for (i = 0; i < paths_num; i++) {
                struct rtrs_clt_sess *sess;

                sess = alloc_sess(clt, &paths[i], nr_cpu_ids,
                                  nr_poll_queues);
                if (IS_ERR(sess)) {
                        err = PTR_ERR(sess);
                        goto close_all_sess;
                }
                if (!i)
                        sess->for_new_clt = 1;
                list_add_tail_rcu(&sess->s.entry, &clt->paths_list);

                err = init_sess(sess);
                if (err) {
                        list_del_rcu(&sess->s.entry);
                        rtrs_clt_close_conns(sess, true);
                        free_percpu(sess->stats->pcpu_stats);
                        kfree(sess->stats);
                        free_sess(sess);
                        goto close_all_sess;
                }

                err = rtrs_clt_create_sess_files(sess);
                if (err) {
                        list_del_rcu(&sess->s.entry);
                        rtrs_clt_close_conns(sess, true);
                        free_percpu(sess->stats->pcpu_stats);
                        kfree(sess->stats);
                        free_sess(sess);
                        goto close_all_sess;
                }
        }
        err = alloc_permits(clt);
        if (err)
                goto close_all_sess;

        return clt;

close_all_sess:
        list_for_each_entry_safe(sess, tmp, &clt->paths_list, s.entry) {
                rtrs_clt_destroy_sess_files(sess, NULL);
                rtrs_clt_close_conns(sess, true);
                kobject_put(&sess->kobj);
        }
        rtrs_clt_destroy_sysfs_root(clt);
        free_clt(clt);

out:
        return ERR_PTR(err);
}
EXPORT_SYMBOL(rtrs_clt_open);

/**
 * rtrs_clt_close() - Close a session
 * @clt: Session handle. Session is freed upon return.
 */
void rtrs_clt_close(struct rtrs_clt *clt)
{
        struct rtrs_clt_sess *sess, *tmp;

        /* Firstly forbid sysfs access */
        rtrs_clt_destroy_sysfs_root(clt);

        /* Now it is safe to iterate over all paths without locks */
        list_for_each_entry_safe(sess, tmp, &clt->paths_list, s.entry) {
                rtrs_clt_close_conns(sess, true);
                rtrs_clt_destroy_sess_files(sess, NULL);
                kobject_put(&sess->kobj);
        }
        free_clt(clt);
}
EXPORT_SYMBOL(rtrs_clt_close);

int rtrs_clt_reconnect_from_sysfs(struct rtrs_clt_sess *sess)
{
        enum rtrs_clt_state old_state;
        int err = -EBUSY;
        bool changed;

        changed = rtrs_clt_change_state_get_old(sess, RTRS_CLT_RECONNECTING,
                                                 &old_state);
        if (changed) {
                sess->reconnect_attempts = 0;
                queue_delayed_work(rtrs_wq, &sess->reconnect_dwork, 0);
        }
        if (changed || old_state == RTRS_CLT_RECONNECTING) {
                /*
                 * flush_delayed_work() queues pending work for immediate
                 * execution, so do the flush if we have queued something
                 * right now or work is pending.
                 */
                flush_delayed_work(&sess->reconnect_dwork);
                err = (READ_ONCE(sess->state) ==
                       RTRS_CLT_CONNECTED ? 0 : -ENOTCONN);
        }

        return err;
}

int rtrs_clt_remove_path_from_sysfs(struct rtrs_clt_sess *sess,
                                     const struct attribute *sysfs_self)
{
        enum rtrs_clt_state old_state;
        bool changed;

        /*
         * Continue stopping path till state was changed to DEAD or
         * state was observed as DEAD:
         * 1. State was changed to DEAD - we were fast and nobody
         *    invoked rtrs_clt_reconnect(), which can again start
         *    reconnecting.
         * 2. State was observed as DEAD - we have someone in parallel
         *    removing the path.
         */
        do {
                rtrs_clt_close_conns(sess, true);
                changed = rtrs_clt_change_state_get_old(sess,
                                                        RTRS_CLT_DEAD,
                                                        &old_state);
        } while (!changed && old_state != RTRS_CLT_DEAD);

        if (likely(changed)) {
                rtrs_clt_remove_path_from_arr(sess);
                rtrs_clt_destroy_sess_files(sess, sysfs_self);
                kobject_put(&sess->kobj);
        }

        return 0;
}

void rtrs_clt_set_max_reconnect_attempts(struct rtrs_clt *clt, int value)
{
        clt->max_reconnect_attempts = (unsigned int)value;
}

int rtrs_clt_get_max_reconnect_attempts(const struct rtrs_clt *clt)
{
        return (int)clt->max_reconnect_attempts;
}

/**
 * rtrs_clt_request() - Request data transfer to/from server via RDMA.
 *
 * @dir:        READ/WRITE
 * @ops:        callback function to be called as confirmation, and the pointer.
 * @clt:        Session
 * @permit:     Preallocated permit
 * @vec:        Message that is sent to server together with the request.
 *              Sum of len of all @vec elements limited to <= IO_MSG_SIZE.
 *              Since the msg is copied internally it can be allocated on stack.
 * @nr:         Number of elements in @vec.
 * @data_len:   length of data sent to/from server
 * @sg:         Pages to be sent/received to/from server.
 * @sg_cnt:     Number of elements in the @sg
 *
 * Return:
 * 0:           Success
 * <0:          Error
 *
 * On dir=READ rtrs client will request a data transfer from Server to client.
 * The data that the server will respond with will be stored in @sg when
 * the user receives an %RTRS_CLT_RDMA_EV_RDMA_REQUEST_WRITE_COMPL event.
 * On dir=WRITE rtrs client will rdma write data in sg to server side.
 */
int rtrs_clt_request(int dir, struct rtrs_clt_req_ops *ops,
                     struct rtrs_clt *clt, struct rtrs_permit *permit,
                      const struct kvec *vec, size_t nr, size_t data_len,
                      struct scatterlist *sg, unsigned int sg_cnt)
{
        struct rtrs_clt_io_req *req;
        struct rtrs_clt_sess *sess;

        enum dma_data_direction dma_dir;
        int err = -ECONNABORTED, i;
        size_t usr_len, hdr_len;
        struct path_it it;

        /* Get kvec length */
        for (i = 0, usr_len = 0; i < nr; i++)
                usr_len += vec[i].iov_len;

        if (dir == READ) {
                hdr_len = sizeof(struct rtrs_msg_rdma_read) +
                          sg_cnt * sizeof(struct rtrs_sg_desc);
                dma_dir = DMA_FROM_DEVICE;
        } else {
                hdr_len = sizeof(struct rtrs_msg_rdma_write);
                dma_dir = DMA_TO_DEVICE;
        }

        rcu_read_lock();
        for (path_it_init(&it, clt);
             (sess = it.next_path(&it)) && it.i < it.clt->paths_num; it.i++) {
                if (unlikely(READ_ONCE(sess->state) != RTRS_CLT_CONNECTED))
                        continue;

                if (unlikely(usr_len + hdr_len > sess->max_hdr_size)) {
                        rtrs_wrn_rl(sess->clt,
                                     "%s request failed, user message size is %zu and header length %zu, but max size is %u\n",
                                     dir == READ ? "Read" : "Write",
                                     usr_len, hdr_len, sess->max_hdr_size);
                        err = -EMSGSIZE;
                        break;
                }