// SPDX-License-Identifier: GPL-2.0-or-later
/* Client connection-specific management code.
 *
 * Copyright (C) 2016, 2020 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * Client connections need to be cached for a little while after they've made a
 * call so as to handle retransmitted DATA packets in case the server didn't
 * receive the final ACK or terminating ABORT we sent it.
 *
 * There are flags of relevance to the cache:
 *
 *  (2) DONT_REUSE - The connection should be discarded as soon as possible and
 *      should not be reused.  This is set when an exclusive connection is used
 *      or a call ID counter overflows.
 *
 * The caching state may only be changed if the cache lock is held.
 *
 * There are two idle client connection expiry durations.  If the total number
 * of connections is below the reap threshold, we use the normal duration; if
 * it's above, we use the fast duration.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/slab.h>
#include <linux/idr.h>
#include <linux/timer.h>
#include <linux/sched/signal.h>

#include "ar-internal.h"

__read_mostly unsigned int rxrpc_reap_client_connections = 900;
__read_mostly unsigned long rxrpc_conn_idle_client_expiry = 2 * 60 * HZ;
__read_mostly unsigned long rxrpc_conn_idle_client_fast_expiry = 2 * HZ;

/*
 * We use machine-unique IDs for our client connections.
 */
DEFINE_IDR(rxrpc_client_conn_ids);
static DEFINE_SPINLOCK(rxrpc_conn_id_lock);

/*
 * Get a connection ID and epoch for a client connection from the global pool.
 * The connection struct pointer is then recorded in the idr radix tree.  The
 * epoch doesn't change until the client is rebooted (or, at least, unless the
 * module is unloaded).
 */
static int rxrpc_get_client_connection_id(struct rxrpc_connection *conn,
                                          gfp_t gfp)
{
        struct rxrpc_net *rxnet = conn->params.local->rxnet;
        int id;

        _enter("");

        idr_preload(gfp);
        spin_lock(&rxrpc_conn_id_lock);

        id = idr_alloc_cyclic(&rxrpc_client_conn_ids, conn,
                              1, 0x40000000, GFP_NOWAIT);
        if (id < 0)
                goto error;

        spin_unlock(&rxrpc_conn_id_lock);
        idr_preload_end();

        conn->proto.epoch = rxnet->epoch;
        conn->proto.cid = id << RXRPC_CIDSHIFT;
        set_bit(RXRPC_CONN_HAS_IDR, &conn->flags);
        _leave(" [CID %x]", conn->proto.cid);
        return 0;

error:
        spin_unlock(&rxrpc_conn_id_lock);
        idr_preload_end();
        _leave(" = %d", id);
        return id;
}

/*
 * Release a connection ID for a client connection from the global pool.
 */
static void rxrpc_put_client_connection_id(struct rxrpc_connection *conn)
{
        if (test_bit(RXRPC_CONN_HAS_IDR, &conn->flags)) {
                spin_lock(&rxrpc_conn_id_lock);
                idr_remove(&rxrpc_client_conn_ids,
                           conn->proto.cid >> RXRPC_CIDSHIFT);
                spin_unlock(&rxrpc_conn_id_lock);
        }
}

/*
 * Destroy the client connection ID tree.
 */
void rxrpc_destroy_client_conn_ids(void)
{
        struct rxrpc_connection *conn;
        int id;

        if (!idr_is_empty(&rxrpc_client_conn_ids)) {
                idr_for_each_entry(&rxrpc_client_conn_ids, conn, id) {
                        pr_err("AF_RXRPC: Leaked client conn %p {%d}\n",
                               conn, atomic_read(&conn->usage));
                }
                BUG();
        }

        idr_destroy(&rxrpc_client_conn_ids);
}

/*
 * Allocate a connection bundle.
 */
static struct rxrpc_bundle *rxrpc_alloc_bundle(struct rxrpc_conn_parameters *cp,
                                               gfp_t gfp)
{
        struct rxrpc_bundle *bundle;

        bundle = kzalloc(sizeof(*bundle), gfp);
        if (bundle) {
                bundle->params = *cp;
                rxrpc_get_peer(bundle->params.peer);
                atomic_set(&bundle->usage, 1);
                spin_lock_init(&bundle->channel_lock);
                INIT_LIST_HEAD(&bundle->waiting_calls);
        }
        return bundle;
}

struct rxrpc_bundle *rxrpc_get_bundle(struct rxrpc_bundle *bundle)
{
        atomic_inc(&bundle->usage);
        return bundle;
}

void rxrpc_put_bundle(struct rxrpc_bundle *bundle)
{
        unsigned int d = bundle->debug_id;
        unsigned int u = atomic_dec_return(&bundle->usage);

        _debug("PUT B=%x %u", d, u);
        if (u == 0) {
                rxrpc_put_peer(bundle->params.peer);
                kfree(bundle);
        }
}

/*
 * Allocate a client connection.
 */
static struct rxrpc_connection *
rxrpc_alloc_client_connection(struct rxrpc_bundle *bundle, gfp_t gfp)
{
        struct rxrpc_connection *conn;
        struct rxrpc_net *rxnet = bundle->params.local->rxnet;
        int ret;

        _enter("");

        conn = rxrpc_alloc_connection(gfp);
        if (!conn) {
                _leave(" = -ENOMEM");
                return ERR_PTR(-ENOMEM);
        }

        atomic_set(&conn->usage, 1);
        conn->bundle            = bundle;
        conn->params            = bundle->params;
        conn->out_clientflag    = RXRPC_CLIENT_INITIATED;
        conn->state             = RXRPC_CONN_CLIENT;
        conn->service_id        = conn->params.service_id;

        ret = rxrpc_get_client_connection_id(conn, gfp);
        if (ret < 0)
                goto error_0;

        ret = rxrpc_init_client_conn_security(conn);
        if (ret < 0)
                goto error_1;

        atomic_inc(&rxnet->nr_conns);
        write_lock(&rxnet->conn_lock);
        list_add_tail(&conn->proc_link, &rxnet->conn_proc_list);
        write_unlock(&rxnet->conn_lock);

        rxrpc_get_bundle(bundle);
        rxrpc_get_peer(conn->params.peer);
        rxrpc_get_local(conn->params.local);
        key_get(conn->params.key);

        trace_rxrpc_conn(conn->debug_id, rxrpc_conn_new_client,
                         atomic_read(&conn->usage),
                         __builtin_return_address(0));

        atomic_inc(&rxnet->nr_client_conns);
        trace_rxrpc_client(conn, -1, rxrpc_client_alloc);
        _leave(" = %p", conn);
        return conn;

error_1:
        rxrpc_put_client_connection_id(conn);
error_0:
        kfree(conn);
        _leave(" = %d", ret);
        return ERR_PTR(ret);
}

/*
 * Determine if a connection may be reused.
 */
static bool rxrpc_may_reuse_conn(struct rxrpc_connection *conn)
{
        struct rxrpc_net *rxnet;
        int id_cursor, id, distance, limit;

        if (!conn)
                goto dont_reuse;

        rxnet = conn->params.local->rxnet;
        if (test_bit(RXRPC_CONN_DONT_REUSE, &conn->flags))
                goto dont_reuse;

        if (conn->state != RXRPC_CONN_CLIENT ||
            conn->proto.epoch != rxnet->epoch)
                goto mark_dont_reuse;

        /* The IDR tree gets very expensive on memory if the connection IDs are
         * widely scattered throughout the number space, so we shall want to
         * kill off connections that, say, have an ID more than about four
         * times the maximum number of client conns away from the current
         * allocation point to try and keep the IDs concentrated.
         */
        id_cursor = idr_get_cursor(&rxrpc_client_conn_ids);
        id = conn->proto.cid >> RXRPC_CIDSHIFT;
        distance = id - id_cursor;
        if (distance < 0)
                distance = -distance;
        limit = max_t(unsigned long, atomic_read(&rxnet->nr_conns) * 4, 1024);
        if (distance > limit)
                goto mark_dont_reuse;

        return true;

mark_dont_reuse:
        set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);
dont_reuse:
        return false;
}

/*
 * Look up the conn bundle that matches the connection parameters, adding it if
 * it doesn't yet exist.
 */
static struct rxrpc_bundle *rxrpc_look_up_bundle(struct rxrpc_conn_parameters *cp,
                                                 gfp_t gfp)
{
        static atomic_t rxrpc_bundle_id;
        struct rxrpc_bundle *bundle, *candidate;
        struct rxrpc_local *local = cp->local;
        struct rb_node *p, **pp, *parent;
        long diff;

        _enter("{%px,%x,%u,%u}",
               cp->peer, key_serial(cp->key), cp->security_level, cp->upgrade);

        if (cp->exclusive)
                return rxrpc_alloc_bundle(cp, gfp);

        /* First, see if the bundle is already there. */
        _debug("search 1");
        spin_lock(&local->client_bundles_lock);
        p = local->client_bundles.rb_node;
        while (p) {
                bundle = rb_entry(p, struct rxrpc_bundle, local_node);

#define cmp(X) ((long)bundle->params.X - (long)cp->X)
                diff = (cmp(peer) ?:
                        cmp(key) ?:
                        cmp(security_level) ?:
                        cmp(upgrade));
#undef cmp
                if (diff < 0)
                        p = p->rb_left;
                else if (diff > 0)
                        p = p->rb_right;
                else
                        goto found_bundle;
        }
        spin_unlock(&local->client_bundles_lock);
        _debug("not found");

        /* It wasn't.  We need to add one. */
        candidate = rxrpc_alloc_bundle(cp, gfp);
        if (!candidate)
                return NULL;

        _debug("search 2");
        spin_lock(&local->client_bundles_lock);
        pp = &local->client_bundles.rb_node;
        parent = NULL;
        while (*pp) {
                parent = *pp;
                bundle = rb_entry(parent, struct rxrpc_bundle, local_node);

#define cmp(X) ((long)bundle->params.X - (long)cp->X)
                diff = (cmp(peer) ?:
                        cmp(key) ?:
                        cmp(security_level) ?:
                        cmp(upgrade));
#undef cmp
                if (diff < 0)
                        pp = &(*pp)->rb_left;
                else if (diff > 0)
                        pp = &(*pp)->rb_right;
                else
                        goto found_bundle_free;
        }

        _debug("new bundle");
        candidate->debug_id = atomic_inc_return(&rxrpc_bundle_id);
        rb_link_node(&candidate->local_node, parent, pp);
        rb_insert_color(&candidate->local_node, &local->client_bundles);
        rxrpc_get_bundle(candidate);
        spin_unlock(&local->client_bundles_lock);
        _leave(" = %u [new]", candidate->debug_id);
        return candidate;

found_bundle_free:
        kfree(candidate);
found_bundle:
        rxrpc_get_bundle(bundle);
        spin_unlock(&local->client_bundles_lock);
        _leave(" = %u [found]", bundle->debug_id);
        return bundle;
}

/*
 * Create or find a client bundle to use for a call.
 *
 * If we return with a connection, the call will be on its waiting list.  It's
 * left to the caller to assign a channel and wake up the call.
 */
static struct rxrpc_bundle *rxrpc_prep_call(struct rxrpc_sock *rx,
                                            struct rxrpc_call *call,
                                            struct rxrpc_conn_parameters *cp,
                                            struct sockaddr_rxrpc *srx,
                                            gfp_t gfp)
{
        struct rxrpc_bundle *bundle;

        _enter("{%d,%lx},", call->debug_id, call->user_call_ID);

        cp->peer = rxrpc_lookup_peer(rx, cp->local, srx, gfp);
        if (!cp->peer)
                goto error;

        call->cong_cwnd = cp->peer->cong_cwnd;
        if (call->cong_cwnd >= call->cong_ssthresh)
                call->cong_mode = RXRPC_CALL_CONGEST_AVOIDANCE;
        else
                call->cong_mode = RXRPC_CALL_SLOW_START;
        if (cp->upgrade)
                __set_bit(RXRPC_CALL_UPGRADE, &call->flags);

        /* Find the client connection bundle. */
        bundle = rxrpc_look_up_bundle(cp, gfp);
        if (!bundle)
                goto error;

        /* Get this call queued.  Someone else may activate it whilst we're
         * lining up a new connection, but that's fine.
         */
        spin_lock(&bundle->channel_lock);
        list_add_tail(&call->chan_wait_link, &bundle->waiting_calls);
        spin_unlock(&bundle->channel_lock);

        _leave(" = [B=%x]", bundle->debug_id);
        return bundle;

error:
        _leave(" = -ENOMEM");
        return ERR_PTR(-ENOMEM);
}

/*
 * Allocate a new connection and add it into a bundle.
 */
static void rxrpc_add_conn_to_bundle(struct rxrpc_bundle *bundle, gfp_t gfp)
        __releases(bundle->channel_lock)
{
        struct rxrpc_connection *candidate = NULL, *old = NULL;
        bool conflict;
        int i;

        _enter("");

        conflict = bundle->alloc_conn;
        if (!conflict)
                bundle->alloc_conn = true;
        spin_unlock(&bundle->channel_lock);
        if (conflict) {
                _leave(" [conf]");
                return;
        }

        candidate = rxrpc_alloc_client_connection(bundle, gfp);

        spin_lock(&bundle->channel_lock);
        bundle->alloc_conn = false;

        if (IS_ERR(candidate)) {
                bundle->alloc_error = PTR_ERR(candidate);
                spin_unlock(&bundle->channel_lock);
                _leave(" [err %ld]", PTR_ERR(candidate));
                return;
        }

        bundle->alloc_error = 0;

        for (i = 0; i < ARRAY_SIZE(bundle->conns); i++) {
                unsigned int shift = i * RXRPC_MAXCALLS;
                int j;

                old = bundle->conns[i];
                if (!rxrpc_may_reuse_conn(old)) {
                        if (old)
                                trace_rxrpc_client(old, -1, rxrpc_client_replace);
                        candidate->bundle_shift = shift;
                        bundle->conns[i] = candidate;
                        for (j = 0; j < RXRPC_MAXCALLS; j++)
                                set_bit(shift + j, &bundle->avail_chans);
                        candidate = NULL;
                        break;
                }

                old = NULL;
        }

        spin_unlock(&bundle->channel_lock);

        if (candidate) {
                _debug("discard C=%x", candidate->debug_id);
                trace_rxrpc_client(candidate, -1, rxrpc_client_duplicate);
                rxrpc_put_connection(candidate);
        }

        rxrpc_put_connection(old);
        _leave("");
}

/*
 * Add a connection to a bundle if there are no usable connections or we have
 * connections waiting for extra capacity.
 */
static void rxrpc_maybe_add_conn(struct rxrpc_bundle *bundle, gfp_t gfp)
{
        struct rxrpc_call *call;
        int i, usable;

        _enter("");

        spin_lock(&bundle->channel_lock);

        /* See if there are any usable connections. */
        usable = 0;
        for (i = 0; i < ARRAY_SIZE(bundle->conns); i++)
                if (rxrpc_may_reuse_conn(bundle->conns[i]))
                        usable++;

        if (!usable && !list_empty(&bundle->waiting_calls)) {
                call = list_first_entry(&bundle->waiting_calls,
                                        struct rxrpc_call, chan_wait_link);
                if (test_bit(RXRPC_CALL_UPGRADE, &call->flags))
                        bundle->try_upgrade = true;
        }

        if (!usable)
                goto alloc_conn;

        if (!bundle->avail_chans &&
            !bundle->try_upgrade &&
            !list_empty(&bundle->waiting_calls) &&
            usable < ARRAY_SIZE(bundle->conns))
                goto alloc_conn;

        spin_unlock(&bundle->channel_lock);
        _leave("");
        return;

alloc_conn:
        return rxrpc_add_conn_to_bundle(bundle, gfp);
}

/*
 * Assign a channel to the call at the front of the queue and wake the call up.
 * We don't increment the callNumber counter until this number has been exposed
 * to the world.
 */
static void rxrpc_activate_one_channel(struct rxrpc_connection *conn,
                                       unsigned int channel)
{
        struct rxrpc_channel *chan = &conn->channels[channel];
        struct rxrpc_bundle *bundle = conn->bundle;
        struct rxrpc_call *call = list_entry(bundle->waiting_calls.next,
                                             struct rxrpc_call, chan_wait_link);
        u32 call_id = chan->call_counter + 1;

        _enter("C=%x,%u", conn->debug_id, channel);

        trace_rxrpc_client(conn, channel, rxrpc_client_chan_activate);

        /* Cancel the final ACK on the previous call if it hasn't been sent yet
         * as the DATA packet will implicitly ACK it.
         */
        clear_bit(RXRPC_CONN_FINAL_ACK_0 + channel, &conn->flags);
        clear_bit(conn->bundle_shift + channel, &bundle->avail_chans);

        rxrpc_see_call(call);
        list_del_init(&call->chan_wait_link);
        call->peer      = rxrpc_get_peer(conn->params.peer);
        call->conn      = rxrpc_get_connection(conn);
        call->cid       = conn->proto.cid | channel;
        call->call_id   = call_id;
        call->security  = conn->security;
        call->security_ix = conn->security_ix;
        call->service_id = conn->service_id;

        trace_rxrpc_connect_call(call);
        _net("CONNECT call %08x:%08x as call %d on conn %d",
             call->cid, call->call_id, call->debug_id, conn->debug_id);

        write_lock_bh(&call->state_lock);
        call->state = RXRPC_CALL_CLIENT_SEND_REQUEST;
        write_unlock_bh(&call->state_lock);

        /* Paired with the read barrier in rxrpc_connect_call().  This orders
         * cid and epoch in the connection wrt to call_id without the need to
         * take the channel_lock.
         *
         * We provisionally assign a callNumber at this point, but we don't
         * confirm it until the call is about to be exposed.
         *
         * TODO: Pair with a barrier in the data_ready handler when that looks
         * at the call ID through a connection channel.
         */
        smp_wmb();

        chan->call_id           = call_id;
        chan->call_debug_id     = call->debug_id;
        rcu_assign_pointer(chan->call, call);
        wake_up(&call->waitq);
}

/*
 * Remove a connection from the idle list if it's on it.
 */
static void rxrpc_unidle_conn(struct rxrpc_bundle *bundle, struct rxrpc_connection *conn)
{
        struct rxrpc_net *rxnet = bundle->params.local->rxnet;
        bool drop_ref;

        if (!list_empty(&conn->cache_link)) {
                drop_ref = false;
                spin_lock(&rxnet->client_conn_cache_lock);
                if (!list_empty(&conn->cache_link)) {
                        list_del_init(&conn->cache_link);
                        drop_ref = true;
                }
                spin_unlock(&rxnet->client_conn_cache_lock);
                if (drop_ref)
                        rxrpc_put_connection(conn);
        }
}

/*
 * Assign channels and callNumbers to waiting calls with channel_lock
 * held by caller.
 */
static void rxrpc_activate_channels_locked(struct rxrpc_bundle *bundle)
{
        struct rxrpc_connection *conn;
        unsigned long avail, mask;
        unsigned int channel, slot;

        if (bundle->try_upgrade)
                mask = 1;
        else
                mask = ULONG_MAX;

        while (!list_empty(&bundle->waiting_calls)) {
                avail = bundle->avail_chans & mask;
                if (!avail)
                        break;
                channel = __ffs(avail);
                clear_bit(channel, &bundle->avail_chans);

                slot = channel / RXRPC_MAXCALLS;
                conn = bundle->conns[slot];
                if (!conn)
                        break;

                if (bundle->try_upgrade)
                        set_bit(RXRPC_CONN_PROBING_FOR_UPGRADE, &conn->flags);
                rxrpc_unidle_conn(bundle, conn);

                channel &= (RXRPC_MAXCALLS - 1);
                conn->act_chans |= 1 << channel;
                rxrpc_activate_one_channel(conn, channel);
        }
}

/*
 * Assign channels and callNumbers to waiting calls.
 */
static void rxrpc_activate_channels(struct rxrpc_bundle *bundle)
{
        _enter("B=%x", bundle->debug_id);

        trace_rxrpc_client(NULL, -1, rxrpc_client_activate_chans);

        if (!bundle->avail_chans)
                return;

        spin_lock(&bundle->channel_lock);
        rxrpc_activate_channels_locked(bundle);
        spin_unlock(&bundle->channel_lock);
        _leave("");
}

/*
 * Wait for a callNumber and a channel to be granted to a call.
 */
static int rxrpc_wait_for_channel(struct rxrpc_bundle *bundle,
                                  struct rxrpc_call *call, gfp_t gfp)
{
        DECLARE_WAITQUEUE(myself, current);
        int ret = 0;

        _enter("%d", call->debug_id);

        if (!gfpflags_allow_blocking(gfp)) {
                rxrpc_maybe_add_conn(bundle, gfp);
                rxrpc_activate_channels(bundle);
                ret = bundle->alloc_error ?: -EAGAIN;
                goto out;
        }

        add_wait_queue_exclusive(&call->waitq, &myself);
        for (;;) {
                rxrpc_maybe_add_conn(bundle, gfp);
                rxrpc_activate_channels(bundle);
                ret = bundle->alloc_error;
                if (ret < 0)
                        break;

                switch (call->interruptibility) {
                case RXRPC_INTERRUPTIBLE:
                case RXRPC_PREINTERRUPTIBLE:
                        set_current_state(TASK_INTERRUPTIBLE);
                        break;
                case RXRPC_UNINTERRUPTIBLE:
                default:
                        set_current_state(TASK_UNINTERRUPTIBLE);
                        break;
                }
                if (READ_ONCE(call->state) != RXRPC_CALL_CLIENT_AWAIT_CONN)
                        break;
                if ((call->interruptibility == RXRPC_INTERRUPTIBLE ||
                     call->interruptibility == RXRPC_PREINTERRUPTIBLE) &&
                    signal_pending(current)) {
                        ret = -ERESTARTSYS;
                        break;
                }
                schedule();
        }
        remove_wait_queue(&call->waitq, &myself);
        __set_current_state(TASK_RUNNING);

out:
        _leave(" = %d", ret);
        return ret;
}

/*
 * find a connection for a call
 * - called in process context with IRQs enabled
 */
int rxrpc_connect_call(struct rxrpc_sock *rx,
                       struct rxrpc_call *call,
                       struct rxrpc_conn_parameters *cp,
                       struct sockaddr_rxrpc *srx,
                       gfp_t gfp)
{
        struct rxrpc_bundle *bundle;
        struct rxrpc_net *rxnet = cp->local->rxnet;
        int ret = 0;

        _enter("{%d,%lx},", call->debug_id, call->user_call_ID);

        rxrpc_discard_expired_client_conns(&rxnet->client_conn_reaper);

        bundle = rxrpc_prep_call(rx, call, cp, srx, gfp);
        if (IS_ERR(bundle)) {
                ret = PTR_ERR(bundle);
                goto out;
        }

        if (call->state == RXRPC_CALL_CLIENT_AWAIT_CONN) {
                ret = rxrpc_wait_for_channel(bundle, call, gfp);
                if (ret < 0)
                        goto wait_failed;
        }

granted_channel:
        /* Paired with the write barrier in rxrpc_activate_one_channel(). */
        smp_rmb();

out_put_bundle:
        rxrpc_put_bundle(bundle);
out:
        _leave(" = %d", ret);
        return ret;

wait_failed:
        spin_lock(&bundle->channel_lock);
        list_del_init(&call->chan_wait_link);
        spin_unlock(&bundle->channel_lock);

        if (call->state != RXRPC_CALL_CLIENT_AWAIT_CONN) {
                ret = 0;
                goto granted_channel;
        }

        trace_rxrpc_client(call->conn, ret, rxrpc_client_chan_wait_failed);
        rxrpc_set_call_completion(call, RXRPC_CALL_LOCAL_ERROR, 0, ret);
        rxrpc_disconnect_client_call(bundle, call);
        goto out_put_bundle;
}

/*
 * Note that a call, and thus a connection, is about to be exposed to the
 * world.
 */
void rxrpc_expose_client_call(struct rxrpc_call *call)
{
        unsigned int channel = call->cid & RXRPC_CHANNELMASK;
        struct rxrpc_connection *conn = call->conn;
        struct rxrpc_channel *chan = &conn->channels[channel];

        if (!test_and_set_bit(RXRPC_CALL_EXPOSED, &call->flags)) {
                /* Mark the call ID as being used.  If the callNumber counter
                 * exceeds ~2 billion, we kill the connection after its
                 * outstanding calls have finished so that the counter doesn't
                 * wrap.
                 */
                chan->call_counter++;
                if (chan->call_counter >= INT_MAX)
                        set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);
                trace_rxrpc_client(conn, channel, rxrpc_client_exposed);
        }
}

/*
 * Set the reap timer.
 */
static void rxrpc_set_client_reap_timer(struct rxrpc_net *rxnet)
{
        if (!rxnet->kill_all_client_conns) {
                unsigned long now = jiffies;
                unsigned long reap_at = now + rxrpc_conn_idle_client_expiry;

                if (rxnet->live)
                        timer_reduce(&rxnet->client_conn_reap_timer, reap_at);
        }
}

/*
 * Disconnect a client call.
 */
void rxrpc_disconnect_client_call(struct rxrpc_bundle *bundle, struct rxrpc_call *call)
{
        struct rxrpc_connection *conn;
        struct rxrpc_channel *chan = NULL;
        struct rxrpc_net *rxnet = bundle->params.local->rxnet;
        unsigned int channel;
        bool may_reuse;
        u32 cid;

        _enter("c=%x", call->debug_id);

        spin_lock(&bundle->channel_lock);
        set_bit(RXRPC_CALL_DISCONNECTED, &call->flags);

        /* Calls that have never actually been assigned a channel can simply be
         * discarded.
         */
        conn = call->conn;
        if (!conn) {
                _debug("call is waiting");
                ASSERTCMP(call->call_id, ==, 0);
                ASSERT(!test_bit(RXRPC_CALL_EXPOSED, &call->flags));
                list_del_init(&call->chan_wait_link);
                goto out;
        }

        cid = call->cid;
        channel = cid & RXRPC_CHANNELMASK;
        chan = &conn->channels[channel];
        trace_rxrpc_client(conn, channel, rxrpc_client_chan_disconnect);

        if (rcu_access_pointer(chan->call) != call) {
                spin_unlock(&bundle->channel_lock);
                BUG();
        }

        may_reuse = rxrpc_may_reuse_conn(conn);

        /* If a client call was exposed to the world, we save the result for
         * retransmission.
         *
         * We use a barrier here so that the call number and abort code can be
         * read without needing to take a lock.
         *
         * TODO: Make the incoming packet handler check this and handle
         * terminal retransmission without requiring access to the call.
         */
        if (test_bit(RXRPC_CALL_EXPOSED, &call->flags)) {
                _debug("exposed %u,%u", call->call_id, call->abort_code);
                __rxrpc_disconnect_call(conn, call);

                if (test_and_clear_bit(RXRPC_CONN_PROBING_FOR_UPGRADE, &conn->flags)) {
                        trace_rxrpc_client(conn, channel, rxrpc_client_to_active);
                        bundle->try_upgrade = false;
                        if (may_reuse)
                                rxrpc_activate_channels_locked(bundle);
                }

        }

        /* See if we can pass the channel directly to another call. */
        if (may_reuse && !list_empty(&bundle->waiting_calls)) {
                trace_rxrpc_client(conn, channel, rxrpc_client_chan_pass);
                rxrpc_activate_one_channel(conn, channel);
                goto out;
        }

        /* Schedule the final ACK to be transmitted in a short while so that it
         * can be skipped if we find a follow-on call.  The first DATA packet
         * of the follow on call will implicitly ACK this call.
         */
        if (call->completion == RXRPC_CALL_SUCCEEDED &&
            test_bit(RXRPC_CALL_EXPOSED, &call->flags)) {
                unsigned long final_ack_at = jiffies + 2;

                WRITE_ONCE(chan->final_ack_at, final_ack_at);
                smp_wmb(); /* vs rxrpc_process_delayed_final_acks() */
                set_bit(RXRPC_CONN_FINAL_ACK_0 + channel, &conn->flags);
                rxrpc_reduce_conn_timer(conn, final_ack_at);
        }

        /* Deactivate the channel. */
        rcu_assign_pointer(chan->call, NULL);
        set_bit(conn->bundle_shift + channel, &conn->bundle->avail_chans);
        conn->act_chans &= ~(1 << channel);

        /* If no channels remain active, then put the connection on the idle
         * list for a short while.  Give it a ref to stop it going away if it
         * becomes unbundled.
         */
        if (!conn->act_chans) {
                trace_rxrpc_client(conn, channel, rxrpc_client_to_idle);
                conn->idle_timestamp = jiffies;

                rxrpc_get_connection(conn);
                spin_lock(&rxnet->client_conn_cache_lock);
                list_move_tail(&conn->cache_link, &rxnet->idle_client_conns);
                spin_unlock(&rxnet->client_conn_cache_lock);

                rxrpc_set_client_reap_timer(rxnet);
        }

out:
        spin_unlock(&bundle->channel_lock);
        _leave("");
        return;
}

/*
 * Remove a connection from a bundle.
 */
static void rxrpc_unbundle_conn(struct rxrpc_connection *conn)
{
        struct rxrpc_bundle *bundle = conn->bundle;
        struct rxrpc_local *local = bundle->params.local;
        unsigned int bindex;
        bool need_drop = false, need_put = false;
        int i;

        _enter("C=%x", conn->debug_id);

        if (conn->flags & RXRPC_CONN_FINAL_ACK_MASK)
                rxrpc_process_delayed_final_acks(conn, true);

        spin_lock(&bundle->channel_lock);
        bindex = conn->bundle_shift / RXRPC_MAXCALLS;
        if (bundle->conns[bindex] == conn) {
                _debug("clear slot %u", bindex);
                bundle->conns[bindex] = NULL;
                for (i = 0; i < RXRPC_MAXCALLS; i++)
                        clear_bit(conn->bundle_shift + i, &bundle->avail_chans);
                need_drop = true;
        }
        spin_unlock(&bundle->channel_lock);

        /* If there are no more connections, remove the bundle */
        if (!bundle->avail_chans) {
                _debug("maybe unbundle");
                spin_lock(&local->client_bundles_lock);

                for (i = 0; i < ARRAY_SIZE(bundle->conns); i++)
                        if (bundle->conns[i])
                                break;
                if (i == ARRAY_SIZE(bundle->conns) && !bundle->params.exclusive) {
                        _debug("erase bundle");
                        rb_erase(&bundle->local_node, &local->client_bundles);
                        need_put = true;
                }

                spin_unlock(&local->client_bundles_lock);
                if (need_put)
                        rxrpc_put_bundle(bundle);
        }

        if (need_drop)
                rxrpc_put_connection(conn);
        _leave("");
}

/*
 * Clean up a dead client connection.
 */
static void rxrpc_kill_client_conn(struct rxrpc_connection *conn)
{
        struct rxrpc_local *local = conn->params.local;
        struct rxrpc_net *rxnet = local->rxnet;

        _enter("C=%x", conn->debug_id);

        trace_rxrpc_client(conn, -1, rxrpc_client_cleanup);
        atomic_dec(&rxnet->nr_client_conns);

        rxrpc_put_client_connection_id(conn);
        rxrpc_kill_connection(conn);
}

/*
 * Clean up a dead client connections.
 */
void rxrpc_put_client_conn(struct rxrpc_connection *conn)
{
        const void *here = __builtin_return_address(0);
        unsigned int debug_id = conn->debug_id;
        int n;

        n = atomic_dec_return(&conn->usage);
        trace_rxrpc_conn(debug_id, rxrpc_conn_put_client, n, here);
        if (n <= 0) {
                ASSERTCMP(n, >=, 0);
                rxrpc_kill_client_conn(conn);
        }
}

/*
 * Discard expired client connections from the idle list.  Each conn in the
 * idle list has been exposed and holds an extra ref because of that.
 *
 * This may be called from conn setup or from a work item so cannot be
 * considered non-reentrant.
 */
void rxrpc_discard_expired_client_conns(struct work_struct *work)
{
        struct rxrpc_connection *conn;
        struct rxrpc_net *rxnet =
                container_of(work, struct rxrpc_net, client_conn_reaper);
        unsigned long expiry, conn_expires_at, now;
        unsigned int nr_conns;

        _enter("");

        if (list_empty(&rxnet->idle_client_conns)) {
                _leave(" [empty]");
                return;
        }

        /* Don't double up on the discarding */
        if (!spin_trylock(&rxnet->client_conn_discard_lock)) {
                _leave(" [already]");
                return;

        }

        /* We keep an estimate of what the number of conns ought to be after
         * we've discarded some so that we don't overdo the discarding.
         */
        nr_conns = atomic_read(&rxnet->nr_client_conns);

next:
        spin_lock(&rxnet->client_conn_cache_lock);

        if (list_empty(&rxnet->idle_client_conns))
                goto out;

        conn = list_entry(rxnet->idle_client_conns.next,
                          struct rxrpc_connection, cache_link);

        if (!rxnet->kill_all_client_conns) {
                /* If the number of connections is over the reap limit, we
                 * expedite discard by reducing the expiry timeout.  We must,
                 * however, have at least a short grace period to be able to do
                 * final-ACK or ABORT retransmission.
                 */
                expiry = rxrpc_conn_idle_client_expiry;
                if (nr_conns > rxrpc_reap_client_connections)
                        expiry = rxrpc_conn_idle_client_fast_expiry;
                if (conn->params.local->service_closed)
                        expiry = rxrpc_closed_conn_expiry * HZ;

                conn_expires_at = conn->idle_timestamp + expiry;

                now = READ_ONCE(jiffies);
                if (time_after(conn_expires_at, now))
                        goto not_yet_expired;
        }

        trace_rxrpc_client(conn, -1, rxrpc_client_discard);
        list_del_init(&conn->cache_link);

        spin_unlock(&rxnet->client_conn_cache_lock);

        rxrpc_unbundle_conn(conn);
        rxrpc_put_connection(conn); /* Drop the ->cache_link ref */

        nr_conns--;
        goto next;

not_yet_expired:
        /* The connection at the front of the queue hasn't yet expired, so
         * schedule the work item for that point if we discarded something.
         *
         * We don't worry if the work item is already scheduled - it can look
         * after rescheduling itself at a later time.  We could cancel it, but
         * then things get messier.
         */
        _debug("not yet");
        if (!rxnet->kill_all_client_conns)
                timer_reduce(&rxnet->client_conn_reap_timer, conn_expires_at);

out:
        spin_unlock(&rxnet->client_conn_cache_lock);
        spin_unlock(&rxnet->client_conn_discard_lock);
        _leave("");
}

/*
 * Preemptively destroy all the client connection records rather than waiting
 * for them to time out
 */
void rxrpc_destroy_all_client_connections(struct rxrpc_net *rxnet)
{
        _enter("");

        spin_lock(&rxnet->client_conn_cache_lock);
        rxnet->kill_all_client_conns = true;
        spin_unlock(&rxnet->client_conn_cache_lock);

        del_timer_sync(&rxnet->client_conn_reap_timer);

        if (!rxrpc_queue_work(&rxnet->client_conn_reaper))
                _debug("destroy: queue failed");

        _leave("");
}

/*
 * Clean up the client connections on a local endpoint.
 */
void rxrpc_clean_up_local_conns(struct rxrpc_local *local)
{
        struct rxrpc_connection *conn, *tmp;
        struct rxrpc_net *rxnet = local->rxnet;
        LIST_HEAD(graveyard);

        _enter("");

        spin_lock(&rxnet->client_conn_cache_lock);

        list_for_each_entry_safe(conn, tmp, &rxnet->idle_client_conns,
                                 cache_link) {
                if (conn->params.local == local) {
                        trace_rxrpc_client(conn, -1, rxrpc_client_discard);
                        list_move(&conn->cache_link, &graveyard);
                }
        }

        spin_unlock(&rxnet->client_conn_cache_lock);

        while (!list_empty(&graveyard)) {
                conn = list_entry(graveyard.next,
                                  struct rxrpc_connection, cache_link);
                list_del_init(&conn->cache_link);
                rxrpc_unbundle_conn(conn);
                rxrpc_put_connection(conn);
        }

        _leave(" [culled]");
}