/* Client connection-specific management code.
   *
   * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public Licence
   * as published by the Free Software Foundation; either version
   * 2 of the Licence, or (at your option) any later version.

   *
   *
   * 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.
   *
   * Client connections can be in one of a number of cache states:
   *
   *  (1) INACTIVE - The connection is not held in any list and may not have been
   *      exposed to the world.  If it has been previously exposed, it was
   *      discarded from the idle list after expiring.
   *
   *  (2) WAITING - The connection is waiting for the number of client conns to
   *      drop below the maximum capacity.  Calls may be in progress upon it from
   *      when it was active and got culled.
   *
   *	The connection is on the rxrpc_waiting_client_conns list which is kept
   *	in to-be-granted order.  Culled conns with waiters go to the back of
   *	the queue just like new conns.
   *
   *  (3) ACTIVE - The connection has at least one call in progress upon it, it
   *      may freely grant available channels to new calls and calls may be
   *      waiting on it for channels to become available.
   *

   *	The connection is on the rxnet->active_client_conns list which is kept

   *	in activation order for culling purposes.
   *
   *	rxrpc_nr_active_client_conns is held incremented also.
   *

   *  (4) UPGRADE - As for ACTIVE, but only one call may be in progress and is
   *      being used to probe for service upgrade.
   *
   *  (5) CULLED - The connection got summarily culled to try and free up

   *      capacity.  Calls currently in progress on the connection are allowed to
   *      continue, but new calls will have to wait.  There can be no waiters in
   *      this state - the conn would have to go to the WAITING state instead.
   *

   *  (6) IDLE - The connection has no calls in progress upon it and must have

   *      been exposed to the world (ie. the EXPOSED flag must be set).  When it
   *      expires, the EXPOSED flag is cleared and the connection transitions to
   *      the INACTIVE state.
   *

   *	The connection is on the rxnet->idle_client_conns list which is kept in

   *	order of how soon they'll expire.
   *
   * There are flags of relevance to the cache:
   *
   *  (1) EXPOSED - The connection ID got exposed to the world.  If this flag is
   *      set, an extra ref is added to the connection preventing it from being
   *      reaped when it has no calls outstanding.  This flag is cleared and the
   *      ref dropped when a conn is discarded from the idle list.
   *
   *      This allows us to move terminal call state retransmission to the
   *      connection and to discard the call immediately we think it is done
   *      with.  It also give us a chance to reuse the connection.
   *
   *  (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_max_client_connections = 1000;
  __read_mostly unsigned int rxrpc_reap_client_connections = 900;
  __read_mostly unsigned int rxrpc_conn_idle_client_expiry = 2 * 60 * HZ;
  __read_mostly unsigned int 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);

  static void rxrpc_cull_active_client_conns(struct rxrpc_net *);

  /*
   * 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}
  ",
  			       conn, atomic_read(&conn->usage));
  		}
  		BUG();
  	}
  
  	idr_destroy(&rxrpc_client_conn_ids);
  }

  
  /*

   * Allocate a client connection.

   */
  static struct rxrpc_connection *
  rxrpc_alloc_client_connection(struct rxrpc_conn_parameters *cp, gfp_t gfp)
  {
  	struct rxrpc_connection *conn;

  	struct rxrpc_net *rxnet = cp->local->rxnet;

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

  	atomic_set(&conn->usage, 1);

  	if (cp->exclusive)

  		__set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);

  	if (cp->upgrade)
  		__set_bit(RXRPC_CONN_PROBING_FOR_UPGRADE, &conn->flags);

  	conn->params		= *cp;

  	conn->out_clientflag	= RXRPC_CLIENT_INITIATED;
  	conn->state		= RXRPC_CONN_CLIENT;

  	conn->service_id	= cp->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;
  
  	ret = conn->security->prime_packet_security(conn);
  	if (ret < 0)
  		goto error_2;

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

  
  	/* We steal the caller's peer ref. */
  	cp->peer = NULL;
  	rxrpc_get_local(conn->params.local);
  	key_get(conn->params.key);

  	trace_rxrpc_conn(conn, rxrpc_conn_new_client, atomic_read(&conn->usage),
  			 __builtin_return_address(0));
  	trace_rxrpc_client(conn, -1, rxrpc_client_alloc);

  	_leave(" = %p", conn);
  	return conn;
  
  error_2:
  	conn->security->clear(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 = conn->params.local->rxnet;

  	int id_cursor, id, distance, limit;
  
  	if (test_bit(RXRPC_CONN_DONT_REUSE, &conn->flags))
  		goto dont_reuse;

  	if (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(rxrpc_max_client_connections * 4, 1024U);

  	if (distance > limit)
  		goto mark_dont_reuse;
  
  	return true;
  
  mark_dont_reuse:
  	set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);
  dont_reuse:
  	return false;
  }
  
  /*
   * Create or find a client connection 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 int rxrpc_get_client_conn(struct rxrpc_call *call,
  				 struct rxrpc_conn_parameters *cp,
  				 struct sockaddr_rxrpc *srx,
  				 gfp_t gfp)

  {
  	struct rxrpc_connection *conn, *candidate = NULL;
  	struct rxrpc_local *local = cp->local;
  	struct rb_node *p, **pp, *parent;
  	long diff;

  	int ret = -ENOMEM;

  
  	_enter("{%d,%lx},", call->debug_id, call->user_call_ID);
  
  	cp->peer = rxrpc_lookup_peer(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 the connection is not meant to be exclusive, search the available
  	 * connections to see if the connection we want to use already exists.
  	 */

  	if (!cp->exclusive) {

  		_debug("search 1");
  		spin_lock(&local->client_conns_lock);
  		p = local->client_conns.rb_node;
  		while (p) {
  			conn = rb_entry(p, struct rxrpc_connection, client_node);
  
  #define cmp(X) ((long)conn->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 {
  				if (rxrpc_may_reuse_conn(conn) &&
  				    rxrpc_get_connection_maybe(conn))
  					goto found_extant_conn;
  				/* The connection needs replacing.  It's better
  				 * to effect that when we have something to
  				 * replace it with so that we don't have to
  				 * rebalance the tree twice.
  				 */
  				break;
  			}

  		}
  		spin_unlock(&local->client_conns_lock);
  	}

  	/* There wasn't a connection yet or we need an exclusive connection.
  	 * We need to create a candidate and then potentially redo the search
  	 * in case we're racing with another thread also trying to connect on a
  	 * shareable connection.
  	 */
  	_debug("new conn");

  	candidate = rxrpc_alloc_client_connection(cp, gfp);

  	if (IS_ERR(candidate)) {
  		ret = PTR_ERR(candidate);
  		goto error_peer;

  	}

  	/* Add the call to the new connection's waiting list in case we're
  	 * going to have to wait for the connection to come live.  It's our
  	 * connection, so we want first dibs on the channel slots.  We would
  	 * normally have to take channel_lock but we do this before anyone else
  	 * can see the connection.
  	 */
  	list_add_tail(&call->chan_wait_link, &candidate->waiting_calls);

  	if (cp->exclusive) {

  		call->conn = candidate;

  		call->security_ix = candidate->security_ix;

  		call->service_id = candidate->service_id;

  		_leave(" = 0 [exclusive %d]", candidate->debug_id);
  		return 0;

  	}

  	/* Publish the new connection for userspace to find.  We need to redo
  	 * the search before doing this lest we race with someone else adding a
  	 * conflicting instance.

  	 */
  	_debug("search 2");
  	spin_lock(&local->client_conns_lock);
  
  	pp = &local->client_conns.rb_node;
  	parent = NULL;
  	while (*pp) {
  		parent = *pp;
  		conn = rb_entry(parent, struct rxrpc_connection, client_node);

  #define cmp(X) ((long)conn->params.X - (long)candidate->params.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 {
  			if (rxrpc_may_reuse_conn(conn) &&
  			    rxrpc_get_connection_maybe(conn))
  				goto found_extant_conn;
  			/* The old connection is from an outdated epoch. */
  			_debug("replace conn");
  			clear_bit(RXRPC_CONN_IN_CLIENT_CONNS, &conn->flags);
  			rb_replace_node(&conn->client_node,
  					&candidate->client_node,
  					&local->client_conns);

  			trace_rxrpc_client(conn, -1, rxrpc_client_replace);

  			goto candidate_published;
  		}

  	}

  	_debug("new conn");

  	rb_link_node(&candidate->client_node, parent, pp);
  	rb_insert_color(&candidate->client_node, &local->client_conns);

  candidate_published:
  	set_bit(RXRPC_CONN_IN_CLIENT_CONNS, &candidate->flags);
  	call->conn = candidate;

  	call->security_ix = candidate->security_ix;

  	call->service_id = candidate->service_id;

  	spin_unlock(&local->client_conns_lock);

  	_leave(" = 0 [new %d]", candidate->debug_id);
  	return 0;

  	/* We come here if we found a suitable connection already in existence.
  	 * Discard any candidate we may have allocated, and try to get a
  	 * channel on this one.
  	 */
  found_extant_conn:
  	_debug("found conn");
  	spin_unlock(&local->client_conns_lock);

  	if (candidate) {
  		trace_rxrpc_client(candidate, -1, rxrpc_client_duplicate);
  		rxrpc_put_connection(candidate);
  		candidate = NULL;
  	}

  	spin_lock(&conn->channel_lock);
  	call->conn = conn;

  	call->security_ix = conn->security_ix;

  	call->service_id = conn->service_id;

  	list_add(&call->chan_wait_link, &conn->waiting_calls);

  	spin_unlock(&conn->channel_lock);

  	_leave(" = 0 [extant %d]", conn->debug_id);
  	return 0;
  
  error_peer:

  	rxrpc_put_peer(cp->peer);
  	cp->peer = NULL;

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

  /*
   * Activate a connection.
   */

  static void rxrpc_activate_conn(struct rxrpc_net *rxnet,
  				struct rxrpc_connection *conn)

  {

  	if (test_bit(RXRPC_CONN_PROBING_FOR_UPGRADE, &conn->flags)) {
  		trace_rxrpc_client(conn, -1, rxrpc_client_to_upgrade);
  		conn->cache_state = RXRPC_CONN_CLIENT_UPGRADE;
  	} else {
  		trace_rxrpc_client(conn, -1, rxrpc_client_to_active);
  		conn->cache_state = RXRPC_CONN_CLIENT_ACTIVE;
  	}

  	rxnet->nr_active_client_conns++;
  	list_move_tail(&conn->cache_link, &rxnet->active_client_conns);

  }
  
  /*
   * Attempt to animate a connection for a new call.
   *
   * If it's not exclusive, the connection is in the endpoint tree, and we're in
   * the conn's list of those waiting to grab a channel.  There is, however, a
   * limit on the number of live connections allowed at any one time, so we may
   * have to wait for capacity to become available.
   *
   * Note that a connection on the waiting queue might *also* have active
   * channels if it has been culled to make space and then re-requested by a new
   * call.
   */

  static void rxrpc_animate_client_conn(struct rxrpc_net *rxnet,
  				      struct rxrpc_connection *conn)

  {
  	unsigned int nr_conns;
  
  	_enter("%d,%d", conn->debug_id, conn->cache_state);

  	if (conn->cache_state == RXRPC_CONN_CLIENT_ACTIVE ||
  	    conn->cache_state == RXRPC_CONN_CLIENT_UPGRADE)

  		goto out;

  	spin_lock(&rxnet->client_conn_cache_lock);

  	nr_conns = rxnet->nr_client_conns;

  	if (!test_and_set_bit(RXRPC_CONN_COUNTED, &conn->flags)) {
  		trace_rxrpc_client(conn, -1, rxrpc_client_count);

  		rxnet->nr_client_conns = nr_conns + 1;

  	}

  
  	switch (conn->cache_state) {
  	case RXRPC_CONN_CLIENT_ACTIVE:

  	case RXRPC_CONN_CLIENT_UPGRADE:

  	case RXRPC_CONN_CLIENT_WAITING:
  		break;
  
  	case RXRPC_CONN_CLIENT_INACTIVE:
  	case RXRPC_CONN_CLIENT_CULLED:
  	case RXRPC_CONN_CLIENT_IDLE:
  		if (nr_conns >= rxrpc_max_client_connections)
  			goto wait_for_capacity;
  		goto activate_conn;
  
  	default:
  		BUG();

  	}

  out_unlock:

  	spin_unlock(&rxnet->client_conn_cache_lock);

  out:
  	_leave(" [%d]", conn->cache_state);
  	return;

  activate_conn:
  	_debug("activate");

  	rxrpc_activate_conn(rxnet, conn);

  	goto out_unlock;
  
  wait_for_capacity:
  	_debug("wait");

  	trace_rxrpc_client(conn, -1, rxrpc_client_to_waiting);

  	conn->cache_state = RXRPC_CONN_CLIENT_WAITING;

  	list_move_tail(&conn->cache_link, &rxnet->waiting_client_conns);

  	goto out_unlock;
  }
  
  /*
   * Deactivate a channel.
   */
  static void rxrpc_deactivate_one_channel(struct rxrpc_connection *conn,
  					 unsigned int channel)
  {
  	struct rxrpc_channel *chan = &conn->channels[channel];
  
  	rcu_assign_pointer(chan->call, NULL);
  	conn->active_chans &= ~(1 << channel);
  }
  
  /*
   * 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_call *call = list_entry(conn->waiting_calls.next,
  					     struct rxrpc_call, chan_wait_link);
  	u32 call_id = chan->call_counter + 1;

  	trace_rxrpc_client(conn, channel, rxrpc_client_chan_activate);

  	write_lock_bh(&call->state_lock);

  	if (!test_bit(RXRPC_CALL_TX_LASTQ, &call->flags))
  		call->state = RXRPC_CALL_CLIENT_SEND_REQUEST;
  	else
  		call->state = RXRPC_CALL_CLIENT_AWAIT_REPLY;

  	write_unlock_bh(&call->state_lock);

  	rxrpc_see_call(call);

  	list_del_init(&call->chan_wait_link);
  	conn->active_chans |= 1 << channel;
  	call->peer	= rxrpc_get_peer(conn->params.peer);
  	call->cid	= conn->proto.cid | channel;
  	call->call_id	= call_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);
  
  	/* Paired with the read barrier in rxrpc_wait_for_channel().  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;
  	rcu_assign_pointer(chan->call, call);
  	wake_up(&call->waitq);
  }
  
  /*

   * Assign channels and callNumbers to waiting calls with channel_lock
   * held by caller.
   */
  static void rxrpc_activate_channels_locked(struct rxrpc_connection *conn)
  {
  	u8 avail, mask;
  
  	switch (conn->cache_state) {
  	case RXRPC_CONN_CLIENT_ACTIVE:
  		mask = RXRPC_ACTIVE_CHANS_MASK;
  		break;

  	case RXRPC_CONN_CLIENT_UPGRADE:
  		mask = 0x01;
  		break;

  	default:
  		return;
  	}
  
  	while (!list_empty(&conn->waiting_calls) &&
  	       (avail = ~conn->active_chans,
  		avail &= mask,
  		avail != 0))
  		rxrpc_activate_one_channel(conn, __ffs(avail));
  }
  
  /*

   * Assign channels and callNumbers to waiting calls.
   */
  static void rxrpc_activate_channels(struct rxrpc_connection *conn)
  {

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

  	trace_rxrpc_client(conn, -1, rxrpc_client_activate_chans);

  	if (conn->active_chans == RXRPC_ACTIVE_CHANS_MASK)

  		return;
  
  	spin_lock(&conn->channel_lock);

  	rxrpc_activate_channels_locked(conn);

  	spin_unlock(&conn->channel_lock);
  	_leave("");
  }
  
  /*
   * Wait for a callNumber and a channel to be granted to a call.
   */
  static int rxrpc_wait_for_channel(struct rxrpc_call *call, gfp_t gfp)
  {
  	int ret = 0;
  
  	_enter("%d", call->debug_id);
  
  	if (!call->call_id) {
  		DECLARE_WAITQUEUE(myself, current);

  		if (!gfpflags_allow_blocking(gfp)) {

  			ret = -EAGAIN;
  			goto out;

  		}

  		add_wait_queue_exclusive(&call->waitq, &myself);

  		for (;;) {
  			set_current_state(TASK_INTERRUPTIBLE);

  			if (call->call_id)
  				break;
  			if (signal_pending(current)) {
  				ret = -ERESTARTSYS;

  				break;

  			}

  			schedule();
  		}

  		remove_wait_queue(&call->waitq, &myself);

  		__set_current_state(TASK_RUNNING);
  	}

  	/* Paired with the write barrier in rxrpc_activate_one_channel(). */
  	smp_rmb();
  
  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_call *call,
  		       struct rxrpc_conn_parameters *cp,
  		       struct sockaddr_rxrpc *srx,
  		       gfp_t gfp)
  {

  	struct rxrpc_net *rxnet = cp->local->rxnet;

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

  	rxrpc_discard_expired_client_conns(&rxnet->client_conn_reaper.work);
  	rxrpc_cull_active_client_conns(rxnet);

  
  	ret = rxrpc_get_client_conn(call, cp, srx, gfp);
  	if (ret < 0)

  		goto out;

  	rxrpc_animate_client_conn(rxnet, call->conn);

  	rxrpc_activate_channels(call->conn);
  
  	ret = rxrpc_wait_for_channel(call, gfp);

  	if (ret < 0) {

  		rxrpc_disconnect_client_call(call);

  		goto out;
  	}
  
  	spin_lock_bh(&call->conn->params.peer->lock);
  	hlist_add_head(&call->error_link,
  		       &call->conn->params.peer->error_targets);
  	spin_unlock_bh(&call->conn->params.peer->lock);

  out:

  	_leave(" = %d", ret);
  	return ret;
  }
  
  /*
   * Note that a connection is about to be exposed to the world.  Once it is
   * exposed, we maintain an extra ref on it that stops it from being summarily
   * discarded before it's (a) had a chance to deal with retransmission and (b)
   * had a chance at re-use (the per-connection security negotiation is
   * expensive).
   */

  static void rxrpc_expose_client_conn(struct rxrpc_connection *conn,
  				     unsigned int channel)

  {

  	if (!test_and_set_bit(RXRPC_CONN_EXPOSED, &conn->flags)) {
  		trace_rxrpc_client(conn, channel, rxrpc_client_exposed);

  		rxrpc_get_connection(conn);

  	}

  }
  
  /*
   * 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);

  		rxrpc_expose_client_conn(conn, channel);

  	}
  }
  
  /*
   * Disconnect a client call.
   */
  void rxrpc_disconnect_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];

  	struct rxrpc_net *rxnet = rxrpc_net(sock_net(&call->socket->sk));

  	trace_rxrpc_client(conn, channel, rxrpc_client_chan_disconnect);

  	call->conn = NULL;

  	spin_lock(&conn->channel_lock);

  	/* Calls that have never actually been assigned a channel can simply be
  	 * discarded.  If the conn didn't get used either, it will follow
  	 * immediately unless someone else grabs it in the meantime.
  	 */
  	if (!list_empty(&call->chan_wait_link)) {
  		_debug("call is waiting");
  		ASSERTCMP(call->call_id, ==, 0);
  		ASSERT(!test_bit(RXRPC_CALL_EXPOSED, &call->flags));
  		list_del_init(&call->chan_wait_link);

  		trace_rxrpc_client(conn, channel, rxrpc_client_chan_unstarted);

  		/* We must deactivate or idle the connection if it's now
  		 * waiting for nothing.
  		 */

  		spin_lock(&rxnet->client_conn_cache_lock);

  		if (conn->cache_state == RXRPC_CONN_CLIENT_WAITING &&
  		    list_empty(&conn->waiting_calls) &&
  		    !conn->active_chans)
  			goto idle_connection;
  		goto out;
  	}
  
  	ASSERTCMP(rcu_access_pointer(chan->call), ==, call);

  
  	/* 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);
  	}
  
  	/* See if we can pass the channel directly to another call. */
  	if (conn->cache_state == RXRPC_CONN_CLIENT_ACTIVE &&
  	    !list_empty(&conn->waiting_calls)) {

  		trace_rxrpc_client(conn, channel, rxrpc_client_chan_pass);

  		rxrpc_activate_one_channel(conn, channel);
  		goto out_2;
  	}
  
  	/* Things are more complex and we need the cache lock.  We might be
  	 * able to simply idle the conn or it might now be lurking on the wait
  	 * list.  It might even get moved back to the active list whilst we're
  	 * waiting for the lock.
  	 */

  	spin_lock(&rxnet->client_conn_cache_lock);

  
  	switch (conn->cache_state) {

  	case RXRPC_CONN_CLIENT_UPGRADE:
  		/* Deal with termination of a service upgrade probe. */
  		if (test_bit(RXRPC_CONN_EXPOSED, &conn->flags)) {
  			clear_bit(RXRPC_CONN_PROBING_FOR_UPGRADE, &conn->flags);
  			trace_rxrpc_client(conn, channel, rxrpc_client_to_active);
  			conn->cache_state = RXRPC_CONN_CLIENT_ACTIVE;
  			rxrpc_activate_channels_locked(conn);
  		}
  		/* fall through */

  	case RXRPC_CONN_CLIENT_ACTIVE:
  		if (list_empty(&conn->waiting_calls)) {
  			rxrpc_deactivate_one_channel(conn, channel);
  			if (!conn->active_chans) {

  				rxnet->nr_active_client_conns--;

  				goto idle_connection;
  			}
  			goto out;
  		}

  		trace_rxrpc_client(conn, channel, rxrpc_client_chan_pass);

  		rxrpc_activate_one_channel(conn, channel);
  		goto out;
  
  	case RXRPC_CONN_CLIENT_CULLED:
  		rxrpc_deactivate_one_channel(conn, channel);
  		ASSERT(list_empty(&conn->waiting_calls));
  		if (!conn->active_chans)
  			goto idle_connection;
  		goto out;
  
  	case RXRPC_CONN_CLIENT_WAITING:
  		rxrpc_deactivate_one_channel(conn, channel);
  		goto out;
  
  	default:
  		BUG();
  	}

  out:

  	spin_unlock(&rxnet->client_conn_cache_lock);

  out_2:
  	spin_unlock(&conn->channel_lock);

  	rxrpc_put_connection(conn);

  	_leave("");
  	return;
  
  idle_connection:
  	/* As no channels remain active, the connection gets deactivated
  	 * immediately or moved to the idle list for a short while.
  	 */
  	if (test_bit(RXRPC_CONN_EXPOSED, &conn->flags)) {

  		trace_rxrpc_client(conn, channel, rxrpc_client_to_idle);

  		conn->idle_timestamp = jiffies;
  		conn->cache_state = RXRPC_CONN_CLIENT_IDLE;

  		list_move_tail(&conn->cache_link, &rxnet->idle_client_conns);
  		if (rxnet->idle_client_conns.next == &conn->cache_link &&
  		    !rxnet->kill_all_client_conns)

  			queue_delayed_work(rxrpc_workqueue,

  					   &rxnet->client_conn_reaper,

  					   rxrpc_conn_idle_client_expiry);
  	} else {

  		trace_rxrpc_client(conn, channel, rxrpc_client_to_inactive);

  		conn->cache_state = RXRPC_CONN_CLIENT_INACTIVE;
  		list_del_init(&conn->cache_link);
  	}
  	goto out;

  }

  
  /*

   * Clean up a dead client connection.

   */

  static struct rxrpc_connection *
  rxrpc_put_one_client_conn(struct rxrpc_connection *conn)

  {

  	struct rxrpc_connection *next = NULL;

  	struct rxrpc_local *local = conn->params.local;

  	struct rxrpc_net *rxnet = local->rxnet;

  	unsigned int nr_conns;

  	trace_rxrpc_client(conn, -1, rxrpc_client_cleanup);

  	if (test_bit(RXRPC_CONN_IN_CLIENT_CONNS, &conn->flags)) {
  		spin_lock(&local->client_conns_lock);
  		if (test_and_clear_bit(RXRPC_CONN_IN_CLIENT_CONNS,
  				       &conn->flags))
  			rb_erase(&conn->client_node, &local->client_conns);
  		spin_unlock(&local->client_conns_lock);
  	}

  
  	rxrpc_put_client_connection_id(conn);

  
  	ASSERTCMP(conn->cache_state, ==, RXRPC_CONN_CLIENT_INACTIVE);

  	if (test_bit(RXRPC_CONN_COUNTED, &conn->flags)) {

  		trace_rxrpc_client(conn, -1, rxrpc_client_uncount);

  		spin_lock(&rxnet->client_conn_cache_lock);
  		nr_conns = --rxnet->nr_client_conns;

  
  		if (nr_conns < rxrpc_max_client_connections &&

  		    !list_empty(&rxnet->waiting_client_conns)) {
  			next = list_entry(rxnet->waiting_client_conns.next,

  					  struct rxrpc_connection, cache_link);
  			rxrpc_get_connection(next);

  			rxrpc_activate_conn(rxnet, next);

  		}

  		spin_unlock(&rxnet->client_conn_cache_lock);

  	}

  	rxrpc_kill_connection(conn);

  	if (next)
  		rxrpc_activate_channels(next);
  
  	/* We need to get rid of the temporary ref we took upon next, but we
  	 * can't call rxrpc_put_connection() recursively.
  	 */
  	return next;
  }
  
  /*
   * Clean up a dead client connections.
   */
  void rxrpc_put_client_conn(struct rxrpc_connection *conn)
  {

  	const void *here = __builtin_return_address(0);
  	int n;

  
  	do {

  		n = atomic_dec_return(&conn->usage);
  		trace_rxrpc_conn(conn, rxrpc_conn_put_client, n, here);
  		if (n > 0)
  			return;
  		ASSERTCMP(n, >=, 0);
  
  		conn = rxrpc_put_one_client_conn(conn);
  	} while (conn);

  }
  
  /*
   * Kill the longest-active client connections to make room for new ones.
   */

  static void rxrpc_cull_active_client_conns(struct rxrpc_net *rxnet)

  {
  	struct rxrpc_connection *conn;

  	unsigned int nr_conns = rxnet->nr_client_conns;

  	unsigned int nr_active, limit;
  
  	_enter("");
  
  	ASSERTCMP(nr_conns, >=, 0);
  	if (nr_conns < rxrpc_max_client_connections) {
  		_leave(" [ok]");
  		return;
  	}
  	limit = rxrpc_reap_client_connections;

  	spin_lock(&rxnet->client_conn_cache_lock);
  	nr_active = rxnet->nr_active_client_conns;

  
  	while (nr_active > limit) {

  		ASSERT(!list_empty(&rxnet->active_client_conns));
  		conn = list_entry(rxnet->active_client_conns.next,

  				  struct rxrpc_connection, cache_link);

  		ASSERTIFCMP(conn->cache_state != RXRPC_CONN_CLIENT_ACTIVE,
  			    conn->cache_state, ==, RXRPC_CONN_CLIENT_UPGRADE);

  
  		if (list_empty(&conn->waiting_calls)) {

  			trace_rxrpc_client(conn, -1, rxrpc_client_to_culled);

  			conn->cache_state = RXRPC_CONN_CLIENT_CULLED;
  			list_del_init(&conn->cache_link);
  		} else {

  			trace_rxrpc_client(conn, -1, rxrpc_client_to_waiting);

  			conn->cache_state = RXRPC_CONN_CLIENT_WAITING;
  			list_move_tail(&conn->cache_link,

  				       &rxnet->waiting_client_conns);

  		}
  
  		nr_active--;
  	}

  	rxnet->nr_active_client_conns = nr_active;
  	spin_unlock(&rxnet->client_conn_cache_lock);

  	ASSERTCMP(nr_active, >=, 0);
  	_leave(" [culled]");
  }
  
  /*
   * 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(to_delayed_work(work),
  			     struct rxrpc_net, client_conn_reaper);

  	unsigned long expiry, conn_expires_at, now;
  	unsigned int nr_conns;
  	bool did_discard = false;

  	_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 = 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);
  	ASSERT(test_bit(RXRPC_CONN_EXPOSED, &conn->flags));

  	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);

  	if (!test_and_clear_bit(RXRPC_CONN_EXPOSED, &conn->flags))
  		BUG();
  	conn->cache_state = RXRPC_CONN_CLIENT_INACTIVE;
  	list_del_init(&conn->cache_link);

  	spin_unlock(&rxnet->client_conn_cache_lock);

  
  	/* When we cleared the EXPOSED flag, we took on responsibility for the
  	 * reference that that had on the usage count.  We deal with that here.
  	 * If someone re-sets the flag and re-gets the ref, that's fine.
  	 */
  	rxrpc_put_connection(conn);
  	did_discard = true;
  	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)

  		queue_delayed_work(rxrpc_workqueue,

  				   &rxnet->client_conn_reaper,

  				   conn_expires_at - now);
  
  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);

  	cancel_delayed_work(&rxnet->client_conn_reaper);

  	if (!queue_delayed_work(rxrpc_workqueue, &rxnet->client_conn_reaper, 0))

  		_debug("destroy: queue failed");
  
  	_leave("");

  }