net/rxrpc/call_accept.c - third_party/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /* incoming call handling
  *
  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
  */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/module.h>
 #include <linux/net.h>
 #include <linux/skbuff.h>
 #include <linux/errqueue.h>
 #include <linux/udp.h>
 #include <linux/in.h>
 #include <linux/in6.h>
 #include <linux/icmp.h>
 #include <linux/gfp.h>
 #include <linux/circ_buf.h>
 #include <net/sock.h>
 #include <net/af_rxrpc.h>
 #include <net/ip.h>
 #include "ar-internal.h"

 static void rxrpc_dummy_notify(struct sock *sk, struct rxrpc_call *call,
 			       unsigned long user_call_ID)
 {
 }

 /*
  * Preallocate a single service call, connection and peer and, if possible,
  * give them a user ID and attach the user's side of the ID to them.
  */
 static int rxrpc_service_prealloc_one(struct rxrpc_sock *rx,
 				      struct rxrpc_backlog *b,
 				      rxrpc_notify_rx_t notify_rx,
 				      rxrpc_user_attach_call_t user_attach_call,
 				      unsigned long user_call_ID, gfp_t gfp,
 				      unsigned int debug_id)
 {
 	const void *here = __builtin_return_address(0);
 	struct rxrpc_call *call, *xcall;
 	struct rxrpc_net *rxnet = rxrpc_net(sock_net(&rx->sk));
 	struct rb_node *parent, **pp;
 	int max, tmp;
 	unsigned int size = RXRPC_BACKLOG_MAX;
 	unsigned int head, tail, call_head, call_tail;

 	max = rx->sk.sk_max_ack_backlog;
 	tmp = rx->sk.sk_ack_backlog;
 	if (tmp >= max) {
 		_leave(" = -ENOBUFS [full %u]", max);
 		return -ENOBUFS;
 	}
 	max -= tmp;

 	/* We don't need more conns and peers than we have calls, but on the
 	 * other hand, we shouldn't ever use more peers than conns or conns
 	 * than calls.
 	 */
 	call_head = b->call_backlog_head;
 	call_tail = READ_ONCE(b->call_backlog_tail);
 	tmp = CIRC_CNT(call_head, call_tail, size);
 	if (tmp >= max) {
 		_leave(" = -ENOBUFS [enough %u]", tmp);
 		return -ENOBUFS;
 	}
 	max = tmp + 1;

 	head = b->peer_backlog_head;
 	tail = READ_ONCE(b->peer_backlog_tail);
 	if (CIRC_CNT(head, tail, size) < max) {
 		struct rxrpc_peer *peer = rxrpc_alloc_peer(rx->local, gfp);
 		if (!peer)
 			return -ENOMEM;
 		b->peer_backlog[head] = peer;
 		smp_store_release(&b->peer_backlog_head,
 				  (head + 1) & (size - 1));
 	}

 	head = b->conn_backlog_head;
 	tail = READ_ONCE(b->conn_backlog_tail);
 	if (CIRC_CNT(head, tail, size) < max) {
 		struct rxrpc_connection *conn;

 		conn = rxrpc_prealloc_service_connection(rxnet, gfp);
 		if (!conn)
 			return -ENOMEM;
 		b->conn_backlog[head] = conn;
 		smp_store_release(&b->conn_backlog_head,
 				  (head + 1) & (size - 1));

 		trace_rxrpc_conn(conn->debug_id, rxrpc_conn_new_service,
 				 refcount_read(&conn->ref), here);
 	}

 	/* Now it gets complicated, because calls get registered with the
 	 * socket here, with a user ID preassigned by the user.
 	 */
 	call = rxrpc_alloc_call(rx, gfp, debug_id);
 	if (!call)
 		return -ENOMEM;
 	call->flags |= (1 << RXRPC_CALL_IS_SERVICE);
 	call->state = RXRPC_CALL_SERVER_PREALLOC;

 	trace_rxrpc_call(call->debug_id, rxrpc_call_new_service,
 			 refcount_read(&call->ref),
 			 here, (const void *)user_call_ID);

 	write_lock(&rx->call_lock);

 	/* Check the user ID isn't already in use */
 	pp = &rx->calls.rb_node;
 	parent = NULL;
 	while (*pp) {
 		parent = *pp;
 		xcall = rb_entry(parent, struct rxrpc_call, sock_node);
 		if (user_call_ID < xcall->user_call_ID)
 			pp = &(*pp)->rb_left;
 		else if (user_call_ID > xcall->user_call_ID)
 			pp = &(*pp)->rb_right;
 		else
 			goto id_in_use;
 	}

 	call->user_call_ID = user_call_ID;
 	call->notify_rx = notify_rx;
 	if (user_attach_call) {
 		rxrpc_get_call(call, rxrpc_call_got_kernel);
 		user_attach_call(call, user_call_ID);
 	}

 	rxrpc_get_call(call, rxrpc_call_got_userid);
 	rb_link_node(&call->sock_node, parent, pp);
 	rb_insert_color(&call->sock_node, &rx->calls);
 	set_bit(RXRPC_CALL_HAS_USERID, &call->flags);

 	list_add(&call->sock_link, &rx->sock_calls);

 	write_unlock(&rx->call_lock);

 	rxnet = call->rxnet;
 	spin_lock_bh(&rxnet->call_lock);
 	list_add_tail_rcu(&call->link, &rxnet->calls);
 	spin_unlock_bh(&rxnet->call_lock);

 	b->call_backlog[call_head] = call;
 	smp_store_release(&b->call_backlog_head, (call_head + 1) & (size - 1));
 	_leave(" = 0 [%d -> %lx]", call->debug_id, user_call_ID);
 	return 0;

 id_in_use:
 	write_unlock(&rx->call_lock);
 	rxrpc_cleanup_call(call);
 	_leave(" = -EBADSLT");
 	return -EBADSLT;
 }

 /*
  * Allocate the preallocation buffers for incoming service calls.  These must
  * be charged manually.
  */
 int rxrpc_service_prealloc(struct rxrpc_sock *rx, gfp_t gfp)
 {
 	struct rxrpc_backlog *b = rx->backlog;

 	if (!b) {
 		b = kzalloc(sizeof(struct rxrpc_backlog), gfp);
 		if (!b)
 			return -ENOMEM;
 		rx->backlog = b;
 	}

 	return 0;
 }

 /*
  * Discard the preallocation on a service.
  */
 void rxrpc_discard_prealloc(struct rxrpc_sock *rx)
 {
 	struct rxrpc_backlog *b = rx->backlog;
 	struct rxrpc_net *rxnet = rxrpc_net(sock_net(&rx->sk));
 	unsigned int size = RXRPC_BACKLOG_MAX, head, tail;

 	if (!b)
 		return;
 	rx->backlog = NULL;

 	/* Make sure that there aren't any incoming calls in progress before we
 	 * clear the preallocation buffers.
 	 */
 	spin_lock_bh(&rx->incoming_lock);
 	spin_unlock_bh(&rx->incoming_lock);

 	head = b->peer_backlog_head;
 	tail = b->peer_backlog_tail;
 	while (CIRC_CNT(head, tail, size) > 0) {
 		struct rxrpc_peer *peer = b->peer_backlog[tail];
 		rxrpc_put_local(peer->local);
 		kfree(peer);
 		tail = (tail + 1) & (size - 1);
 	}

 	head = b->conn_backlog_head;
 	tail = b->conn_backlog_tail;
 	while (CIRC_CNT(head, tail, size) > 0) {
 		struct rxrpc_connection *conn = b->conn_backlog[tail];
 		write_lock(&rxnet->conn_lock);
 		list_del(&conn->link);
 		list_del(&conn->proc_link);
 		write_unlock(&rxnet->conn_lock);
 		kfree(conn);
 		if (atomic_dec_and_test(&rxnet->nr_conns))
 			wake_up_var(&rxnet->nr_conns);
 		tail = (tail + 1) & (size - 1);
 	}

 	head = b->call_backlog_head;
 	tail = b->call_backlog_tail;
 	while (CIRC_CNT(head, tail, size) > 0) {
 		struct rxrpc_call *call = b->call_backlog[tail];
 		rcu_assign_pointer(call->socket, rx);
 		if (rx->discard_new_call) {
 			_debug("discard %lx", call->user_call_ID);
 			rx->discard_new_call(call, call->user_call_ID);
 			if (call->notify_rx)
 				call->notify_rx = rxrpc_dummy_notify;
 			rxrpc_put_call(call, rxrpc_call_put_kernel);
 		}
 		rxrpc_call_completed(call);
 		rxrpc_release_call(rx, call);
 		rxrpc_put_call(call, rxrpc_call_put);
 		tail = (tail + 1) & (size - 1);
 	}

 	kfree(b);
 }

 /*
  * Ping the other end to fill our RTT cache and to retrieve the rwind
  * and MTU parameters.
  */
 static void rxrpc_send_ping(struct rxrpc_call *call, struct sk_buff *skb)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	ktime_t now = skb->tstamp;

 	if (call->peer->rtt_count < 3 ||
 	    ktime_before(ktime_add_ms(call->peer->rtt_last_req, 1000), now))
 		rxrpc_propose_ACK(call, RXRPC_ACK_PING, sp->hdr.serial,
 				  true, true,
 				  rxrpc_propose_ack_ping_for_params);
 }

 /*
  * Allocate a new incoming call from the prealloc pool, along with a connection
  * and a peer as necessary.
  */
 static struct rxrpc_call *rxrpc_alloc_incoming_call(struct rxrpc_sock *rx,
 						    struct rxrpc_local *local,
 						    struct rxrpc_peer *peer,
 						    struct rxrpc_connection *conn,
 						    const struct rxrpc_security *sec,
 						    struct sk_buff *skb)
 {
 	struct rxrpc_backlog *b = rx->backlog;
 	struct rxrpc_call *call;
 	unsigned short call_head, conn_head, peer_head;
 	unsigned short call_tail, conn_tail, peer_tail;
 	unsigned short call_count, conn_count;

 	/* #calls >= #conns >= #peers must hold true. */
 	call_head = smp_load_acquire(&b->call_backlog_head);
 	call_tail = b->call_backlog_tail;
 	call_count = CIRC_CNT(call_head, call_tail, RXRPC_BACKLOG_MAX);
 	conn_head = smp_load_acquire(&b->conn_backlog_head);
 	conn_tail = b->conn_backlog_tail;
 	conn_count = CIRC_CNT(conn_head, conn_tail, RXRPC_BACKLOG_MAX);
 	ASSERTCMP(conn_count, >=, call_count);
 	peer_head = smp_load_acquire(&b->peer_backlog_head);
 	peer_tail = b->peer_backlog_tail;
 	ASSERTCMP(CIRC_CNT(peer_head, peer_tail, RXRPC_BACKLOG_MAX), >=,
 		  conn_count);

 	if (call_count == 0)
 		return NULL;

 	if (!conn) {
 		if (peer && !rxrpc_get_peer_maybe(peer))
 			peer = NULL;
 		if (!peer) {
 			peer = b->peer_backlog[peer_tail];
 			if (rxrpc_extract_addr_from_skb(&peer->srx, skb) < 0)
 				return NULL;
 			b->peer_backlog[peer_tail] = NULL;
 			smp_store_release(&b->peer_backlog_tail,
 					  (peer_tail + 1) &
 					  (RXRPC_BACKLOG_MAX - 1));

 			rxrpc_new_incoming_peer(rx, local, peer);
 		}

 		/* Now allocate and set up the connection */
 		conn = b->conn_backlog[conn_tail];
 		b->conn_backlog[conn_tail] = NULL;
 		smp_store_release(&b->conn_backlog_tail,
 				  (conn_tail + 1) & (RXRPC_BACKLOG_MAX - 1));
 		conn->params.local = rxrpc_get_local(local);
 		conn->params.peer = peer;
 		rxrpc_see_connection(conn);
 		rxrpc_new_incoming_connection(rx, conn, sec, skb);
 	} else {
 		rxrpc_get_connection(conn);
 	}

 	/* And now we can allocate and set up a new call */
 	call = b->call_backlog[call_tail];
 	b->call_backlog[call_tail] = NULL;
 	smp_store_release(&b->call_backlog_tail,
 			  (call_tail + 1) & (RXRPC_BACKLOG_MAX - 1));

 	rxrpc_see_call(call);
 	call->conn = conn;
 	call->security = conn->security;
 	call->security_ix = conn->security_ix;
 	call->peer = rxrpc_get_peer(conn->params.peer);
 	call->cong_cwnd = call->peer->cong_cwnd;
 	return call;
 }

 /*
  * Set up a new incoming call.  Called in BH context with the RCU read lock
  * held.
  *
  * If this is for a kernel service, when we allocate the call, it will have
  * three refs on it: (1) the kernel service, (2) the user_call_ID tree, (3) the
  * retainer ref obtained from the backlog buffer.  Prealloc calls for userspace
  * services only have the ref from the backlog buffer.  We want to pass this
  * ref to non-BH context to dispose of.
  *
  * If we want to report an error, we mark the skb with the packet type and
  * abort code and return NULL.
  *
  * The call is returned with the user access mutex held.
  */
 struct rxrpc_call *rxrpc_new_incoming_call(struct rxrpc_local *local,
 					   struct rxrpc_sock *rx,
 					   struct sk_buff *skb)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	const struct rxrpc_security *sec = NULL;
 	struct rxrpc_connection *conn;
 	struct rxrpc_peer *peer = NULL;
 	struct rxrpc_call *call = NULL;

 	_enter("");

 	spin_lock(&rx->incoming_lock);
 	if (rx->sk.sk_state == RXRPC_SERVER_LISTEN_DISABLED ||
 	    rx->sk.sk_state == RXRPC_CLOSE) {
 		trace_rxrpc_abort(0, "CLS", sp->hdr.cid, sp->hdr.callNumber,
 				  sp->hdr.seq, RX_INVALID_OPERATION, ESHUTDOWN);
 		skb->mark = RXRPC_SKB_MARK_REJECT_ABORT;
 		skb->priority = RX_INVALID_OPERATION;
 		goto no_call;
 	}

 	/* The peer, connection and call may all have sprung into existence due
 	 * to a duplicate packet being handled on another CPU in parallel, so
 	 * we have to recheck the routing.  However, we're now holding
 	 * rx->incoming_lock, so the values should remain stable.
 	 */
 	conn = rxrpc_find_connection_rcu(local, skb, &peer);

 	if (!conn) {
 		sec = rxrpc_get_incoming_security(rx, skb);
 		if (!sec)
 			goto no_call;
 	}

 	call = rxrpc_alloc_incoming_call(rx, local, peer, conn, sec, skb);
 	if (!call) {
 		skb->mark = RXRPC_SKB_MARK_REJECT_BUSY;
 		goto no_call;
 	}

 	trace_rxrpc_receive(call, rxrpc_receive_incoming,
 			    sp->hdr.serial, sp->hdr.seq);

 	/* Make the call live. */
 	rxrpc_incoming_call(rx, call, skb);
 	conn = call->conn;

 	if (rx->notify_new_call)
 		rx->notify_new_call(&rx->sk, call, call->user_call_ID);

 	spin_lock(&conn->state_lock);
 	switch (conn->state) {
 	case RXRPC_CONN_SERVICE_UNSECURED:
 		conn->state = RXRPC_CONN_SERVICE_CHALLENGING;
 		set_bit(RXRPC_CONN_EV_CHALLENGE, &call->conn->events);
 		rxrpc_queue_conn(call->conn);
 		break;

 	case RXRPC_CONN_SERVICE:
 		write_lock(&call->state_lock);
 		if (call->state < RXRPC_CALL_COMPLETE)
 			call->state = RXRPC_CALL_SERVER_RECV_REQUEST;
 		write_unlock(&call->state_lock);
 		break;

 	case RXRPC_CONN_REMOTELY_ABORTED:
 		rxrpc_set_call_completion(call, RXRPC_CALL_REMOTELY_ABORTED,
 					  conn->abort_code, conn->error);
 		break;
 	case RXRPC_CONN_LOCALLY_ABORTED:
 		rxrpc_abort_call("CON", call, sp->hdr.seq,
 				 conn->abort_code, conn->error);
 		break;
 	default:
 		BUG();
 	}
 	spin_unlock(&conn->state_lock);
 	spin_unlock(&rx->incoming_lock);

 	rxrpc_send_ping(call, skb);

 	/* We have to discard the prealloc queue's ref here and rely on a
 	 * combination of the RCU read lock and refs held either by the socket
 	 * (recvmsg queue, to-be-accepted queue or user ID tree) or the kernel
 	 * service to prevent the call from being deallocated too early.
 	 */
 	rxrpc_put_call(call, rxrpc_call_put);

 	_leave(" = %p{%d}", call, call->debug_id);
 	return call;

 no_call:
 	spin_unlock(&rx->incoming_lock);
 	_leave(" = NULL [%u]", skb->mark);
 	return NULL;
 }

 /*
  * Charge up socket with preallocated calls, attaching user call IDs.
  */
 int rxrpc_user_charge_accept(struct rxrpc_sock *rx, unsigned long user_call_ID)
 {
 	struct rxrpc_backlog *b = rx->backlog;

 	if (rx->sk.sk_state == RXRPC_CLOSE)
 		return -ESHUTDOWN;

 	return rxrpc_service_prealloc_one(rx, b, NULL, NULL, user_call_ID,
 					  GFP_KERNEL,
 					  atomic_inc_return(&rxrpc_debug_id));
 }

 /*
  * rxrpc_kernel_charge_accept - Charge up socket with preallocated calls
  * @sock: The socket on which to preallocate
  * @notify_rx: Event notification function for the call
  * @user_attach_call: Func to attach call to user_call_ID
  * @user_call_ID: The tag to attach to the preallocated call
  * @gfp: The allocation conditions.
  * @debug_id: The tracing debug ID.
  *
  * Charge up the socket with preallocated calls, each with a user ID.  A
  * function should be provided to effect the attachment from the user's side.
  * The user is given a ref to hold on the call.
  *
  * Note that the call may be come connected before this function returns.
  */
 int rxrpc_kernel_charge_accept(struct socket *sock,
 			       rxrpc_notify_rx_t notify_rx,
 			       rxrpc_user_attach_call_t user_attach_call,
 			       unsigned long user_call_ID, gfp_t gfp,
 			       unsigned int debug_id)
 {
 	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
 	struct rxrpc_backlog *b = rx->backlog;

 	if (sock->sk->sk_state == RXRPC_CLOSE)
 		return -ESHUTDOWN;

 	return rxrpc_service_prealloc_one(rx, b, notify_rx,
 					  user_attach_call, user_call_ID,
 					  gfp, debug_id);
 }
 EXPORT_SYMBOL(rxrpc_kernel_charge_accept);
	// SPDX-License-Identifier: GPL-2.0-or-later
	/* incoming call handling
	*
	* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
	* Written by David Howells (dhowells@redhat.com)
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/module.h>
	#include <linux/net.h>
	#include <linux/skbuff.h>
	#include <linux/errqueue.h>
	#include <linux/udp.h>
	#include <linux/in.h>
	#include <linux/in6.h>
	#include <linux/icmp.h>
	#include <linux/gfp.h>
	#include <linux/circ_buf.h>
	#include <net/sock.h>
	#include <net/af_rxrpc.h>
	#include <net/ip.h>
	#include "ar-internal.h"

	static void rxrpc_dummy_notify(struct sock sk, struct rxrpc_call call,
	unsigned long user_call_ID)
	{
	}

	/*
	* Preallocate a single service call, connection and peer and, if possible,
	* give them a user ID and attach the user's side of the ID to them.
	*/
	static int rxrpc_service_prealloc_one(struct rxrpc_sock *rx,
	struct rxrpc_backlog *b,
	rxrpc_notify_rx_t notify_rx,
	rxrpc_user_attach_call_t user_attach_call,
	unsigned long user_call_ID, gfp_t gfp,
	unsigned int debug_id)
	{
	const void *here = __builtin_return_address(0);
	struct rxrpc_call call, xcall;
	struct rxrpc_net *rxnet = rxrpc_net(sock_net(&rx->sk));
	struct rb_node parent, *pp;
	int max, tmp;
	unsigned int size = RXRPC_BACKLOG_MAX;
	unsigned int head, tail, call_head, call_tail;

	max = rx->sk.sk_max_ack_backlog;
	tmp = rx->sk.sk_ack_backlog;
	if (tmp >= max) {
	_leave(" = -ENOBUFS [full %u]", max);
	return -ENOBUFS;
	}
	max -= tmp;

	/* We don't need more conns and peers than we have calls, but on the
	* other hand, we shouldn't ever use more peers than conns or conns
	* than calls.
	*/
	call_head = b->call_backlog_head;
	call_tail = READ_ONCE(b->call_backlog_tail);
	tmp = CIRC_CNT(call_head, call_tail, size);
	if (tmp >= max) {
	_leave(" = -ENOBUFS [enough %u]", tmp);
	return -ENOBUFS;
	}
	max = tmp + 1;

	head = b->peer_backlog_head;
	tail = READ_ONCE(b->peer_backlog_tail);
	if (CIRC_CNT(head, tail, size) < max) {
	struct rxrpc_peer *peer = rxrpc_alloc_peer(rx->local, gfp);
	if (!peer)
	return -ENOMEM;
	b->peer_backlog[head] = peer;
	smp_store_release(&b->peer_backlog_head,
	(head + 1) & (size - 1));
	}

	head = b->conn_backlog_head;
	tail = READ_ONCE(b->conn_backlog_tail);
	if (CIRC_CNT(head, tail, size) < max) {
	struct rxrpc_connection *conn;

	conn = rxrpc_prealloc_service_connection(rxnet, gfp);
	if (!conn)
	return -ENOMEM;
	b->conn_backlog[head] = conn;
	smp_store_release(&b->conn_backlog_head,
	(head + 1) & (size - 1));

	trace_rxrpc_conn(conn->debug_id, rxrpc_conn_new_service,
	refcount_read(&conn->ref), here);
	}

	/* Now it gets complicated, because calls get registered with the
	* socket here, with a user ID preassigned by the user.
	*/
	call = rxrpc_alloc_call(rx, gfp, debug_id);
	if (!call)
	return -ENOMEM;
	call->flags \|= (1 << RXRPC_CALL_IS_SERVICE);
	call->state = RXRPC_CALL_SERVER_PREALLOC;

	trace_rxrpc_call(call->debug_id, rxrpc_call_new_service,
	refcount_read(&call->ref),
	here, (const void *)user_call_ID);

	write_lock(&rx->call_lock);

	/* Check the user ID isn't already in use */
	pp = &rx->calls.rb_node;
	parent = NULL;
	while (*pp) {
	parent = *pp;
	xcall = rb_entry(parent, struct rxrpc_call, sock_node);
	if (user_call_ID < xcall->user_call_ID)
	pp = &(*pp)->rb_left;
	else if (user_call_ID > xcall->user_call_ID)
	pp = &(*pp)->rb_right;
	else
	goto id_in_use;
	}

	call->user_call_ID = user_call_ID;
	call->notify_rx = notify_rx;
	if (user_attach_call) {
	rxrpc_get_call(call, rxrpc_call_got_kernel);
	user_attach_call(call, user_call_ID);
	}

	rxrpc_get_call(call, rxrpc_call_got_userid);
	rb_link_node(&call->sock_node, parent, pp);
	rb_insert_color(&call->sock_node, &rx->calls);
	set_bit(RXRPC_CALL_HAS_USERID, &call->flags);

	list_add(&call->sock_link, &rx->sock_calls);

	write_unlock(&rx->call_lock);

	rxnet = call->rxnet;
	spin_lock_bh(&rxnet->call_lock);
	list_add_tail_rcu(&call->link, &rxnet->calls);
	spin_unlock_bh(&rxnet->call_lock);

	b->call_backlog[call_head] = call;
	smp_store_release(&b->call_backlog_head, (call_head + 1) & (size - 1));
	_leave(" = 0 [%d -> %lx]", call->debug_id, user_call_ID);
	return 0;

	id_in_use:
	write_unlock(&rx->call_lock);
	rxrpc_cleanup_call(call);
	_leave(" = -EBADSLT");
	return -EBADSLT;
	}

	/*
	* Allocate the preallocation buffers for incoming service calls. These must
	* be charged manually.
	*/
	int rxrpc_service_prealloc(struct rxrpc_sock *rx, gfp_t gfp)
	{
	struct rxrpc_backlog *b = rx->backlog;

	if (!b) {
	b = kzalloc(sizeof(struct rxrpc_backlog), gfp);
	if (!b)
	return -ENOMEM;
	rx->backlog = b;
	}

	return 0;
	}

	/*
	* Discard the preallocation on a service.
	*/
	void rxrpc_discard_prealloc(struct rxrpc_sock *rx)
	{
	struct rxrpc_backlog *b = rx->backlog;
	struct rxrpc_net *rxnet = rxrpc_net(sock_net(&rx->sk));
	unsigned int size = RXRPC_BACKLOG_MAX, head, tail;

	if (!b)
	return;
	rx->backlog = NULL;

	/* Make sure that there aren't any incoming calls in progress before we
	* clear the preallocation buffers.
	*/
	spin_lock_bh(&rx->incoming_lock);
	spin_unlock_bh(&rx->incoming_lock);

	head = b->peer_backlog_head;
	tail = b->peer_backlog_tail;
	while (CIRC_CNT(head, tail, size) > 0) {
	struct rxrpc_peer *peer = b->peer_backlog[tail];
	rxrpc_put_local(peer->local);
	kfree(peer);
	tail = (tail + 1) & (size - 1);
	}

	head = b->conn_backlog_head;
	tail = b->conn_backlog_tail;
	while (CIRC_CNT(head, tail, size) > 0) {
	struct rxrpc_connection *conn = b->conn_backlog[tail];
	write_lock(&rxnet->conn_lock);
	list_del(&conn->link);
	list_del(&conn->proc_link);
	write_unlock(&rxnet->conn_lock);
	kfree(conn);
	if (atomic_dec_and_test(&rxnet->nr_conns))
	wake_up_var(&rxnet->nr_conns);
	tail = (tail + 1) & (size - 1);
	}

	head = b->call_backlog_head;
	tail = b->call_backlog_tail;
	while (CIRC_CNT(head, tail, size) > 0) {
	struct rxrpc_call *call = b->call_backlog[tail];
	rcu_assign_pointer(call->socket, rx);
	if (rx->discard_new_call) {
	_debug("discard %lx", call->user_call_ID);
	rx->discard_new_call(call, call->user_call_ID);
	if (call->notify_rx)
	call->notify_rx = rxrpc_dummy_notify;
	rxrpc_put_call(call, rxrpc_call_put_kernel);
	}
	rxrpc_call_completed(call);
	rxrpc_release_call(rx, call);
	rxrpc_put_call(call, rxrpc_call_put);
	tail = (tail + 1) & (size - 1);
	}

	kfree(b);
	}

	/*
	* Ping the other end to fill our RTT cache and to retrieve the rwind
	* and MTU parameters.
	*/
	static void rxrpc_send_ping(struct rxrpc_call call, struct sk_buff skb)
	{
	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
	ktime_t now = skb->tstamp;

	if (call->peer->rtt_count < 3 \|\|
	ktime_before(ktime_add_ms(call->peer->rtt_last_req, 1000), now))
	rxrpc_propose_ACK(call, RXRPC_ACK_PING, sp->hdr.serial,
	true, true,
	rxrpc_propose_ack_ping_for_params);
	}

	/*
	* Allocate a new incoming call from the prealloc pool, along with a connection
	* and a peer as necessary.
	*/
	static struct rxrpc_call rxrpc_alloc_incoming_call(struct rxrpc_sock rx,
	struct rxrpc_local *local,
	struct rxrpc_peer *peer,
	struct rxrpc_connection *conn,
	const struct rxrpc_security *sec,
	struct sk_buff *skb)
	{
	struct rxrpc_backlog *b = rx->backlog;
	struct rxrpc_call *call;
	unsigned short call_head, conn_head, peer_head;
	unsigned short call_tail, conn_tail, peer_tail;
	unsigned short call_count, conn_count;

	/* #calls >= #conns >= #peers must hold true. */
	call_head = smp_load_acquire(&b->call_backlog_head);
	call_tail = b->call_backlog_tail;
	call_count = CIRC_CNT(call_head, call_tail, RXRPC_BACKLOG_MAX);
	conn_head = smp_load_acquire(&b->conn_backlog_head);
	conn_tail = b->conn_backlog_tail;
	conn_count = CIRC_CNT(conn_head, conn_tail, RXRPC_BACKLOG_MAX);
	ASSERTCMP(conn_count, >=, call_count);
	peer_head = smp_load_acquire(&b->peer_backlog_head);
	peer_tail = b->peer_backlog_tail;
	ASSERTCMP(CIRC_CNT(peer_head, peer_tail, RXRPC_BACKLOG_MAX), >=,
	conn_count);

	if (call_count == 0)
	return NULL;

	if (!conn) {
	if (peer && !rxrpc_get_peer_maybe(peer))
	peer = NULL;
	if (!peer) {
	peer = b->peer_backlog[peer_tail];
	if (rxrpc_extract_addr_from_skb(&peer->srx, skb) < 0)
	return NULL;
	b->peer_backlog[peer_tail] = NULL;
	smp_store_release(&b->peer_backlog_tail,
	(peer_tail + 1) &
	(RXRPC_BACKLOG_MAX - 1));

	rxrpc_new_incoming_peer(rx, local, peer);
	}

	/* Now allocate and set up the connection */
	conn = b->conn_backlog[conn_tail];
	b->conn_backlog[conn_tail] = NULL;
	smp_store_release(&b->conn_backlog_tail,
	(conn_tail + 1) & (RXRPC_BACKLOG_MAX - 1));
	conn->params.local = rxrpc_get_local(local);
	conn->params.peer = peer;
	rxrpc_see_connection(conn);
	rxrpc_new_incoming_connection(rx, conn, sec, skb);
	} else {
	rxrpc_get_connection(conn);
	}

	/* And now we can allocate and set up a new call */
	call = b->call_backlog[call_tail];
	b->call_backlog[call_tail] = NULL;
	smp_store_release(&b->call_backlog_tail,
	(call_tail + 1) & (RXRPC_BACKLOG_MAX - 1));

	rxrpc_see_call(call);
	call->conn = conn;
	call->security = conn->security;
	call->security_ix = conn->security_ix;
	call->peer = rxrpc_get_peer(conn->params.peer);
	call->cong_cwnd = call->peer->cong_cwnd;
	return call;
	}

	/*
	* Set up a new incoming call. Called in BH context with the RCU read lock
	* held.
	*
	* If this is for a kernel service, when we allocate the call, it will have
	* three refs on it: (1) the kernel service, (2) the user_call_ID tree, (3) the
	* retainer ref obtained from the backlog buffer. Prealloc calls for userspace
	* services only have the ref from the backlog buffer. We want to pass this
	* ref to non-BH context to dispose of.
	*
	* If we want to report an error, we mark the skb with the packet type and
	* abort code and return NULL.
	*
	* The call is returned with the user access mutex held.
	*/
	struct rxrpc_call rxrpc_new_incoming_call(struct rxrpc_local local,
	struct rxrpc_sock *rx,
	struct sk_buff *skb)
	{
	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
	const struct rxrpc_security *sec = NULL;
	struct rxrpc_connection *conn;
	struct rxrpc_peer *peer = NULL;
	struct rxrpc_call *call = NULL;

	_enter("");

	spin_lock(&rx->incoming_lock);
	if (rx->sk.sk_state == RXRPC_SERVER_LISTEN_DISABLED \|\|
	rx->sk.sk_state == RXRPC_CLOSE) {
	trace_rxrpc_abort(0, "CLS", sp->hdr.cid, sp->hdr.callNumber,
	sp->hdr.seq, RX_INVALID_OPERATION, ESHUTDOWN);
	skb->mark = RXRPC_SKB_MARK_REJECT_ABORT;
	skb->priority = RX_INVALID_OPERATION;
	goto no_call;
	}

	/* The peer, connection and call may all have sprung into existence due
	* to a duplicate packet being handled on another CPU in parallel, so
	* we have to recheck the routing. However, we're now holding
	* rx->incoming_lock, so the values should remain stable.
	*/
	conn = rxrpc_find_connection_rcu(local, skb, &peer);

	if (!conn) {
	sec = rxrpc_get_incoming_security(rx, skb);
	if (!sec)
	goto no_call;
	}

	call = rxrpc_alloc_incoming_call(rx, local, peer, conn, sec, skb);
	if (!call) {
	skb->mark = RXRPC_SKB_MARK_REJECT_BUSY;
	goto no_call;
	}

	trace_rxrpc_receive(call, rxrpc_receive_incoming,
	sp->hdr.serial, sp->hdr.seq);

	/* Make the call live. */
	rxrpc_incoming_call(rx, call, skb);
	conn = call->conn;

	if (rx->notify_new_call)
	rx->notify_new_call(&rx->sk, call, call->user_call_ID);

	spin_lock(&conn->state_lock);
	switch (conn->state) {
	case RXRPC_CONN_SERVICE_UNSECURED:
	conn->state = RXRPC_CONN_SERVICE_CHALLENGING;
	set_bit(RXRPC_CONN_EV_CHALLENGE, &call->conn->events);
	rxrpc_queue_conn(call->conn);
	break;

	case RXRPC_CONN_SERVICE:
	write_lock(&call->state_lock);
	if (call->state < RXRPC_CALL_COMPLETE)
	call->state = RXRPC_CALL_SERVER_RECV_REQUEST;
	write_unlock(&call->state_lock);
	break;

	case RXRPC_CONN_REMOTELY_ABORTED:
	rxrpc_set_call_completion(call, RXRPC_CALL_REMOTELY_ABORTED,
	conn->abort_code, conn->error);
	break;
	case RXRPC_CONN_LOCALLY_ABORTED:
	rxrpc_abort_call("CON", call, sp->hdr.seq,
	conn->abort_code, conn->error);
	break;
	default:
	BUG();
	}
	spin_unlock(&conn->state_lock);
	spin_unlock(&rx->incoming_lock);

	rxrpc_send_ping(call, skb);

	/* We have to discard the prealloc queue's ref here and rely on a
	* combination of the RCU read lock and refs held either by the socket
	* (recvmsg queue, to-be-accepted queue or user ID tree) or the kernel
	* service to prevent the call from being deallocated too early.
	*/
	rxrpc_put_call(call, rxrpc_call_put);

	_leave(" = %p{%d}", call, call->debug_id);
	return call;

	no_call:
	spin_unlock(&rx->incoming_lock);
	_leave(" = NULL [%u]", skb->mark);
	return NULL;
	}

	/*
	* Charge up socket with preallocated calls, attaching user call IDs.
	*/
	int rxrpc_user_charge_accept(struct rxrpc_sock *rx, unsigned long user_call_ID)
	{
	struct rxrpc_backlog *b = rx->backlog;

	if (rx->sk.sk_state == RXRPC_CLOSE)
	return -ESHUTDOWN;

	return rxrpc_service_prealloc_one(rx, b, NULL, NULL, user_call_ID,
	GFP_KERNEL,
	atomic_inc_return(&rxrpc_debug_id));
	}

	/*
	* rxrpc_kernel_charge_accept - Charge up socket with preallocated calls
	* @sock: The socket on which to preallocate
	* @notify_rx: Event notification function for the call
	* @user_attach_call: Func to attach call to user_call_ID
	* @user_call_ID: The tag to attach to the preallocated call
	* @gfp: The allocation conditions.
	* @debug_id: The tracing debug ID.
	*
	* Charge up the socket with preallocated calls, each with a user ID. A
	* function should be provided to effect the attachment from the user's side.
	* The user is given a ref to hold on the call.
	*
	* Note that the call may be come connected before this function returns.
	*/
	int rxrpc_kernel_charge_accept(struct socket *sock,
	rxrpc_notify_rx_t notify_rx,
	rxrpc_user_attach_call_t user_attach_call,
	unsigned long user_call_ID, gfp_t gfp,
	unsigned int debug_id)
	{
	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
	struct rxrpc_backlog *b = rx->backlog;

	if (sock->sk->sk_state == RXRPC_CLOSE)
	return -ESHUTDOWN;

	return rxrpc_service_prealloc_one(rx, b, notify_rx,
	user_attach_call, user_call_ID,
	gfp, debug_id);
	}
	EXPORT_SYMBOL(rxrpc_kernel_charge_accept);