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ar-ack.c

/* Management of Tx window, Tx resend, ACKs and out-of-sequence reception
 *
 * Copyright (C) 2007 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 License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/circ_buf.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/udp.h>
#include <net/sock.h>
#include <net/af_rxrpc.h>
#include "ar-internal.h"

static unsigned rxrpc_ack_defer = 1;

static const char *rxrpc_acks[] = {
      "---", "REQ", "DUP", "OOS", "WIN", "MEM", "PNG", "PNR", "DLY", "IDL",
      "-?-"
};

static const s8 rxrpc_ack_priority[] = {
      [0]                     = 0,
      [RXRPC_ACK_DELAY]       = 1,
      [RXRPC_ACK_REQUESTED]         = 2,
      [RXRPC_ACK_IDLE]        = 3,
      [RXRPC_ACK_PING_RESPONSE]     = 4,
      [RXRPC_ACK_DUPLICATE]         = 5,
      [RXRPC_ACK_OUT_OF_SEQUENCE]   = 6,
      [RXRPC_ACK_EXCEEDS_WINDOW]    = 7,
      [RXRPC_ACK_NOSPACE]           = 8,
};

/*
 * propose an ACK be sent
 */
void __rxrpc_propose_ACK(struct rxrpc_call *call, uint8_t ack_reason,
                   __be32 serial, bool immediate)
{
      unsigned long expiry;
      s8 prior = rxrpc_ack_priority[ack_reason];

      ASSERTCMP(prior, >, 0);

      _enter("{%d},%s,%%%x,%u",
             call->debug_id, rxrpc_acks[ack_reason], ntohl(serial),
             immediate);

      if (prior < rxrpc_ack_priority[call->ackr_reason]) {
            if (immediate)
                  goto cancel_timer;
            return;
      }

      /* update DELAY, IDLE, REQUESTED and PING_RESPONSE ACK serial
       * numbers */
      if (prior == rxrpc_ack_priority[call->ackr_reason]) {
            if (prior <= 4)
                  call->ackr_serial = serial;
            if (immediate)
                  goto cancel_timer;
            return;
      }

      call->ackr_reason = ack_reason;
      call->ackr_serial = serial;

      switch (ack_reason) {
      case RXRPC_ACK_DELAY:
            _debug("run delay timer");
            call->ack_timer.expires = jiffies + rxrpc_ack_timeout * HZ;
            add_timer(&call->ack_timer);
            return;

      case RXRPC_ACK_IDLE:
            if (!immediate) {
                  _debug("run defer timer");
                  expiry = 1;
                  goto run_timer;
            }
            goto cancel_timer;

      case RXRPC_ACK_REQUESTED:
            if (!rxrpc_ack_defer)
                  goto cancel_timer;
            if (!immediate || serial == cpu_to_be32(1)) {
                  _debug("run defer timer");
                  expiry = rxrpc_ack_defer;
                  goto run_timer;
            }

      default:
            _debug("immediate ACK");
            goto cancel_timer;
      }

run_timer:
      expiry += jiffies;
      if (!timer_pending(&call->ack_timer) ||
          time_after(call->ack_timer.expires, expiry))
            mod_timer(&call->ack_timer, expiry);
      return;

cancel_timer:
      _debug("cancel timer %%%u", ntohl(serial));
      try_to_del_timer_sync(&call->ack_timer);
      read_lock_bh(&call->state_lock);
      if (call->state <= RXRPC_CALL_COMPLETE &&
          !test_and_set_bit(RXRPC_CALL_ACK, &call->events))
            rxrpc_queue_call(call);
      read_unlock_bh(&call->state_lock);
}

/*
 * propose an ACK be sent, locking the call structure
 */
void rxrpc_propose_ACK(struct rxrpc_call *call, uint8_t ack_reason,
                   __be32 serial, bool immediate)
{
      s8 prior = rxrpc_ack_priority[ack_reason];

      if (prior > rxrpc_ack_priority[call->ackr_reason]) {
            spin_lock_bh(&call->lock);
            __rxrpc_propose_ACK(call, ack_reason, serial, immediate);
            spin_unlock_bh(&call->lock);
      }
}

/*
 * set the resend timer
 */
static void rxrpc_set_resend(struct rxrpc_call *call, u8 resend,
                       unsigned long resend_at)
{
      read_lock_bh(&call->state_lock);
      if (call->state >= RXRPC_CALL_COMPLETE)
            resend = 0;

      if (resend & 1) {
            _debug("SET RESEND");
            set_bit(RXRPC_CALL_RESEND, &call->events);
      }

      if (resend & 2) {
            _debug("MODIFY RESEND TIMER");
            set_bit(RXRPC_CALL_RUN_RTIMER, &call->flags);
            mod_timer(&call->resend_timer, resend_at);
      } else {
            _debug("KILL RESEND TIMER");
            del_timer_sync(&call->resend_timer);
            clear_bit(RXRPC_CALL_RESEND_TIMER, &call->events);
            clear_bit(RXRPC_CALL_RUN_RTIMER, &call->flags);
      }
      read_unlock_bh(&call->state_lock);
}

/*
 * resend packets
 */
static void rxrpc_resend(struct rxrpc_call *call)
{
      struct rxrpc_skb_priv *sp;
      struct rxrpc_header *hdr;
      struct sk_buff *txb;
      unsigned long *p_txb, resend_at;
      int loop, stop;
      u8 resend;

      _enter("{%d,%d,%d,%d},",
             call->acks_hard, call->acks_unacked,
             atomic_read(&call->sequence),
             CIRC_CNT(call->acks_head, call->acks_tail, call->acks_winsz));

      stop = 0;
      resend = 0;
      resend_at = 0;

      for (loop = call->acks_tail;
           loop != call->acks_head || stop;
           loop = (loop + 1) &  (call->acks_winsz - 1)
           ) {
            p_txb = call->acks_window + loop;
            smp_read_barrier_depends();
            if (*p_txb & 1)
                  continue;

            txb = (struct sk_buff *) *p_txb;
            sp = rxrpc_skb(txb);

            if (sp->need_resend) {
                  sp->need_resend = 0;

                  /* each Tx packet has a new serial number */
                  sp->hdr.serial =
                        htonl(atomic_inc_return(&call->conn->serial));

                  hdr = (struct rxrpc_header *) txb->head;
                  hdr->serial = sp->hdr.serial;

                  _proto("Tx DATA %%%u { #%d }",
                         ntohl(sp->hdr.serial), ntohl(sp->hdr.seq));
                  if (rxrpc_send_packet(call->conn->trans, txb) < 0) {
                        stop = 0;
                        sp->resend_at = jiffies + 3;
                  } else {
                        sp->resend_at =
                              jiffies + rxrpc_resend_timeout * HZ;
                  }
            }

            if (time_after_eq(jiffies + 1, sp->resend_at)) {
                  sp->need_resend = 1;
                  resend |= 1;
            } else if (resend & 2) {
                  if (time_before(sp->resend_at, resend_at))
                        resend_at = sp->resend_at;
            } else {
                  resend_at = sp->resend_at;
                  resend |= 2;
            }
      }

      rxrpc_set_resend(call, resend, resend_at);
      _leave("");
}

/*
 * handle resend timer expiry
 */
static void rxrpc_resend_timer(struct rxrpc_call *call)
{
      struct rxrpc_skb_priv *sp;
      struct sk_buff *txb;
      unsigned long *p_txb, resend_at;
      int loop;
      u8 resend;

      _enter("%d,%d,%d",
             call->acks_tail, call->acks_unacked, call->acks_head);

      resend = 0;
      resend_at = 0;

      for (loop = call->acks_unacked;
           loop != call->acks_head;
           loop = (loop + 1) &  (call->acks_winsz - 1)
           ) {
            p_txb = call->acks_window + loop;
            smp_read_barrier_depends();
            txb = (struct sk_buff *) (*p_txb & ~1);
            sp = rxrpc_skb(txb);

            ASSERT(!(*p_txb & 1));

            if (sp->need_resend) {
                  ;
            } else if (time_after_eq(jiffies + 1, sp->resend_at)) {
                  sp->need_resend = 1;
                  resend |= 1;
            } else if (resend & 2) {
                  if (time_before(sp->resend_at, resend_at))
                        resend_at = sp->resend_at;
            } else {
                  resend_at = sp->resend_at;
                  resend |= 2;
            }
      }

      rxrpc_set_resend(call, resend, resend_at);
      _leave("");
}

/*
 * process soft ACKs of our transmitted packets
 * - these indicate packets the peer has or has not received, but hasn't yet
 *   given to the consumer, and so can still be discarded and re-requested
 */
static int rxrpc_process_soft_ACKs(struct rxrpc_call *call,
                           struct rxrpc_ackpacket *ack,
                           struct sk_buff *skb)
{
      struct rxrpc_skb_priv *sp;
      struct sk_buff *txb;
      unsigned long *p_txb, resend_at;
      int loop;
      u8 sacks[RXRPC_MAXACKS], resend;

      _enter("{%d,%d},{%d},",
             call->acks_hard,
             CIRC_CNT(call->acks_head, call->acks_tail, call->acks_winsz),
             ack->nAcks);

      if (skb_copy_bits(skb, 0, sacks, ack->nAcks) < 0)
            goto protocol_error;

      resend = 0;
      resend_at = 0;
      for (loop = 0; loop < ack->nAcks; loop++) {
            p_txb = call->acks_window;
            p_txb += (call->acks_tail + loop) & (call->acks_winsz - 1);
            smp_read_barrier_depends();
            txb = (struct sk_buff *) (*p_txb & ~1);
            sp = rxrpc_skb(txb);

            switch (sacks[loop]) {
            case RXRPC_ACK_TYPE_ACK:
                  sp->need_resend = 0;
                  *p_txb |= 1;
                  break;
            case RXRPC_ACK_TYPE_NACK:
                  sp->need_resend = 1;
                  *p_txb &= ~1;
                  resend = 1;
                  break;
            default:
                  _debug("Unsupported ACK type %d", sacks[loop]);
                  goto protocol_error;
            }
      }

      smp_mb();
      call->acks_unacked = (call->acks_tail + loop) & (call->acks_winsz - 1);

      /* anything not explicitly ACK'd is implicitly NACK'd, but may just not
       * have been received or processed yet by the far end */
      for (loop = call->acks_unacked;
           loop != call->acks_head;
           loop = (loop + 1) &  (call->acks_winsz - 1)
           ) {
            p_txb = call->acks_window + loop;
            smp_read_barrier_depends();
            txb = (struct sk_buff *) (*p_txb & ~1);
            sp = rxrpc_skb(txb);

            if (*p_txb & 1) {
                  /* packet must have been discarded */
                  sp->need_resend = 1;
                  *p_txb &= ~1;
                  resend |= 1;
            } else if (sp->need_resend) {
                  ;
            } else if (time_after_eq(jiffies + 1, sp->resend_at)) {
                  sp->need_resend = 1;
                  resend |= 1;
            } else if (resend & 2) {
                  if (time_before(sp->resend_at, resend_at))
                        resend_at = sp->resend_at;
            } else {
                  resend_at = sp->resend_at;
                  resend |= 2;
            }
      }

      rxrpc_set_resend(call, resend, resend_at);
      _leave(" = 0");
      return 0;

protocol_error:
      _leave(" = -EPROTO");
      return -EPROTO;
}

/*
 * discard hard-ACK'd packets from the Tx window
 */
static void rxrpc_rotate_tx_window(struct rxrpc_call *call, u32 hard)
{
      struct rxrpc_skb_priv *sp;
      unsigned long _skb;
      int tail = call->acks_tail, old_tail;
      int win = CIRC_CNT(call->acks_head, tail, call->acks_winsz);

      _enter("{%u,%u},%u", call->acks_hard, win, hard);

      ASSERTCMP(hard - call->acks_hard, <=, win);

      while (call->acks_hard < hard) {
            smp_read_barrier_depends();
            _skb = call->acks_window[tail] & ~1;
            sp = rxrpc_skb((struct sk_buff *) _skb);
            rxrpc_free_skb((struct sk_buff *) _skb);
            old_tail = tail;
            tail = (tail + 1) & (call->acks_winsz - 1);
            call->acks_tail = tail;
            if (call->acks_unacked == old_tail)
                  call->acks_unacked = tail;
            call->acks_hard++;
      }

      wake_up(&call->tx_waitq);
}

/*
 * clear the Tx window in the event of a failure
 */
static void rxrpc_clear_tx_window(struct rxrpc_call *call)
{
      rxrpc_rotate_tx_window(call, atomic_read(&call->sequence));
}

/*
 * drain the out of sequence received packet queue into the packet Rx queue
 */
static int rxrpc_drain_rx_oos_queue(struct rxrpc_call *call)
{
      struct rxrpc_skb_priv *sp;
      struct sk_buff *skb;
      bool terminal;
      int ret;

      _enter("{%d,%d}", call->rx_data_post, call->rx_first_oos);

      spin_lock_bh(&call->lock);

      ret = -ECONNRESET;
      if (test_bit(RXRPC_CALL_RELEASED, &call->flags))
            goto socket_unavailable;

      skb = skb_dequeue(&call->rx_oos_queue);
      if (skb) {
            sp = rxrpc_skb(skb);

            _debug("drain OOS packet %d [%d]",
                   ntohl(sp->hdr.seq), call->rx_first_oos);

            if (ntohl(sp->hdr.seq) != call->rx_first_oos) {
                  skb_queue_head(&call->rx_oos_queue, skb);
                  call->rx_first_oos = ntohl(rxrpc_skb(skb)->hdr.seq);
                  _debug("requeue %p {%u}", skb, call->rx_first_oos);
            } else {
                  skb->mark = RXRPC_SKB_MARK_DATA;
                  terminal = ((sp->hdr.flags & RXRPC_LAST_PACKET) &&
                        !(sp->hdr.flags & RXRPC_CLIENT_INITIATED));
                  ret = rxrpc_queue_rcv_skb(call, skb, true, terminal);
                  BUG_ON(ret < 0);
                  _debug("drain #%u", call->rx_data_post);
                  call->rx_data_post++;

                  /* find out what the next packet is */
                  skb = skb_peek(&call->rx_oos_queue);
                  if (skb)
                        call->rx_first_oos =
                              ntohl(rxrpc_skb(skb)->hdr.seq);
                  else
                        call->rx_first_oos = 0;
                  _debug("peek %p {%u}", skb, call->rx_first_oos);
            }
      }

      ret = 0;
socket_unavailable:
      spin_unlock_bh(&call->lock);
      _leave(" = %d", ret);
      return ret;
}

/*
 * insert an out of sequence packet into the buffer
 */
static void rxrpc_insert_oos_packet(struct rxrpc_call *call,
                            struct sk_buff *skb)
{
      struct rxrpc_skb_priv *sp, *psp;
      struct sk_buff *p;
      u32 seq;

      sp = rxrpc_skb(skb);
      seq = ntohl(sp->hdr.seq);
      _enter(",,{%u}", seq);

      skb->destructor = rxrpc_packet_destructor;
      ASSERTCMP(sp->call, ==, NULL);
      sp->call = call;
      rxrpc_get_call(call);

      /* insert into the buffer in sequence order */
      spin_lock_bh(&call->lock);

      skb_queue_walk(&call->rx_oos_queue, p) {
            psp = rxrpc_skb(p);
            if (ntohl(psp->hdr.seq) > seq) {
                  _debug("insert oos #%u before #%u",
                         seq, ntohl(psp->hdr.seq));
                  skb_insert(p, skb, &call->rx_oos_queue);
                  goto inserted;
            }
      }

      _debug("append oos #%u", seq);
      skb_queue_tail(&call->rx_oos_queue, skb);
inserted:

      /* we might now have a new front to the queue */
      if (call->rx_first_oos == 0 || seq < call->rx_first_oos)
            call->rx_first_oos = seq;

      read_lock(&call->state_lock);
      if (call->state < RXRPC_CALL_COMPLETE &&
          call->rx_data_post == call->rx_first_oos) {
            _debug("drain rx oos now");
            set_bit(RXRPC_CALL_DRAIN_RX_OOS, &call->events);
      }
      read_unlock(&call->state_lock);

      spin_unlock_bh(&call->lock);
      _leave(" [stored #%u]", call->rx_first_oos);
}

/*
 * clear the Tx window on final ACK reception
 */
static void rxrpc_zap_tx_window(struct rxrpc_call *call)
{
      struct rxrpc_skb_priv *sp;
      struct sk_buff *skb;
      unsigned long _skb, *acks_window;
      uint8_t winsz = call->acks_winsz;
      int tail;

      acks_window = call->acks_window;
      call->acks_window = NULL;

      while (CIRC_CNT(call->acks_head, call->acks_tail, winsz) > 0) {
            tail = call->acks_tail;
            smp_read_barrier_depends();
            _skb = acks_window[tail] & ~1;
            smp_mb();
            call->acks_tail = (call->acks_tail + 1) & (winsz - 1);

            skb = (struct sk_buff *) _skb;
            sp = rxrpc_skb(skb);
            _debug("+++ clear Tx %u", ntohl(sp->hdr.seq));
            rxrpc_free_skb(skb);
      }

      kfree(acks_window);
}

/*
 * process the extra information that may be appended to an ACK packet
 */
static void rxrpc_extract_ackinfo(struct rxrpc_call *call, struct sk_buff *skb,
                          unsigned latest, int nAcks)
{
      struct rxrpc_ackinfo ackinfo;
      struct rxrpc_peer *peer;
      unsigned mtu;

      if (skb_copy_bits(skb, nAcks + 3, &ackinfo, sizeof(ackinfo)) < 0) {
            _leave(" [no ackinfo]");
            return;
      }

      _proto("Rx ACK %%%u Info { rx=%u max=%u rwin=%u jm=%u }",
             latest,
             ntohl(ackinfo.rxMTU), ntohl(ackinfo.maxMTU),
             ntohl(ackinfo.rwind), ntohl(ackinfo.jumbo_max));

      mtu = min(ntohl(ackinfo.rxMTU), ntohl(ackinfo.maxMTU));

      peer = call->conn->trans->peer;
      if (mtu < peer->maxdata) {
            spin_lock_bh(&peer->lock);
            peer->maxdata = mtu;
            peer->mtu = mtu + peer->hdrsize;
            spin_unlock_bh(&peer->lock);
            _net("Net MTU %u (maxdata %u)", peer->mtu, peer->maxdata);
      }
}

/*
 * process packets in the reception queue
 */
static int rxrpc_process_rx_queue(struct rxrpc_call *call,
                          u32 *_abort_code)
{
      struct rxrpc_ackpacket ack;
      struct rxrpc_skb_priv *sp;
      struct sk_buff *skb;
      bool post_ACK;
      int latest;
      u32 hard, tx;

      _enter("");

process_further:
      skb = skb_dequeue(&call->rx_queue);
      if (!skb)
            return -EAGAIN;

      _net("deferred skb %p", skb);

      sp = rxrpc_skb(skb);

      _debug("process %s [st %d]", rxrpc_pkts[sp->hdr.type], call->state);

      post_ACK = false;

      switch (sp->hdr.type) {
            /* data packets that wind up here have been received out of
             * order, need security processing or are jumbo packets */
      case RXRPC_PACKET_TYPE_DATA:
            _proto("OOSQ DATA %%%u { #%u }",
                   ntohl(sp->hdr.serial), ntohl(sp->hdr.seq));

            /* secured packets must be verified and possibly decrypted */
            if (rxrpc_verify_packet(call, skb, _abort_code) < 0)
                  goto protocol_error;

            rxrpc_insert_oos_packet(call, skb);
            goto process_further;

            /* partial ACK to process */
      case RXRPC_PACKET_TYPE_ACK:
            if (skb_copy_bits(skb, 0, &ack, sizeof(ack)) < 0) {
                  _debug("extraction failure");
                  goto protocol_error;
            }
            if (!skb_pull(skb, sizeof(ack)))
                  BUG();

            latest = ntohl(sp->hdr.serial);
            hard = ntohl(ack.firstPacket);
            tx = atomic_read(&call->sequence);

            _proto("Rx ACK %%%u { m=%hu f=#%u p=#%u s=%%%u r=%s n=%u }",
                   latest,
                   ntohs(ack.maxSkew),
                   hard,
                   ntohl(ack.previousPacket),
                   ntohl(ack.serial),
                   rxrpc_acks[ack.reason],
                   ack.nAcks);

            rxrpc_extract_ackinfo(call, skb, latest, ack.nAcks);

            if (ack.reason == RXRPC_ACK_PING) {
                  _proto("Rx ACK %%%u PING Request", latest);
                  rxrpc_propose_ACK(call, RXRPC_ACK_PING_RESPONSE,
                                sp->hdr.serial, true);
            }

            /* discard any out-of-order or duplicate ACKs */
            if (latest - call->acks_latest <= 0) {
                  _debug("discard ACK %d <= %d",
                         latest, call->acks_latest);
                  goto discard;
            }
            call->acks_latest = latest;

            if (call->state != RXRPC_CALL_CLIENT_SEND_REQUEST &&
                call->state != RXRPC_CALL_CLIENT_AWAIT_REPLY &&
                call->state != RXRPC_CALL_SERVER_SEND_REPLY &&
                call->state != RXRPC_CALL_SERVER_AWAIT_ACK)
                  goto discard;

            _debug("Tx=%d H=%u S=%d", tx, call->acks_hard, call->state);

            if (hard > 0) {
                  if (hard - 1 > tx) {
                        _debug("hard-ACK'd packet %d not transmitted"
                               " (%d top)",
                               hard - 1, tx);
                        goto protocol_error;
                  }

                  if ((call->state == RXRPC_CALL_CLIENT_AWAIT_REPLY ||
                       call->state == RXRPC_CALL_SERVER_AWAIT_ACK) &&
                      hard > tx)
                        goto all_acked;

                  smp_rmb();
                  rxrpc_rotate_tx_window(call, hard - 1);
            }

            if (ack.nAcks > 0) {
                  if (hard - 1 + ack.nAcks > tx) {
                        _debug("soft-ACK'd packet %d+%d not"
                               " transmitted (%d top)",
                               hard - 1, ack.nAcks, tx);
                        goto protocol_error;
                  }

                  if (rxrpc_process_soft_ACKs(call, &ack, skb) < 0)
                        goto protocol_error;
            }
            goto discard;

            /* complete ACK to process */
      case RXRPC_PACKET_TYPE_ACKALL:
            goto all_acked;

            /* abort and busy are handled elsewhere */
      case RXRPC_PACKET_TYPE_BUSY:
      case RXRPC_PACKET_TYPE_ABORT:
            BUG();

            /* connection level events - also handled elsewhere */
      case RXRPC_PACKET_TYPE_CHALLENGE:
      case RXRPC_PACKET_TYPE_RESPONSE:
      case RXRPC_PACKET_TYPE_DEBUG:
            BUG();
      }

      /* if we've had a hard ACK that covers all the packets we've sent, then
       * that ends that phase of the operation */
all_acked:
      write_lock_bh(&call->state_lock);
      _debug("ack all %d", call->state);

      switch (call->state) {
      case RXRPC_CALL_CLIENT_AWAIT_REPLY:
            call->state = RXRPC_CALL_CLIENT_RECV_REPLY;
            break;
      case RXRPC_CALL_SERVER_AWAIT_ACK:
            _debug("srv complete");
            call->state = RXRPC_CALL_COMPLETE;
            post_ACK = true;
            break;
      case RXRPC_CALL_CLIENT_SEND_REQUEST:
      case RXRPC_CALL_SERVER_RECV_REQUEST:
            goto protocol_error_unlock; /* can't occur yet */
      default:
            write_unlock_bh(&call->state_lock);
            goto discard; /* assume packet left over from earlier phase */
      }

      write_unlock_bh(&call->state_lock);

      /* if all the packets we sent are hard-ACK'd, then we can discard
       * whatever we've got left */
      _debug("clear Tx %d",
             CIRC_CNT(call->acks_head, call->acks_tail, call->acks_winsz));

      del_timer_sync(&call->resend_timer);
      clear_bit(RXRPC_CALL_RUN_RTIMER, &call->flags);
      clear_bit(RXRPC_CALL_RESEND_TIMER, &call->events);

      if (call->acks_window)
            rxrpc_zap_tx_window(call);

      if (post_ACK) {
            /* post the final ACK message for userspace to pick up */
            _debug("post ACK");
            skb->mark = RXRPC_SKB_MARK_FINAL_ACK;
            sp->call = call;
            rxrpc_get_call(call);
            spin_lock_bh(&call->lock);
            if (rxrpc_queue_rcv_skb(call, skb, true, true) < 0)
                  BUG();
            spin_unlock_bh(&call->lock);
            goto process_further;
      }

discard:
      rxrpc_free_skb(skb);
      goto process_further;

protocol_error_unlock:
      write_unlock_bh(&call->state_lock);
protocol_error:
      rxrpc_free_skb(skb);
      _leave(" = -EPROTO");
      return -EPROTO;
}

/*
 * post a message to the socket Rx queue for recvmsg() to pick up
 */
static int rxrpc_post_message(struct rxrpc_call *call, u32 mark, u32 error,
                        bool fatal)
{
      struct rxrpc_skb_priv *sp;
      struct sk_buff *skb;
      int ret;

      _enter("{%d,%lx},%u,%u,%d",
             call->debug_id, call->flags, mark, error, fatal);

      /* remove timers and things for fatal messages */
      if (fatal) {
            del_timer_sync(&call->resend_timer);
            del_timer_sync(&call->ack_timer);
            clear_bit(RXRPC_CALL_RUN_RTIMER, &call->flags);
      }

      if (mark != RXRPC_SKB_MARK_NEW_CALL &&
          !test_bit(RXRPC_CALL_HAS_USERID, &call->flags)) {
            _leave("[no userid]");
            return 0;
      }

      if (!test_bit(RXRPC_CALL_TERMINAL_MSG, &call->flags)) {
            skb = alloc_skb(0, GFP_NOFS);
            if (!skb)
                  return -ENOMEM;

            rxrpc_new_skb(skb);

            skb->mark = mark;

            sp = rxrpc_skb(skb);
            memset(sp, 0, sizeof(*sp));
            sp->error = error;
            sp->call = call;
            rxrpc_get_call(call);

            spin_lock_bh(&call->lock);
            ret = rxrpc_queue_rcv_skb(call, skb, true, fatal);
            spin_unlock_bh(&call->lock);
            if (ret < 0)
                  BUG();
      }

      return 0;
}

/*
 * handle background processing of incoming call packets and ACK / abort
 * generation
 */
void rxrpc_process_call(struct work_struct *work)
{
      struct rxrpc_call *call =
            container_of(work, struct rxrpc_call, processor);
      struct rxrpc_ackpacket ack;
      struct rxrpc_ackinfo ackinfo;
      struct rxrpc_header hdr;
      struct msghdr msg;
      struct kvec iov[5];
      unsigned long bits;
      __be32 data, pad;
      size_t len;
      int genbit, loop, nbit, ioc, ret, mtu;
      u32 abort_code = RX_PROTOCOL_ERROR;
      u8 *acks = NULL;

      //printk("\n--------------------\n");
      _enter("{%d,%s,%lx} [%lu]",
             call->debug_id, rxrpc_call_states[call->state], call->events,
             (jiffies - call->creation_jif) / (HZ / 10));

      if (test_and_set_bit(RXRPC_CALL_PROC_BUSY, &call->flags)) {
            _debug("XXXXXXXXXXXXX RUNNING ON MULTIPLE CPUS XXXXXXXXXXXXX");
            return;
      }

      /* there's a good chance we're going to have to send a message, so set
       * one up in advance */
      msg.msg_name      = &call->conn->trans->peer->srx.transport.sin;
      msg.msg_namelen   = sizeof(call->conn->trans->peer->srx.transport.sin);
      msg.msg_control   = NULL;
      msg.msg_controllen = 0;
      msg.msg_flags     = 0;

      hdr.epoch   = call->conn->epoch;
      hdr.cid           = call->cid;
      hdr.callNumber    = call->call_id;
      hdr.seq           = 0;
      hdr.type    = RXRPC_PACKET_TYPE_ACK;
      hdr.flags   = call->conn->out_clientflag;
      hdr.userStatus    = 0;
      hdr.securityIndex = call->conn->security_ix;
      hdr._rsvd   = 0;
      hdr.serviceId     = call->conn->service_id;

      memset(iov, 0, sizeof(iov));
      iov[0].iov_base   = &hdr;
      iov[0].iov_len    = sizeof(hdr);

      /* deal with events of a final nature */
      if (test_bit(RXRPC_CALL_RELEASE, &call->events)) {
            rxrpc_release_call(call);
            clear_bit(RXRPC_CALL_RELEASE, &call->events);
      }

      if (test_bit(RXRPC_CALL_RCVD_ERROR, &call->events)) {
            int error;

            clear_bit(RXRPC_CALL_CONN_ABORT, &call->events);
            clear_bit(RXRPC_CALL_REJECT_BUSY, &call->events);
            clear_bit(RXRPC_CALL_ABORT, &call->events);

            error = call->conn->trans->peer->net_error;
            _debug("post net error %d", error);

            if (rxrpc_post_message(call, RXRPC_SKB_MARK_NET_ERROR,
                               error, true) < 0)
                  goto no_mem;
            clear_bit(RXRPC_CALL_RCVD_ERROR, &call->events);
            goto kill_ACKs;
      }

      if (test_bit(RXRPC_CALL_CONN_ABORT, &call->events)) {
            ASSERTCMP(call->state, >, RXRPC_CALL_COMPLETE);

            clear_bit(RXRPC_CALL_REJECT_BUSY, &call->events);
            clear_bit(RXRPC_CALL_ABORT, &call->events);

            _debug("post conn abort");

            if (rxrpc_post_message(call, RXRPC_SKB_MARK_LOCAL_ERROR,
                               call->conn->error, true) < 0)
                  goto no_mem;
            clear_bit(RXRPC_CALL_CONN_ABORT, &call->events);
            goto kill_ACKs;
      }

      if (test_bit(RXRPC_CALL_REJECT_BUSY, &call->events)) {
            hdr.type = RXRPC_PACKET_TYPE_BUSY;
            genbit = RXRPC_CALL_REJECT_BUSY;
            goto send_message;
      }

      if (test_bit(RXRPC_CALL_ABORT, &call->events)) {
            ASSERTCMP(call->state, >, RXRPC_CALL_COMPLETE);

            if (rxrpc_post_message(call, RXRPC_SKB_MARK_LOCAL_ERROR,
                               ECONNABORTED, true) < 0)
                  goto no_mem;
            hdr.type = RXRPC_PACKET_TYPE_ABORT;
            data = htonl(call->abort_code);
            iov[1].iov_base = &data;
            iov[1].iov_len = sizeof(data);
            genbit = RXRPC_CALL_ABORT;
            goto send_message;
      }

      if (test_bit(RXRPC_CALL_ACK_FINAL, &call->events)) {
            genbit = RXRPC_CALL_ACK_FINAL;

            ack.bufferSpace   = htons(8);
            ack.maxSkew = 0;
            ack.serial  = 0;
            ack.reason  = RXRPC_ACK_IDLE;
            ack.nAcks   = 0;
            call->ackr_reason = 0;

            spin_lock_bh(&call->lock);
            ack.serial = call->ackr_serial;
            ack.previousPacket = call->ackr_prev_seq;
            ack.firstPacket = htonl(call->rx_data_eaten + 1);
            spin_unlock_bh(&call->lock);

            pad = 0;

            iov[1].iov_base = &ack;
            iov[1].iov_len    = sizeof(ack);
            iov[2].iov_base = &pad;
            iov[2].iov_len    = 3;
            iov[3].iov_base = &ackinfo;
            iov[3].iov_len    = sizeof(ackinfo);
            goto send_ACK;
      }

      if (call->events & ((1 << RXRPC_CALL_RCVD_BUSY) |
                      (1 << RXRPC_CALL_RCVD_ABORT))
          ) {
            u32 mark;

            if (test_bit(RXRPC_CALL_RCVD_ABORT, &call->events))
                  mark = RXRPC_SKB_MARK_REMOTE_ABORT;
            else
                  mark = RXRPC_SKB_MARK_BUSY;

            _debug("post abort/busy");
            rxrpc_clear_tx_window(call);
            if (rxrpc_post_message(call, mark, ECONNABORTED, true) < 0)
                  goto no_mem;

            clear_bit(RXRPC_CALL_RCVD_BUSY, &call->events);
            clear_bit(RXRPC_CALL_RCVD_ABORT, &call->events);
            goto kill_ACKs;
      }

      if (test_and_clear_bit(RXRPC_CALL_RCVD_ACKALL, &call->events)) {
            _debug("do implicit ackall");
            rxrpc_clear_tx_window(call);
      }

      if (test_bit(RXRPC_CALL_LIFE_TIMER, &call->events)) {
            write_lock_bh(&call->state_lock);
            if (call->state <= RXRPC_CALL_COMPLETE) {
                  call->state = RXRPC_CALL_LOCALLY_ABORTED;
                  call->abort_code = RX_CALL_TIMEOUT;
                  set_bit(RXRPC_CALL_ABORT, &call->events);
            }
            write_unlock_bh(&call->state_lock);

            _debug("post timeout");
            if (rxrpc_post_message(call, RXRPC_SKB_MARK_LOCAL_ERROR,
                               ETIME, true) < 0)
                  goto no_mem;

            clear_bit(RXRPC_CALL_LIFE_TIMER, &call->events);
            goto kill_ACKs;
      }

      /* deal with assorted inbound messages */
      if (!skb_queue_empty(&call->rx_queue)) {
            switch (rxrpc_process_rx_queue(call, &abort_code)) {
            case 0:
            case -EAGAIN:
                  break;
            case -ENOMEM:
                  goto no_mem;
            case -EKEYEXPIRED:
            case -EKEYREJECTED:
            case -EPROTO:
                  rxrpc_abort_call(call, abort_code);
                  goto kill_ACKs;
            }
      }

      /* handle resending */
      if (test_and_clear_bit(RXRPC_CALL_RESEND_TIMER, &call->events))
            rxrpc_resend_timer(call);
      if (test_and_clear_bit(RXRPC_CALL_RESEND, &call->events))
            rxrpc_resend(call);

      /* consider sending an ordinary ACK */
      if (test_bit(RXRPC_CALL_ACK, &call->events)) {
            _debug("send ACK: window: %d - %d { %lx }",
                   call->rx_data_eaten, call->ackr_win_top,
                   call->ackr_window[0]);

            if (call->state > RXRPC_CALL_SERVER_ACK_REQUEST &&
                call->ackr_reason != RXRPC_ACK_PING_RESPONSE) {
                  /* ACK by sending reply DATA packet in this state */
                  clear_bit(RXRPC_CALL_ACK, &call->events);
                  goto maybe_reschedule;
            }

            genbit = RXRPC_CALL_ACK;

            acks = kzalloc(call->ackr_win_top - call->rx_data_eaten,
                         GFP_NOFS);
            if (!acks)
                  goto no_mem;

            //hdr.flags = RXRPC_SLOW_START_OK;
            ack.bufferSpace   = htons(8);
            ack.maxSkew = 0;
            ack.serial  = 0;
            ack.reason  = 0;

            spin_lock_bh(&call->lock);
            ack.reason = call->ackr_reason;
            ack.serial = call->ackr_serial;
            ack.previousPacket = call->ackr_prev_seq;
            ack.firstPacket = htonl(call->rx_data_eaten + 1);

            ack.nAcks = 0;
            for (loop = 0; loop < RXRPC_ACKR_WINDOW_ASZ; loop++) {
                  nbit = loop * BITS_PER_LONG;
                  for (bits = call->ackr_window[loop]; bits; bits >>= 1
                       ) {
                        _debug("- l=%d n=%d b=%lx", loop, nbit, bits);
                        if (bits & 1) {
                              acks[nbit] = RXRPC_ACK_TYPE_ACK;
                              ack.nAcks = nbit + 1;
                        }
                        nbit++;
                  }
            }
            call->ackr_reason = 0;
            spin_unlock_bh(&call->lock);

            pad = 0;

            iov[1].iov_base = &ack;
            iov[1].iov_len    = sizeof(ack);
            iov[2].iov_base = acks;
            iov[2].iov_len    = ack.nAcks;
            iov[3].iov_base = &pad;
            iov[3].iov_len    = 3;
            iov[4].iov_base = &ackinfo;
            iov[4].iov_len    = sizeof(ackinfo);

            switch (ack.reason) {
            case RXRPC_ACK_REQUESTED:
            case RXRPC_ACK_DUPLICATE:
            case RXRPC_ACK_OUT_OF_SEQUENCE:
            case RXRPC_ACK_EXCEEDS_WINDOW:
            case RXRPC_ACK_NOSPACE:
            case RXRPC_ACK_PING:
            case RXRPC_ACK_PING_RESPONSE:
                  goto send_ACK_with_skew;
            case RXRPC_ACK_DELAY:
            case RXRPC_ACK_IDLE:
                  goto send_ACK;
            }
      }

      /* handle completion of security negotiations on an incoming
       * connection */
      if (test_and_clear_bit(RXRPC_CALL_SECURED, &call->events)) {
            _debug("secured");
            spin_lock_bh(&call->lock);

            if (call->state == RXRPC_CALL_SERVER_SECURING) {
                  _debug("securing");
                  write_lock(&call->conn->lock);
                  if (!test_bit(RXRPC_CALL_RELEASED, &call->flags) &&
                      !test_bit(RXRPC_CALL_RELEASE, &call->events)) {
                        _debug("not released");
                        call->state = RXRPC_CALL_SERVER_ACCEPTING;
                        list_move_tail(&call->accept_link,
                                     &call->socket->acceptq);
                  }
                  write_unlock(&call->conn->lock);
                  read_lock(&call->state_lock);
                  if (call->state < RXRPC_CALL_COMPLETE)
                        set_bit(RXRPC_CALL_POST_ACCEPT, &call->events);
                  read_unlock(&call->state_lock);
            }

            spin_unlock_bh(&call->lock);
            if (!test_bit(RXRPC_CALL_POST_ACCEPT, &call->events))
                  goto maybe_reschedule;
      }

      /* post a notification of an acceptable connection to the app */
      if (test_bit(RXRPC_CALL_POST_ACCEPT, &call->events)) {
            _debug("post accept");
            if (rxrpc_post_message(call, RXRPC_SKB_MARK_NEW_CALL,
                               0, false) < 0)
                  goto no_mem;
            clear_bit(RXRPC_CALL_POST_ACCEPT, &call->events);
            goto maybe_reschedule;
      }

      /* handle incoming call acceptance */
      if (test_and_clear_bit(RXRPC_CALL_ACCEPTED, &call->events)) {
            _debug("accepted");
            ASSERTCMP(call->rx_data_post, ==, 0);
            call->rx_data_post = 1;
            read_lock_bh(&call->state_lock);
            if (call->state < RXRPC_CALL_COMPLETE)
                  set_bit(RXRPC_CALL_DRAIN_RX_OOS, &call->events);
            read_unlock_bh(&call->state_lock);
      }

      /* drain the out of sequence received packet queue into the packet Rx
       * queue */
      if (test_and_clear_bit(RXRPC_CALL_DRAIN_RX_OOS, &call->events)) {
            while (call->rx_data_post == call->rx_first_oos)
                  if (rxrpc_drain_rx_oos_queue(call) < 0)
                        break;
            goto maybe_reschedule;
      }

      /* other events may have been raised since we started checking */
      goto maybe_reschedule;

send_ACK_with_skew:
      ack.maxSkew = htons(atomic_read(&call->conn->hi_serial) -
                      ntohl(ack.serial));
send_ACK:
      mtu = call->conn->trans->peer->if_mtu;
      mtu -= call->conn->trans->peer->hdrsize;
      ackinfo.maxMTU    = htonl(mtu);
      ackinfo.rwind     = htonl(32);

      /* permit the peer to send us jumbo packets if it wants to */
      ackinfo.rxMTU     = htonl(5692);
      ackinfo.jumbo_max = htonl(4);

      hdr.serial = htonl(atomic_inc_return(&call->conn->serial));
      _proto("Tx ACK %%%u { m=%hu f=#%u p=#%u s=%%%u r=%s n=%u }",
             ntohl(hdr.serial),
             ntohs(ack.maxSkew),
             ntohl(ack.firstPacket),
             ntohl(ack.previousPacket),
             ntohl(ack.serial),
             rxrpc_acks[ack.reason],
             ack.nAcks);

      del_timer_sync(&call->ack_timer);
      if (ack.nAcks > 0)
            set_bit(RXRPC_CALL_TX_SOFT_ACK, &call->flags);
      goto send_message_2;

send_message:
      _debug("send message");

      hdr.serial = htonl(atomic_inc_return(&call->conn->serial));
      _proto("Tx %s %%%u", rxrpc_pkts[hdr.type], ntohl(hdr.serial));
send_message_2:

      len = iov[0].iov_len;
      ioc = 1;
      if (iov[4].iov_len) {
            ioc = 5;
            len += iov[4].iov_len;
            len += iov[3].iov_len;
            len += iov[2].iov_len;
            len += iov[1].iov_len;
      } else if (iov[3].iov_len) {
            ioc = 4;
            len += iov[3].iov_len;
            len += iov[2].iov_len;
            len += iov[1].iov_len;
      } else if (iov[2].iov_len) {
            ioc = 3;
            len += iov[2].iov_len;
            len += iov[1].iov_len;
      } else if (iov[1].iov_len) {
            ioc = 2;
            len += iov[1].iov_len;
      }

      ret = kernel_sendmsg(call->conn->trans->local->socket,
                       &msg, iov, ioc, len);
      if (ret < 0) {
            _debug("sendmsg failed: %d", ret);
            read_lock_bh(&call->state_lock);
            if (call->state < RXRPC_CALL_DEAD)
                  rxrpc_queue_call(call);
            read_unlock_bh(&call->state_lock);
            goto error;
      }

      switch (genbit) {
      case RXRPC_CALL_ABORT:
            clear_bit(genbit, &call->events);
            clear_bit(RXRPC_CALL_RCVD_ABORT, &call->events);
            goto kill_ACKs;

      case RXRPC_CALL_ACK_FINAL:
            write_lock_bh(&call->state_lock);
            if (call->state == RXRPC_CALL_CLIENT_FINAL_ACK)
                  call->state = RXRPC_CALL_COMPLETE;
            write_unlock_bh(&call->state_lock);
            goto kill_ACKs;

      default:
            clear_bit(genbit, &call->events);
            switch (call->state) {
            case RXRPC_CALL_CLIENT_AWAIT_REPLY:
            case RXRPC_CALL_CLIENT_RECV_REPLY:
            case RXRPC_CALL_SERVER_RECV_REQUEST:
            case RXRPC_CALL_SERVER_ACK_REQUEST:
                  _debug("start ACK timer");
                  rxrpc_propose_ACK(call, RXRPC_ACK_DELAY,
                                call->ackr_serial, false);
            default:
                  break;
            }
            goto maybe_reschedule;
      }

kill_ACKs:
      del_timer_sync(&call->ack_timer);
      if (test_and_clear_bit(RXRPC_CALL_ACK_FINAL, &call->events))
            rxrpc_put_call(call);
      clear_bit(RXRPC_CALL_ACK, &call->events);

maybe_reschedule:
      if (call->events || !skb_queue_empty(&call->rx_queue)) {
            read_lock_bh(&call->state_lock);
            if (call->state < RXRPC_CALL_DEAD)
                  rxrpc_queue_call(call);
            read_unlock_bh(&call->state_lock);
      }

      /* don't leave aborted connections on the accept queue */
      if (call->state >= RXRPC_CALL_COMPLETE &&
          !list_empty(&call->accept_link)) {
            _debug("X unlinking once-pending call %p { e=%lx f=%lx c=%x }",
                   call, call->events, call->flags,
                   ntohl(call->conn->cid));

            read_lock_bh(&call->state_lock);
            if (!test_bit(RXRPC_CALL_RELEASED, &call->flags) &&
                !test_and_set_bit(RXRPC_CALL_RELEASE, &call->events))
                  rxrpc_queue_call(call);
            read_unlock_bh(&call->state_lock);
      }

error:
      clear_bit(RXRPC_CALL_PROC_BUSY, &call->flags);
      kfree(acks);

      /* because we don't want two CPUs both processing the work item for one
       * call at the same time, we use a flag to note when it's busy; however
       * this means there's a race between clearing the flag and setting the
       * work pending bit and the work item being processed again */
      if (call->events && !work_pending(&call->processor)) {
            _debug("jumpstart %x", ntohl(call->conn->cid));
            rxrpc_queue_call(call);
      }

      _leave("");
      return;

no_mem:
      _debug("out of memory");
      goto maybe_reschedule;
}

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