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xpc_main.c

/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (c) 2004-2007 Silicon Graphics, Inc.  All Rights Reserved.
 */


/*
 * Cross Partition Communication (XPC) support - standard version.
 *
 *    XPC provides a message passing capability that crosses partition
 *    boundaries. This module is made up of two parts:
 *
 *        partition     This part detects the presence/absence of other
 *                partitions. It provides a heartbeat and monitors
 *                the heartbeats of other partitions.
 *
 *        channel This part manages the channels and sends/receives
 *                messages across them to/from other partitions.
 *
 *    There are a couple of additional functions residing in XP, which
 *    provide an interface to XPC for its users.
 *
 *
 *    Caveats:
 *
 *      . We currently have no way to determine which nasid an IPI came
 *        from. Thus, xpc_IPI_send() does a remote AMO write followed by
 *        an IPI. The AMO indicates where data is to be pulled from, so
 *        after the IPI arrives, the remote partition checks the AMO word.
 *        The IPI can actually arrive before the AMO however, so other code
 *        must periodically check for this case. Also, remote AMO operations
 *        do not reliably time out. Thus we do a remote PIO read solely to
 *        know whether the remote partition is down and whether we should
 *        stop sending IPIs to it. This remote PIO read operation is set up
 *        in a special nofault region so SAL knows to ignore (and cleanup)
 *        any errors due to the remote AMO write, PIO read, and/or PIO
 *        write operations.
 *
 *        If/when new hardware solves this IPI problem, we should abandon
 *        the current approach.
 *
 */


#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/cache.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/reboot.h>
#include <linux/completion.h>
#include <linux/kdebug.h>
#include <asm/sn/intr.h>
#include <asm/sn/sn_sal.h>
#include <asm/uaccess.h>
#include <asm/sn/xpc.h>


/* define two XPC debug device structures to be used with dev_dbg() et al */

struct device_driver xpc_dbg_name = {
      .name = "xpc"
};

struct device xpc_part_dbg_subname = {
      .bus_id = {0},          /* set to "part" at xpc_init() time */
      .driver = &xpc_dbg_name
};

struct device xpc_chan_dbg_subname = {
      .bus_id = {0},          /* set to "chan" at xpc_init() time */
      .driver = &xpc_dbg_name
};

struct device *xpc_part = &xpc_part_dbg_subname;
struct device *xpc_chan = &xpc_chan_dbg_subname;


static int xpc_kdebug_ignore;


/* systune related variables for /proc/sys directories */

static int xpc_hb_interval = XPC_HB_DEFAULT_INTERVAL;
static int xpc_hb_min_interval = 1;
static int xpc_hb_max_interval = 10;

static int xpc_hb_check_interval = XPC_HB_CHECK_DEFAULT_INTERVAL;
static int xpc_hb_check_min_interval = 10;
static int xpc_hb_check_max_interval = 120;

int xpc_disengage_request_timelimit = XPC_DISENGAGE_REQUEST_DEFAULT_TIMELIMIT;
static int xpc_disengage_request_min_timelimit = 0;
static int xpc_disengage_request_max_timelimit = 120;

static ctl_table xpc_sys_xpc_hb_dir[] = {
      {
            .ctl_name   = CTL_UNNUMBERED,
            .procname   = "hb_interval",
            .data       = &xpc_hb_interval,
            .maxlen           = sizeof(int),
            .mode       = 0644,
            .proc_handler     = &proc_dointvec_minmax,
            .strategy   = &sysctl_intvec,
            .extra1           = &xpc_hb_min_interval,
            .extra2           = &xpc_hb_max_interval
      },
      {
            .ctl_name   = CTL_UNNUMBERED,
            .procname   = "hb_check_interval",
            .data       = &xpc_hb_check_interval,
            .maxlen           = sizeof(int),
            .mode       = 0644,
            .proc_handler     = &proc_dointvec_minmax,
            .strategy   = &sysctl_intvec,
            .extra1           = &xpc_hb_check_min_interval,
            .extra2           = &xpc_hb_check_max_interval
      },
      {}
};
static ctl_table xpc_sys_xpc_dir[] = {
      {
            .ctl_name   = CTL_UNNUMBERED,
            .procname   = "hb",
            .mode       = 0555,
            .child            = xpc_sys_xpc_hb_dir
      },
      {
            .ctl_name   = CTL_UNNUMBERED,
            .procname   = "disengage_request_timelimit",
            .data       = &xpc_disengage_request_timelimit,
            .maxlen           = sizeof(int),
            .mode       = 0644,
            .proc_handler     = &proc_dointvec_minmax,
            .strategy   = &sysctl_intvec,
            .extra1           = &xpc_disengage_request_min_timelimit,
            .extra2           = &xpc_disengage_request_max_timelimit
      },
      {}
};
static ctl_table xpc_sys_dir[] = {
      {
            .ctl_name   = CTL_UNNUMBERED,
            .procname   = "xpc",
            .mode       = 0555,
            .child            = xpc_sys_xpc_dir
      },
      {}
};
static struct ctl_table_header *xpc_sysctl;

/* non-zero if any remote partition disengage request was timed out */
int xpc_disengage_request_timedout;

/* #of IRQs received */
static atomic_t xpc_act_IRQ_rcvd;

/* IRQ handler notifies this wait queue on receipt of an IRQ */
static DECLARE_WAIT_QUEUE_HEAD(xpc_act_IRQ_wq);

static unsigned long xpc_hb_check_timeout;

/* notification that the xpc_hb_checker thread has exited */
static DECLARE_COMPLETION(xpc_hb_checker_exited);

/* notification that the xpc_discovery thread has exited */
static DECLARE_COMPLETION(xpc_discovery_exited);


static struct timer_list xpc_hb_timer;


static void xpc_kthread_waitmsgs(struct xpc_partition *, struct xpc_channel *);


static int xpc_system_reboot(struct notifier_block *, unsigned long, void *);
static struct notifier_block xpc_reboot_notifier = {
      .notifier_call = xpc_system_reboot,
};

static int xpc_system_die(struct notifier_block *, unsigned long, void *);
static struct notifier_block xpc_die_notifier = {
      .notifier_call = xpc_system_die,
};


/*
 * Timer function to enforce the timelimit on the partition disengage request.
 */
static void
xpc_timeout_partition_disengage_request(unsigned long data)
{
      struct xpc_partition *part = (struct xpc_partition *) data;


      DBUG_ON(jiffies < part->disengage_request_timeout);

      (void) xpc_partition_disengaged(part);

      DBUG_ON(part->disengage_request_timeout != 0);
      DBUG_ON(xpc_partition_engaged(1UL << XPC_PARTID(part)) != 0);
}


/*
 * Notify the heartbeat check thread that an IRQ has been received.
 */
static irqreturn_t
xpc_act_IRQ_handler(int irq, void *dev_id)
{
      atomic_inc(&xpc_act_IRQ_rcvd);
      wake_up_interruptible(&xpc_act_IRQ_wq);
      return IRQ_HANDLED;
}


/*
 * Timer to produce the heartbeat.  The timer structures function is
 * already set when this is initially called.  A tunable is used to
 * specify when the next timeout should occur.
 */
static void
xpc_hb_beater(unsigned long dummy)
{
      xpc_vars->heartbeat++;

      if (jiffies >= xpc_hb_check_timeout) {
            wake_up_interruptible(&xpc_act_IRQ_wq);
      }

      xpc_hb_timer.expires = jiffies + (xpc_hb_interval * HZ);
      add_timer(&xpc_hb_timer);
}


/*
 * This thread is responsible for nearly all of the partition
 * activation/deactivation.
 */
static int
xpc_hb_checker(void *ignore)
{
      int last_IRQ_count = 0;
      int new_IRQ_count;
      int force_IRQ=0;


      /* this thread was marked active by xpc_hb_init() */

      daemonize(XPC_HB_CHECK_THREAD_NAME);

      set_cpus_allowed(current, cpumask_of_cpu(XPC_HB_CHECK_CPU));

      /* set our heartbeating to other partitions into motion */
      xpc_hb_check_timeout = jiffies + (xpc_hb_check_interval * HZ);
      xpc_hb_beater(0);

      while (!(volatile int) xpc_exiting) {

            dev_dbg(xpc_part, "woke up with %d ticks rem; %d IRQs have "
                  "been received\n",
                  (int) (xpc_hb_check_timeout - jiffies),
                  atomic_read(&xpc_act_IRQ_rcvd) - last_IRQ_count);


            /* checking of remote heartbeats is skewed by IRQ handling */
            if (jiffies >= xpc_hb_check_timeout) {
                  dev_dbg(xpc_part, "checking remote heartbeats\n");
                  xpc_check_remote_hb();

                  /*
                   * We need to periodically recheck to ensure no
                   * IPI/AMO pairs have been missed.  That check
                   * must always reset xpc_hb_check_timeout.
                   */
                  force_IRQ = 1;
            }


            /* check for outstanding IRQs */
            new_IRQ_count = atomic_read(&xpc_act_IRQ_rcvd);
            if (last_IRQ_count < new_IRQ_count || force_IRQ != 0) {
                  force_IRQ = 0;

                  dev_dbg(xpc_part, "found an IRQ to process; will be "
                        "resetting xpc_hb_check_timeout\n");

                  last_IRQ_count += xpc_identify_act_IRQ_sender();
                  if (last_IRQ_count < new_IRQ_count) {
                        /* retry once to help avoid missing AMO */
                        (void) xpc_identify_act_IRQ_sender();
                  }
                  last_IRQ_count = new_IRQ_count;

                  xpc_hb_check_timeout = jiffies +
                                 (xpc_hb_check_interval * HZ);
            }

            /* wait for IRQ or timeout */
            (void) wait_event_interruptible(xpc_act_IRQ_wq,
                      (last_IRQ_count < atomic_read(&xpc_act_IRQ_rcvd) ||
                              jiffies >= xpc_hb_check_timeout ||
                                    (volatile int) xpc_exiting));
      }

      dev_dbg(xpc_part, "heartbeat checker is exiting\n");


      /* mark this thread as having exited */
      complete(&xpc_hb_checker_exited);
      return 0;
}


/*
 * This thread will attempt to discover other partitions to activate
 * based on info provided by SAL. This new thread is short lived and
 * will exit once discovery is complete.
 */
static int
xpc_initiate_discovery(void *ignore)
{
      daemonize(XPC_DISCOVERY_THREAD_NAME);

      xpc_discovery();

      dev_dbg(xpc_part, "discovery thread is exiting\n");

      /* mark this thread as having exited */
      complete(&xpc_discovery_exited);
      return 0;
}


/*
 * Establish first contact with the remote partititon. This involves pulling
 * the XPC per partition variables from the remote partition and waiting for
 * the remote partition to pull ours.
 */
static enum xpc_retval
xpc_make_first_contact(struct xpc_partition *part)
{
      enum xpc_retval ret;


      while ((ret = xpc_pull_remote_vars_part(part)) != xpcSuccess) {
            if (ret != xpcRetry) {
                  XPC_DEACTIVATE_PARTITION(part, ret);
                  return ret;
            }

            dev_dbg(xpc_chan, "waiting to make first contact with "
                  "partition %d\n", XPC_PARTID(part));

            /* wait a 1/4 of a second or so */
            (void) msleep_interruptible(250);

            if (part->act_state == XPC_P_DEACTIVATING) {
                  return part->reason;
            }
      }

      return xpc_mark_partition_active(part);
}


/*
 * The first kthread assigned to a newly activated partition is the one
 * created by XPC HB with which it calls xpc_partition_up(). XPC hangs on to
 * that kthread until the partition is brought down, at which time that kthread
 * returns back to XPC HB. (The return of that kthread will signify to XPC HB
 * that XPC has dismantled all communication infrastructure for the associated
 * partition.) This kthread becomes the channel manager for that partition.
 *
 * Each active partition has a channel manager, who, besides connecting and
 * disconnecting channels, will ensure that each of the partition's connected
 * channels has the required number of assigned kthreads to get the work done.
 */
static void
xpc_channel_mgr(struct xpc_partition *part)
{
      while (part->act_state != XPC_P_DEACTIVATING ||
                  atomic_read(&part->nchannels_active) > 0 ||
                              !xpc_partition_disengaged(part)) {

            xpc_process_channel_activity(part);


            /*
             * Wait until we've been requested to activate kthreads or
             * all of the channel's message queues have been torn down or
             * a signal is pending.
             *
             * The channel_mgr_requests is set to 1 after being awakened,
             * This is done to prevent the channel mgr from making one pass
             * through the loop for each request, since he will
             * be servicing all the requests in one pass. The reason it's
             * set to 1 instead of 0 is so that other kthreads will know
             * that the channel mgr is running and won't bother trying to
             * wake him up.
             */
            atomic_dec(&part->channel_mgr_requests);
            (void) wait_event_interruptible(part->channel_mgr_wq,
                        (atomic_read(&part->channel_mgr_requests) > 0 ||
                        (volatile u64) part->local_IPI_amo != 0 ||
                        ((volatile u8) part->act_state ==
                                          XPC_P_DEACTIVATING &&
                        atomic_read(&part->nchannels_active) == 0 &&
                        xpc_partition_disengaged(part))));
            atomic_set(&part->channel_mgr_requests, 1);

            // >>> Does it need to wakeup periodically as well? In case we
            // >>> miscalculated the #of kthreads to wakeup or create?
      }
}


/*
 * When XPC HB determines that a partition has come up, it will create a new
 * kthread and that kthread will call this function to attempt to set up the
 * basic infrastructure used for Cross Partition Communication with the newly
 * upped partition.
 *
 * The kthread that was created by XPC HB and which setup the XPC
 * infrastructure will remain assigned to the partition until the partition
 * goes down. At which time the kthread will teardown the XPC infrastructure
 * and then exit.
 *
 * XPC HB will put the remote partition's XPC per partition specific variables
 * physical address into xpc_partitions[partid].remote_vars_part_pa prior to
 * calling xpc_partition_up().
 */
static void
xpc_partition_up(struct xpc_partition *part)
{
      DBUG_ON(part->channels != NULL);

      dev_dbg(xpc_chan, "activating partition %d\n", XPC_PARTID(part));

      if (xpc_setup_infrastructure(part) != xpcSuccess) {
            return;
      }

      /*
       * The kthread that XPC HB called us with will become the
       * channel manager for this partition. It will not return
       * back to XPC HB until the partition's XPC infrastructure
       * has been dismantled.
       */

      (void) xpc_part_ref(part);    /* this will always succeed */

      if (xpc_make_first_contact(part) == xpcSuccess) {
            xpc_channel_mgr(part);
      }

      xpc_part_deref(part);

      xpc_teardown_infrastructure(part);
}


static int
xpc_activating(void *__partid)
{
      partid_t partid = (u64) __partid;
      struct xpc_partition *part = &xpc_partitions[partid];
      unsigned long irq_flags;
      struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
      int ret;


      DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);

      spin_lock_irqsave(&part->act_lock, irq_flags);

      if (part->act_state == XPC_P_DEACTIVATING) {
            part->act_state = XPC_P_INACTIVE;
            spin_unlock_irqrestore(&part->act_lock, irq_flags);
            part->remote_rp_pa = 0;
            return 0;
      }

      /* indicate the thread is activating */
      DBUG_ON(part->act_state != XPC_P_ACTIVATION_REQ);
      part->act_state = XPC_P_ACTIVATING;

      XPC_SET_REASON(part, 0, 0);
      spin_unlock_irqrestore(&part->act_lock, irq_flags);

      dev_dbg(xpc_part, "bringing partition %d up\n", partid);

      daemonize("xpc%02d", partid);

      /*
       * This thread needs to run at a realtime priority to prevent a
       * significant performance degradation.
       */
      ret = sched_setscheduler(current, SCHED_FIFO, &param);
      if (ret != 0) {
            dev_warn(xpc_part, "unable to set pid %d to a realtime "
                  "priority, ret=%d\n", current->pid, ret);
      }

      /* allow this thread and its children to run on any CPU */
      set_cpus_allowed(current, CPU_MASK_ALL);

      /*
       * Register the remote partition's AMOs with SAL so it can handle
       * and cleanup errors within that address range should the remote
       * partition go down. We don't unregister this range because it is
       * difficult to tell when outstanding writes to the remote partition
       * are finished and thus when it is safe to unregister. This should
       * not result in wasted space in the SAL xp_addr_region table because
       * we should get the same page for remote_amos_page_pa after module
       * reloads and system reboots.
       */
      if (sn_register_xp_addr_region(part->remote_amos_page_pa,
                                          PAGE_SIZE, 1) < 0) {
            dev_warn(xpc_part, "xpc_partition_up(%d) failed to register "
                  "xp_addr region\n", partid);

            spin_lock_irqsave(&part->act_lock, irq_flags);
            part->act_state = XPC_P_INACTIVE;
            XPC_SET_REASON(part, xpcPhysAddrRegFailed, __LINE__);
            spin_unlock_irqrestore(&part->act_lock, irq_flags);
            part->remote_rp_pa = 0;
            return 0;
      }

      xpc_allow_hb(partid, xpc_vars);
      xpc_IPI_send_activated(part);


      /*
       * xpc_partition_up() holds this thread and marks this partition as
       * XPC_P_ACTIVE by calling xpc_hb_mark_active().
       */
      (void) xpc_partition_up(part);

      xpc_disallow_hb(partid, xpc_vars);
      xpc_mark_partition_inactive(part);

      if (part->reason == xpcReactivating) {
            /* interrupting ourselves results in activating partition */
            xpc_IPI_send_reactivate(part);
      }

      return 0;
}


void
xpc_activate_partition(struct xpc_partition *part)
{
      partid_t partid = XPC_PARTID(part);
      unsigned long irq_flags;
      pid_t pid;


      spin_lock_irqsave(&part->act_lock, irq_flags);

      DBUG_ON(part->act_state != XPC_P_INACTIVE);

      part->act_state = XPC_P_ACTIVATION_REQ;
      XPC_SET_REASON(part, xpcCloneKThread, __LINE__);

      spin_unlock_irqrestore(&part->act_lock, irq_flags);

      pid = kernel_thread(xpc_activating, (void *) ((u64) partid), 0);

      if (unlikely(pid <= 0)) {
            spin_lock_irqsave(&part->act_lock, irq_flags);
            part->act_state = XPC_P_INACTIVE;
            XPC_SET_REASON(part, xpcCloneKThreadFailed, __LINE__);
            spin_unlock_irqrestore(&part->act_lock, irq_flags);
      }
}


/*
 * Handle the receipt of a SGI_XPC_NOTIFY IRQ by seeing whether the specified
 * partition actually sent it. Since SGI_XPC_NOTIFY IRQs may be shared by more
 * than one partition, we use an AMO_t structure per partition to indicate
 * whether a partition has sent an IPI or not.  >>> If it has, then wake up the
 * associated kthread to handle it.
 *
 * All SGI_XPC_NOTIFY IRQs received by XPC are the result of IPIs sent by XPC
 * running on other partitions.
 *
 * Noteworthy Arguments:
 *
 *    irq - Interrupt ReQuest number. NOT USED.
 *
 *    dev_id - partid of IPI's potential sender.
 */
irqreturn_t
xpc_notify_IRQ_handler(int irq, void *dev_id)
{
      partid_t partid = (partid_t) (u64) dev_id;
      struct xpc_partition *part = &xpc_partitions[partid];


      DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);

      if (xpc_part_ref(part)) {
            xpc_check_for_channel_activity(part);

            xpc_part_deref(part);
      }
      return IRQ_HANDLED;
}


/*
 * Check to see if xpc_notify_IRQ_handler() dropped any IPIs on the floor
 * because the write to their associated IPI amo completed after the IRQ/IPI
 * was received.
 */
void
xpc_dropped_IPI_check(struct xpc_partition *part)
{
      if (xpc_part_ref(part)) {
            xpc_check_for_channel_activity(part);

            part->dropped_IPI_timer.expires = jiffies +
                                          XPC_P_DROPPED_IPI_WAIT;
            add_timer(&part->dropped_IPI_timer);
            xpc_part_deref(part);
      }
}


void
xpc_activate_kthreads(struct xpc_channel *ch, int needed)
{
      int idle = atomic_read(&ch->kthreads_idle);
      int assigned = atomic_read(&ch->kthreads_assigned);
      int wakeup;


      DBUG_ON(needed <= 0);

      if (idle > 0) {
            wakeup = (needed > idle) ? idle : needed;
            needed -= wakeup;

            dev_dbg(xpc_chan, "wakeup %d idle kthreads, partid=%d, "
                  "channel=%d\n", wakeup, ch->partid, ch->number);

            /* only wakeup the requested number of kthreads */
            wake_up_nr(&ch->idle_wq, wakeup);
      }

      if (needed <= 0) {
            return;
      }

      if (needed + assigned > ch->kthreads_assigned_limit) {
            needed = ch->kthreads_assigned_limit - assigned;
            // >>>should never be less than 0
            if (needed <= 0) {
                  return;
            }
      }

      dev_dbg(xpc_chan, "create %d new kthreads, partid=%d, channel=%d\n",
            needed, ch->partid, ch->number);

      xpc_create_kthreads(ch, needed, 0);
}


/*
 * This function is where XPC's kthreads wait for messages to deliver.
 */
static void
xpc_kthread_waitmsgs(struct xpc_partition *part, struct xpc_channel *ch)
{
      do {
            /* deliver messages to their intended recipients */

            while ((volatile s64) ch->w_local_GP.get <
                        (volatile s64) ch->w_remote_GP.put &&
                              !((volatile u32) ch->flags &
                                    XPC_C_DISCONNECTING)) {
                  xpc_deliver_msg(ch);
            }

            if (atomic_inc_return(&ch->kthreads_idle) >
                                    ch->kthreads_idle_limit) {
                  /* too many idle kthreads on this channel */
                  atomic_dec(&ch->kthreads_idle);
                  break;
            }

            dev_dbg(xpc_chan, "idle kthread calling "
                  "wait_event_interruptible_exclusive()\n");

            (void) wait_event_interruptible_exclusive(ch->idle_wq,
                        ((volatile s64) ch->w_local_GP.get <
                              (volatile s64) ch->w_remote_GP.put ||
                        ((volatile u32) ch->flags &
                                    XPC_C_DISCONNECTING)));

            atomic_dec(&ch->kthreads_idle);

      } while (!((volatile u32) ch->flags & XPC_C_DISCONNECTING));
}


static int
xpc_daemonize_kthread(void *args)
{
      partid_t partid = XPC_UNPACK_ARG1(args);
      u16 ch_number = XPC_UNPACK_ARG2(args);
      struct xpc_partition *part = &xpc_partitions[partid];
      struct xpc_channel *ch;
      int n_needed;
      unsigned long irq_flags;


      daemonize("xpc%02dc%d", partid, ch_number);

      dev_dbg(xpc_chan, "kthread starting, partid=%d, channel=%d\n",
            partid, ch_number);

      ch = &part->channels[ch_number];

      if (!(ch->flags & XPC_C_DISCONNECTING)) {

            /* let registerer know that connection has been established */

            spin_lock_irqsave(&ch->lock, irq_flags);
            if (!(ch->flags & XPC_C_CONNECTEDCALLOUT)) {
                  ch->flags |= XPC_C_CONNECTEDCALLOUT;
                  spin_unlock_irqrestore(&ch->lock, irq_flags);

                  xpc_connected_callout(ch);

                  spin_lock_irqsave(&ch->lock, irq_flags);
                  ch->flags |= XPC_C_CONNECTEDCALLOUT_MADE;
                  spin_unlock_irqrestore(&ch->lock, irq_flags);

                  /*
                   * It is possible that while the callout was being
                   * made that the remote partition sent some messages.
                   * If that is the case, we may need to activate
                   * additional kthreads to help deliver them. We only
                   * need one less than total #of messages to deliver.
                   */
                  n_needed = ch->w_remote_GP.put - ch->w_local_GP.get - 1;
                  if (n_needed > 0 &&
                              !(ch->flags & XPC_C_DISCONNECTING)) {
                        xpc_activate_kthreads(ch, n_needed);
                  }
            } else {
                  spin_unlock_irqrestore(&ch->lock, irq_flags);
            }

            xpc_kthread_waitmsgs(part, ch);
      }

      /* let registerer know that connection is disconnecting */

      spin_lock_irqsave(&ch->lock, irq_flags);
      if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
                  !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
            ch->flags |= XPC_C_DISCONNECTINGCALLOUT;
            spin_unlock_irqrestore(&ch->lock, irq_flags);

            xpc_disconnect_callout(ch, xpcDisconnecting);

            spin_lock_irqsave(&ch->lock, irq_flags);
            ch->flags |= XPC_C_DISCONNECTINGCALLOUT_MADE;
      }
      spin_unlock_irqrestore(&ch->lock, irq_flags);

      if (atomic_dec_return(&ch->kthreads_assigned) == 0) {
            if (atomic_dec_return(&part->nchannels_engaged) == 0) {
                  xpc_mark_partition_disengaged(part);
                  xpc_IPI_send_disengage(part);
            }
      }

      xpc_msgqueue_deref(ch);

      dev_dbg(xpc_chan, "kthread exiting, partid=%d, channel=%d\n",
            partid, ch_number);

      xpc_part_deref(part);
      return 0;
}


/*
 * For each partition that XPC has established communications with, there is
 * a minimum of one kernel thread assigned to perform any operation that
 * may potentially sleep or block (basically the callouts to the asynchronous
 * functions registered via xpc_connect()).
 *
 * Additional kthreads are created and destroyed by XPC as the workload
 * demands.
 *
 * A kthread is assigned to one of the active channels that exists for a given
 * partition.
 */
void
xpc_create_kthreads(struct xpc_channel *ch, int needed,
                  int ignore_disconnecting)
{
      unsigned long irq_flags;
      pid_t pid;
      u64 args = XPC_PACK_ARGS(ch->partid, ch->number);
      struct xpc_partition *part = &xpc_partitions[ch->partid];


      while (needed-- > 0) {

            /*
             * The following is done on behalf of the newly created
             * kthread. That kthread is responsible for doing the
             * counterpart to the following before it exits.
             */
            if (ignore_disconnecting) {
                  if (!atomic_inc_not_zero(&ch->kthreads_assigned)) {
                        /* kthreads assigned had gone to zero */
                        BUG_ON(!(ch->flags &
                              XPC_C_DISCONNECTINGCALLOUT_MADE));
                        break;
                  }

            } else if (ch->flags & XPC_C_DISCONNECTING) {
                  break;

            } else if (atomic_inc_return(&ch->kthreads_assigned) == 1) {
                  if (atomic_inc_return(&part->nchannels_engaged) == 1)
                        xpc_mark_partition_engaged(part);
            }
            (void) xpc_part_ref(part);
            xpc_msgqueue_ref(ch);

            pid = kernel_thread(xpc_daemonize_kthread, (void *) args, 0);
            if (pid < 0) {
                  /* the fork failed */

                  /*
                   * NOTE: if (ignore_disconnecting &&
                   * !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) is true,
                   * then we'll deadlock if all other kthreads assigned
                   * to this channel are blocked in the channel's
                   * registerer, because the only thing that will unblock
                   * them is the xpcDisconnecting callout that this
                   * failed kernel_thread would have made.
                   */

                  if (atomic_dec_return(&ch->kthreads_assigned) == 0 &&
                      atomic_dec_return(&part->nchannels_engaged) == 0) {
                        xpc_mark_partition_disengaged(part);
                        xpc_IPI_send_disengage(part);
                  }
                  xpc_msgqueue_deref(ch);
                  xpc_part_deref(part);

                  if (atomic_read(&ch->kthreads_assigned) <
                                    ch->kthreads_idle_limit) {
                        /*
                         * Flag this as an error only if we have an
                         * insufficient #of kthreads for the channel
                         * to function.
                         */
                        spin_lock_irqsave(&ch->lock, irq_flags);
                        XPC_DISCONNECT_CHANNEL(ch, xpcLackOfResources,
                                                &irq_flags);
                        spin_unlock_irqrestore(&ch->lock, irq_flags);
                  }
                  break;
            }

            ch->kthreads_created++; // >>> temporary debug only!!!
      }
}


void
xpc_disconnect_wait(int ch_number)
{
      unsigned long irq_flags;
      partid_t partid;
      struct xpc_partition *part;
      struct xpc_channel *ch;
      int wakeup_channel_mgr;


      /* now wait for all callouts to the caller's function to cease */
      for (partid = 1; partid < XP_MAX_PARTITIONS; partid++) {
            part = &xpc_partitions[partid];

            if (!xpc_part_ref(part)) {
                  continue;
            }

            ch = &part->channels[ch_number];

            if (!(ch->flags & XPC_C_WDISCONNECT)) {
                  xpc_part_deref(part);
                  continue;
            }

            wait_for_completion(&ch->wdisconnect_wait);

            spin_lock_irqsave(&ch->lock, irq_flags);
            DBUG_ON(!(ch->flags & XPC_C_DISCONNECTED));
            wakeup_channel_mgr = 0;

            if (ch->delayed_IPI_flags) {
                  if (part->act_state != XPC_P_DEACTIVATING) {
                        spin_lock(&part->IPI_lock);
                        XPC_SET_IPI_FLAGS(part->local_IPI_amo,
                              ch->number, ch->delayed_IPI_flags);
                        spin_unlock(&part->IPI_lock);
                        wakeup_channel_mgr = 1;
                  }
                  ch->delayed_IPI_flags = 0;
            }

            ch->flags &= ~XPC_C_WDISCONNECT;
            spin_unlock_irqrestore(&ch->lock, irq_flags);

            if (wakeup_channel_mgr) {
                  xpc_wakeup_channel_mgr(part);
            }

            xpc_part_deref(part);
      }
}


static void
xpc_do_exit(enum xpc_retval reason)
{
      partid_t partid;
      int active_part_count, printed_waiting_msg = 0;
      struct xpc_partition *part;
      unsigned long printmsg_time, disengage_request_timeout = 0;


      /* a 'rmmod XPC' and a 'reboot' cannot both end up here together */
      DBUG_ON(xpc_exiting == 1);

      /*
       * Let the heartbeat checker thread and the discovery thread
       * (if one is running) know that they should exit. Also wake up
       * the heartbeat checker thread in case it's sleeping.
       */
      xpc_exiting = 1;
      wake_up_interruptible(&xpc_act_IRQ_wq);

      /* ignore all incoming interrupts */
      free_irq(SGI_XPC_ACTIVATE, NULL);

      /* wait for the discovery thread to exit */
      wait_for_completion(&xpc_discovery_exited);

      /* wait for the heartbeat checker thread to exit */
      wait_for_completion(&xpc_hb_checker_exited);


      /* sleep for a 1/3 of a second or so */
      (void) msleep_interruptible(300);


      /* wait for all partitions to become inactive */

      printmsg_time = jiffies + (XPC_DISENGAGE_PRINTMSG_INTERVAL * HZ);
      xpc_disengage_request_timedout = 0;

      do {
            active_part_count = 0;

            for (partid = 1; partid < XP_MAX_PARTITIONS; partid++) {
                  part = &xpc_partitions[partid];

                  if (xpc_partition_disengaged(part) &&
                              part->act_state == XPC_P_INACTIVE) {
                        continue;
                  }

                  active_part_count++;

                  XPC_DEACTIVATE_PARTITION(part, reason);

                  if (part->disengage_request_timeout >
                                    disengage_request_timeout) {
                        disengage_request_timeout =
                                    part->disengage_request_timeout;
                  }
            }

            if (xpc_partition_engaged(-1UL)) {
                  if (time_after(jiffies, printmsg_time)) {
                        dev_info(xpc_part, "waiting for remote "
                              "partitions to disengage, timeout in "
                              "%ld seconds\n",
                              (disengage_request_timeout - jiffies)
                                                      / HZ);
                        printmsg_time = jiffies +
                              (XPC_DISENGAGE_PRINTMSG_INTERVAL * HZ);
                        printed_waiting_msg = 1;
                  }

            } else if (active_part_count > 0) {
                  if (printed_waiting_msg) {
                        dev_info(xpc_part, "waiting for local partition"
                              " to disengage\n");
                        printed_waiting_msg = 0;
                  }

            } else {
                  if (!xpc_disengage_request_timedout) {
                        dev_info(xpc_part, "all partitions have "
                              "disengaged\n");
                  }
                  break;
            }

            /* sleep for a 1/3 of a second or so */
            (void) msleep_interruptible(300);

      } while (1);

      DBUG_ON(xpc_partition_engaged(-1UL));


      /* indicate to others that our reserved page is uninitialized */
      xpc_rsvd_page->vars_pa = 0;

      /* now it's time to eliminate our heartbeat */
      del_timer_sync(&xpc_hb_timer);
      DBUG_ON(xpc_vars->heartbeating_to_mask != 0);

      if (reason == xpcUnloading) {
            /* take ourselves off of the reboot_notifier_list */
            (void) unregister_reboot_notifier(&xpc_reboot_notifier);

            /* take ourselves off of the die_notifier list */
            (void) unregister_die_notifier(&xpc_die_notifier);
      }

      /* close down protections for IPI operations */
      xpc_restrict_IPI_ops();


      /* clear the interface to XPC's functions */
      xpc_clear_interface();

      if (xpc_sysctl) {
            unregister_sysctl_table(xpc_sysctl);
      }

      kfree(xpc_remote_copy_buffer_base);
}


/*
 * This function is called when the system is being rebooted.
 */
static int
xpc_system_reboot(struct notifier_block *nb, unsigned long event, void *unused)
{
      enum xpc_retval reason;


      switch (event) {
      case SYS_RESTART:
            reason = xpcSystemReboot;
            break;
      case SYS_HALT:
            reason = xpcSystemHalt;
            break;
      case SYS_POWER_OFF:
            reason = xpcSystemPoweroff;
            break;
      default:
            reason = xpcSystemGoingDown;
      }

      xpc_do_exit(reason);
      return NOTIFY_DONE;
}


/*
 * Notify other partitions to disengage from all references to our memory.
 */
static void
xpc_die_disengage(void)
{
      struct xpc_partition *part;
      partid_t partid;
      unsigned long engaged;
      long time, printmsg_time, disengage_request_timeout;


      /* keep xpc_hb_checker thread from doing anything (just in case) */
      xpc_exiting = 1;

      xpc_vars->heartbeating_to_mask = 0;  /* indicate we're deactivated */

      for (partid = 1; partid < XP_MAX_PARTITIONS; partid++) {
            part = &xpc_partitions[partid];

            if (!XPC_SUPPORTS_DISENGAGE_REQUEST(part->
                                          remote_vars_version)) {

                  /* just in case it was left set by an earlier XPC */
                  xpc_clear_partition_engaged(1UL << partid);
                  continue;
            }

            if (xpc_partition_engaged(1UL << partid) ||
                              part->act_state != XPC_P_INACTIVE) {
                  xpc_request_partition_disengage(part);
                  xpc_mark_partition_disengaged(part);
                  xpc_IPI_send_disengage(part);
            }
      }

      time = rtc_time();
      printmsg_time = time +
            (XPC_DISENGAGE_PRINTMSG_INTERVAL * sn_rtc_cycles_per_second);
      disengage_request_timeout = time +
            (xpc_disengage_request_timelimit * sn_rtc_cycles_per_second);

      /* wait for all other partitions to disengage from us */

      while (1) {
            engaged = xpc_partition_engaged(-1UL);
            if (!engaged) {
                  dev_info(xpc_part, "all partitions have disengaged\n");
                  break;
            }

            time = rtc_time();
            if (time >= disengage_request_timeout) {
                  for (partid = 1; partid < XP_MAX_PARTITIONS; partid++) {
                        if (engaged & (1UL << partid)) {
                              dev_info(xpc_part, "disengage from "
                                    "remote partition %d timed "
                                    "out\n", partid);
                        }
                  }
                  break;
            }

            if (time >= printmsg_time) {
                  dev_info(xpc_part, "waiting for remote partitions to "
                        "disengage, timeout in %ld seconds\n",
                        (disengage_request_timeout - time) /
                                    sn_rtc_cycles_per_second);
                  printmsg_time = time +
                              (XPC_DISENGAGE_PRINTMSG_INTERVAL *
                                    sn_rtc_cycles_per_second);
            }
      }
}


/*
 * This function is called when the system is being restarted or halted due
 * to some sort of system failure. If this is the case we need to notify the
 * other partitions to disengage from all references to our memory.
 * This function can also be called when our heartbeater could be offlined
 * for a time. In this case we need to notify other partitions to not worry
 * about the lack of a heartbeat.
 */
static int
xpc_system_die(struct notifier_block *nb, unsigned long event, void *unused)
{
      switch (event) {
      case DIE_MACHINE_RESTART:
      case DIE_MACHINE_HALT:
            xpc_die_disengage();
            break;

      case DIE_KDEBUG_ENTER:
            /* Should lack of heartbeat be ignored by other partitions? */
            if (!xpc_kdebug_ignore) {
                  break;
            }
            /* fall through */
      case DIE_MCA_MONARCH_ENTER:
      case DIE_INIT_MONARCH_ENTER:
            xpc_vars->heartbeat++;
            xpc_vars->heartbeat_offline = 1;
            break;

      case DIE_KDEBUG_LEAVE:
            /* Is lack of heartbeat being ignored by other partitions? */
            if (!xpc_kdebug_ignore) {
                  break;
            }
            /* fall through */
      case DIE_MCA_MONARCH_LEAVE:
      case DIE_INIT_MONARCH_LEAVE:
            xpc_vars->heartbeat++;
            xpc_vars->heartbeat_offline = 0;
            break;
      }

      return NOTIFY_DONE;
}


int __init
xpc_init(void)
{
      int ret;
      partid_t partid;
      struct xpc_partition *part;
      pid_t pid;
      size_t buf_size;


      if (!ia64_platform_is("sn2")) {
            return -ENODEV;
      }


      buf_size = max(XPC_RP_VARS_SIZE,
                        XPC_RP_HEADER_SIZE + XP_NASID_MASK_BYTES);
      xpc_remote_copy_buffer = xpc_kmalloc_cacheline_aligned(buf_size,
                             GFP_KERNEL, &xpc_remote_copy_buffer_base);
      if (xpc_remote_copy_buffer == NULL)
            return -ENOMEM;

      snprintf(xpc_part->bus_id, BUS_ID_SIZE, "part");
      snprintf(xpc_chan->bus_id, BUS_ID_SIZE, "chan");

      xpc_sysctl = register_sysctl_table(xpc_sys_dir);

      /*
       * The first few fields of each entry of xpc_partitions[] need to
       * be initialized now so that calls to xpc_connect() and
       * xpc_disconnect() can be made prior to the activation of any remote
       * partition. NOTE THAT NONE OF THE OTHER FIELDS BELONGING TO THESE
       * ENTRIES ARE MEANINGFUL UNTIL AFTER AN ENTRY'S CORRESPONDING
       * PARTITION HAS BEEN ACTIVATED.
       */
      for (partid = 1; partid < XP_MAX_PARTITIONS; partid++) {
            part = &xpc_partitions[partid];

            DBUG_ON((u64) part != L1_CACHE_ALIGN((u64) part));

            part->act_IRQ_rcvd = 0;
            spin_lock_init(&part->act_lock);
            part->act_state = XPC_P_INACTIVE;
            XPC_SET_REASON(part, 0, 0);

            init_timer(&part->disengage_request_timer);
            part->disengage_request_timer.function =
                        xpc_timeout_partition_disengage_request;
            part->disengage_request_timer.data = (unsigned long) part;

            part->setup_state = XPC_P_UNSET;
            init_waitqueue_head(&part->teardown_wq);
            atomic_set(&part->references, 0);
      }

      /*
       * Open up protections for IPI operations (and AMO operations on
       * Shub 1.1 systems).
       */
      xpc_allow_IPI_ops();

      /*
       * Interrupts being processed will increment this atomic variable and
       * awaken the heartbeat thread which will process the interrupts.
       */
      atomic_set(&xpc_act_IRQ_rcvd, 0);

      /*
       * This is safe to do before the xpc_hb_checker thread has started
       * because the handler releases a wait queue.  If an interrupt is
       * received before the thread is waiting, it will not go to sleep,
       * but rather immediately process the interrupt.
       */
      ret = request_irq(SGI_XPC_ACTIVATE, xpc_act_IRQ_handler, 0,
                                          "xpc hb", NULL);
      if (ret != 0) {
            dev_err(xpc_part, "can't register ACTIVATE IRQ handler, "
                  "errno=%d\n", -ret);

            xpc_restrict_IPI_ops();

            if (xpc_sysctl) {
                  unregister_sysctl_table(xpc_sysctl);
            }

            kfree(xpc_remote_copy_buffer_base);
            return -EBUSY;
      }

      /*
       * Fill the partition reserved page with the information needed by
       * other partitions to discover we are alive and establish initial
       * communications.
       */
      xpc_rsvd_page = xpc_rsvd_page_init();
      if (xpc_rsvd_page == NULL) {
            dev_err(xpc_part, "could not setup our reserved page\n");

            free_irq(SGI_XPC_ACTIVATE, NULL);
            xpc_restrict_IPI_ops();

            if (xpc_sysctl) {
                  unregister_sysctl_table(xpc_sysctl);
            }

            kfree(xpc_remote_copy_buffer_base);
            return -EBUSY;
      }


      /* add ourselves to the reboot_notifier_list */
      ret = register_reboot_notifier(&xpc_reboot_notifier);
      if (ret != 0) {
            dev_warn(xpc_part, "can't register reboot notifier\n");
      }

      /* add ourselves to the die_notifier list */
      ret = register_die_notifier(&xpc_die_notifier);
      if (ret != 0) {
            dev_warn(xpc_part, "can't register die notifier\n");
      }

      init_timer(&xpc_hb_timer);
      xpc_hb_timer.function = xpc_hb_beater;

      /*
       * The real work-horse behind xpc.  This processes incoming
       * interrupts and monitors remote heartbeats.
       */
      pid = kernel_thread(xpc_hb_checker, NULL, 0);
      if (pid < 0) {
            dev_err(xpc_part, "failed while forking hb check thread\n");

            /* indicate to others that our reserved page is uninitialized */
            xpc_rsvd_page->vars_pa = 0;

            /* take ourselves off of the reboot_notifier_list */
            (void) unregister_reboot_notifier(&xpc_reboot_notifier);

            /* take ourselves off of the die_notifier list */
            (void) unregister_die_notifier(&xpc_die_notifier);

            del_timer_sync(&xpc_hb_timer);
            free_irq(SGI_XPC_ACTIVATE, NULL);
            xpc_restrict_IPI_ops();

            if (xpc_sysctl) {
                  unregister_sysctl_table(xpc_sysctl);
            }

            kfree(xpc_remote_copy_buffer_base);
            return -EBUSY;
      }


      /*
       * Startup a thread that will attempt to discover other partitions to
       * activate based on info provided by SAL. This new thread is short
       * lived and will exit once discovery is complete.
       */
      pid = kernel_thread(xpc_initiate_discovery, NULL, 0);
      if (pid < 0) {
            dev_err(xpc_part, "failed while forking discovery thread\n");

            /* mark this new thread as a non-starter */
            complete(&xpc_discovery_exited);

            xpc_do_exit(xpcUnloading);
            return -EBUSY;
      }


      /* set the interface to point at XPC's functions */
      xpc_set_interface(xpc_initiate_connect, xpc_initiate_disconnect,
                    xpc_initiate_allocate, xpc_initiate_send,
                    xpc_initiate_send_notify, xpc_initiate_received,
                    xpc_initiate_partid_to_nasids);

      return 0;
}
module_init(xpc_init);


void __exit
xpc_exit(void)
{
      xpc_do_exit(xpcUnloading);
}
module_exit(xpc_exit);


MODULE_AUTHOR("Silicon Graphics, Inc.");
MODULE_DESCRIPTION("Cross Partition Communication (XPC) support");
MODULE_LICENSE("GPL");

module_param(xpc_hb_interval, int, 0);
MODULE_PARM_DESC(xpc_hb_interval, "Number of seconds between "
            "heartbeat increments.");

module_param(xpc_hb_check_interval, int, 0);
MODULE_PARM_DESC(xpc_hb_check_interval, "Number of seconds between "
            "heartbeat checks.");

module_param(xpc_disengage_request_timelimit, int, 0);
MODULE_PARM_DESC(xpc_disengage_request_timelimit, "Number of seconds to wait "
            "for disengage request to complete.");

module_param(xpc_kdebug_ignore, int, 0);
MODULE_PARM_DESC(xpc_kdebug_ignore, "Should lack of heartbeat be ignored by "
            "other partitions when dropping into kdebug.");


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