Add linux-next specific files for 20110831

[linux-2.6/next.git] / drivers / misc / sgi-xp / 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) 2004-2009 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:
 *
 *        . Currently on sn2, we have no way to determine which nasid an IRQ
 *          came from. Thus, xpc_send_IRQ_sn2() 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/module.h>
#include <linux/slab.h>
#include <linux/sysctl.h>
#include <linux/device.h>
#include <linux/delay.h>
#include <linux/reboot.h>
#include <linux/kdebug.h>
#include <linux/kthread.h>
#include "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 = {
        .init_name = "",        /* set to "part" at xpc_init() time */
        .driver = &xpc_dbg_name
};

struct device xpc_chan_dbg_subname = {
        .init_name = "",        /* 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_timelimit = XPC_DISENGAGE_DEFAULT_TIMELIMIT;
static int xpc_disengage_min_timelimit; /* = 0 */
static int xpc_disengage_max_timelimit = 120;

static ctl_table xpc_sys_xpc_hb_dir[] = {
        {
         .procname = "hb_interval",
         .data = &xpc_hb_interval,
         .maxlen = sizeof(int),
         .mode = 0644,
         .proc_handler = proc_dointvec_minmax,
         .extra1 = &xpc_hb_min_interval,
         .extra2 = &xpc_hb_max_interval},
        {
         .procname = "hb_check_interval",
         .data = &xpc_hb_check_interval,
         .maxlen = sizeof(int),
         .mode = 0644,
         .proc_handler = proc_dointvec_minmax,
         .extra1 = &xpc_hb_check_min_interval,
         .extra2 = &xpc_hb_check_max_interval},
        {}
};
static ctl_table xpc_sys_xpc_dir[] = {
        {
         .procname = "hb",
         .mode = 0555,
         .child = xpc_sys_xpc_hb_dir},
        {
         .procname = "disengage_timelimit",
         .data = &xpc_disengage_timelimit,
         .maxlen = sizeof(int),
         .mode = 0644,
         .proc_handler = proc_dointvec_minmax,
         .extra1 = &xpc_disengage_min_timelimit,
         .extra2 = &xpc_disengage_max_timelimit},
        {}
};
static ctl_table xpc_sys_dir[] = {
        {
         .procname = "xpc",
         .mode = 0555,
         .child = xpc_sys_xpc_dir},
        {}
};
static struct ctl_table_header *xpc_sysctl;

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

/* #of activate IRQs received and not yet processed */
int xpc_activate_IRQ_rcvd;
DEFINE_SPINLOCK(xpc_activate_IRQ_rcvd_lock);

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

static unsigned long xpc_hb_check_timeout;
static struct timer_list xpc_hb_timer;

/* 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 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,
};

struct xpc_arch_operations xpc_arch_ops;

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

        DBUG_ON(time_is_after_jiffies(part->disengage_timeout));

        (void)xpc_partition_disengaged(part);

        DBUG_ON(part->disengage_timeout != 0);
        DBUG_ON(xpc_arch_ops.partition_engaged(XPC_PARTID(part)));
}

/*
 * 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_arch_ops.increment_heartbeat();

        if (time_is_before_eq_jiffies(xpc_hb_check_timeout))
                wake_up_interruptible(&xpc_activate_IRQ_wq);

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

static void
xpc_start_hb_beater(void)
{
        xpc_arch_ops.heartbeat_init();
        init_timer(&xpc_hb_timer);
        xpc_hb_timer.function = xpc_hb_beater;
        xpc_hb_beater(0);
}

static void
xpc_stop_hb_beater(void)
{
        del_timer_sync(&xpc_hb_timer);
        xpc_arch_ops.heartbeat_exit();
}

/*
 * At periodic intervals, scan through all active partitions and ensure
 * their heartbeat is still active.  If not, the partition is deactivated.
 */
static void
xpc_check_remote_hb(void)
{
        struct xpc_partition *part;
        short partid;
        enum xp_retval ret;

        for (partid = 0; partid < xp_max_npartitions; partid++) {

                if (xpc_exiting)
                        break;

                if (partid == xp_partition_id)
                        continue;

                part = &xpc_partitions[partid];

                if (part->act_state == XPC_P_AS_INACTIVE ||
                    part->act_state == XPC_P_AS_DEACTIVATING) {
                        continue;
                }

                ret = xpc_arch_ops.get_remote_heartbeat(part);
                if (ret != xpSuccess)
                        XPC_DEACTIVATE_PARTITION(part, ret);
        }
}

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

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

        set_cpus_allowed_ptr(current, cpumask_of(XPC_HB_CHECK_CPU));

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

        while (!xpc_exiting) {

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

                /* checking of remote heartbeats is skewed by IRQ handling */
                if (time_is_before_eq_jiffies(xpc_hb_check_timeout)) {
                        xpc_hb_check_timeout = jiffies +
                            (xpc_hb_check_interval * HZ);

                        dev_dbg(xpc_part, "checking remote heartbeats\n");
                        xpc_check_remote_hb();

                        /*
                         * On sn2 we need to periodically recheck to ensure no
                         * IRQ/amo pairs have been missed.
                         */
                        if (is_shub())
                                force_IRQ = 1;
                }

                /* check for outstanding IRQs */
                if (xpc_activate_IRQ_rcvd > 0 || force_IRQ != 0) {
                        force_IRQ = 0;
                        dev_dbg(xpc_part, "processing activate IRQs "
                                "received\n");
                        xpc_arch_ops.process_activate_IRQ_rcvd();
                }

                /* wait for IRQ or timeout */
                (void)wait_event_interruptible(xpc_activate_IRQ_wq,
                                               (time_is_before_eq_jiffies(
                                                xpc_hb_check_timeout) ||
                                                xpc_activate_IRQ_rcvd > 0 ||
                                                xpc_exiting));
        }

        xpc_stop_hb_beater();

        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)
{
        xpc_discovery();

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

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

/*
 * The first kthread assigned to a newly activated partition is the one
 * created by XPC HB with which it calls xpc_activating(). 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_AS_DEACTIVATING ||
               atomic_read(&part->nchannels_active) > 0 ||
               !xpc_partition_disengaged(part)) {

                xpc_process_sent_chctl_flags(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 ||
                                 part->chctl.all_flags != 0 ||
                                 (part->act_state == XPC_P_AS_DEACTIVATING &&
                                 atomic_read(&part->nchannels_active) == 0 &&
                                 xpc_partition_disengaged(part))));
                atomic_set(&part->channel_mgr_requests, 1);
        }
}

/*
 * Guarantee that the kzalloc'd memory is cacheline aligned.
 */
void *
xpc_kzalloc_cacheline_aligned(size_t size, gfp_t flags, void **base)
{
        /* see if kzalloc will give us cachline aligned memory by default */
        *base = kzalloc(size, flags);
        if (*base == NULL)
                return NULL;

        if ((u64)*base == L1_CACHE_ALIGN((u64)*base))
                return *base;

        kfree(*base);

        /* nope, we'll have to do it ourselves */
        *base = kzalloc(size + L1_CACHE_BYTES, flags);
        if (*base == NULL)
                return NULL;

        return (void *)L1_CACHE_ALIGN((u64)*base);
}

/*
 * Setup the channel structures necessary to support XPartition Communication
 * between the specified remote partition and the local one.
 */
static enum xp_retval
xpc_setup_ch_structures(struct xpc_partition *part)
{
        enum xp_retval ret;
        int ch_number;
        struct xpc_channel *ch;
        short partid = XPC_PARTID(part);

        /*
         * Allocate all of the channel structures as a contiguous chunk of
         * memory.
         */
        DBUG_ON(part->channels != NULL);
        part->channels = kzalloc(sizeof(struct xpc_channel) * XPC_MAX_NCHANNELS,
                                 GFP_KERNEL);
        if (part->channels == NULL) {
                dev_err(xpc_chan, "can't get memory for channels\n");
                return xpNoMemory;
        }

        /* allocate the remote open and close args */

        part->remote_openclose_args =
            xpc_kzalloc_cacheline_aligned(XPC_OPENCLOSE_ARGS_SIZE,
                                          GFP_KERNEL, &part->
                                          remote_openclose_args_base);
        if (part->remote_openclose_args == NULL) {
                dev_err(xpc_chan, "can't get memory for remote connect args\n");
                ret = xpNoMemory;
                goto out_1;
        }

        part->chctl.all_flags = 0;
        spin_lock_init(&part->chctl_lock);

        atomic_set(&part->channel_mgr_requests, 1);
        init_waitqueue_head(&part->channel_mgr_wq);

        part->nchannels = XPC_MAX_NCHANNELS;

        atomic_set(&part->nchannels_active, 0);
        atomic_set(&part->nchannels_engaged, 0);

        for (ch_number = 0; ch_number < part->nchannels; ch_number++) {
                ch = &part->channels[ch_number];

                ch->partid = partid;
                ch->number = ch_number;
                ch->flags = XPC_C_DISCONNECTED;

                atomic_set(&ch->kthreads_assigned, 0);
                atomic_set(&ch->kthreads_idle, 0);
                atomic_set(&ch->kthreads_active, 0);

                atomic_set(&ch->references, 0);
                atomic_set(&ch->n_to_notify, 0);

                spin_lock_init(&ch->lock);
                init_completion(&ch->wdisconnect_wait);

                atomic_set(&ch->n_on_msg_allocate_wq, 0);
                init_waitqueue_head(&ch->msg_allocate_wq);
                init_waitqueue_head(&ch->idle_wq);
        }

        ret = xpc_arch_ops.setup_ch_structures(part);
        if (ret != xpSuccess)
                goto out_2;

        /*
         * With the setting of the partition setup_state to XPC_P_SS_SETUP,
         * we're declaring that this partition is ready to go.
         */
        part->setup_state = XPC_P_SS_SETUP;

        return xpSuccess;

        /* setup of ch structures failed */
out_2:
        kfree(part->remote_openclose_args_base);
        part->remote_openclose_args = NULL;
out_1:
        kfree(part->channels);
        part->channels = NULL;
        return ret;
}

/*
 * Teardown the channel structures necessary to support XPartition Communication
 * between the specified remote partition and the local one.
 */
static void
xpc_teardown_ch_structures(struct xpc_partition *part)
{
        DBUG_ON(atomic_read(&part->nchannels_engaged) != 0);
        DBUG_ON(atomic_read(&part->nchannels_active) != 0);

        /*
         * Make this partition inaccessible to local processes by marking it
         * as no longer setup. Then wait before proceeding with the teardown
         * until all existing references cease.
         */
        DBUG_ON(part->setup_state != XPC_P_SS_SETUP);
        part->setup_state = XPC_P_SS_WTEARDOWN;

        wait_event(part->teardown_wq, (atomic_read(&part->references) == 0));

        /* now we can begin tearing down the infrastructure */

        xpc_arch_ops.teardown_ch_structures(part);

        kfree(part->remote_openclose_args_base);
        part->remote_openclose_args = NULL;
        kfree(part->channels);
        part->channels = NULL;

        part->setup_state = XPC_P_SS_TORNDOWN;
}

/*
 * 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 becoming the channel
 * manager for that partition until the partition is deactivating, at which
 * time the kthread will teardown the XPC infrastructure and then exit.
 */
static int
xpc_activating(void *__partid)
{
        short partid = (u64)__partid;
        struct xpc_partition *part = &xpc_partitions[partid];
        unsigned long irq_flags;

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

        spin_lock_irqsave(&part->act_lock, irq_flags);

        if (part->act_state == XPC_P_AS_DEACTIVATING) {
                part->act_state = XPC_P_AS_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_AS_ACTIVATION_REQ);
        part->act_state = XPC_P_AS_ACTIVATING;

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

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

        xpc_arch_ops.allow_hb(partid);

        if (xpc_setup_ch_structures(part) == xpSuccess) {
                (void)xpc_part_ref(part);       /* this will always succeed */

                if (xpc_arch_ops.make_first_contact(part) == xpSuccess) {
                        xpc_mark_partition_active(part);
                        xpc_channel_mgr(part);
                        /* won't return until partition is deactivating */
                }

                xpc_part_deref(part);
                xpc_teardown_ch_structures(part);
        }

        xpc_arch_ops.disallow_hb(partid);
        xpc_mark_partition_inactive(part);

        if (part->reason == xpReactivating) {
                /* interrupting ourselves results in activating partition */
                xpc_arch_ops.request_partition_reactivation(part);
        }

        return 0;
}

void
xpc_activate_partition(struct xpc_partition *part)
{
        short partid = XPC_PARTID(part);
        unsigned long irq_flags;
        struct task_struct *kthread;

        spin_lock_irqsave(&part->act_lock, irq_flags);

        DBUG_ON(part->act_state != XPC_P_AS_INACTIVE);

        part->act_state = XPC_P_AS_ACTIVATION_REQ;
        XPC_SET_REASON(part, xpCloneKThread, __LINE__);

        spin_unlock_irqrestore(&part->act_lock, irq_flags);

        kthread = kthread_run(xpc_activating, (void *)((u64)partid), "xpc%02d",
                              partid);
        if (IS_ERR(kthread)) {
                spin_lock_irqsave(&part->act_lock, irq_flags);
                part->act_state = XPC_P_AS_INACTIVE;
                XPC_SET_REASON(part, xpCloneKThreadFailed, __LINE__);
                spin_unlock_irqrestore(&part->act_lock, irq_flags);
        }
}

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;
                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)
{
        int (*n_of_deliverable_payloads) (struct xpc_channel *) =
                xpc_arch_ops.n_of_deliverable_payloads;

        do {
                /* deliver messages to their intended recipients */

                while (n_of_deliverable_payloads(ch) > 0 &&
                       !(ch->flags & XPC_C_DISCONNECTING)) {
                        xpc_deliver_payload(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,
                                (n_of_deliverable_payloads(ch) > 0 ||
                                 (ch->flags & XPC_C_DISCONNECTING)));

                atomic_dec(&ch->kthreads_idle);

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

static int
xpc_kthread_start(void *args)
{
        short 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;
        int (*n_of_deliverable_payloads) (struct xpc_channel *) =
                xpc_arch_ops.n_of_deliverable_payloads;

        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 = n_of_deliverable_payloads(ch) - 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, xpDisconnecting);

                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 &&
            atomic_dec_return(&part->nchannels_engaged) == 0) {
                xpc_arch_ops.indicate_partition_disengaged(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;
        u64 args = XPC_PACK_ARGS(ch->partid, ch->number);
        struct xpc_partition *part = &xpc_partitions[ch->partid];
        struct task_struct *kthread;
        void (*indicate_partition_disengaged) (struct xpc_partition *) =
                xpc_arch_ops.indicate_partition_disengaged;

        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 &&
                           atomic_inc_return(&part->nchannels_engaged) == 1) {
                        xpc_arch_ops.indicate_partition_engaged(part);
                }
                (void)xpc_part_ref(part);
                xpc_msgqueue_ref(ch);

                kthread = kthread_run(xpc_kthread_start, (void *)args,
                                      "xpc%02dc%d", ch->partid, ch->number);
                if (IS_ERR(kthread)) {
                        /* 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 xpDisconnecting callout that this
                         * failed kthread_run() would have made.
                         */

                        if (atomic_dec_return(&ch->kthreads_assigned) == 0 &&
                            atomic_dec_return(&part->nchannels_engaged) == 0) {
                                indicate_partition_disengaged(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, xpLackOfResources,
                                                       &irq_flags);
                                spin_unlock_irqrestore(&ch->lock, irq_flags);
                        }
                        break;
                }
        }
}

void
xpc_disconnect_wait(int ch_number)
{
        unsigned long irq_flags;
        short 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 = 0; partid < xp_max_npartitions; 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_chctl_flags) {
                        if (part->act_state != XPC_P_AS_DEACTIVATING) {
                                spin_lock(&part->chctl_lock);
                                part->chctl.flags[ch->number] |=
                                    ch->delayed_chctl_flags;
                                spin_unlock(&part->chctl_lock);
                                wakeup_channel_mgr = 1;
                        }
                        ch->delayed_chctl_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 int
xpc_setup_partitions(void)
{
        short partid;
        struct xpc_partition *part;

        xpc_partitions = kzalloc(sizeof(struct xpc_partition) *
                                 xp_max_npartitions, GFP_KERNEL);
        if (xpc_partitions == NULL) {
                dev_err(xpc_part, "can't get memory for partition structure\n");
                return -ENOMEM;
        }

        /*
         * 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 = 0; partid < xp_max_npartitions; partid++) {
                part = &xpc_partitions[partid];

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

                part->activate_IRQ_rcvd = 0;
                spin_lock_init(&part->act_lock);
                part->act_state = XPC_P_AS_INACTIVE;
                XPC_SET_REASON(part, 0, 0);

                init_timer(&part->disengage_timer);
                part->disengage_timer.function =
                    xpc_timeout_partition_disengage;
                part->disengage_timer.data = (unsigned long)part;

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

        return xpc_arch_ops.setup_partitions();
}

static void
xpc_teardown_partitions(void)
{
        xpc_arch_ops.teardown_partitions();
        kfree(xpc_partitions);
}

static void
xpc_do_exit(enum xp_retval reason)
{
        short partid;
        int active_part_count, printed_waiting_msg = 0;
        struct xpc_partition *part;
        unsigned long printmsg_time, disengage_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_activate_IRQ_wq);

        /* 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_DEACTIVATE_PRINTMSG_INTERVAL * HZ);
        xpc_disengage_timedout = 0;

        do {
                active_part_count = 0;

                for (partid = 0; partid < xp_max_npartitions; partid++) {
                        part = &xpc_partitions[partid];

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

                        active_part_count++;

                        XPC_DEACTIVATE_PARTITION(part, reason);

                        if (part->disengage_timeout > disengage_timeout)
                                disengage_timeout = part->disengage_timeout;
                }

                if (xpc_arch_ops.any_partition_engaged()) {
                        if (time_is_before_jiffies(printmsg_time)) {
                                dev_info(xpc_part, "waiting for remote "
                                         "partitions to deactivate, timeout in "
                                         "%ld seconds\n", (disengage_timeout -
                                         jiffies) / HZ);
                                printmsg_time = jiffies +
                                    (XPC_DEACTIVATE_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 deactivate\n");
                                printed_waiting_msg = 0;
                        }

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

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

        } while (1);

        DBUG_ON(xpc_arch_ops.any_partition_engaged());

        xpc_teardown_rsvd_page();

        if (reason == xpUnloading) {
                (void)unregister_die_notifier(&xpc_die_notifier);
                (void)unregister_reboot_notifier(&xpc_reboot_notifier);
        }

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

        if (xpc_sysctl)
                unregister_sysctl_table(xpc_sysctl);

        xpc_teardown_partitions();

        if (is_shub())
                xpc_exit_sn2();
        else if (is_uv())
                xpc_exit_uv();
}

/*
 * 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 xp_retval reason;

        switch (event) {
        case SYS_RESTART:
                reason = xpSystemReboot;
                break;
        case SYS_HALT:
                reason = xpSystemHalt;
                break;
        case SYS_POWER_OFF:
                reason = xpSystemPoweroff;
                break;
        default:
                reason = xpSystemGoingDown;
        }

        xpc_do_exit(reason);
        return NOTIFY_DONE;
}

/*
 * Notify other partitions to deactivate from us by first disengaging from all
 * references to our memory.
 */
static void
xpc_die_deactivate(void)
{
        struct xpc_partition *part;
        short partid;
        int any_engaged;
        long keep_waiting;
        long wait_to_print;

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

        xpc_arch_ops.disallow_all_hbs();   /*indicate we're deactivated */

        for (partid = 0; partid < xp_max_npartitions; partid++) {
                part = &xpc_partitions[partid];

                if (xpc_arch_ops.partition_engaged(partid) ||
                    part->act_state != XPC_P_AS_INACTIVE) {
                        xpc_arch_ops.request_partition_deactivation(part);
                        xpc_arch_ops.indicate_partition_disengaged(part);
                }
        }

        /*
         * Though we requested that all other partitions deactivate from us,
         * we only wait until they've all disengaged or we've reached the
         * defined timelimit.
         *
         * Given that one iteration through the following while-loop takes
         * approximately 200 microseconds, calculate the #of loops to take
         * before bailing and the #of loops before printing a waiting message.
         */
        keep_waiting = xpc_disengage_timelimit * 1000 * 5;
        wait_to_print = XPC_DEACTIVATE_PRINTMSG_INTERVAL * 1000 * 5;

        while (1) {
                any_engaged = xpc_arch_ops.any_partition_engaged();
                if (!any_engaged) {
                        dev_info(xpc_part, "all partitions have deactivated\n");
                        break;
                }

                if (!keep_waiting--) {
                        for (partid = 0; partid < xp_max_npartitions;
                             partid++) {
                                if (xpc_arch_ops.partition_engaged(partid)) {
                                        dev_info(xpc_part, "deactivate from "
                                                 "remote partition %d timed "
                                                 "out\n", partid);
                                }
                        }
                        break;
                }

                if (!wait_to_print--) {
                        dev_info(xpc_part, "waiting for remote partitions to "
                                 "deactivate, timeout in %ld seconds\n",
                                 keep_waiting / (1000 * 5));
                        wait_to_print = XPC_DEACTIVATE_PRINTMSG_INTERVAL *
                            1000 * 5;
                }

                udelay(200);
        }
}

/*
 * 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)
{
#ifdef CONFIG_IA64              /* !!! temporary kludge */
        switch (event) {
        case DIE_MACHINE_RESTART:
        case DIE_MACHINE_HALT:
                xpc_die_deactivate();
                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_arch_ops.offline_heartbeat();
                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_arch_ops.online_heartbeat();
                break;
        }
#else
        xpc_die_deactivate();
#endif

        return NOTIFY_DONE;
}

int __init
xpc_init(void)
{
        int ret;
        struct task_struct *kthread;

        dev_set_name(xpc_part, "part");
        dev_set_name(xpc_chan, "chan");

        if (is_shub()) {
                /*
                 * The ia64-sn2 architecture supports at most 64 partitions.
                 * And the inability to unregister remote amos restricts us
                 * further to only support exactly 64 partitions on this
                 * architecture, no less.
                 */
                if (xp_max_npartitions != 64) {
                        dev_err(xpc_part, "max #of partitions not set to 64\n");
                        ret = -EINVAL;
                } else {
                        ret = xpc_init_sn2();
                }

        } else if (is_uv()) {
                ret = xpc_init_uv();

        } else {
                ret = -ENODEV;
        }

        if (ret != 0)
                return ret;

        ret = xpc_setup_partitions();
        if (ret != 0) {
                dev_err(xpc_part, "can't get memory for partition structure\n");
                goto out_1;
        }

        xpc_sysctl = register_sysctl_table(xpc_sys_dir);

        /*
         * Fill the partition reserved page with the information needed by
         * other partitions to discover we are alive and establish initial
         * communications.
         */
        ret = xpc_setup_rsvd_page();
        if (ret != 0) {
                dev_err(xpc_part, "can't setup our reserved page\n");
                goto out_2;
        }

        /* 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");

        /*
         * The real work-horse behind xpc.  This processes incoming
         * interrupts and monitors remote heartbeats.
         */
        kthread = kthread_run(xpc_hb_checker, NULL, XPC_HB_CHECK_THREAD_NAME);
        if (IS_ERR(kthread)) {
                dev_err(xpc_part, "failed while forking hb check thread\n");
                ret = -EBUSY;
                goto out_3;
        }

        /*
         * 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.
         */
        kthread = kthread_run(xpc_initiate_discovery, NULL,
                              XPC_DISCOVERY_THREAD_NAME);
        if (IS_ERR(kthread)) {
                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(xpUnloading);
                return -EBUSY;
        }

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

        return 0;

        /* initialization was not successful */
out_3:
        xpc_teardown_rsvd_page();

        (void)unregister_die_notifier(&xpc_die_notifier);
        (void)unregister_reboot_notifier(&xpc_reboot_notifier);
out_2:
        if (xpc_sysctl)
                unregister_sysctl_table(xpc_sysctl);

        xpc_teardown_partitions();
out_1:
        if (is_shub())
                xpc_exit_sn2();
        else if (is_uv())
                xpc_exit_uv();
        return ret;
}

module_init(xpc_init);

void __exit
xpc_exit(void)
{
        xpc_do_exit(xpUnloading);
}

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_timelimit, int, 0);
MODULE_PARM_DESC(xpc_disengage_timelimit, "Number of seconds to wait "
                 "for disengage 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.");