[IA64-SGI] SGI Altix cross partition functionality [2/3]

This patch contains the communication module (XPC) for cross partition
communication on a partitioned SGI Altix.

Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 1064 insertions, 0 deletions

diff --git a/arch/ia64/sn/kernel/xpc_main.c b/arch/ia64/sn/kernel/xpc_main.c
new file mode 100644
index 000000000000..177ddb748ebe
--- /dev/null
+++ b/arch/ia64/sn/kernel/xpc_main.c
@@ -0,0 +1,1064 @@
+/*
+ * 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) 2004-2005 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/slab.h>
+#include <asm/sn/intr.h>
+#include <asm/sn/sn_sal.h>
+#include <asm/uaccess.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 = {
+        .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;
+
+
+/* systune related variables for /proc/sys directories */
+
+static int xpc_hb_min = 1;
+static int xpc_hb_max = 10;
+
+static int xpc_hb_check_min = 10;
+static int xpc_hb_check_max = 120;
+
+static ctl_table xpc_sys_xpc_hb_dir[] = {
+        {
+                1,
+                "hb_interval",
+                &xpc_hb_interval,
+                sizeof(int),
+                0644,
+                NULL,
+                &proc_dointvec_minmax,
+                &sysctl_intvec,
+                NULL,
+                &xpc_hb_min, &xpc_hb_max
+        },
+        {
+                2,
+                "hb_check_interval",
+                &xpc_hb_check_interval,
+                sizeof(int),
+                0644,
+                NULL,
+                &proc_dointvec_minmax,
+                &sysctl_intvec,
+                NULL,
+                &xpc_hb_check_min, &xpc_hb_check_max
+        },
+        {0}
+};
+static ctl_table xpc_sys_xpc_dir[] = {
+        {
+                1,
+                "hb",
+                NULL,
+                0,
+                0555,
+                xpc_sys_xpc_hb_dir
+        },
+        {0}
+};
+static ctl_table xpc_sys_dir[] = {
+        {
+                1,
+                "xpc",
+                NULL,
+                0,
+                0555,
+                xpc_sys_xpc_dir
+        },
+        {0}
+};
+static struct ctl_table_header *xpc_sysctl;
+
+
+/* #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;
+
+/* xpc_hb_checker thread exited notification */
+static DECLARE_MUTEX_LOCKED(xpc_hb_checker_exited);
+
+/* xpc_discovery thread exited notification */
+static DECLARE_MUTEX_LOCKED(xpc_discovery_exited);
+
+
+static struct timer_list xpc_hb_timer;
+
+
+static void xpc_kthread_waitmsgs(struct xpc_partition *, struct xpc_channel *);
+
+
+/*
+ * Notify the heartbeat check thread that an IRQ has been received.
+ */
+static irqreturn_t
+xpc_act_IRQ_handler(int irq, void *dev_id, struct pt_regs *regs)
+{
+        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));
+
+        xpc_hb_check_timeout = jiffies + (xpc_hb_check_interval * HZ);
+
+        while (!(volatile int) xpc_exiting) {
+
+                /* 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, "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;
+                }
+
+
+                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);
+                }
+        }
+
+        dev_dbg(xpc_part, "heartbeat checker is exiting\n");
+
+
+        /* mark this thread as inactive */
+        up(&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 inactive */
+        up(&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 */
+                set_current_state(TASK_INTERRUPTIBLE);
+                (void) schedule_timeout(0.25 * HZ);
+
+                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_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)));
+                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_USER_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_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);
+
+        pid = kernel_thread(xpc_activating, (void *) ((u64) partid), 0);
+
+        DBUG_ON(part->act_state != XPC_P_INACTIVE);
+
+        if (pid > 0) {
+                part->act_state = XPC_P_ACTIVATION_REQ;
+                XPC_SET_REASON(part, xpcCloneKThread, __LINE__);
+        } else {
+                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.
+ *
+ *      regs - processor's context before the processor entered
+ *             interrupt code. NOT USED.
+ */
+irqreturn_t
+xpc_notify_IRQ_handler(int irq, void *dev_id, struct pt_regs *regs)
+{
+        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);
+}
+
+
+/*
+ * 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;
+
+
+        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)) {
+                DBUG_ON(!(ch->flags & XPC_C_CONNECTED));
+
+                /* let registerer know that connection has been established */
+
+                if (atomic_read(&ch->kthreads_assigned) == 1) {
+                        xpc_connected_callout(ch);
+
+                        /*
+                         * 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);
+                        }
+                }
+
+                xpc_kthread_waitmsgs(part, ch);
+        }
+
+        if (atomic_dec_return(&ch->kthreads_assigned) == 0 &&
+                        ((ch->flags & XPC_C_CONNECTCALLOUT) ||
+                                (ch->reason != xpcUnregistering &&
+                                        ch->reason != xpcOtherUnregistering))) {
+                xpc_disconnected_callout(ch);
+        }
+
+
+        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)
+{
+        unsigned long irq_flags;
+        pid_t pid;
+        u64 args = XPC_PACK_ARGS(ch->partid, ch->number);
+
+
+        while (needed-- > 0) {
+                pid = kernel_thread(xpc_daemonize_kthread, (void *) args, 0);
+                if (pid < 0) {
+                        /* the fork failed */
+
+                        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.
+                                 *
+                                 * No xpc_msgqueue_ref() is needed here since
+                                 * the channel mgr is doing this.
+                                 */
+                                spin_lock_irqsave(&ch->lock, irq_flags);
+                                XPC_DISCONNECT_CHANNEL(ch, xpcLackOfResources,
+                                                                &irq_flags);
+                                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        }
+                        break;
+                }
+
+                /*
+                 * 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.
+                 */
+                (void) xpc_part_ref(&xpc_partitions[ch->partid]);
+                xpc_msgqueue_ref(ch);
+                atomic_inc(&ch->kthreads_assigned);
+                ch->kthreads_created++; // >>> temporary debug only!!!
+        }
+}
+
+
+void
+xpc_disconnect_wait(int ch_number)
+{
+        partid_t partid;
+        struct xpc_partition *part;
+        struct xpc_channel *ch;
+
+
+        /* 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)) {
+                        ch = &part->channels[ch_number];
+
+// >>> how do we keep from falling into the window between our check and going
+// >>> down and coming back up where sema is re-inited?
+                        if (ch->flags & XPC_C_SETUP) {
+                                (void) down(&ch->teardown_sema);
+                        }
+
+                        xpc_part_deref(part);
+                }
+        }
+}
+
+
+static void
+xpc_do_exit(void)
+{
+        partid_t partid;
+        int active_part_count;
+        struct xpc_partition *part;
+
+
+        /* now it's time to eliminate our heartbeat */
+        del_timer_sync(&xpc_hb_timer);
+        xpc_vars->heartbeating_to_mask = 0;
+
+        /* indicate to others that our reserved page is uninitialized */
+        xpc_rsvd_page->vars_pa = 0;
+
+        /*
+         * Ignore all incoming interrupts. Without interupts the heartbeat
+         * checker won't activate any new partitions that may come up.
+         */
+        free_irq(SGI_XPC_ACTIVATE, NULL);
+
+        /*
+         * Cause the heartbeat checker and the discovery threads to exit.
+         * We don't want them attempting to activate new partitions as we
+         * try to deactivate the existing ones.
+         */
+        xpc_exiting = 1;
+        wake_up_interruptible(&xpc_act_IRQ_wq);
+
+        /* wait for the heartbeat checker thread to mark itself inactive */
+        down(&xpc_hb_checker_exited);
+
+        /* wait for the discovery thread to mark itself inactive */
+        down(&xpc_discovery_exited);
+
+
+        set_current_state(TASK_INTERRUPTIBLE);
+        schedule_timeout(0.3 * HZ);
+        set_current_state(TASK_RUNNING);
+
+
+        /* wait for all partitions to become inactive */
+
+        do {
+                active_part_count = 0;
+
+                for (partid = 1; partid < XP_MAX_PARTITIONS; partid++) {
+                        part = &xpc_partitions[partid];
+                        if (part->act_state != XPC_P_INACTIVE) {
+                                active_part_count++;
+
+                                XPC_DEACTIVATE_PARTITION(part, xpcUnloading);
+                        }
+                }
+
+                if (active_part_count) {
+                        set_current_state(TASK_INTERRUPTIBLE);
+                        schedule_timeout(0.3 * HZ);
+                        set_current_state(TASK_RUNNING);
+                }
+
+        } while (active_part_count > 0);
+
+
+        /* 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);
+        }
+}
+
+
+int __init
+xpc_init(void)
+{
+        int ret;
+        partid_t partid;
+        struct xpc_partition *part;
+        pid_t pid;
+
+
+        /*
+         * xpc_remote_copy_buffer is used as a temporary buffer for bte_copy'ng
+         * both a partition's reserved page and its XPC variables. Its size was
+         * based on the size of a reserved page. So we need to ensure that the
+         * XPC variables will fit as well.
+         */
+        if (XPC_VARS_ALIGNED_SIZE > XPC_RSVD_PAGE_ALIGNED_SIZE) {
+                dev_err(xpc_part, "xpc_remote_copy_buffer is not big enough\n");
+                return -EPERM;
+        }
+        DBUG_ON((u64) xpc_remote_copy_buffer !=
+                                L1_CACHE_ALIGN((u64) xpc_remote_copy_buffer));
+
+        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, 1);
+
+        /*
+         * 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);
+                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);
+                }
+                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);
+                }
+                return -EBUSY;
+        }
+
+
+        /*
+         * Set the beating to other partitions into motion.  This is
+         * the last requirement for other partitions' discovery to
+         * initiate communications with us.
+         */
+        init_timer(&xpc_hb_timer);
+        xpc_hb_timer.function = xpc_hb_beater;
+        xpc_hb_beater(0);
+
+
+        /*
+         * 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;
+
+                del_timer_sync(&xpc_hb_timer);
+                free_irq(SGI_XPC_ACTIVATE, NULL);
+                xpc_restrict_IPI_ops();
+
+                if (xpc_sysctl) {
+                        unregister_sysctl_table(xpc_sysctl);
+                }
+                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 */
+                up(&xpc_discovery_exited);
+
+                xpc_do_exit();
+                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();
+}
+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.");
+