[mirror_spl-debian.git] / module / spl / spl-taskq.c

/*****************************************************************************\
 *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
 *  Copyright (C) 2007 The Regents of the University of California.
 *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
 *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
 *  UCRL-CODE-235197
 *
 *  This file is part of the SPL, Solaris Porting Layer.
 *  For details, see <http://github.com/behlendorf/spl/>.
 *
 *  The SPL is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU General Public License as published by the
 *  Free Software Foundation; either version 2 of the License, or (at your
 *  option) any later version.
 *
 *  The SPL is distributed in the hope that it will be useful, but WITHOUT
 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
 *****************************************************************************
 *  Solaris Porting Layer (SPL) Task Queue Implementation.
\*****************************************************************************/

#include <sys/taskq.h>
#include <sys/kmem.h>
#include <spl-debug.h>

#ifdef SS_DEBUG_SUBSYS
#undef SS_DEBUG_SUBSYS
#endif

#define SS_DEBUG_SUBSYS SS_TASKQ

/* Global system-wide dynamic task queue available for all consumers */
taskq_t *system_taskq;
EXPORT_SYMBOL(system_taskq);

static int
task_km_flags(uint_t flags)
{
        if (flags & TQ_NOSLEEP)
                return KM_NOSLEEP;

        if (flags & TQ_PUSHPAGE)
                return KM_PUSHPAGE;

        return KM_SLEEP;
}

/*
 * NOTE: Must be called with tq->tq_lock held, returns a list_t which
 * is not attached to the free, work, or pending taskq lists.
 */
static taskq_ent_t *
task_alloc(taskq_t *tq, uint_t flags)
{
        taskq_ent_t *t;
        int count = 0;
        SENTRY;

        ASSERT(tq);
        ASSERT(spin_is_locked(&tq->tq_lock));
retry:
        /* Acquire taskq_ent_t's from free list if available */
        if (!list_empty(&tq->tq_free_list) && !(flags & TQ_NEW)) {
                t = list_entry(tq->tq_free_list.next, taskq_ent_t, tqent_list);

                ASSERT(!(t->tqent_flags & TQENT_FLAG_PREALLOC));
                ASSERT(!(t->tqent_flags & TQENT_FLAG_CANCEL));
                ASSERT(!timer_pending(&t->tqent_timer));

                list_del_init(&t->tqent_list);
                SRETURN(t);
        }

        /* Free list is empty and memory allocations are prohibited */
        if (flags & TQ_NOALLOC)
                SRETURN(NULL);

        /* Hit maximum taskq_ent_t pool size */
        if (tq->tq_nalloc >= tq->tq_maxalloc) {
                if (flags & TQ_NOSLEEP)
                        SRETURN(NULL);

                /*
                 * Sleep periodically polling the free list for an available
                 * taskq_ent_t. Dispatching with TQ_SLEEP should always succeed
                 * but we cannot block forever waiting for an taskq_ent_t to
                 * show up in the free list, otherwise a deadlock can happen.
                 *
                 * Therefore, we need to allocate a new task even if the number
                 * of allocated tasks is above tq->tq_maxalloc, but we still
                 * end up delaying the task allocation by one second, thereby
                 * throttling the task dispatch rate.
                 */
                spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
                schedule_timeout(HZ / 100);
                spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
                if (count < 100)
                        SGOTO(retry, count++);
        }

        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
        t = kmem_alloc(sizeof(taskq_ent_t), task_km_flags(flags));
        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);

        if (t) {
                taskq_init_ent(t);
                tq->tq_nalloc++;
        }

        SRETURN(t);
}

/*
 * NOTE: Must be called with tq->tq_lock held, expects the taskq_ent_t
 * to already be removed from the free, work, or pending taskq lists.
 */
static void
task_free(taskq_t *tq, taskq_ent_t *t)
{
        SENTRY;

        ASSERT(tq);
        ASSERT(t);
        ASSERT(spin_is_locked(&tq->tq_lock));
        ASSERT(list_empty(&t->tqent_list));
        ASSERT(!timer_pending(&t->tqent_timer));

        kmem_free(t, sizeof(taskq_ent_t));
        tq->tq_nalloc--;

        SEXIT;
}

/*
 * NOTE: Must be called with tq->tq_lock held, either destroys the
 * taskq_ent_t if too many exist or moves it to the free list for later use.
 */
static void
task_done(taskq_t *tq, taskq_ent_t *t)
{
        SENTRY;
        ASSERT(tq);
        ASSERT(t);
        ASSERT(spin_is_locked(&tq->tq_lock));

        /* Wake tasks blocked in taskq_wait_id() */
        wake_up_all(&t->tqent_waitq);

        list_del_init(&t->tqent_list);

        if (tq->tq_nalloc <= tq->tq_minalloc) {
                t->tqent_id = 0;
                t->tqent_func = NULL;
                t->tqent_arg = NULL;
                t->tqent_flags = 0;

                list_add_tail(&t->tqent_list, &tq->tq_free_list);
        } else {
                task_free(tq, t);
        }

        SEXIT;
}

/*
 * When a delayed task timer expires remove it from the delay list and
 * add it to the priority list in order for immediate processing.
 */
static void
task_expire(unsigned long data)
{
        taskq_ent_t *w, *t = (taskq_ent_t *)data;
        taskq_t *tq = t->tqent_taskq;
        struct list_head *l;

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);

        if (t->tqent_flags & TQENT_FLAG_CANCEL) {
                ASSERT(list_empty(&t->tqent_list));
                spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
                return;
        }

        /*
         * The priority list must be maintained in strict task id order
         * from lowest to highest for lowest_id to be easily calculable.
         */
        list_del(&t->tqent_list);
        list_for_each_prev(l, &tq->tq_prio_list) {
                w = list_entry(l, taskq_ent_t, tqent_list);
                if (w->tqent_id < t->tqent_id) {
                        list_add(&t->tqent_list, l);
                        break;
                }
        }
        if (l == &tq->tq_prio_list)
                list_add(&t->tqent_list, &tq->tq_prio_list);

        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        wake_up(&tq->tq_work_waitq);
}

/*
 * Returns the lowest incomplete taskqid_t.  The taskqid_t may
 * be queued on the pending list, on the priority list, on the
 * delay list, or on the work list currently being handled, but
 * it is not 100% complete yet.
 */
static taskqid_t
taskq_lowest_id(taskq_t *tq)
{
        taskqid_t lowest_id = tq->tq_next_id;
        taskq_ent_t *t;
        taskq_thread_t *tqt;
        SENTRY;

        ASSERT(tq);
        ASSERT(spin_is_locked(&tq->tq_lock));

        if (!list_empty(&tq->tq_pend_list)) {
                t = list_entry(tq->tq_pend_list.next, taskq_ent_t, tqent_list);
                lowest_id = MIN(lowest_id, t->tqent_id);
        }

        if (!list_empty(&tq->tq_prio_list)) {
                t = list_entry(tq->tq_prio_list.next, taskq_ent_t, tqent_list);
                lowest_id = MIN(lowest_id, t->tqent_id);
        }

        if (!list_empty(&tq->tq_delay_list)) {
                t = list_entry(tq->tq_delay_list.next, taskq_ent_t, tqent_list);
                lowest_id = MIN(lowest_id, t->tqent_id);
        }

        if (!list_empty(&tq->tq_active_list)) {
                tqt = list_entry(tq->tq_active_list.next, taskq_thread_t,
                    tqt_active_list);
                ASSERT(tqt->tqt_id != 0);
                lowest_id = MIN(lowest_id, tqt->tqt_id);
        }

        SRETURN(lowest_id);
}

/*
 * Insert a task into a list keeping the list sorted by increasing taskqid.
 */
static void
taskq_insert_in_order(taskq_t *tq, taskq_thread_t *tqt)
{
        taskq_thread_t *w;
        struct list_head *l;

        SENTRY;
        ASSERT(tq);
        ASSERT(tqt);
        ASSERT(spin_is_locked(&tq->tq_lock));

        list_for_each_prev(l, &tq->tq_active_list) {
                w = list_entry(l, taskq_thread_t, tqt_active_list);
                if (w->tqt_id < tqt->tqt_id) {
                        list_add(&tqt->tqt_active_list, l);
                        break;
                }
        }
        if (l == &tq->tq_active_list)
                list_add(&tqt->tqt_active_list, &tq->tq_active_list);

        SEXIT;
}

/*
 * Find and return a task from the given list if it exists.  The list
 * must be in lowest to highest task id order.
 */
static taskq_ent_t *
taskq_find_list(taskq_t *tq, struct list_head *lh, taskqid_t id)
{
        struct list_head *l;
        taskq_ent_t *t;
        SENTRY;

        ASSERT(spin_is_locked(&tq->tq_lock));

        list_for_each(l, lh) {
                t = list_entry(l, taskq_ent_t, tqent_list);

                if (t->tqent_id == id)
                        SRETURN(t);

                if (t->tqent_id > id)
                        break;
        }

        SRETURN(NULL);
}

/*
 * Find an already dispatched task given the task id regardless of what
 * state it is in.  If a task is still pending or executing it will be
 * returned and 'active' set appropriately.  If the task has already
 * been run then NULL is returned.
 */
static taskq_ent_t *
taskq_find(taskq_t *tq, taskqid_t id, int *active)
{
        taskq_thread_t *tqt;
        struct list_head *l;
        taskq_ent_t *t;
        SENTRY;

        ASSERT(spin_is_locked(&tq->tq_lock));
        *active = 0;

        t = taskq_find_list(tq, &tq->tq_delay_list, id);
        if (t)
                SRETURN(t);

        t = taskq_find_list(tq, &tq->tq_prio_list, id);
        if (t)
                SRETURN(t);

        t = taskq_find_list(tq, &tq->tq_pend_list, id);
        if (t)
                SRETURN(t);

        list_for_each(l, &tq->tq_active_list) {
                tqt = list_entry(l, taskq_thread_t, tqt_active_list);
                if (tqt->tqt_id == id) {
                        t = tqt->tqt_task;
                        *active = 1;
                        SRETURN(t);
                }
        }

        SRETURN(NULL);
}

/*
 * The taskq_wait_id() function blocks until the passed task id completes.
 * This does not guarantee that all lower task id's have completed.
 */
void
taskq_wait_id(taskq_t *tq, taskqid_t id)
{
        DEFINE_WAIT(wait);
        taskq_ent_t *t;
        int active = 0;
        SENTRY;

        ASSERT(tq);
        ASSERT(id > 0);

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
        t = taskq_find(tq, id, &active);
        if (t)
                prepare_to_wait(&t->tqent_waitq, &wait, TASK_UNINTERRUPTIBLE);
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        /*
         * We rely on the kernels autoremove_wake_function() function to
         * remove us from the wait queue in the context of wake_up().
         * Once woken the taskq_ent_t pointer must never be accessed.
         */
        if (t) {
                t = NULL;
                schedule();
                __set_current_state(TASK_RUNNING);
        }

        SEXIT;
}
EXPORT_SYMBOL(taskq_wait_id);

/*
 * The taskq_wait() function will block until all previously submitted
 * tasks have been completed.  A previously submitted task is defined as
 * a task with a lower task id than the current task queue id.  Note that
 * all task id's are assigned monotonically at dispatch time.
 *
 * Waiting for all previous tasks to complete is accomplished by tracking
 * the lowest outstanding task id.  As tasks are dispatched they are added
 * added to the tail of the pending, priority, or delay lists.  And as
 * worker threads become available the tasks are removed from the heads
 * of these lists and linked to the worker threads.  This ensures the
 * lists are kept in lowest to highest task id order.
 *
 * Therefore the lowest outstanding task id can be quickly determined by
 * checking the head item from all of these lists.  This value is stored
 * with the task queue as the lowest id.  It only needs to be recalculated
 * when either the task with the current lowest id completes or is canceled.
 *
 * By blocking until the lowest task id exceeds the current task id when
 * the function was called we ensure all previous tasks have completed.
 *
 * NOTE: When there are multiple worked threads it is possible for larger
 * task ids to complete before smaller ones.  Conversely when the task
 * queue contains delay tasks with small task ids, you may block for a
 * considerable length of time waiting for them to expire and execute.
 */
static int
taskq_wait_check(taskq_t *tq, taskqid_t id)
{
        int rc;

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
        rc = (id < tq->tq_lowest_id);
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        SRETURN(rc);
}

void
taskq_wait_all(taskq_t *tq, taskqid_t id)
{
        wait_event(tq->tq_wait_waitq, taskq_wait_check(tq, id));
}
EXPORT_SYMBOL(taskq_wait_all);

void
taskq_wait(taskq_t *tq)
{
        taskqid_t id;
        SENTRY;
        ASSERT(tq);

        /* Wait for the largest outstanding taskqid */
        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
        id = tq->tq_next_id - 1;
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        taskq_wait_all(tq, id);

        SEXIT;

}
EXPORT_SYMBOL(taskq_wait);

int
taskq_member(taskq_t *tq, void *t)
{
        struct list_head *l;
        taskq_thread_t *tqt;
        SENTRY;

        ASSERT(tq);
        ASSERT(t);

        list_for_each(l, &tq->tq_thread_list) {
                tqt = list_entry(l, taskq_thread_t, tqt_thread_list);
                if (tqt->tqt_thread == (struct task_struct *)t)
                        SRETURN(1);
        }

        SRETURN(0);
}
EXPORT_SYMBOL(taskq_member);

/*
 * Cancel an already dispatched task given the task id.  Still pending tasks
 * will be immediately canceled, and if the task is active the function will
 * block until it completes.  Preallocated tasks which are canceled must be
 * freed by the caller.
 */
int
taskq_cancel_id(taskq_t *tq, taskqid_t id)
{
        taskq_ent_t *t;
        int active = 0;
        int rc = ENOENT;
        SENTRY;

        ASSERT(tq);

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
        t = taskq_find(tq, id, &active);
        if (t && !active) {
                list_del_init(&t->tqent_list);
                t->tqent_flags |= TQENT_FLAG_CANCEL;

                /*
                 * When canceling the lowest outstanding task id we
                 * must recalculate the new lowest outstanding id.
                 */
                if (tq->tq_lowest_id == t->tqent_id) {
                        tq->tq_lowest_id = taskq_lowest_id(tq);
                        ASSERT3S(tq->tq_lowest_id, >, t->tqent_id);
                }

                /*
                 * The task_expire() function takes the tq->tq_lock so drop
                 * drop the lock before synchronously cancelling the timer.
                 */
                if (timer_pending(&t->tqent_timer)) {
                        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
                        del_timer_sync(&t->tqent_timer);
                        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
                }

                if (!(t->tqent_flags & TQENT_FLAG_PREALLOC))
                        task_done(tq, t);

                rc = 0;
        }
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        if (active) {
                taskq_wait_id(tq, id);
                rc = EBUSY;
        }

        SRETURN(rc);
}
EXPORT_SYMBOL(taskq_cancel_id);

taskqid_t
taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
{
        taskq_ent_t *t;
        taskqid_t rc = 0;
        SENTRY;

        ASSERT(tq);
        ASSERT(func);

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);

        /* Taskq being destroyed and all tasks drained */
        if (!(tq->tq_flags & TQ_ACTIVE))
                SGOTO(out, rc = 0);

        /* Do not queue the task unless there is idle thread for it */
        ASSERT(tq->tq_nactive <= tq->tq_nthreads);
        if ((flags & TQ_NOQUEUE) && (tq->tq_nactive == tq->tq_nthreads))
                SGOTO(out, rc = 0);

        if ((t = task_alloc(tq, flags)) == NULL)
                SGOTO(out, rc = 0);

        spin_lock(&t->tqent_lock);

        /* Queue to the priority list instead of the pending list */
        if (flags & TQ_FRONT)
                list_add_tail(&t->tqent_list, &tq->tq_prio_list);
        else
                list_add_tail(&t->tqent_list, &tq->tq_pend_list);

        t->tqent_id = rc = tq->tq_next_id;
        tq->tq_next_id++;
        t->tqent_func = func;
        t->tqent_arg = arg;
        t->tqent_taskq = tq;
        t->tqent_timer.data = 0;
        t->tqent_timer.function = NULL;
        t->tqent_timer.expires = 0;

        ASSERT(!(t->tqent_flags & TQENT_FLAG_PREALLOC));

        spin_unlock(&t->tqent_lock);

        wake_up(&tq->tq_work_waitq);
out:
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
        SRETURN(rc);
}
EXPORT_SYMBOL(taskq_dispatch);

taskqid_t
taskq_dispatch_delay(taskq_t *tq, task_func_t func, void *arg,
    uint_t flags, clock_t expire_time)
{
        taskq_ent_t *t;
        taskqid_t rc = 0;
        SENTRY;

        ASSERT(tq);
        ASSERT(func);

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);

        /* Taskq being destroyed and all tasks drained */
        if (!(tq->tq_flags & TQ_ACTIVE))
                SGOTO(out, rc = 0);

        if ((t = task_alloc(tq, flags)) == NULL)
                SGOTO(out, rc = 0);

        spin_lock(&t->tqent_lock);

        /* Queue to the delay list for subsequent execution */
        list_add_tail(&t->tqent_list, &tq->tq_delay_list);

        t->tqent_id = rc = tq->tq_next_id;
        tq->tq_next_id++;
        t->tqent_func = func;
        t->tqent_arg = arg;
        t->tqent_taskq = tq;
        t->tqent_timer.data = (unsigned long)t;
        t->tqent_timer.function = task_expire;
        t->tqent_timer.expires = (unsigned long)expire_time;
        add_timer(&t->tqent_timer);

        ASSERT(!(t->tqent_flags & TQENT_FLAG_PREALLOC));

        spin_unlock(&t->tqent_lock);
out:
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
        SRETURN(rc);
}
EXPORT_SYMBOL(taskq_dispatch_delay);

void
taskq_dispatch_ent(taskq_t *tq, task_func_t func, void *arg, uint_t flags,
   taskq_ent_t *t)
{
        SENTRY;

        ASSERT(tq);
        ASSERT(func);
        ASSERT(!(tq->tq_flags & TASKQ_DYNAMIC));

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);

        /* Taskq being destroyed and all tasks drained */
        if (!(tq->tq_flags & TQ_ACTIVE)) {
                t->tqent_id = 0;
                goto out;
        }

        spin_lock(&t->tqent_lock);

        /*
         * Mark it as a prealloc'd task.  This is important
         * to ensure that we don't free it later.
         */
        t->tqent_flags |= TQENT_FLAG_PREALLOC;

        /* Queue to the priority list instead of the pending list */
        if (flags & TQ_FRONT)
                list_add_tail(&t->tqent_list, &tq->tq_prio_list);
        else
                list_add_tail(&t->tqent_list, &tq->tq_pend_list);

        t->tqent_id = tq->tq_next_id;
        tq->tq_next_id++;
        t->tqent_func = func;
        t->tqent_arg = arg;
        t->tqent_taskq = tq;

        spin_unlock(&t->tqent_lock);

        wake_up(&tq->tq_work_waitq);
out:
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
        SEXIT;
}
EXPORT_SYMBOL(taskq_dispatch_ent);

int
taskq_empty_ent(taskq_ent_t *t)
{
        return list_empty(&t->tqent_list);
}
EXPORT_SYMBOL(taskq_empty_ent);

void
taskq_init_ent(taskq_ent_t *t)
{
        spin_lock_init(&t->tqent_lock);
        init_waitqueue_head(&t->tqent_waitq);
        init_timer(&t->tqent_timer);
        INIT_LIST_HEAD(&t->tqent_list);
        t->tqent_id = 0;
        t->tqent_func = NULL;
        t->tqent_arg = NULL;
        t->tqent_flags = 0;
        t->tqent_taskq = NULL;
}
EXPORT_SYMBOL(taskq_init_ent);

static int
taskq_thread(void *args)
{
        DECLARE_WAITQUEUE(wait, current);
        sigset_t blocked;
        taskq_thread_t *tqt = args;
        taskq_t *tq;
        taskq_ent_t *t;
        struct list_head *pend_list;
        SENTRY;

        ASSERT(tqt);
        tq = tqt->tqt_tq;
        current->flags |= PF_NOFREEZE;

        sigfillset(&blocked);
        sigprocmask(SIG_BLOCK, &blocked, NULL);
        flush_signals(current);

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
        tq->tq_nthreads++;
        wake_up(&tq->tq_wait_waitq);
        set_current_state(TASK_INTERRUPTIBLE);

        while (!kthread_should_stop()) {

                if (list_empty(&tq->tq_pend_list) &&
                    list_empty(&tq->tq_prio_list)) {
                        add_wait_queue_exclusive(&tq->tq_work_waitq, &wait);
                        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
                        schedule();
                        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
                        remove_wait_queue(&tq->tq_work_waitq, &wait);
                } else {
                        __set_current_state(TASK_RUNNING);
                }


                if (!list_empty(&tq->tq_prio_list))
                        pend_list = &tq->tq_prio_list;
                else if (!list_empty(&tq->tq_pend_list))
                        pend_list = &tq->tq_pend_list;
                else
                        pend_list = NULL;

                if (pend_list) {
                        t = list_entry(pend_list->next,taskq_ent_t,tqent_list);
                        list_del_init(&t->tqent_list);

                        /* In order to support recursively dispatching a
                         * preallocated taskq_ent_t, tqent_id must be
                         * stored prior to executing tqent_func. */
                        tqt->tqt_id = t->tqent_id;
                        tqt->tqt_task = t;

                        /* We must store a copy of the flags prior to
                         * servicing the task (servicing a prealloc'd task
                         * returns the ownership of the tqent back to
                         * the caller of taskq_dispatch). Thus,
                         * tqent_flags _may_ change within the call. */
                        tqt->tqt_flags = t->tqent_flags;

                        taskq_insert_in_order(tq, tqt);
                        tq->tq_nactive++;
                        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

                        /* Perform the requested task */
                        t->tqent_func(t->tqent_arg);

                        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
                        tq->tq_nactive--;
                        list_del_init(&tqt->tqt_active_list);
                        tqt->tqt_task = NULL;

                        /* For prealloc'd tasks, we don't free anything. */
                        if ((tq->tq_flags & TASKQ_DYNAMIC) ||
                            !(tqt->tqt_flags & TQENT_FLAG_PREALLOC))
                                task_done(tq, t);

                        /* When the current lowest outstanding taskqid is
                         * done calculate the new lowest outstanding id */
                        if (tq->tq_lowest_id == tqt->tqt_id) {
                                tq->tq_lowest_id = taskq_lowest_id(tq);
                                ASSERT3S(tq->tq_lowest_id, >, tqt->tqt_id);
                        }

                        tqt->tqt_id = 0;
                        tqt->tqt_flags = 0;
                        wake_up_all(&tq->tq_wait_waitq);
                }

                set_current_state(TASK_INTERRUPTIBLE);

        }

        __set_current_state(TASK_RUNNING);
        tq->tq_nthreads--;
        list_del_init(&tqt->tqt_thread_list);
        kmem_free(tqt, sizeof(taskq_thread_t));

        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        SRETURN(0);
}

taskq_t *
taskq_create(const char *name, int nthreads, pri_t pri,
    int minalloc, int maxalloc, uint_t flags)
{
        taskq_t *tq;
        taskq_thread_t *tqt;
        int rc = 0, i, j = 0;
        SENTRY;

        ASSERT(name != NULL);
        ASSERT(pri <= maxclsyspri);
        ASSERT(minalloc >= 0);
        ASSERT(maxalloc <= INT_MAX);
        ASSERT(!(flags & (TASKQ_CPR_SAFE | TASKQ_DYNAMIC))); /* Unsupported */

        /* Scale the number of threads using nthreads as a percentage */
        if (flags & TASKQ_THREADS_CPU_PCT) {
                ASSERT(nthreads <= 100);
                ASSERT(nthreads >= 0);
                nthreads = MIN(nthreads, 100);
                nthreads = MAX(nthreads, 0);
                nthreads = MAX((num_online_cpus() * nthreads) / 100, 1);
        }

        tq = kmem_alloc(sizeof(*tq), KM_PUSHPAGE);
        if (tq == NULL)
                SRETURN(NULL);

        spin_lock_init(&tq->tq_lock);
        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
        INIT_LIST_HEAD(&tq->tq_thread_list);
        INIT_LIST_HEAD(&tq->tq_active_list);
        tq->tq_name      = name;
        tq->tq_nactive   = 0;
        tq->tq_nthreads  = 0;
        tq->tq_pri       = pri;
        tq->tq_minalloc  = minalloc;
        tq->tq_maxalloc  = maxalloc;
        tq->tq_nalloc    = 0;
        tq->tq_flags     = (flags | TQ_ACTIVE);
        tq->tq_next_id   = 1;
        tq->tq_lowest_id = 1;
        INIT_LIST_HEAD(&tq->tq_free_list);
        INIT_LIST_HEAD(&tq->tq_pend_list);
        INIT_LIST_HEAD(&tq->tq_prio_list);
        INIT_LIST_HEAD(&tq->tq_delay_list);
        init_waitqueue_head(&tq->tq_work_waitq);
        init_waitqueue_head(&tq->tq_wait_waitq);

        if (flags & TASKQ_PREPOPULATE)
                for (i = 0; i < minalloc; i++)
                        task_done(tq, task_alloc(tq, TQ_PUSHPAGE | TQ_NEW));

        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        for (i = 0; i < nthreads; i++) {
                tqt = kmem_alloc(sizeof(*tqt), KM_PUSHPAGE);
                INIT_LIST_HEAD(&tqt->tqt_thread_list);
                INIT_LIST_HEAD(&tqt->tqt_active_list);
                tqt->tqt_tq = tq;
                tqt->tqt_id = 0;

                tqt->tqt_thread = kthread_create(taskq_thread, tqt,
                    "%s/%d", name, i);
                if (tqt->tqt_thread) {
                        list_add(&tqt->tqt_thread_list, &tq->tq_thread_list);
                        kthread_bind(tqt->tqt_thread, i % num_online_cpus());
                        set_user_nice(tqt->tqt_thread, PRIO_TO_NICE(pri));
                        wake_up_process(tqt->tqt_thread);
                        j++;
                } else {
                        kmem_free(tqt, sizeof(taskq_thread_t));
                        rc = 1;
                }
        }

        /* Wait for all threads to be started before potential destroy */
        wait_event(tq->tq_wait_waitq, tq->tq_nthreads == j);

        if (rc) {
                taskq_destroy(tq);
                tq = NULL;
        }

        SRETURN(tq);
}
EXPORT_SYMBOL(taskq_create);

void
taskq_destroy(taskq_t *tq)
{
        struct task_struct *thread;
        taskq_thread_t *tqt;
        taskq_ent_t *t;
        SENTRY;

        ASSERT(tq);
        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
        tq->tq_flags &= ~TQ_ACTIVE;
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        /* TQ_ACTIVE cleared prevents new tasks being added to pending */
        taskq_wait(tq);

        spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);

        /*
         * Signal each thread to exit and block until it does.  Each thread
         * is responsible for removing itself from the list and freeing its
         * taskq_thread_t.  This allows for idle threads to opt to remove
         * themselves from the taskq.  They can be recreated as needed.
         */
        while (!list_empty(&tq->tq_thread_list)) {
                tqt = list_entry(tq->tq_thread_list.next,
                                 taskq_thread_t, tqt_thread_list);
                thread = tqt->tqt_thread;
                spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

                kthread_stop(thread);

                spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
        }

        while (!list_empty(&tq->tq_free_list)) {
                t = list_entry(tq->tq_free_list.next, taskq_ent_t, tqent_list);

                ASSERT(!(t->tqent_flags & TQENT_FLAG_PREALLOC));

                list_del_init(&t->tqent_list);
                task_free(tq, t);
        }

        ASSERT(tq->tq_nthreads == 0);
        ASSERT(tq->tq_nalloc == 0);
        ASSERT(list_empty(&tq->tq_thread_list));
        ASSERT(list_empty(&tq->tq_active_list));
        ASSERT(list_empty(&tq->tq_free_list));
        ASSERT(list_empty(&tq->tq_pend_list));
        ASSERT(list_empty(&tq->tq_prio_list));
        ASSERT(list_empty(&tq->tq_delay_list));

        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);

        kmem_free(tq, sizeof(taskq_t));

        SEXIT;
}
EXPORT_SYMBOL(taskq_destroy);

int
spl_taskq_init(void)
{
        SENTRY;

        /* Solaris creates a dynamic taskq of up to 64 threads, however in
         * a Linux environment 1 thread per-core is usually about right */
        system_taskq = taskq_create("spl_system_taskq", num_online_cpus(),
                                    minclsyspri, 4, 512, TASKQ_PREPOPULATE);
        if (system_taskq == NULL)
                SRETURN(1);

        SRETURN(0);
}

void
spl_taskq_fini(void)
{
        SENTRY;
        taskq_destroy(system_taskq);
        SEXIT;
}