FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/os/linux/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.
      *
     *  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/timer.h>
    #include <sys/taskq.h>
    #include <sys/kmem.h>
    #include <sys/tsd.h>
    #include <sys/trace_spl.h>
    #ifdef HAVE_CPU_HOTPLUG
    #include <linux/cpuhotplug.h>
    #endif
    
    static int spl_taskq_thread_bind = 0;
    module_param(spl_taskq_thread_bind, int, 0644);
    MODULE_PARM_DESC(spl_taskq_thread_bind, "Bind taskq thread to CPU by default");
    
    
    static int spl_taskq_thread_dynamic = 1;
    module_param(spl_taskq_thread_dynamic, int, 0444);
    MODULE_PARM_DESC(spl_taskq_thread_dynamic, "Allow dynamic taskq threads");
    
    static int spl_taskq_thread_priority = 1;
    module_param(spl_taskq_thread_priority, int, 0644);
    MODULE_PARM_DESC(spl_taskq_thread_priority,
            "Allow non-default priority for taskq threads");
    
    static uint_t spl_taskq_thread_sequential = 4;
    /* BEGIN CSTYLED */
    module_param(spl_taskq_thread_sequential, uint, 0644);
    /* END CSTYLED */
    MODULE_PARM_DESC(spl_taskq_thread_sequential,
            "Create new taskq threads after N sequential tasks");
    
    /*
     * Global system-wide dynamic task queue available for all consumers. This
     * taskq is not intended for long-running tasks; instead, a dedicated taskq
     * should be created.
     */
    taskq_t *system_taskq;
    EXPORT_SYMBOL(system_taskq);
    /* Global dynamic task queue for long delay */
    taskq_t *system_delay_taskq;
    EXPORT_SYMBOL(system_delay_taskq);
    
    /* Private dedicated taskq for creating new taskq threads on demand. */
    static taskq_t *dynamic_taskq;
    static taskq_thread_t *taskq_thread_create(taskq_t *);
    
    #ifdef HAVE_CPU_HOTPLUG
    /* Multi-callback id for cpu hotplugging. */
    static int spl_taskq_cpuhp_state;
    #endif
    
    /* List of all taskqs */
    LIST_HEAD(tq_list);
    struct rw_semaphore tq_list_sem;
    static uint_t taskq_tsd;
    
    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);
    }
    
    /*
     * taskq_find_by_name - Find the largest instance number of a named taskq.
     */
    static int
    taskq_find_by_name(const char *name)
    {
            struct list_head *tql = NULL;
           taskq_t *tq;
   
           list_for_each_prev(tql, &tq_list) {
                   tq = list_entry(tql, taskq_t, tq_taskqs);
                   if (strcmp(name, tq->tq_name) == 0)
                           return (tq->tq_instance);
           }
           return (-1);
   }
   
   /*
    * 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, unsigned long *irqflags)
   {
           taskq_ent_t *t;
           int count = 0;
   
           ASSERT(tq);
   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);
                   return (t);
           }
   
           /* Free list is empty and memory allocations are prohibited */
           if (flags & TQ_NOALLOC)
                   return (NULL);
   
           /* Hit maximum taskq_ent_t pool size */
           if (tq->tq_nalloc >= tq->tq_maxalloc) {
                   if (flags & TQ_NOSLEEP)
                           return (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, *irqflags);
                   schedule_timeout(HZ / 100);
                   spin_lock_irqsave_nested(&tq->tq_lock, *irqflags,
                       tq->tq_lock_class);
                   if (count < 100) {
                           count++;
                           goto retry;
                   }
           }
   
           spin_unlock_irqrestore(&tq->tq_lock, *irqflags);
           t = kmem_alloc(sizeof (taskq_ent_t), task_km_flags(flags));
           spin_lock_irqsave_nested(&tq->tq_lock, *irqflags, tq->tq_lock_class);
   
           if (t) {
                   taskq_init_ent(t);
                   tq->tq_nalloc++;
           }
   
           return (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)
   {
           ASSERT(tq);
           ASSERT(t);
           ASSERT(list_empty(&t->tqent_list));
           ASSERT(!timer_pending(&t->tqent_timer));
   
           kmem_free(t, sizeof (taskq_ent_t));
           tq->tq_nalloc--;
   }
   
   /*
    * 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)
   {
           ASSERT(tq);
           ASSERT(t);
   
           /* 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 = TASKQID_INVALID;
                   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);
           }
   }
   
   /*
    * 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_impl(taskq_ent_t *t)
   {
           taskq_ent_t *w;
           taskq_t *tq = t->tqent_taskq;
           struct list_head *l = NULL;
           unsigned long flags;
   
           spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
   
           if (t->tqent_flags & TQENT_FLAG_CANCEL) {
                   ASSERT(list_empty(&t->tqent_list));
                   spin_unlock_irqrestore(&tq->tq_lock, flags);
                   return;
           }
   
           t->tqent_birth = jiffies;
           DTRACE_PROBE1(taskq_ent__birth, taskq_ent_t *, t);
   
           /*
            * 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, flags);
   
           wake_up(&tq->tq_work_waitq);
   }
   
   static void
   task_expire(spl_timer_list_t tl)
   {
           struct timer_list *tmr = (struct timer_list *)tl;
           taskq_ent_t *t = from_timer(t, tmr, tqent_timer);
           task_expire_impl(t);
   }
   
   /*
    * 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;
   
           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 != TASKQID_INVALID);
                   lowest_id = MIN(lowest_id, tqt->tqt_id);
           }
   
           return (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 = NULL;
   
           ASSERT(tq);
           ASSERT(tqt);
   
           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);
   }
   
   /*
    * 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 = NULL;
           taskq_ent_t *t;
   
           list_for_each(l, lh) {
                   t = list_entry(l, taskq_ent_t, tqent_list);
   
                   if (t->tqent_id == id)
                           return (t);
   
                   if (t->tqent_id > id)
                           break;
           }
   
           return (NULL);
   }
   
   /*
    * Find an already dispatched task given the task id regardless of what
    * state it is in.  If a task is still pending it will be returned.
    * If a task is executing, then -EBUSY will be returned instead.
    * If the task has already been run then NULL is returned.
    */
   static taskq_ent_t *
   taskq_find(taskq_t *tq, taskqid_t id)
   {
           taskq_thread_t *tqt;
           struct list_head *l = NULL;
           taskq_ent_t *t;
   
           t = taskq_find_list(tq, &tq->tq_delay_list, id);
           if (t)
                   return (t);
   
           t = taskq_find_list(tq, &tq->tq_prio_list, id);
           if (t)
                   return (t);
   
           t = taskq_find_list(tq, &tq->tq_pend_list, id);
           if (t)
                   return (t);
   
           list_for_each(l, &tq->tq_active_list) {
                   tqt = list_entry(l, taskq_thread_t, tqt_active_list);
                   if (tqt->tqt_id == id) {
                           /*
                            * Instead of returning tqt_task, we just return a non
                            * NULL value to prevent misuse, since tqt_task only
                            * has two valid fields.
                            */
                           return (ERR_PTR(-EBUSY));
                   }
           }
   
           return (NULL);
   }
   
   /*
    * Theory for the taskq_wait_id(), taskq_wait_outstanding(), and
    * taskq_wait() functions below.
    *
    * Taskq waiting is accomplished by tracking the lowest outstanding task
    * id and the next available task id.  As tasks are dispatched they are
    * added to the tail of the pending, priority, or delay lists.  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 sorted by lowest to highest task id.
    *
    * 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 taskq 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 passed task id the
    * taskq_wait_outstanding() function can be easily implemented.  Similarly,
    * by blocking until the lowest task id matches the next task id taskq_wait()
    * can be implemented.
    *
    * Callers should be aware that when there are multiple worked threads it
    * is possible for larger task ids to complete before smaller ones.  Also
    * when the taskq contains delay tasks with small task ids callers may
    * block for a considerable length of time waiting for them to expire and
    * execute.
    */
   static int
   taskq_wait_id_check(taskq_t *tq, taskqid_t id)
   {
           int rc;
           unsigned long flags;
   
           spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
           rc = (taskq_find(tq, id) == NULL);
           spin_unlock_irqrestore(&tq->tq_lock, flags);
   
           return (rc);
   }
   
   /*
    * The taskq_wait_id() function blocks until the passed task id completes.
    * This does not guarantee that all lower task ids have completed.
    */
   void
   taskq_wait_id(taskq_t *tq, taskqid_t id)
   {
           wait_event(tq->tq_wait_waitq, taskq_wait_id_check(tq, id));
   }
   EXPORT_SYMBOL(taskq_wait_id);
   
   static int
   taskq_wait_outstanding_check(taskq_t *tq, taskqid_t id)
   {
           int rc;
           unsigned long flags;
   
           spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
           rc = (id < tq->tq_lowest_id);
           spin_unlock_irqrestore(&tq->tq_lock, flags);
   
           return (rc);
   }
   
   /*
    * The taskq_wait_outstanding() function will block until all tasks with a
    * lower taskqid than the passed 'id' have been completed.  Note that all
    * task id's are assigned monotonically at dispatch time.  Zero may be
    * passed for the id to indicate all tasks dispatch up to this point,
    * but not after, should be waited for.
    */
   void
   taskq_wait_outstanding(taskq_t *tq, taskqid_t id)
   {
           id = id ? id : tq->tq_next_id - 1;
           wait_event(tq->tq_wait_waitq, taskq_wait_outstanding_check(tq, id));
   }
   EXPORT_SYMBOL(taskq_wait_outstanding);
   
   static int
   taskq_wait_check(taskq_t *tq)
   {
           int rc;
           unsigned long flags;
   
           spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
           rc = (tq->tq_lowest_id == tq->tq_next_id);
           spin_unlock_irqrestore(&tq->tq_lock, flags);
   
           return (rc);
   }
   
   /*
    * The taskq_wait() function will block until the taskq is empty.
    * This means that if a taskq re-dispatches work to itself taskq_wait()
    * callers will block indefinitely.
    */
   void
   taskq_wait(taskq_t *tq)
   {
           wait_event(tq->tq_wait_waitq, taskq_wait_check(tq));
   }
   EXPORT_SYMBOL(taskq_wait);
   
   int
   taskq_member(taskq_t *tq, kthread_t *t)
   {
           return (tq == (taskq_t *)tsd_get_by_thread(taskq_tsd, t));
   }
   EXPORT_SYMBOL(taskq_member);
   
   taskq_t *
   taskq_of_curthread(void)
   {
           return (tsd_get(taskq_tsd));
   }
   EXPORT_SYMBOL(taskq_of_curthread);
   
   /*
    * 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 rc = ENOENT;
           unsigned long flags;
   
           ASSERT(tq);
   
           spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
           t = taskq_find(tq, id);
           if (t && t != ERR_PTR(-EBUSY)) {
                   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, flags);
                           del_timer_sync(&t->tqent_timer);
                           spin_lock_irqsave_nested(&tq->tq_lock, flags,
                               tq->tq_lock_class);
                   }
   
                   if (!(t->tqent_flags & TQENT_FLAG_PREALLOC))
                           task_done(tq, t);
   
                   rc = 0;
           }
           spin_unlock_irqrestore(&tq->tq_lock, flags);
   
           if (t == ERR_PTR(-EBUSY)) {
                   taskq_wait_id(tq, id);
                   rc = EBUSY;
           }
   
           return (rc);
   }
   EXPORT_SYMBOL(taskq_cancel_id);
   
   static int taskq_thread_spawn(taskq_t *tq);
   
   taskqid_t
   taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
   {
           taskq_ent_t *t;
           taskqid_t rc = TASKQID_INVALID;
           unsigned long irqflags;
   
           ASSERT(tq);
           ASSERT(func);
   
           spin_lock_irqsave_nested(&tq->tq_lock, irqflags, tq->tq_lock_class);
   
           /* Taskq being destroyed and all tasks drained */
           if (!(tq->tq_flags & TASKQ_ACTIVE))
                   goto out;
   
           /* 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)) {
                   /* Dynamic taskq may be able to spawn another thread */
                   if (!(tq->tq_flags & TASKQ_DYNAMIC) ||
                       taskq_thread_spawn(tq) == 0)
                           goto out;
           }
   
           if ((t = task_alloc(tq, flags, &irqflags)) == NULL)
                   goto out;
   
           spin_lock(&t->tqent_lock);
   
           /* Queue to the front of the list to enforce TQ_NOQUEUE semantics */
           if (flags & TQ_NOQUEUE)
                   list_add(&t->tqent_list, &tq->tq_prio_list);
           /* Queue to the priority list instead of the pending list */
           else 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.function = NULL;
           t->tqent_timer.expires = 0;
   
           t->tqent_birth = jiffies;
           DTRACE_PROBE1(taskq_ent__birth, taskq_ent_t *, t);
   
           ASSERT(!(t->tqent_flags & TQENT_FLAG_PREALLOC));
   
           spin_unlock(&t->tqent_lock);
   
           wake_up(&tq->tq_work_waitq);
   out:
           /* Spawn additional taskq threads if required. */
           if (!(flags & TQ_NOQUEUE) && tq->tq_nactive == tq->tq_nthreads)
                   (void) taskq_thread_spawn(tq);
   
           spin_unlock_irqrestore(&tq->tq_lock, irqflags);
           return (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)
   {
           taskqid_t rc = TASKQID_INVALID;
           taskq_ent_t *t;
           unsigned long irqflags;
   
           ASSERT(tq);
           ASSERT(func);
   
           spin_lock_irqsave_nested(&tq->tq_lock, irqflags, tq->tq_lock_class);
   
           /* Taskq being destroyed and all tasks drained */
           if (!(tq->tq_flags & TASKQ_ACTIVE))
                   goto out;
   
           if ((t = task_alloc(tq, flags, &irqflags)) == NULL)
                   goto out;
   
           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.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:
           /* Spawn additional taskq threads if required. */
           if (tq->tq_nactive == tq->tq_nthreads)
                   (void) taskq_thread_spawn(tq);
           spin_unlock_irqrestore(&tq->tq_lock, irqflags);
           return (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)
   {
           unsigned long irqflags;
           ASSERT(tq);
           ASSERT(func);
   
           spin_lock_irqsave_nested(&tq->tq_lock, irqflags,
               tq->tq_lock_class);
   
           /* Taskq being destroyed and all tasks drained */
           if (!(tq->tq_flags & TASKQ_ACTIVE)) {
                   t->tqent_id = TASKQID_INVALID;
                   goto out;
           }
   
           if ((flags & TQ_NOQUEUE) && (tq->tq_nactive == tq->tq_nthreads)) {
                   /* Dynamic taskq may be able to spawn another thread */
                   if (!(tq->tq_flags & TASKQ_DYNAMIC) ||
                       taskq_thread_spawn(tq) == 0)
                           goto out2;
                   flags |= TQ_FRONT;
           }
   
           spin_lock(&t->tqent_lock);
   
           /*
            * Make sure the entry is not on some other taskq; it is important to
            * ASSERT() under lock
            */
           ASSERT(taskq_empty_ent(t));
   
           /*
            * 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;
   
           t->tqent_birth = jiffies;
           DTRACE_PROBE1(taskq_ent__birth, taskq_ent_t *, t);
   
           spin_unlock(&t->tqent_lock);
   
           wake_up(&tq->tq_work_waitq);
   out:
           /* Spawn additional taskq threads if required. */
           if (tq->tq_nactive == tq->tq_nthreads)
                   (void) taskq_thread_spawn(tq);
   out2:
           spin_unlock_irqrestore(&tq->tq_lock, irqflags);
   }
   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);
           timer_setup(&t->tqent_timer, NULL, 0);
           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);
   
   /*
    * Return the next pending task, preference is given to tasks on the
    * priority list which were dispatched with TQ_FRONT.
    */
   static taskq_ent_t *
   taskq_next_ent(taskq_t *tq)
   {
           struct list_head *list;
   
           if (!list_empty(&tq->tq_prio_list))
                   list = &tq->tq_prio_list;
           else if (!list_empty(&tq->tq_pend_list))
                   list = &tq->tq_pend_list;
           else
                   return (NULL);
   
           return (list_entry(list->next, taskq_ent_t, tqent_list));
   }
   
   /*
    * Spawns a new thread for the specified taskq.
    */
   static void
   taskq_thread_spawn_task(void *arg)
   {
           taskq_t *tq = (taskq_t *)arg;
           unsigned long flags;
   
           if (taskq_thread_create(tq) == NULL) {
                   /* restore spawning count if failed */
                   spin_lock_irqsave_nested(&tq->tq_lock, flags,
                       tq->tq_lock_class);
                   tq->tq_nspawn--;
                   spin_unlock_irqrestore(&tq->tq_lock, flags);
           }
   }
   
   /*
    * Spawn addition threads for dynamic taskqs (TASKQ_DYNAMIC) the current
    * number of threads is insufficient to handle the pending tasks.  These
    * new threads must be created by the dedicated dynamic_taskq to avoid
    * deadlocks between thread creation and memory reclaim.  The system_taskq
    * which is also a dynamic taskq cannot be safely used for this.
    */
   static int
   taskq_thread_spawn(taskq_t *tq)
   {
           int spawning = 0;
   
           if (!(tq->tq_flags & TASKQ_DYNAMIC))
                   return (0);
   
           if ((tq->tq_nthreads + tq->tq_nspawn < tq->tq_maxthreads) &&
               (tq->tq_flags & TASKQ_ACTIVE)) {
                   spawning = (++tq->tq_nspawn);
                   taskq_dispatch(dynamic_taskq, taskq_thread_spawn_task,
                       tq, TQ_NOSLEEP);
           }
   
           return (spawning);
   }
   
   /*
    * Threads in a dynamic taskq should only exit once it has been completely
    * drained and no other threads are actively servicing tasks.  This prevents
    * threads from being created and destroyed more than is required.
    *
    * The first thread is the thread list is treated as the primary thread.
    * There is nothing special about the primary thread but in order to avoid
    * all the taskq pids from changing we opt to make it long running.
    */
   static int
   taskq_thread_should_stop(taskq_t *tq, taskq_thread_t *tqt)
   {
           if (!(tq->tq_flags & TASKQ_DYNAMIC))
                   return (0);
   
           if (list_first_entry(&(tq->tq_thread_list), taskq_thread_t,
               tqt_thread_list) == tqt)
                   return (0);
   
           return
               ((tq->tq_nspawn == 0) &&    /* No threads are being spawned */
               (tq->tq_nactive == 0) &&    /* No threads are handling tasks */
               (tq->tq_nthreads > 1) &&    /* More than 1 thread is running */
               (!taskq_next_ent(tq)) &&    /* There are no pending tasks */
               (spl_taskq_thread_dynamic)); /* Dynamic taskqs are allowed */
   }
   
   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;
           int seq_tasks = 0;
           unsigned long flags;
           taskq_ent_t dup_task = {};
   
           ASSERT(tqt);
           ASSERT(tqt->tqt_tq);
           tq = tqt->tqt_tq;
           current->flags |= PF_NOFREEZE;
   
           (void) spl_fstrans_mark();
   
           sigfillset(&blocked);
           sigprocmask(SIG_BLOCK, &blocked, NULL);
           flush_signals(current);
   
           tsd_set(taskq_tsd, tq);
           spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
           /*
            * If we are dynamically spawned, decrease spawning count. Note that
            * we could be created during taskq_create, in which case we shouldn't
            * do the decrement. But it's fine because taskq_create will reset
            * tq_nspawn later.
            */
           if (tq->tq_flags & TASKQ_DYNAMIC)
                   tq->tq_nspawn--;
   
           /* Immediately exit if more threads than allowed were created. */
           if (tq->tq_nthreads >= tq->tq_maxthreads)
                   goto error;
   
           tq->tq_nthreads++;
           list_add_tail(&tqt->tqt_thread_list, &tq->tq_thread_list);
           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)) {
   
                           if (taskq_thread_should_stop(tq, tqt)) {
                                   wake_up_all(&tq->tq_wait_waitq);
                                   break;
                           }
   
                           add_wait_queue_exclusive(&tq->tq_work_waitq, &wait);
                           spin_unlock_irqrestore(&tq->tq_lock, flags);
   
                           schedule();
                           seq_tasks = 0;
   
                           spin_lock_irqsave_nested(&tq->tq_lock, flags,
                               tq->tq_lock_class);
                           remove_wait_queue(&tq->tq_work_waitq, &wait);
                   } else {
                           __set_current_state(TASK_RUNNING);
                   }
   
                   if ((t = taskq_next_ent(tq)) != NULL) {
                           list_del_init(&t->tqent_list);
   
                           /*
                            * A TQENT_FLAG_PREALLOC task may be reused or freed
                            * during the task function call. Store tqent_id and
                            * tqent_flags here.
                            *
                            * Also use an on stack taskq_ent_t for tqt_task
                            * assignment in this case; we want to make sure
                            * to duplicate all fields, so the values are
                            * correct when it's accessed via DTRACE_PROBE*.
                            */
                           tqt->tqt_id = t->tqent_id;
                           tqt->tqt_flags = t->tqent_flags;
   
                           if (t->tqent_flags & TQENT_FLAG_PREALLOC) {
                                   dup_task = *t;
                                   t = &dup_task;
                           }
                           tqt->tqt_task = t;
   
                           taskq_insert_in_order(tq, tqt);
                           tq->tq_nactive++;
                           spin_unlock_irqrestore(&tq->tq_lock, flags);
   
                           DTRACE_PROBE1(taskq_ent__start, taskq_ent_t *, t);
   
                           /* Perform the requested task */
                           t->tqent_func(t->tqent_arg);
   
                           DTRACE_PROBE1(taskq_ent__finish, taskq_ent_t *, t);
   
                           spin_lock_irqsave_nested(&tq->tq_lock, flags,
                               tq->tq_lock_class);
                           tq->tq_nactive--;
                           list_del_init(&tqt->tqt_active_list);
                           tqt->tqt_task = NULL;
   
                           /* For prealloc'd tasks, we don't free anything. */
                           if (!(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);
                           }
   
                           /* Spawn additional taskq threads if required. */
                           if ((++seq_tasks) > spl_taskq_thread_sequential &&
                               taskq_thread_spawn(tq))
                                   seq_tasks = 0;
   
                           tqt->tqt_id = TASKQID_INVALID;
                           tqt->tqt_flags = 0;
                           wake_up_all(&tq->tq_wait_waitq);
                   } else {
                           if (taskq_thread_should_stop(tq, tqt))
                                   break;
                   }
   
                   set_current_state(TASK_INTERRUPTIBLE);
   
           }
   
           __set_current_state(TASK_RUNNING);
           tq->tq_nthreads--;
           list_del_init(&tqt->tqt_thread_list);
   error:
           kmem_free(tqt, sizeof (taskq_thread_t));
           spin_unlock_irqrestore(&tq->tq_lock, flags);
  
          tsd_set(taskq_tsd, NULL);
          thread_exit();
  
          return (0);
  }
  
  static taskq_thread_t *
  taskq_thread_create(taskq_t *tq)
  {
          static int last_used_cpu = 0;
          taskq_thread_t *tqt;
  
          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 = TASKQID_INVALID;
  
          tqt->tqt_thread = spl_kthread_create(taskq_thread, tqt,
              "%s", tq->tq_name);
          if (tqt->tqt_thread == NULL) {
                  kmem_free(tqt, sizeof (taskq_thread_t));
                  return (NULL);
          }
  
          if (spl_taskq_thread_bind) {
                  last_used_cpu = (last_used_cpu + 1) % num_online_cpus();
                  kthread_bind(tqt->tqt_thread, last_used_cpu);
          }
  
          if (spl_taskq_thread_priority)
                  set_user_nice(tqt->tqt_thread, PRIO_TO_NICE(tq->tq_pri));
  
          wake_up_process(tqt->tqt_thread);
  
          return (tqt);
  }
  
  taskq_t *
  taskq_create(const char *name, int threads_arg, pri_t pri,
      int minalloc, int maxalloc, uint_t flags)
  {
          taskq_t *tq;
          taskq_thread_t *tqt;
          int count = 0, rc = 0, i;
          unsigned long irqflags;
          int nthreads = threads_arg;
  
          ASSERT(name != NULL);
          ASSERT(minalloc >= 0);
          ASSERT(!(flags & (TASKQ_CPR_SAFE))); /* 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(threads_arg, 100);
                  nthreads = MAX(nthreads, 0);
                  nthreads = MAX((num_online_cpus() * nthreads) /100, 1);
          }
  
          tq = kmem_alloc(sizeof (*tq), KM_PUSHPAGE);
          if (tq == NULL)
                  return (NULL);
  
          tq->tq_hp_support = B_FALSE;
  #ifdef HAVE_CPU_HOTPLUG
          if (flags & TASKQ_THREADS_CPU_PCT) {
                  tq->tq_hp_support = B_TRUE;
                  if (cpuhp_state_add_instance_nocalls(spl_taskq_cpuhp_state,
                      &tq->tq_hp_cb_node) != 0) {
                          kmem_free(tq, sizeof (*tq));
                          return (NULL);
                  }
          }
  #endif
  
          spin_lock_init(&tq->tq_lock);
          INIT_LIST_HEAD(&tq->tq_thread_list);
          INIT_LIST_HEAD(&tq->tq_active_list);
          tq->tq_name = kmem_strdup(name);
          tq->tq_nactive = 0;
          tq->tq_nthreads = 0;
          tq->tq_nspawn = 0;
          tq->tq_maxthreads = nthreads;
          tq->tq_cpu_pct = threads_arg;
          tq->tq_pri = pri;
          tq->tq_minalloc = minalloc;
          tq->tq_maxalloc = maxalloc;
          tq->tq_nalloc = 0;
          tq->tq_flags = (flags | TASKQ_ACTIVE);
          tq->tq_next_id = TASKQID_INITIAL;
          tq->tq_lowest_id = TASKQID_INITIAL;
          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);
          tq->tq_lock_class = TQ_LOCK_GENERAL;
          INIT_LIST_HEAD(&tq->tq_taskqs);
  
          if (flags & TASKQ_PREPOPULATE) {
                  spin_lock_irqsave_nested(&tq->tq_lock, irqflags,
                      tq->tq_lock_class);
  
                  for (i = 0; i < minalloc; i++)
                          task_done(tq, task_alloc(tq, TQ_PUSHPAGE | TQ_NEW,
                              &irqflags));
  
                  spin_unlock_irqrestore(&tq->tq_lock, irqflags);
          }
  
          if ((flags & TASKQ_DYNAMIC) && spl_taskq_thread_dynamic)
                  nthreads = 1;
  
          for (i = 0; i < nthreads; i++) {
                  tqt = taskq_thread_create(tq);
                  if (tqt == NULL)
                          rc = 1;
                  else
                          count++;
          }
  
          /* Wait for all threads to be started before potential destroy */
          wait_event(tq->tq_wait_waitq, tq->tq_nthreads == count);
          /*
           * taskq_thread might have touched nspawn, but we don't want them to
           * because they're not dynamically spawned. So we reset it to 0
           */
          tq->tq_nspawn = 0;
  
          if (rc) {
                  taskq_destroy(tq);
                  tq = NULL;
          } else {
                  down_write(&tq_list_sem);
                  tq->tq_instance = taskq_find_by_name(name) + 1;
                  list_add_tail(&tq->tq_taskqs, &tq_list);
                  up_write(&tq_list_sem);
          }
  
          return (tq);
  }
  EXPORT_SYMBOL(taskq_create);
  
  void
  taskq_destroy(taskq_t *tq)
  {
          struct task_struct *thread;
          taskq_thread_t *tqt;
          taskq_ent_t *t;
          unsigned long flags;
  
          ASSERT(tq);
          spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
          tq->tq_flags &= ~TASKQ_ACTIVE;
          spin_unlock_irqrestore(&tq->tq_lock, flags);
  
  #ifdef HAVE_CPU_HOTPLUG
          if (tq->tq_hp_support) {
                  VERIFY0(cpuhp_state_remove_instance_nocalls(
                      spl_taskq_cpuhp_state, &tq->tq_hp_cb_node));
          }
  #endif
          /*
           * When TASKQ_ACTIVE is clear new tasks may not be added nor may
           * new worker threads be spawned for dynamic taskq.
           */
          if (dynamic_taskq != NULL)
                  taskq_wait_outstanding(dynamic_taskq, 0);
  
          taskq_wait(tq);
  
          /* remove taskq from global list used by the kstats */
          down_write(&tq_list_sem);
          list_del(&tq->tq_taskqs);
          up_write(&tq_list_sem);
  
          spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
          /* wait for spawning threads to insert themselves to the list */
          while (tq->tq_nspawn) {
                  spin_unlock_irqrestore(&tq->tq_lock, flags);
                  schedule_timeout_interruptible(1);
                  spin_lock_irqsave_nested(&tq->tq_lock, flags,
                      tq->tq_lock_class);
          }
  
          /*
           * 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, flags);
  
                  kthread_stop(thread);
  
                  spin_lock_irqsave_nested(&tq->tq_lock, flags,
                      tq->tq_lock_class);
          }
  
          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);
          }
  
          ASSERT0(tq->tq_nthreads);
          ASSERT0(tq->tq_nalloc);
          ASSERT0(tq->tq_nspawn);
          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, flags);
  
          kmem_strfree(tq->tq_name);
          kmem_free(tq, sizeof (taskq_t));
  }
  EXPORT_SYMBOL(taskq_destroy);
  
  static unsigned int spl_taskq_kick = 0;
  
  /*
   * 2.6.36 API Change
   * module_param_cb is introduced to take kernel_param_ops and
   * module_param_call is marked as obsolete. Also set and get operations
   * were changed to take a 'const struct kernel_param *'.
   */
  static int
  #ifdef module_param_cb
  param_set_taskq_kick(const char *val, const struct kernel_param *kp)
  #else
  param_set_taskq_kick(const char *val, struct kernel_param *kp)
  #endif
  {
          int ret;
          taskq_t *tq = NULL;
          taskq_ent_t *t;
          unsigned long flags;
  
          ret = param_set_uint(val, kp);
          if (ret < 0 || !spl_taskq_kick)
                  return (ret);
          /* reset value */
          spl_taskq_kick = 0;
  
          down_read(&tq_list_sem);
          list_for_each_entry(tq, &tq_list, tq_taskqs) {
                  spin_lock_irqsave_nested(&tq->tq_lock, flags,
                      tq->tq_lock_class);
                  /* Check if the first pending is older than 5 seconds */
                  t = taskq_next_ent(tq);
                  if (t && time_after(jiffies, t->tqent_birth + 5*HZ)) {
                          (void) taskq_thread_spawn(tq);
                          printk(KERN_INFO "spl: Kicked taskq %s/%d\n",
                              tq->tq_name, tq->tq_instance);
                  }
                  spin_unlock_irqrestore(&tq->tq_lock, flags);
          }
          up_read(&tq_list_sem);
          return (ret);
  }
  
  #ifdef module_param_cb
  static const struct kernel_param_ops param_ops_taskq_kick = {
          .set = param_set_taskq_kick,
          .get = param_get_uint,
  };
  module_param_cb(spl_taskq_kick, &param_ops_taskq_kick, &spl_taskq_kick, 0644);
  #else
  module_param_call(spl_taskq_kick, param_set_taskq_kick, param_get_uint,
          &spl_taskq_kick, 0644);
  #endif
  MODULE_PARM_DESC(spl_taskq_kick,
          "Write nonzero to kick stuck taskqs to spawn more threads");
  
  #ifdef HAVE_CPU_HOTPLUG
  /*
   * This callback will be called exactly once for each core that comes online,
   * for each dynamic taskq. We attempt to expand taskqs that have
   * TASKQ_THREADS_CPU_PCT set. We need to redo the percentage calculation every
   * time, to correctly determine whether or not to add a thread.
   */
  static int
  spl_taskq_expand(unsigned int cpu, struct hlist_node *node)
  {
          taskq_t *tq = list_entry(node, taskq_t, tq_hp_cb_node);
          unsigned long flags;
          int err = 0;
  
          ASSERT(tq);
          spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
  
          if (!(tq->tq_flags & TASKQ_ACTIVE)) {
                  spin_unlock_irqrestore(&tq->tq_lock, flags);
                  return (err);
          }
  
          ASSERT(tq->tq_flags & TASKQ_THREADS_CPU_PCT);
          int nthreads = MIN(tq->tq_cpu_pct, 100);
          nthreads = MAX(((num_online_cpus() + 1) * nthreads) / 100, 1);
          tq->tq_maxthreads = nthreads;
  
          if (!((tq->tq_flags & TASKQ_DYNAMIC) && spl_taskq_thread_dynamic) &&
              tq->tq_maxthreads > tq->tq_nthreads) {
                  spin_unlock_irqrestore(&tq->tq_lock, flags);
                  taskq_thread_t *tqt = taskq_thread_create(tq);
                  if (tqt == NULL)
                          err = -1;
                  return (err);
          }
          spin_unlock_irqrestore(&tq->tq_lock, flags);
          return (err);
  }
  
  /*
   * While we don't support offlining CPUs, it is possible that CPUs will fail
   * to online successfully. We do need to be able to handle this case
   * gracefully.
   */
  static int
  spl_taskq_prepare_down(unsigned int cpu, struct hlist_node *node)
  {
          taskq_t *tq = list_entry(node, taskq_t, tq_hp_cb_node);
          unsigned long flags;
  
          ASSERT(tq);
          spin_lock_irqsave_nested(&tq->tq_lock, flags, tq->tq_lock_class);
  
          if (!(tq->tq_flags & TASKQ_ACTIVE))
                  goto out;
  
          ASSERT(tq->tq_flags & TASKQ_THREADS_CPU_PCT);
          int nthreads = MIN(tq->tq_cpu_pct, 100);
          nthreads = MAX(((num_online_cpus()) * nthreads) / 100, 1);
          tq->tq_maxthreads = nthreads;
  
          if (!((tq->tq_flags & TASKQ_DYNAMIC) && spl_taskq_thread_dynamic) &&
              tq->tq_maxthreads < tq->tq_nthreads) {
                  ASSERT3U(tq->tq_maxthreads, ==, tq->tq_nthreads - 1);
                  taskq_thread_t *tqt = list_entry(tq->tq_thread_list.next,
                      taskq_thread_t, tqt_thread_list);
                  struct task_struct *thread = tqt->tqt_thread;
                  spin_unlock_irqrestore(&tq->tq_lock, flags);
  
                  kthread_stop(thread);
  
                  return (0);
          }
  
  out:
          spin_unlock_irqrestore(&tq->tq_lock, flags);
          return (0);
  }
  #endif
  
  int
  spl_taskq_init(void)
  {
          init_rwsem(&tq_list_sem);
          tsd_create(&taskq_tsd, NULL);
  
  #ifdef HAVE_CPU_HOTPLUG
          spl_taskq_cpuhp_state = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN,
              "fs/spl_taskq:online", spl_taskq_expand, spl_taskq_prepare_down);
  #endif
  
          system_taskq = taskq_create("spl_system_taskq", MAX(boot_ncpus, 64),
              maxclsyspri, boot_ncpus, INT_MAX, TASKQ_PREPOPULATE|TASKQ_DYNAMIC);
          if (system_taskq == NULL)
                  return (-ENOMEM);
  
          system_delay_taskq = taskq_create("spl_delay_taskq", MAX(boot_ncpus, 4),
              maxclsyspri, boot_ncpus, INT_MAX, TASKQ_PREPOPULATE|TASKQ_DYNAMIC);
          if (system_delay_taskq == NULL) {
  #ifdef HAVE_CPU_HOTPLUG
                  cpuhp_remove_multi_state(spl_taskq_cpuhp_state);
  #endif
                  taskq_destroy(system_taskq);
                  return (-ENOMEM);
          }
  
          dynamic_taskq = taskq_create("spl_dynamic_taskq", 1,
              maxclsyspri, boot_ncpus, INT_MAX, TASKQ_PREPOPULATE);
          if (dynamic_taskq == NULL) {
  #ifdef HAVE_CPU_HOTPLUG
                  cpuhp_remove_multi_state(spl_taskq_cpuhp_state);
  #endif
                  taskq_destroy(system_taskq);
                  taskq_destroy(system_delay_taskq);
                  return (-ENOMEM);
          }
  
          /*
           * This is used to annotate tq_lock, so
           *   taskq_dispatch -> taskq_thread_spawn -> taskq_dispatch
           * does not trigger a lockdep warning re: possible recursive locking
           */
          dynamic_taskq->tq_lock_class = TQ_LOCK_DYNAMIC;
  
          return (0);
  }
  
  void
  spl_taskq_fini(void)
  {
          taskq_destroy(dynamic_taskq);
          dynamic_taskq = NULL;
  
          taskq_destroy(system_delay_taskq);
          system_delay_taskq = NULL;
  
          taskq_destroy(system_taskq);
          system_taskq = NULL;
  
          tsd_destroy(&taskq_tsd);
  
  #ifdef HAVE_CPU_HOTPLUG
          cpuhp_remove_multi_state(spl_taskq_cpuhp_state);
          spl_taskq_cpuhp_state = 0;
  #endif
  }

Cache object: 9017603e4816759dde23c7396c0155f7