fs/btrfs/async-thread.c - kernel/msm-5.4 - Gitiles

 /*
  * Copyright (C) 2007 Oracle.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public
  * License v2 as published by the Free Software Foundation.
  *
  * This program 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 this program; if not, write to the
  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  * Boston, MA 021110-1307, USA.
  */

 #include <linux/kthread.h>
 #include <linux/slab.h>
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/freezer.h>
 #include "async-thread.h"

 #define WORK_QUEUED_BIT 0
 #define WORK_DONE_BIT 1
 #define WORK_ORDER_DONE_BIT 2
 #define WORK_HIGH_PRIO_BIT 3

 /*
  * container for the kthread task pointer and the list of pending work
  * One of these is allocated per thread.
  */
 struct btrfs_worker_thread {
 	/* pool we belong to */
 	struct btrfs_workers *workers;

 	/* list of struct btrfs_work that are waiting for service */
 	struct list_head pending;
 	struct list_head prio_pending;

 	/* list of worker threads from struct btrfs_workers */
 	struct list_head worker_list;

 	/* kthread */
 	struct task_struct *task;

 	/* number of things on the pending list */
 	atomic_t num_pending;

 	/* reference counter for this struct */
 	atomic_t refs;

 	unsigned long sequence;

 	/* protects the pending list. */
 	spinlock_t lock;

 	/* set to non-zero when this thread is already awake and kicking */
 	int working;

 	/* are we currently idle */
 	int idle;
 };

 static int __btrfs_start_workers(struct btrfs_workers *workers);

 /*
  * btrfs_start_workers uses kthread_run, which can block waiting for memory
  * for a very long time.  It will actually throttle on page writeback,
  * and so it may not make progress until after our btrfs worker threads
  * process all of the pending work structs in their queue
  *
  * This means we can't use btrfs_start_workers from inside a btrfs worker
  * thread that is used as part of cleaning dirty memory, which pretty much
  * involves all of the worker threads.
  *
  * Instead we have a helper queue who never has more than one thread
  * where we scheduler thread start operations.  This worker_start struct
  * is used to contain the work and hold a pointer to the queue that needs
  * another worker.
  */
 struct worker_start {
 	struct btrfs_work work;
 	struct btrfs_workers *queue;
 };

 static void start_new_worker_func(struct btrfs_work *work)
 {
 	struct worker_start *start;
 	start = container_of(work, struct worker_start, work);
 	__btrfs_start_workers(start->queue);
 	kfree(start);
 }

 /*
  * helper function to move a thread onto the idle list after it
  * has finished some requests.
  */
 static void check_idle_worker(struct btrfs_worker_thread *worker)
 {
 	if (!worker->idle && atomic_read(&worker->num_pending) <
 	    worker->workers->idle_thresh / 2) {
 		unsigned long flags;
 		spin_lock_irqsave(&worker->workers->lock, flags);
 		worker->idle = 1;

 		/* the list may be empty if the worker is just starting */
 		if (!list_empty(&worker->worker_list)) {
 			list_move(&worker->worker_list,
 				 &worker->workers->idle_list);
 		}
 		spin_unlock_irqrestore(&worker->workers->lock, flags);
 	}
 }

 /*
  * helper function to move a thread off the idle list after new
  * pending work is added.
  */
 static void check_busy_worker(struct btrfs_worker_thread *worker)
 {
 	if (worker->idle && atomic_read(&worker->num_pending) >=
 	    worker->workers->idle_thresh) {
 		unsigned long flags;
 		spin_lock_irqsave(&worker->workers->lock, flags);
 		worker->idle = 0;

 		if (!list_empty(&worker->worker_list)) {
 			list_move_tail(&worker->worker_list,
 				      &worker->workers->worker_list);
 		}
 		spin_unlock_irqrestore(&worker->workers->lock, flags);
 	}
 }

 static void check_pending_worker_creates(struct btrfs_worker_thread *worker)
 {
 	struct btrfs_workers *workers = worker->workers;
 	struct worker_start *start;
 	unsigned long flags;

 	rmb();
 	if (!workers->atomic_start_pending)
 		return;

 	start = kzalloc(sizeof(*start), GFP_NOFS);
 	if (!start)
 		return;

 	start->work.func = start_new_worker_func;
 	start->queue = workers;

 	spin_lock_irqsave(&workers->lock, flags);
 	if (!workers->atomic_start_pending)
 		goto out;

 	workers->atomic_start_pending = 0;
 	if (workers->num_workers + workers->num_workers_starting >=
 	    workers->max_workers)
 		goto out;

 	workers->num_workers_starting += 1;
 	spin_unlock_irqrestore(&workers->lock, flags);
 	btrfs_queue_worker(workers->atomic_worker_start, &start->work);
 	return;

 out:
 	kfree(start);
 	spin_unlock_irqrestore(&workers->lock, flags);
 }

 static noinline int run_ordered_completions(struct btrfs_workers *workers,
 					    struct btrfs_work *work)
 {
 	if (!workers->ordered)
 		return 0;

 	set_bit(WORK_DONE_BIT, &work->flags);

 	spin_lock(&workers->order_lock);

 	while (1) {
 		if (!list_empty(&workers->prio_order_list)) {
 			work = list_entry(workers->prio_order_list.next,
 					  struct btrfs_work, order_list);
 		} else if (!list_empty(&workers->order_list)) {
 			work = list_entry(workers->order_list.next,
 					  struct btrfs_work, order_list);
 		} else {
 			break;
 		}
 		if (!test_bit(WORK_DONE_BIT, &work->flags))
 			break;

 		/* we are going to call the ordered done function, but
 		 * we leave the work item on the list as a barrier so
 		 * that later work items that are done don't have their
 		 * functions called before this one returns
 		 */
 		if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
 			break;

 		spin_unlock(&workers->order_lock);

 		work->ordered_func(work);

 		/* now take the lock again and call the freeing code */
 		spin_lock(&workers->order_lock);
 		list_del(&work->order_list);
 		work->ordered_free(work);
 	}

 	spin_unlock(&workers->order_lock);
 	return 0;
 }

 static void put_worker(struct btrfs_worker_thread *worker)
 {
 	if (atomic_dec_and_test(&worker->refs))
 		kfree(worker);
 }

 static int try_worker_shutdown(struct btrfs_worker_thread *worker)
 {
 	int freeit = 0;

 	spin_lock_irq(&worker->lock);
 	spin_lock(&worker->workers->lock);
 	if (worker->workers->num_workers > 1 &&
 	    worker->idle &&
 	    !worker->working &&
 	    !list_empty(&worker->worker_list) &&
 	    list_empty(&worker->prio_pending) &&
 	    list_empty(&worker->pending) &&
 	    atomic_read(&worker->num_pending) == 0) {
 		freeit = 1;
 		list_del_init(&worker->worker_list);
 		worker->workers->num_workers--;
 	}
 	spin_unlock(&worker->workers->lock);
 	spin_unlock_irq(&worker->lock);

 	if (freeit)
 		put_worker(worker);
 	return freeit;
 }

 static struct btrfs_work *get_next_work(struct btrfs_worker_thread *worker,
 					struct list_head *prio_head,
 					struct list_head *head)
 {
 	struct btrfs_work *work = NULL;
 	struct list_head *cur = NULL;

 	if(!list_empty(prio_head))
 		cur = prio_head->next;

 	smp_mb();
 	if (!list_empty(&worker->prio_pending))
 		goto refill;

 	if (!list_empty(head))
 		cur = head->next;

 	if (cur)
 		goto out;

 refill:
 	spin_lock_irq(&worker->lock);
 	list_splice_tail_init(&worker->prio_pending, prio_head);
 	list_splice_tail_init(&worker->pending, head);

 	if (!list_empty(prio_head))
 		cur = prio_head->next;
 	else if (!list_empty(head))
 		cur = head->next;
 	spin_unlock_irq(&worker->lock);

 	if (!cur)
 		goto out_fail;

 out:
 	work = list_entry(cur, struct btrfs_work, list);

 out_fail:
 	return work;
 }

 /*
  * main loop for servicing work items
  */
 static int worker_loop(void *arg)
 {
 	struct btrfs_worker_thread *worker = arg;
 	struct list_head head;
 	struct list_head prio_head;
 	struct btrfs_work *work;

 	INIT_LIST_HEAD(&head);
 	INIT_LIST_HEAD(&prio_head);

 	do {
 again:
 		while (1) {


 			work = get_next_work(worker, &prio_head, &head);
 			if (!work)
 				break;

 			list_del(&work->list);
 			clear_bit(WORK_QUEUED_BIT, &work->flags);

 			work->worker = worker;

 			work->func(work);

 			atomic_dec(&worker->num_pending);
 			/*
 			 * unless this is an ordered work queue,
 			 * 'work' was probably freed by func above.
 			 */
 			run_ordered_completions(worker->workers, work);

 			check_pending_worker_creates(worker);
 			cond_resched();
 		}

 		spin_lock_irq(&worker->lock);
 		check_idle_worker(worker);

 		if (freezing(current)) {
 			worker->working = 0;
 			spin_unlock_irq(&worker->lock);
 			try_to_freeze();
 		} else {
 			spin_unlock_irq(&worker->lock);
 			if (!kthread_should_stop()) {
 				cpu_relax();
 				/*
 				 * we've dropped the lock, did someone else
 				 * jump_in?
 				 */
 				smp_mb();
 				if (!list_empty(&worker->pending) ||
 				    !list_empty(&worker->prio_pending))
 					continue;

 				/*
 				 * this short schedule allows more work to
 				 * come in without the queue functions
 				 * needing to go through wake_up_process()
 				 *
 				 * worker->working is still 1, so nobody
 				 * is going to try and wake us up
 				 */
 				schedule_timeout(1);
 				smp_mb();
 				if (!list_empty(&worker->pending) ||
 				    !list_empty(&worker->prio_pending))
 					continue;

 				if (kthread_should_stop())
 					break;

 				/* still no more work?, sleep for real */
 				spin_lock_irq(&worker->lock);
 				set_current_state(TASK_INTERRUPTIBLE);
 				if (!list_empty(&worker->pending) ||
 				    !list_empty(&worker->prio_pending)) {
 					spin_unlock_irq(&worker->lock);
 					set_current_state(TASK_RUNNING);
 					goto again;
 				}

 				/*
 				 * this makes sure we get a wakeup when someone
 				 * adds something new to the queue
 				 */
 				worker->working = 0;
 				spin_unlock_irq(&worker->lock);

 				if (!kthread_should_stop()) {
 					schedule_timeout(HZ * 120);
 					if (!worker->working &&
 					    try_worker_shutdown(worker)) {
 						return 0;
 					}
 				}
 			}
 			__set_current_state(TASK_RUNNING);
 		}
 	} while (!kthread_should_stop());
 	return 0;
 }

 /*
  * this will wait for all the worker threads to shutdown
  */
 int btrfs_stop_workers(struct btrfs_workers *workers)
 {
 	struct list_head *cur;
 	struct btrfs_worker_thread *worker;
 	int can_stop;

 	spin_lock_irq(&workers->lock);
 	list_splice_init(&workers->idle_list, &workers->worker_list);
 	while (!list_empty(&workers->worker_list)) {
 		cur = workers->worker_list.next;
 		worker = list_entry(cur, struct btrfs_worker_thread,
 				    worker_list);

 		atomic_inc(&worker->refs);
 		workers->num_workers -= 1;
 		if (!list_empty(&worker->worker_list)) {
 			list_del_init(&worker->worker_list);
 			put_worker(worker);
 			can_stop = 1;
 		} else
 			can_stop = 0;
 		spin_unlock_irq(&workers->lock);
 		if (can_stop)
 			kthread_stop(worker->task);
 		spin_lock_irq(&workers->lock);
 		put_worker(worker);
 	}
 	spin_unlock_irq(&workers->lock);
 	return 0;
 }

 /*
  * simple init on struct btrfs_workers
  */
 void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max,
 			struct btrfs_workers *async_helper)
 {
 	workers->num_workers = 0;
 	workers->num_workers_starting = 0;
 	INIT_LIST_HEAD(&workers->worker_list);
 	INIT_LIST_HEAD(&workers->idle_list);
 	INIT_LIST_HEAD(&workers->order_list);
 	INIT_LIST_HEAD(&workers->prio_order_list);
 	spin_lock_init(&workers->lock);
 	spin_lock_init(&workers->order_lock);
 	workers->max_workers = max;
 	workers->idle_thresh = 32;
 	workers->name = name;
 	workers->ordered = 0;
 	workers->atomic_start_pending = 0;
 	workers->atomic_worker_start = async_helper;
 }

 /*
  * starts new worker threads.  This does not enforce the max worker
  * count in case you need to temporarily go past it.
  */
 static int __btrfs_start_workers(struct btrfs_workers *workers)
 {
 	struct btrfs_worker_thread *worker;
 	int ret = 0;

 	worker = kzalloc(sizeof(*worker), GFP_NOFS);
 	if (!worker) {
 		ret = -ENOMEM;
 		goto fail;
 	}

 	INIT_LIST_HEAD(&worker->pending);
 	INIT_LIST_HEAD(&worker->prio_pending);
 	INIT_LIST_HEAD(&worker->worker_list);
 	spin_lock_init(&worker->lock);

 	atomic_set(&worker->num_pending, 0);
 	atomic_set(&worker->refs, 1);
 	worker->workers = workers;
 	worker->task = kthread_run(worker_loop, worker,
 				   "btrfs-%s-%d", workers->name,
 				   workers->num_workers + 1);
 	if (IS_ERR(worker->task)) {
 		ret = PTR_ERR(worker->task);
 		kfree(worker);
 		goto fail;
 	}
 	spin_lock_irq(&workers->lock);
 	list_add_tail(&worker->worker_list, &workers->idle_list);
 	worker->idle = 1;
 	workers->num_workers++;
 	workers->num_workers_starting--;
 	WARN_ON(workers->num_workers_starting < 0);
 	spin_unlock_irq(&workers->lock);

 	return 0;
 fail:
 	spin_lock_irq(&workers->lock);
 	workers->num_workers_starting--;
 	spin_unlock_irq(&workers->lock);
 	return ret;
 }

 int btrfs_start_workers(struct btrfs_workers *workers)
 {
 	spin_lock_irq(&workers->lock);
 	workers->num_workers_starting++;
 	spin_unlock_irq(&workers->lock);
 	return __btrfs_start_workers(workers);
 }

 /*
  * run through the list and find a worker thread that doesn't have a lot
  * to do right now.  This can return null if we aren't yet at the thread
  * count limit and all of the threads are busy.
  */
 static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
 {
 	struct btrfs_worker_thread *worker;
 	struct list_head *next;
 	int enforce_min;

 	enforce_min = (workers->num_workers + workers->num_workers_starting) <
 		workers->max_workers;

 	/*
 	 * if we find an idle thread, don't move it to the end of the
 	 * idle list.  This improves the chance that the next submission
 	 * will reuse the same thread, and maybe catch it while it is still
 	 * working
 	 */
 	if (!list_empty(&workers->idle_list)) {
 		next = workers->idle_list.next;
 		worker = list_entry(next, struct btrfs_worker_thread,
 				    worker_list);
 		return worker;
 	}
 	if (enforce_min || list_empty(&workers->worker_list))
 		return NULL;

 	/*
 	 * if we pick a busy task, move the task to the end of the list.
 	 * hopefully this will keep things somewhat evenly balanced.
 	 * Do the move in batches based on the sequence number.  This groups
 	 * requests submitted at roughly the same time onto the same worker.
 	 */
 	next = workers->worker_list.next;
 	worker = list_entry(next, struct btrfs_worker_thread, worker_list);
 	worker->sequence++;

 	if (worker->sequence % workers->idle_thresh == 0)
 		list_move_tail(next, &workers->worker_list);
 	return worker;
 }

 /*
  * selects a worker thread to take the next job.  This will either find
  * an idle worker, start a new worker up to the max count, or just return
  * one of the existing busy workers.
  */
 static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
 {
 	struct btrfs_worker_thread *worker;
 	unsigned long flags;
 	struct list_head *fallback;
 	int ret;

 	spin_lock_irqsave(&workers->lock, flags);
 again:
 	worker = next_worker(workers);

 	if (!worker) {
 		if (workers->num_workers + workers->num_workers_starting >=
 		    workers->max_workers) {
 			goto fallback;
 		} else if (workers->atomic_worker_start) {
 			workers->atomic_start_pending = 1;
 			goto fallback;
 		} else {
 			workers->num_workers_starting++;
 			spin_unlock_irqrestore(&workers->lock, flags);
 			/* we're below the limit, start another worker */
 			ret = __btrfs_start_workers(workers);
 			spin_lock_irqsave(&workers->lock, flags);
 			if (ret)
 				goto fallback;
 			goto again;
 		}
 	}
 	goto found;

 fallback:
 	fallback = NULL;
 	/*
 	 * we have failed to find any workers, just
 	 * return the first one we can find.
 	 */
 	if (!list_empty(&workers->worker_list))
 		fallback = workers->worker_list.next;
 	if (!list_empty(&workers->idle_list))
 		fallback = workers->idle_list.next;
 	BUG_ON(!fallback);
 	worker = list_entry(fallback,
 		  struct btrfs_worker_thread, worker_list);
 found:
 	/*
 	 * this makes sure the worker doesn't exit before it is placed
 	 * onto a busy/idle list
 	 */
 	atomic_inc(&worker->num_pending);
 	spin_unlock_irqrestore(&workers->lock, flags);
 	return worker;
 }

 /*
  * btrfs_requeue_work just puts the work item back on the tail of the list
  * it was taken from.  It is intended for use with long running work functions
  * that make some progress and want to give the cpu up for others.
  */
 int btrfs_requeue_work(struct btrfs_work *work)
 {
 	struct btrfs_worker_thread *worker = work->worker;
 	unsigned long flags;
 	int wake = 0;

 	if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
 		goto out;

 	spin_lock_irqsave(&worker->lock, flags);
 	if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
 		list_add_tail(&work->list, &worker->prio_pending);
 	else
 		list_add_tail(&work->list, &worker->pending);
 	atomic_inc(&worker->num_pending);

 	/* by definition we're busy, take ourselves off the idle
 	 * list
 	 */
 	if (worker->idle) {
 		spin_lock(&worker->workers->lock);
 		worker->idle = 0;
 		list_move_tail(&worker->worker_list,
 			      &worker->workers->worker_list);
 		spin_unlock(&worker->workers->lock);
 	}
 	if (!worker->working) {
 		wake = 1;
 		worker->working = 1;
 	}

 	if (wake)
 		wake_up_process(worker->task);
 	spin_unlock_irqrestore(&worker->lock, flags);
 out:

 	return 0;
 }

 void btrfs_set_work_high_prio(struct btrfs_work *work)
 {
 	set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
 }

 /*
  * places a struct btrfs_work into the pending queue of one of the kthreads
  */
 void btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
 {
 	struct btrfs_worker_thread *worker;
 	unsigned long flags;
 	int wake = 0;

 	/* don't requeue something already on a list */
 	if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
 		return;

 	worker = find_worker(workers);
 	if (workers->ordered) {
 		/*
 		 * you're not allowed to do ordered queues from an
 		 * interrupt handler
 		 */
 		spin_lock(&workers->order_lock);
 		if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags)) {
 			list_add_tail(&work->order_list,
 				      &workers->prio_order_list);
 		} else {
 			list_add_tail(&work->order_list, &workers->order_list);
 		}
 		spin_unlock(&workers->order_lock);
 	} else {
 		INIT_LIST_HEAD(&work->order_list);
 	}

 	spin_lock_irqsave(&worker->lock, flags);

 	if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
 		list_add_tail(&work->list, &worker->prio_pending);
 	else
 		list_add_tail(&work->list, &worker->pending);
 	check_busy_worker(worker);

 	/*
 	 * avoid calling into wake_up_process if this thread has already
 	 * been kicked
 	 */
 	if (!worker->working)
 		wake = 1;
 	worker->working = 1;

 	if (wake)
 		wake_up_process(worker->task);
 	spin_unlock_irqrestore(&worker->lock, flags);
 }
	/*
	* Copyright (C) 2007 Oracle. All rights reserved.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public
	* License v2 as published by the Free Software Foundation.
	*
	* This program 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 this program; if not, write to the
	* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	* Boston, MA 021110-1307, USA.
	*/

	#include <linux/kthread.h>
	#include <linux/slab.h>
	#include <linux/list.h>
	#include <linux/spinlock.h>
	#include <linux/freezer.h>
	#include "async-thread.h"

	#define WORK_QUEUED_BIT 0
	#define WORK_DONE_BIT 1
	#define WORK_ORDER_DONE_BIT 2
	#define WORK_HIGH_PRIO_BIT 3

	/*
	* container for the kthread task pointer and the list of pending work
	* One of these is allocated per thread.
	*/
	struct btrfs_worker_thread {
	/* pool we belong to */
	struct btrfs_workers *workers;

	/* list of struct btrfs_work that are waiting for service */
	struct list_head pending;
	struct list_head prio_pending;

	/* list of worker threads from struct btrfs_workers */
	struct list_head worker_list;

	/* kthread */
	struct task_struct *task;

	/* number of things on the pending list */
	atomic_t num_pending;

	/* reference counter for this struct */
	atomic_t refs;

	unsigned long sequence;

	/* protects the pending list. */
	spinlock_t lock;

	/* set to non-zero when this thread is already awake and kicking */
	int working;

	/* are we currently idle */
	int idle;
	};

	static int __btrfs_start_workers(struct btrfs_workers *workers);

	/*
	* btrfs_start_workers uses kthread_run, which can block waiting for memory
	* for a very long time. It will actually throttle on page writeback,
	* and so it may not make progress until after our btrfs worker threads
	* process all of the pending work structs in their queue
	*
	* This means we can't use btrfs_start_workers from inside a btrfs worker
	* thread that is used as part of cleaning dirty memory, which pretty much
	* involves all of the worker threads.
	*
	* Instead we have a helper queue who never has more than one thread
	* where we scheduler thread start operations. This worker_start struct
	* is used to contain the work and hold a pointer to the queue that needs
	* another worker.
	*/
	struct worker_start {
	struct btrfs_work work;
	struct btrfs_workers *queue;
	};

	static void start_new_worker_func(struct btrfs_work *work)
	{
	struct worker_start *start;
	start = container_of(work, struct worker_start, work);
	__btrfs_start_workers(start->queue);
	kfree(start);
	}

	/*
	* helper function to move a thread onto the idle list after it
	* has finished some requests.
	*/
	static void check_idle_worker(struct btrfs_worker_thread *worker)
	{
	if (!worker->idle && atomic_read(&worker->num_pending) <
	worker->workers->idle_thresh / 2) {
	unsigned long flags;
	spin_lock_irqsave(&worker->workers->lock, flags);
	worker->idle = 1;

	/* the list may be empty if the worker is just starting */
	if (!list_empty(&worker->worker_list)) {
	list_move(&worker->worker_list,
	&worker->workers->idle_list);
	}
	spin_unlock_irqrestore(&worker->workers->lock, flags);
	}
	}

	/*
	* helper function to move a thread off the idle list after new
	* pending work is added.
	*/
	static void check_busy_worker(struct btrfs_worker_thread *worker)
	{
	if (worker->idle && atomic_read(&worker->num_pending) >=
	worker->workers->idle_thresh) {
	unsigned long flags;
	spin_lock_irqsave(&worker->workers->lock, flags);
	worker->idle = 0;

	if (!list_empty(&worker->worker_list)) {
	list_move_tail(&worker->worker_list,
	&worker->workers->worker_list);
	}
	spin_unlock_irqrestore(&worker->workers->lock, flags);
	}
	}

	static void check_pending_worker_creates(struct btrfs_worker_thread *worker)
	{
	struct btrfs_workers *workers = worker->workers;
	struct worker_start *start;
	unsigned long flags;

	rmb();
	if (!workers->atomic_start_pending)
	return;

	start = kzalloc(sizeof(*start), GFP_NOFS);
	if (!start)
	return;

	start->work.func = start_new_worker_func;
	start->queue = workers;

	spin_lock_irqsave(&workers->lock, flags);
	if (!workers->atomic_start_pending)
	goto out;

	workers->atomic_start_pending = 0;
	if (workers->num_workers + workers->num_workers_starting >=
	workers->max_workers)
	goto out;

	workers->num_workers_starting += 1;
	spin_unlock_irqrestore(&workers->lock, flags);
	btrfs_queue_worker(workers->atomic_worker_start, &start->work);
	return;

	out:
	kfree(start);
	spin_unlock_irqrestore(&workers->lock, flags);
	}

	static noinline int run_ordered_completions(struct btrfs_workers *workers,
	struct btrfs_work *work)
	{
	if (!workers->ordered)
	return 0;

	set_bit(WORK_DONE_BIT, &work->flags);

	spin_lock(&workers->order_lock);

	while (1) {
	if (!list_empty(&workers->prio_order_list)) {
	work = list_entry(workers->prio_order_list.next,
	struct btrfs_work, order_list);
	} else if (!list_empty(&workers->order_list)) {
	work = list_entry(workers->order_list.next,
	struct btrfs_work, order_list);
	} else {
	break;
	}
	if (!test_bit(WORK_DONE_BIT, &work->flags))
	break;

	/* we are going to call the ordered done function, but
	* we leave the work item on the list as a barrier so
	* that later work items that are done don't have their
	* functions called before this one returns
	*/
	if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
	break;

	spin_unlock(&workers->order_lock);

	work->ordered_func(work);

	/* now take the lock again and call the freeing code */
	spin_lock(&workers->order_lock);
	list_del(&work->order_list);
	work->ordered_free(work);
	}

	spin_unlock(&workers->order_lock);
	return 0;
	}

	static void put_worker(struct btrfs_worker_thread *worker)
	{
	if (atomic_dec_and_test(&worker->refs))
	kfree(worker);
	}

	static int try_worker_shutdown(struct btrfs_worker_thread *worker)
	{
	int freeit = 0;

	spin_lock_irq(&worker->lock);
	spin_lock(&worker->workers->lock);
	if (worker->workers->num_workers > 1 &&
	worker->idle &&
	!worker->working &&
	!list_empty(&worker->worker_list) &&
	list_empty(&worker->prio_pending) &&
	list_empty(&worker->pending) &&
	atomic_read(&worker->num_pending) == 0) {
	freeit = 1;
	list_del_init(&worker->worker_list);
	worker->workers->num_workers--;
	}
	spin_unlock(&worker->workers->lock);
	spin_unlock_irq(&worker->lock);

	if (freeit)
	put_worker(worker);
	return freeit;
	}

	static struct btrfs_work get_next_work(struct btrfs_worker_thread worker,
	struct list_head *prio_head,
	struct list_head *head)
	{
	struct btrfs_work *work = NULL;
	struct list_head *cur = NULL;

	if(!list_empty(prio_head))
	cur = prio_head->next;

	smp_mb();
	if (!list_empty(&worker->prio_pending))
	goto refill;

	if (!list_empty(head))
	cur = head->next;

	if (cur)
	goto out;

	refill:
	spin_lock_irq(&worker->lock);
	list_splice_tail_init(&worker->prio_pending, prio_head);
	list_splice_tail_init(&worker->pending, head);

	if (!list_empty(prio_head))
	cur = prio_head->next;
	else if (!list_empty(head))
	cur = head->next;
	spin_unlock_irq(&worker->lock);

	if (!cur)
	goto out_fail;

	out:
	work = list_entry(cur, struct btrfs_work, list);

	out_fail:
	return work;
	}

	/*
	* main loop for servicing work items
	*/
	static int worker_loop(void *arg)
	{
	struct btrfs_worker_thread *worker = arg;
	struct list_head head;
	struct list_head prio_head;
	struct btrfs_work *work;

	INIT_LIST_HEAD(&head);
	INIT_LIST_HEAD(&prio_head);

	do {
	again:
	while (1) {


	work = get_next_work(worker, &prio_head, &head);
	if (!work)
	break;

	list_del(&work->list);
	clear_bit(WORK_QUEUED_BIT, &work->flags);

	work->worker = worker;

	work->func(work);

	atomic_dec(&worker->num_pending);
	/*
	* unless this is an ordered work queue,
	* 'work' was probably freed by func above.
	*/
	run_ordered_completions(worker->workers, work);

	check_pending_worker_creates(worker);
	cond_resched();
	}

	spin_lock_irq(&worker->lock);
	check_idle_worker(worker);

	if (freezing(current)) {
	worker->working = 0;
	spin_unlock_irq(&worker->lock);
	try_to_freeze();
	} else {
	spin_unlock_irq(&worker->lock);
	if (!kthread_should_stop()) {
	cpu_relax();
	/*
	* we've dropped the lock, did someone else
	* jump_in?
	*/
	smp_mb();
	if (!list_empty(&worker->pending) \|\|
	!list_empty(&worker->prio_pending))
	continue;

	/*
	* this short schedule allows more work to
	* come in without the queue functions
	* needing to go through wake_up_process()
	*
	* worker->working is still 1, so nobody
	* is going to try and wake us up
	*/
	schedule_timeout(1);
	smp_mb();
	if (!list_empty(&worker->pending) \|\|
	!list_empty(&worker->prio_pending))
	continue;

	if (kthread_should_stop())
	break;

	/* still no more work?, sleep for real */
	spin_lock_irq(&worker->lock);
	set_current_state(TASK_INTERRUPTIBLE);
	if (!list_empty(&worker->pending) \|\|
	!list_empty(&worker->prio_pending)) {
	spin_unlock_irq(&worker->lock);
	set_current_state(TASK_RUNNING);
	goto again;
	}

	/*
	* this makes sure we get a wakeup when someone
	* adds something new to the queue
	*/
	worker->working = 0;
	spin_unlock_irq(&worker->lock);

	if (!kthread_should_stop()) {
	schedule_timeout(HZ * 120);
	if (!worker->working &&
	try_worker_shutdown(worker)) {
	return 0;
	}
	}
	}
	__set_current_state(TASK_RUNNING);
	}
	} while (!kthread_should_stop());
	return 0;
	}

	/*
	* this will wait for all the worker threads to shutdown
	*/
	int btrfs_stop_workers(struct btrfs_workers *workers)
	{
	struct list_head *cur;
	struct btrfs_worker_thread *worker;
	int can_stop;

	spin_lock_irq(&workers->lock);
	list_splice_init(&workers->idle_list, &workers->worker_list);
	while (!list_empty(&workers->worker_list)) {
	cur = workers->worker_list.next;
	worker = list_entry(cur, struct btrfs_worker_thread,
	worker_list);

	atomic_inc(&worker->refs);
	workers->num_workers -= 1;
	if (!list_empty(&worker->worker_list)) {
	list_del_init(&worker->worker_list);
	put_worker(worker);
	can_stop = 1;
	} else
	can_stop = 0;
	spin_unlock_irq(&workers->lock);
	if (can_stop)
	kthread_stop(worker->task);
	spin_lock_irq(&workers->lock);
	put_worker(worker);
	}
	spin_unlock_irq(&workers->lock);
	return 0;
	}

	/*
	* simple init on struct btrfs_workers
	*/
	void btrfs_init_workers(struct btrfs_workers workers, char name, int max,
	struct btrfs_workers *async_helper)
	{
	workers->num_workers = 0;
	workers->num_workers_starting = 0;
	INIT_LIST_HEAD(&workers->worker_list);
	INIT_LIST_HEAD(&workers->idle_list);
	INIT_LIST_HEAD(&workers->order_list);
	INIT_LIST_HEAD(&workers->prio_order_list);
	spin_lock_init(&workers->lock);
	spin_lock_init(&workers->order_lock);
	workers->max_workers = max;
	workers->idle_thresh = 32;
	workers->name = name;
	workers->ordered = 0;
	workers->atomic_start_pending = 0;
	workers->atomic_worker_start = async_helper;
	}

	/*
	* starts new worker threads. This does not enforce the max worker
	* count in case you need to temporarily go past it.
	*/
	static int __btrfs_start_workers(struct btrfs_workers *workers)
	{
	struct btrfs_worker_thread *worker;
	int ret = 0;

	worker = kzalloc(sizeof(*worker), GFP_NOFS);
	if (!worker) {
	ret = -ENOMEM;
	goto fail;
	}

	INIT_LIST_HEAD(&worker->pending);
	INIT_LIST_HEAD(&worker->prio_pending);
	INIT_LIST_HEAD(&worker->worker_list);
	spin_lock_init(&worker->lock);

	atomic_set(&worker->num_pending, 0);
	atomic_set(&worker->refs, 1);
	worker->workers = workers;
	worker->task = kthread_run(worker_loop, worker,
	"btrfs-%s-%d", workers->name,
	workers->num_workers + 1);
	if (IS_ERR(worker->task)) {
	ret = PTR_ERR(worker->task);
	kfree(worker);
	goto fail;
	}
	spin_lock_irq(&workers->lock);
	list_add_tail(&worker->worker_list, &workers->idle_list);
	worker->idle = 1;
	workers->num_workers++;
	workers->num_workers_starting--;
	WARN_ON(workers->num_workers_starting < 0);
	spin_unlock_irq(&workers->lock);

	return 0;
	fail:
	spin_lock_irq(&workers->lock);
	workers->num_workers_starting--;
	spin_unlock_irq(&workers->lock);
	return ret;
	}

	int btrfs_start_workers(struct btrfs_workers *workers)
	{
	spin_lock_irq(&workers->lock);
	workers->num_workers_starting++;
	spin_unlock_irq(&workers->lock);
	return __btrfs_start_workers(workers);
	}

	/*
	* run through the list and find a worker thread that doesn't have a lot
	* to do right now. This can return null if we aren't yet at the thread
	* count limit and all of the threads are busy.
	*/
	static struct btrfs_worker_thread next_worker(struct btrfs_workers workers)
	{
	struct btrfs_worker_thread *worker;
	struct list_head *next;
	int enforce_min;

	enforce_min = (workers->num_workers + workers->num_workers_starting) <
	workers->max_workers;

	/*
	* if we find an idle thread, don't move it to the end of the
	* idle list. This improves the chance that the next submission
	* will reuse the same thread, and maybe catch it while it is still
	* working
	*/
	if (!list_empty(&workers->idle_list)) {
	next = workers->idle_list.next;
	worker = list_entry(next, struct btrfs_worker_thread,
	worker_list);
	return worker;
	}
	if (enforce_min \|\| list_empty(&workers->worker_list))
	return NULL;

	/*
	* if we pick a busy task, move the task to the end of the list.
	* hopefully this will keep things somewhat evenly balanced.
	* Do the move in batches based on the sequence number. This groups
	* requests submitted at roughly the same time onto the same worker.
	*/
	next = workers->worker_list.next;
	worker = list_entry(next, struct btrfs_worker_thread, worker_list);
	worker->sequence++;

	if (worker->sequence % workers->idle_thresh == 0)
	list_move_tail(next, &workers->worker_list);
	return worker;
	}

	/*
	* selects a worker thread to take the next job. This will either find
	* an idle worker, start a new worker up to the max count, or just return
	* one of the existing busy workers.
	*/
	static struct btrfs_worker_thread find_worker(struct btrfs_workers workers)
	{
	struct btrfs_worker_thread *worker;
	unsigned long flags;
	struct list_head *fallback;
	int ret;

	spin_lock_irqsave(&workers->lock, flags);
	again:
	worker = next_worker(workers);

	if (!worker) {
	if (workers->num_workers + workers->num_workers_starting >=
	workers->max_workers) {
	goto fallback;
	} else if (workers->atomic_worker_start) {
	workers->atomic_start_pending = 1;
	goto fallback;
	} else {
	workers->num_workers_starting++;
	spin_unlock_irqrestore(&workers->lock, flags);
	/* we're below the limit, start another worker */
	ret = __btrfs_start_workers(workers);
	spin_lock_irqsave(&workers->lock, flags);
	if (ret)
	goto fallback;
	goto again;
	}
	}
	goto found;

	fallback:
	fallback = NULL;
	/*
	* we have failed to find any workers, just
	* return the first one we can find.
	*/
	if (!list_empty(&workers->worker_list))
	fallback = workers->worker_list.next;
	if (!list_empty(&workers->idle_list))
	fallback = workers->idle_list.next;
	BUG_ON(!fallback);
	worker = list_entry(fallback,
	struct btrfs_worker_thread, worker_list);
	found:
	/*
	* this makes sure the worker doesn't exit before it is placed
	* onto a busy/idle list
	*/
	atomic_inc(&worker->num_pending);
	spin_unlock_irqrestore(&workers->lock, flags);
	return worker;
	}

	/*
	* btrfs_requeue_work just puts the work item back on the tail of the list
	* it was taken from. It is intended for use with long running work functions
	* that make some progress and want to give the cpu up for others.
	*/
	int btrfs_requeue_work(struct btrfs_work *work)
	{
	struct btrfs_worker_thread *worker = work->worker;
	unsigned long flags;
	int wake = 0;

	if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
	goto out;

	spin_lock_irqsave(&worker->lock, flags);
	if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
	list_add_tail(&work->list, &worker->prio_pending);
	else
	list_add_tail(&work->list, &worker->pending);
	atomic_inc(&worker->num_pending);

	/* by definition we're busy, take ourselves off the idle
	* list
	*/
	if (worker->idle) {
	spin_lock(&worker->workers->lock);
	worker->idle = 0;
	list_move_tail(&worker->worker_list,
	&worker->workers->worker_list);
	spin_unlock(&worker->workers->lock);
	}
	if (!worker->working) {
	wake = 1;
	worker->working = 1;
	}

	if (wake)
	wake_up_process(worker->task);
	spin_unlock_irqrestore(&worker->lock, flags);
	out:

	return 0;
	}

	void btrfs_set_work_high_prio(struct btrfs_work *work)
	{
	set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
	}

	/*
	* places a struct btrfs_work into the pending queue of one of the kthreads
	*/
	void btrfs_queue_worker(struct btrfs_workers workers, struct btrfs_work work)
	{
	struct btrfs_worker_thread *worker;
	unsigned long flags;
	int wake = 0;

	/* don't requeue something already on a list */
	if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
	return;

	worker = find_worker(workers);
	if (workers->ordered) {
	/*
	* you're not allowed to do ordered queues from an
	* interrupt handler
	*/
	spin_lock(&workers->order_lock);
	if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags)) {
	list_add_tail(&work->order_list,
	&workers->prio_order_list);
	} else {
	list_add_tail(&work->order_list, &workers->order_list);
	}
	spin_unlock(&workers->order_lock);
	} else {
	INIT_LIST_HEAD(&work->order_list);
	}

	spin_lock_irqsave(&worker->lock, flags);

	if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
	list_add_tail(&work->list, &worker->prio_pending);
	else
	list_add_tail(&work->list, &worker->pending);
	check_busy_worker(worker);

	/*
	* avoid calling into wake_up_process if this thread has already
	* been kicked
	*/
	if (!worker->working)
	wake = 1;
	worker->working = 1;

	if (wake)
	wake_up_process(worker->task);
	spin_unlock_irqrestore(&worker->lock, flags);
	}