/*

   *  CFQ, or complete fairness queueing, disk scheduler.
   *
   *  Based on ideas from a previously unfinished io
   *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
   *

   *  Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>

   */

  #include <linux/module.h>

  #include <linux/blkdev.h>
  #include <linux/elevator.h>

  #include <linux/rbtree.h>

  #include <linux/ioprio.h>

  #include <linux/blktrace_api.h>

  
  /*
   * tunables
   */

  /* max queue in one round of service */
  static const int cfq_quantum = 4;

  static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };

  /* maximum backwards seek, in KiB */
  static const int cfq_back_max = 16 * 1024;
  /* penalty of a backwards seek */
  static const int cfq_back_penalty = 2;

  static const int cfq_slice_sync = HZ / 10;

  static int cfq_slice_async = HZ / 25;

  static const int cfq_slice_async_rq = 2;

  static int cfq_slice_idle = HZ / 125;

  /*

   * offset from end of service tree

   */

  #define CFQ_IDLE_DELAY		(HZ / 5)

  
  /*
   * below this threshold, we consider thinktime immediate
   */
  #define CFQ_MIN_TT		(2)

  #define CFQ_SLICE_SCALE		(5)

  #define CFQ_HW_QUEUE_MIN	(5)

  #define RQ_CIC(rq)		\
  	((struct cfq_io_context *) (rq)->elevator_private)

  #define RQ_CFQQ(rq)		(struct cfq_queue *) ((rq)->elevator_private2)

  static struct kmem_cache *cfq_pool;
  static struct kmem_cache *cfq_ioc_pool;

  static DEFINE_PER_CPU(unsigned long, ioc_count);

  static struct completion *ioc_gone;

  static DEFINE_SPINLOCK(ioc_gone_lock);

  #define CFQ_PRIO_LISTS		IOPRIO_BE_NR
  #define cfq_class_idle(cfqq)	((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)

  #define cfq_class_rt(cfqq)	((cfqq)->ioprio_class == IOPRIO_CLASS_RT)

  #define sample_valid(samples)	((samples) > 80)

  /*

   * Most of our rbtree usage is for sorting with min extraction, so
   * if we cache the leftmost node we don't have to walk down the tree
   * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
   * move this into the elevator for the rq sorting as well.
   */
  struct cfq_rb_root {
  	struct rb_root rb;
  	struct rb_node *left;
  };
  #define CFQ_RB_ROOT	(struct cfq_rb_root) { RB_ROOT, NULL, }
  
  /*

   * Per process-grouping structure
   */
  struct cfq_queue {
  	/* reference count */
  	atomic_t ref;
  	/* various state flags, see below */
  	unsigned int flags;
  	/* parent cfq_data */
  	struct cfq_data *cfqd;
  	/* service_tree member */
  	struct rb_node rb_node;
  	/* service_tree key */
  	unsigned long rb_key;
  	/* prio tree member */
  	struct rb_node p_node;
  	/* prio tree root we belong to, if any */
  	struct rb_root *p_root;
  	/* sorted list of pending requests */
  	struct rb_root sort_list;
  	/* if fifo isn't expired, next request to serve */
  	struct request *next_rq;
  	/* requests queued in sort_list */
  	int queued[2];
  	/* currently allocated requests */
  	int allocated[2];
  	/* fifo list of requests in sort_list */
  	struct list_head fifo;
  
  	unsigned long slice_end;
  	long slice_resid;
  	unsigned int slice_dispatch;
  
  	/* pending metadata requests */
  	int meta_pending;
  	/* number of requests that are on the dispatch list or inside driver */
  	int dispatched;
  
  	/* io prio of this group */
  	unsigned short ioprio, org_ioprio;
  	unsigned short ioprio_class, org_ioprio_class;
  
  	pid_t pid;
  };
  
  /*

   * Per block device queue structure
   */

  struct cfq_data {

  	struct request_queue *queue;

  
  	/*
  	 * rr list of queues with requests and the count of them
  	 */

  	struct cfq_rb_root service_tree;

  
  	/*
  	 * Each priority tree is sorted by next_request position.  These
  	 * trees are used when determining if two or more queues are
  	 * interleaving requests (see cfq_close_cooperator).
  	 */
  	struct rb_root prio_trees[CFQ_PRIO_LISTS];

  	unsigned int busy_queues;

  	/*
  	 * Used to track any pending rt requests so we can pre-empt current
  	 * non-RT cfqq in service when this value is non-zero.
  	 */
  	unsigned int busy_rt_queues;

  	int rq_in_driver;

  	int sync_flight;

  
  	/*
  	 * queue-depth detection
  	 */
  	int rq_queued;

  	int hw_tag;

  	int hw_tag_samples;
  	int rq_in_driver_peak;

  	/*

  	 * idle window management
  	 */
  	struct timer_list idle_slice_timer;
  	struct work_struct unplug_work;

  	struct cfq_queue *active_queue;
  	struct cfq_io_context *active_cic;

  	/*
  	 * async queue for each priority case
  	 */
  	struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
  	struct cfq_queue *async_idle_cfqq;

  	sector_t last_position;

  	/*
  	 * tunables, see top of file
  	 */
  	unsigned int cfq_quantum;

  	unsigned int cfq_fifo_expire[2];

  	unsigned int cfq_back_penalty;
  	unsigned int cfq_back_max;

  	unsigned int cfq_slice[2];
  	unsigned int cfq_slice_async_rq;
  	unsigned int cfq_slice_idle;

  
  	struct list_head cic_list;

  	/*
  	 * Fallback dummy cfqq for extreme OOM conditions
  	 */
  	struct cfq_queue oom_cfqq;

  };

  enum cfqq_state_flags {

  	CFQ_CFQQ_FLAG_on_rr = 0,	/* on round-robin busy list */
  	CFQ_CFQQ_FLAG_wait_request,	/* waiting for a request */

  	CFQ_CFQQ_FLAG_must_dispatch,	/* must be allowed a dispatch */

  	CFQ_CFQQ_FLAG_must_alloc,	/* must be allowed rq alloc */
  	CFQ_CFQQ_FLAG_must_alloc_slice,	/* per-slice must_alloc flag */

  	CFQ_CFQQ_FLAG_fifo_expire,	/* FIFO checked in this slice */
  	CFQ_CFQQ_FLAG_idle_window,	/* slice idling enabled */
  	CFQ_CFQQ_FLAG_prio_changed,	/* task priority has changed */

  	CFQ_CFQQ_FLAG_slice_new,	/* no requests dispatched in slice */

  	CFQ_CFQQ_FLAG_sync,		/* synchronous queue */

  	CFQ_CFQQ_FLAG_coop,		/* has done a coop jump of the queue */

  };
  
  #define CFQ_CFQQ_FNS(name)						\
  static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)		\
  {									\

  	(cfqq)->flags |= (1 << CFQ_CFQQ_FLAG_##name);			\

  }									\
  static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)	\
  {									\

  	(cfqq)->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);			\

  }									\
  static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)		\
  {									\

  	return ((cfqq)->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;	\

  }
  
  CFQ_CFQQ_FNS(on_rr);
  CFQ_CFQQ_FNS(wait_request);

  CFQ_CFQQ_FNS(must_dispatch);

  CFQ_CFQQ_FNS(must_alloc);
  CFQ_CFQQ_FNS(must_alloc_slice);

  CFQ_CFQQ_FNS(fifo_expire);
  CFQ_CFQQ_FNS(idle_window);
  CFQ_CFQQ_FNS(prio_changed);

  CFQ_CFQQ_FNS(slice_new);

  CFQ_CFQQ_FNS(sync);

  CFQ_CFQQ_FNS(coop);

  #undef CFQ_CFQQ_FNS

  #define cfq_log_cfqq(cfqd, cfqq, fmt, args...)	\
  	blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)
  #define cfq_log(cfqd, fmt, args...)	\
  	blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)

  static void cfq_dispatch_insert(struct request_queue *, struct request *);

  static struct cfq_queue *cfq_get_queue(struct cfq_data *, int,

  				       struct io_context *, gfp_t);

  static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,

  						struct io_context *);
  
  static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,
  					    int is_sync)
  {
  	return cic->cfqq[!!is_sync];
  }
  
  static inline void cic_set_cfqq(struct cfq_io_context *cic,
  				struct cfq_queue *cfqq, int is_sync)
  {
  	cic->cfqq[!!is_sync] = cfqq;
  }
  
  /*
   * We regard a request as SYNC, if it's either a read or has the SYNC bit
   * set (in which case it could also be direct WRITE).
   */
  static inline int cfq_bio_sync(struct bio *bio)
  {
  	if (bio_data_dir(bio) == READ || bio_sync(bio))
  		return 1;
  
  	return 0;
  }

  /*

   * scheduler run of queue, if there are requests pending and no one in the
   * driver that will restart queueing
   */
  static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
  {

  	if (cfqd->busy_queues) {
  		cfq_log(cfqd, "schedule dispatch");

  		kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);

  	}

  }

  static int cfq_queue_empty(struct request_queue *q)

  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	return !cfqd->busy_queues;

  }

  /*

   * Scale schedule slice based on io priority. Use the sync time slice only
   * if a queue is marked sync and has sync io queued. A sync queue with async
   * io only, should not get full sync slice length.
   */

  static inline int cfq_prio_slice(struct cfq_data *cfqd, int sync,
  				 unsigned short prio)

  {

  	const int base_slice = cfqd->cfq_slice[sync];

  	WARN_ON(prio >= IOPRIO_BE_NR);
  
  	return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
  }

  static inline int
  cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);

  }
  
  static inline void
  cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;

  	cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);

  }
  
  /*
   * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
   * isn't valid until the first request from the dispatch is activated
   * and the slice time set.
   */
  static inline int cfq_slice_used(struct cfq_queue *cfqq)
  {
  	if (cfq_cfqq_slice_new(cfqq))
  		return 0;
  	if (time_before(jiffies, cfqq->slice_end))
  		return 0;
  
  	return 1;
  }
  
  /*

   * Lifted from AS - choose which of rq1 and rq2 that is best served now.

   * We choose the request that is closest to the head right now. Distance

   * behind the head is penalized and only allowed to a certain extent.

   */

  static struct request *
  cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2)

  {
  	sector_t last, s1, s2, d1 = 0, d2 = 0;

  	unsigned long back_max;

  #define CFQ_RQ1_WRAP	0x01 /* request 1 wraps */
  #define CFQ_RQ2_WRAP	0x02 /* request 2 wraps */
  	unsigned wrap = 0; /* bit mask: requests behind the disk head? */

  	if (rq1 == NULL || rq1 == rq2)
  		return rq2;
  	if (rq2 == NULL)
  		return rq1;

  	if (rq_is_sync(rq1) && !rq_is_sync(rq2))
  		return rq1;
  	else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
  		return rq2;

  	if (rq_is_meta(rq1) && !rq_is_meta(rq2))
  		return rq1;
  	else if (rq_is_meta(rq2) && !rq_is_meta(rq1))
  		return rq2;

  	s1 = blk_rq_pos(rq1);
  	s2 = blk_rq_pos(rq2);

  	last = cfqd->last_position;

  	/*
  	 * by definition, 1KiB is 2 sectors
  	 */
  	back_max = cfqd->cfq_back_max * 2;
  
  	/*
  	 * Strict one way elevator _except_ in the case where we allow
  	 * short backward seeks which are biased as twice the cost of a
  	 * similar forward seek.
  	 */
  	if (s1 >= last)
  		d1 = s1 - last;
  	else if (s1 + back_max >= last)
  		d1 = (last - s1) * cfqd->cfq_back_penalty;
  	else

  		wrap |= CFQ_RQ1_WRAP;

  
  	if (s2 >= last)
  		d2 = s2 - last;
  	else if (s2 + back_max >= last)
  		d2 = (last - s2) * cfqd->cfq_back_penalty;
  	else

  		wrap |= CFQ_RQ2_WRAP;

  
  	/* Found required data */

  
  	/*
  	 * By doing switch() on the bit mask "wrap" we avoid having to
  	 * check two variables for all permutations: --> faster!
  	 */
  	switch (wrap) {

  	case 0: /* common case for CFQ: rq1 and rq2 not wrapped */

  		if (d1 < d2)

  			return rq1;

  		else if (d2 < d1)

  			return rq2;

  		else {
  			if (s1 >= s2)

  				return rq1;

  			else

  				return rq2;

  		}

  	case CFQ_RQ2_WRAP:

  		return rq1;

  	case CFQ_RQ1_WRAP:

  		return rq2;
  	case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */

  	default:
  		/*
  		 * Since both rqs are wrapped,
  		 * start with the one that's further behind head
  		 * (--> only *one* back seek required),
  		 * since back seek takes more time than forward.
  		 */
  		if (s1 <= s2)

  			return rq1;

  		else

  			return rq2;

  	}
  }

  /*
   * The below is leftmost cache rbtree addon
   */

  static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)

  {
  	if (!root->left)
  		root->left = rb_first(&root->rb);

  	if (root->left)
  		return rb_entry(root->left, struct cfq_queue, rb_node);
  
  	return NULL;

  }

  static void rb_erase_init(struct rb_node *n, struct rb_root *root)
  {
  	rb_erase(n, root);
  	RB_CLEAR_NODE(n);
  }

  static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
  {
  	if (root->left == n)
  		root->left = NULL;

  	rb_erase_init(n, &root->rb);

  }

  /*
   * would be nice to take fifo expire time into account as well
   */

  static struct request *
  cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  		  struct request *last)

  {

  	struct rb_node *rbnext = rb_next(&last->rb_node);
  	struct rb_node *rbprev = rb_prev(&last->rb_node);

  	struct request *next = NULL, *prev = NULL;

  	BUG_ON(RB_EMPTY_NODE(&last->rb_node));

  
  	if (rbprev)

  		prev = rb_entry_rq(rbprev);

  	if (rbnext)

  		next = rb_entry_rq(rbnext);

  	else {
  		rbnext = rb_first(&cfqq->sort_list);
  		if (rbnext && rbnext != &last->rb_node)

  			next = rb_entry_rq(rbnext);

  	}

  	return cfq_choose_req(cfqd, next, prev);

  }

  static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
  				      struct cfq_queue *cfqq)

  {

  	/*
  	 * just an approximation, should be ok.
  	 */

  	return (cfqd->busy_queues - 1) * (cfq_prio_slice(cfqd, 1, 0) -
  		       cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));

  }

  /*
   * The cfqd->service_tree holds all pending cfq_queue's that have
   * requests waiting to be processed. It is sorted in the order that
   * we will service the queues.
   */

  static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  				 int add_front)

  {

  	struct rb_node **p, *parent;
  	struct cfq_queue *__cfqq;

  	unsigned long rb_key;

  	int left;

  	if (cfq_class_idle(cfqq)) {
  		rb_key = CFQ_IDLE_DELAY;
  		parent = rb_last(&cfqd->service_tree.rb);
  		if (parent && parent != &cfqq->rb_node) {
  			__cfqq = rb_entry(parent, struct cfq_queue, rb_node);
  			rb_key += __cfqq->rb_key;
  		} else
  			rb_key += jiffies;
  	} else if (!add_front) {

  		rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
  		rb_key += cfqq->slice_resid;
  		cfqq->slice_resid = 0;
  	} else
  		rb_key = 0;

  	if (!RB_EMPTY_NODE(&cfqq->rb_node)) {

  		/*

  		 * same position, nothing more to do

  		 */

  		if (rb_key == cfqq->rb_key)
  			return;

  		cfq_rb_erase(&cfqq->rb_node, &cfqd->service_tree);

  	}

  	left = 1;

  	parent = NULL;
  	p = &cfqd->service_tree.rb.rb_node;

  	while (*p) {

  		struct rb_node **n;

  		parent = *p;
  		__cfqq = rb_entry(parent, struct cfq_queue, rb_node);

  		/*
  		 * sort RT queues first, we always want to give

  		 * preference to them. IDLE queues goes to the back.
  		 * after that, sort on the next service time.

  		 */
  		if (cfq_class_rt(cfqq) > cfq_class_rt(__cfqq))

  			n = &(*p)->rb_left;

  		else if (cfq_class_rt(cfqq) < cfq_class_rt(__cfqq))

  			n = &(*p)->rb_right;
  		else if (cfq_class_idle(cfqq) < cfq_class_idle(__cfqq))
  			n = &(*p)->rb_left;
  		else if (cfq_class_idle(cfqq) > cfq_class_idle(__cfqq))
  			n = &(*p)->rb_right;

  		else if (rb_key < __cfqq->rb_key)

  			n = &(*p)->rb_left;
  		else
  			n = &(*p)->rb_right;
  
  		if (n == &(*p)->rb_right)

  			left = 0;

  
  		p = n;

  	}

  	if (left)
  		cfqd->service_tree.left = &cfqq->rb_node;

  	cfqq->rb_key = rb_key;
  	rb_link_node(&cfqq->rb_node, parent, p);

  	rb_insert_color(&cfqq->rb_node, &cfqd->service_tree.rb);

  }

  static struct cfq_queue *

  cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
  		     sector_t sector, struct rb_node **ret_parent,
  		     struct rb_node ***rb_link)

  {

  	struct rb_node **p, *parent;
  	struct cfq_queue *cfqq = NULL;
  
  	parent = NULL;
  	p = &root->rb_node;
  	while (*p) {
  		struct rb_node **n;
  
  		parent = *p;
  		cfqq = rb_entry(parent, struct cfq_queue, p_node);
  
  		/*
  		 * Sort strictly based on sector.  Smallest to the left,
  		 * largest to the right.
  		 */

  		if (sector > blk_rq_pos(cfqq->next_rq))

  			n = &(*p)->rb_right;

  		else if (sector < blk_rq_pos(cfqq->next_rq))

  			n = &(*p)->rb_left;
  		else
  			break;
  		p = n;

  		cfqq = NULL;

  	}
  
  	*ret_parent = parent;
  	if (rb_link)
  		*rb_link = p;

  	return cfqq;

  }
  
  static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {

  	struct rb_node **p, *parent;
  	struct cfq_queue *__cfqq;

  	if (cfqq->p_root) {
  		rb_erase(&cfqq->p_node, cfqq->p_root);
  		cfqq->p_root = NULL;
  	}

  
  	if (cfq_class_idle(cfqq))
  		return;
  	if (!cfqq->next_rq)
  		return;

  	cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];

  	__cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
  				      blk_rq_pos(cfqq->next_rq), &parent, &p);

  	if (!__cfqq) {
  		rb_link_node(&cfqq->p_node, parent, p);

  		rb_insert_color(&cfqq->p_node, cfqq->p_root);
  	} else
  		cfqq->p_root = NULL;

  }

  /*
   * Update cfqq's position in the service tree.
   */

  static void cfq_resort_rr_list(struct cfq_data *cfqd, struct cfq_queue *cfqq)

  {

  	/*
  	 * Resorting requires the cfqq to be on the RR list already.
  	 */

  	if (cfq_cfqq_on_rr(cfqq)) {

  		cfq_service_tree_add(cfqd, cfqq, 0);

  		cfq_prio_tree_add(cfqd, cfqq);
  	}

  }

  /*
   * add to busy list of queues for service, trying to be fair in ordering

   * the pending list according to last request service

   */

  static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)

  {

  	cfq_log_cfqq(cfqd, cfqq, "add_to_rr");

  	BUG_ON(cfq_cfqq_on_rr(cfqq));
  	cfq_mark_cfqq_on_rr(cfqq);

  	cfqd->busy_queues++;

  	if (cfq_class_rt(cfqq))
  		cfqd->busy_rt_queues++;

  	cfq_resort_rr_list(cfqd, cfqq);

  }

  /*
   * Called when the cfqq no longer has requests pending, remove it from
   * the service tree.
   */

  static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)

  {

  	cfq_log_cfqq(cfqd, cfqq, "del_from_rr");

  	BUG_ON(!cfq_cfqq_on_rr(cfqq));
  	cfq_clear_cfqq_on_rr(cfqq);

  	if (!RB_EMPTY_NODE(&cfqq->rb_node))
  		cfq_rb_erase(&cfqq->rb_node, &cfqd->service_tree);

  	if (cfqq->p_root) {
  		rb_erase(&cfqq->p_node, cfqq->p_root);
  		cfqq->p_root = NULL;
  	}

  	BUG_ON(!cfqd->busy_queues);
  	cfqd->busy_queues--;

  	if (cfq_class_rt(cfqq))
  		cfqd->busy_rt_queues--;

  }
  
  /*
   * rb tree support functions
   */

  static void cfq_del_rq_rb(struct request *rq)

  {

  	struct cfq_queue *cfqq = RQ_CFQQ(rq);

  	struct cfq_data *cfqd = cfqq->cfqd;

  	const int sync = rq_is_sync(rq);

  	BUG_ON(!cfqq->queued[sync]);
  	cfqq->queued[sync]--;

  	elv_rb_del(&cfqq->sort_list, rq);

  	if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))

  		cfq_del_cfqq_rr(cfqd, cfqq);

  }

  static void cfq_add_rq_rb(struct request *rq)

  {

  	struct cfq_queue *cfqq = RQ_CFQQ(rq);

  	struct cfq_data *cfqd = cfqq->cfqd;

  	struct request *__alias, *prev;

  	cfqq->queued[rq_is_sync(rq)]++;

  
  	/*
  	 * looks a little odd, but the first insert might return an alias.
  	 * if that happens, put the alias on the dispatch list
  	 */

  	while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL)

  		cfq_dispatch_insert(cfqd->queue, __alias);

  
  	if (!cfq_cfqq_on_rr(cfqq))
  		cfq_add_cfqq_rr(cfqd, cfqq);

  
  	/*
  	 * check if this request is a better next-serve candidate
  	 */

  	prev = cfqq->next_rq;

  	cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq);

  
  	/*
  	 * adjust priority tree position, if ->next_rq changes
  	 */
  	if (prev != cfqq->next_rq)
  		cfq_prio_tree_add(cfqd, cfqq);

  	BUG_ON(!cfqq->next_rq);

  }

  static void cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)

  {

  	elv_rb_del(&cfqq->sort_list, rq);
  	cfqq->queued[rq_is_sync(rq)]--;

  	cfq_add_rq_rb(rq);

  }

  static struct request *
  cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)

  {

  	struct task_struct *tsk = current;

  	struct cfq_io_context *cic;

  	struct cfq_queue *cfqq;

  	cic = cfq_cic_lookup(cfqd, tsk->io_context);

  	if (!cic)
  		return NULL;
  
  	cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));

  	if (cfqq) {
  		sector_t sector = bio->bi_sector + bio_sectors(bio);

  		return elv_rb_find(&cfqq->sort_list, sector);

  	}

  	return NULL;
  }

  static void cfq_activate_request(struct request_queue *q, struct request *rq)

  {

  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	cfqd->rq_in_driver++;

  	cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
  						cfqd->rq_in_driver);

  	cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);

  }

  static void cfq_deactivate_request(struct request_queue *q, struct request *rq)

  {

  	struct cfq_data *cfqd = q->elevator->elevator_data;
  
  	WARN_ON(!cfqd->rq_in_driver);
  	cfqd->rq_in_driver--;

  	cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
  						cfqd->rq_in_driver);

  }

  static void cfq_remove_request(struct request *rq)

  {

  	struct cfq_queue *cfqq = RQ_CFQQ(rq);

  	if (cfqq->next_rq == rq)
  		cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);

  	list_del_init(&rq->queuelist);

  	cfq_del_rq_rb(rq);

  	cfqq->cfqd->rq_queued--;

  	if (rq_is_meta(rq)) {
  		WARN_ON(!cfqq->meta_pending);
  		cfqq->meta_pending--;
  	}

  }

  static int cfq_merge(struct request_queue *q, struct request **req,
  		     struct bio *bio)

  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	struct request *__rq;

  	__rq = cfq_find_rq_fmerge(cfqd, bio);

  	if (__rq && elv_rq_merge_ok(__rq, bio)) {

  		*req = __rq;
  		return ELEVATOR_FRONT_MERGE;

  	}
  
  	return ELEVATOR_NO_MERGE;

  }

  static void cfq_merged_request(struct request_queue *q, struct request *req,

  			       int type)

  {

  	if (type == ELEVATOR_FRONT_MERGE) {

  		struct cfq_queue *cfqq = RQ_CFQQ(req);

  		cfq_reposition_rq_rb(cfqq, req);

  	}

  }
  
  static void

  cfq_merged_requests(struct request_queue *q, struct request *rq,

  		    struct request *next)
  {

  	/*
  	 * reposition in fifo if next is older than rq
  	 */
  	if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
  	    time_before(next->start_time, rq->start_time))
  		list_move(&rq->queuelist, &next->queuelist);

  	cfq_remove_request(next);

  }

  static int cfq_allow_merge(struct request_queue *q, struct request *rq,

  			   struct bio *bio)
  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	struct cfq_io_context *cic;

  	struct cfq_queue *cfqq;

  
  	/*

  	 * Disallow merge of a sync bio into an async request.

  	 */

  	if (cfq_bio_sync(bio) && !rq_is_sync(rq))

  		return 0;
  
  	/*

  	 * Lookup the cfqq that this bio will be queued with. Allow
  	 * merge only if rq is queued there.

  	 */

  	cic = cfq_cic_lookup(cfqd, current->io_context);

  	if (!cic)
  		return 0;

  	cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));

  	if (cfqq == RQ_CFQQ(rq))
  		return 1;

  	return 0;

  }

  static void __cfq_set_active_queue(struct cfq_data *cfqd,
  				   struct cfq_queue *cfqq)

  {
  	if (cfqq) {

  		cfq_log_cfqq(cfqd, cfqq, "set_active");

  		cfqq->slice_end = 0;

  		cfqq->slice_dispatch = 0;

  		cfq_clear_cfqq_wait_request(cfqq);

  		cfq_clear_cfqq_must_dispatch(cfqq);

  		cfq_clear_cfqq_must_alloc_slice(cfqq);
  		cfq_clear_cfqq_fifo_expire(cfqq);

  		cfq_mark_cfqq_slice_new(cfqq);

  
  		del_timer(&cfqd->idle_slice_timer);

  	}
  
  	cfqd->active_queue = cfqq;
  }
  
  /*

   * current cfqq expired its slice (or was too idle), select new one
   */
  static void
  __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,

  		    int timed_out)

  {

  	cfq_log_cfqq(cfqd, cfqq, "slice expired t=%d", timed_out);

  	if (cfq_cfqq_wait_request(cfqq))
  		del_timer(&cfqd->idle_slice_timer);

  	cfq_clear_cfqq_wait_request(cfqq);
  
  	/*

  	 * store what was left of this slice, if the queue idled/timed out

  	 */

  	if (timed_out && !cfq_cfqq_slice_new(cfqq)) {

  		cfqq->slice_resid = cfqq->slice_end - jiffies;

  		cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
  	}

  	cfq_resort_rr_list(cfqd, cfqq);

  
  	if (cfqq == cfqd->active_queue)
  		cfqd->active_queue = NULL;
  
  	if (cfqd->active_cic) {
  		put_io_context(cfqd->active_cic->ioc);
  		cfqd->active_cic = NULL;
  	}

  }

  static inline void cfq_slice_expired(struct cfq_data *cfqd, int timed_out)

  {
  	struct cfq_queue *cfqq = cfqd->active_queue;
  
  	if (cfqq)

  		__cfq_slice_expired(cfqd, cfqq, timed_out);

  }

  /*
   * Get next queue for service. Unless we have a queue preemption,
   * we'll simply select the first cfqq in the service tree.
   */

  static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)

  {

  	if (RB_EMPTY_ROOT(&cfqd->service_tree.rb))
  		return NULL;

  	return cfq_rb_first(&cfqd->service_tree);

  }

  /*
   * Get and set a new active queue for service.
   */

  static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd,
  					      struct cfq_queue *cfqq)

  {

  	if (!cfqq) {
  		cfqq = cfq_get_next_queue(cfqd);
  		if (cfqq)
  			cfq_clear_cfqq_coop(cfqq);
  	}

  	__cfq_set_active_queue(cfqd, cfqq);

  	return cfqq;

  }

  static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
  					  struct request *rq)
  {

  	if (blk_rq_pos(rq) >= cfqd->last_position)
  		return blk_rq_pos(rq) - cfqd->last_position;

  	else

  		return cfqd->last_position - blk_rq_pos(rq);

  }

  #define CIC_SEEK_THR	8 * 1024
  #define CIC_SEEKY(cic)	((cic)->seek_mean > CIC_SEEK_THR)

  static inline int cfq_rq_close(struct cfq_data *cfqd, struct request *rq)
  {
  	struct cfq_io_context *cic = cfqd->active_cic;

  	sector_t sdist = cic->seek_mean;

  
  	if (!sample_valid(cic->seek_samples))

  		sdist = CIC_SEEK_THR;

  	return cfq_dist_from_last(cfqd, rq) <= sdist;

  }

  static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
  				    struct cfq_queue *cur_cfqq)
  {

  	struct rb_root *root = &cfqd->prio_trees[cur_cfqq->org_ioprio];

  	struct rb_node *parent, *node;
  	struct cfq_queue *__cfqq;
  	sector_t sector = cfqd->last_position;
  
  	if (RB_EMPTY_ROOT(root))
  		return NULL;
  
  	/*
  	 * First, if we find a request starting at the end of the last
  	 * request, choose it.
  	 */

  	__cfqq = cfq_prio_tree_lookup(cfqd, root, sector, &parent, NULL);

  	if (__cfqq)
  		return __cfqq;
  
  	/*
  	 * If the exact sector wasn't found, the parent of the NULL leaf
  	 * will contain the closest sector.
  	 */
  	__cfqq = rb_entry(parent, struct cfq_queue, p_node);
  	if (cfq_rq_close(cfqd, __cfqq->next_rq))
  		return __cfqq;

  	if (blk_rq_pos(__cfqq->next_rq) < sector)

  		node = rb_next(&__cfqq->p_node);
  	else
  		node = rb_prev(&__cfqq->p_node);
  	if (!node)
  		return NULL;
  
  	__cfqq = rb_entry(node, struct cfq_queue, p_node);
  	if (cfq_rq_close(cfqd, __cfqq->next_rq))
  		return __cfqq;
  
  	return NULL;
  }
  
  /*
   * cfqd - obvious
   * cur_cfqq - passed in so that we don't decide that the current queue is
   * 	      closely cooperating with itself.
   *
   * So, basically we're assuming that that cur_cfqq has dispatched at least
   * one request, and that cfqd->last_position reflects a position on the disk
   * associated with the I/O issued by cur_cfqq.  I'm not sure this is a valid
   * assumption.
   */
  static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
  					      struct cfq_queue *cur_cfqq,
  					      int probe)

  {

  	struct cfq_queue *cfqq;
  
  	/*
  	 * A valid cfq_io_context is necessary to compare requests against
  	 * the seek_mean of the current cfqq.
  	 */
  	if (!cfqd->active_cic)
  		return NULL;

  	/*

  	 * We should notice if some of the queues are cooperating, eg
  	 * working closely on the same area of the disk. In that case,
  	 * we can group them together and don't waste time idling.

  	 */

  	cfqq = cfqq_close(cfqd, cur_cfqq);
  	if (!cfqq)
  		return NULL;
  
  	if (cfq_cfqq_coop(cfqq))
  		return NULL;
  
  	if (!probe)
  		cfq_mark_cfqq_coop(cfqq);
  	return cfqq;

  }

  static void cfq_arm_slice_timer(struct cfq_data *cfqd)

  {

  	struct cfq_queue *cfqq = cfqd->active_queue;

  	struct cfq_io_context *cic;

  	unsigned long sl;

  	/*

  	 * SSD device without seek penalty, disable idling. But only do so
  	 * for devices that support queuing, otherwise we still have a problem
  	 * with sync vs async workloads.

  	 */

  	if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag)

  		return;

  	WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));

  	WARN_ON(cfq_cfqq_slice_new(cfqq));

  
  	/*
  	 * idle is disabled, either manually or by past process history
  	 */

  	if (!cfqd->cfq_slice_idle || !cfq_cfqq_idle_window(cfqq))
  		return;

  	/*

  	 * still requests with the driver, don't idle
  	 */
  	if (cfqd->rq_in_driver)
  		return;
  
  	/*

  	 * task has exited, don't wait
  	 */

  	cic = cfqd->active_cic;

  	if (!cic || !atomic_read(&cic->ioc->nr_tasks))

  		return;

  	cfq_mark_cfqq_wait_request(cfqq);

  	/*
  	 * we don't want to idle for seeks, but we do want to allow
  	 * fair distribution of slice time for a process doing back-to-back
  	 * seeks. so allow a little bit of time for him to submit a new rq
  	 */

  	sl = cfqd->cfq_slice_idle;

  	if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))

  		sl = min(sl, msecs_to_jiffies(CFQ_MIN_TT));

  	mod_timer(&cfqd->idle_slice_timer, jiffies + sl);

  	cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu", sl);

  }

  /*
   * Move request from internal lists to the request queue dispatch list.
   */

  static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)

  {

  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	struct cfq_queue *cfqq = RQ_CFQQ(rq);

  	cfq_log_cfqq(cfqd, cfqq, "dispatch_insert");

  	cfq_remove_request(rq);

  	cfqq->dispatched++;

  	elv_dispatch_sort(q, rq);

  
  	if (cfq_cfqq_sync(cfqq))
  		cfqd->sync_flight++;

  }
  
  /*
   * return expired entry, or NULL to just start from scratch in rbtree
   */

  static struct request *cfq_check_fifo(struct cfq_queue *cfqq)

  {
  	struct cfq_data *cfqd = cfqq->cfqd;

  	struct request *rq;

  	int fifo;

  	if (cfq_cfqq_fifo_expire(cfqq))

  		return NULL;

  
  	cfq_mark_cfqq_fifo_expire(cfqq);

  	if (list_empty(&cfqq->fifo))
  		return NULL;

  	fifo = cfq_cfqq_sync(cfqq);

  	rq = rq_entry_fifo(cfqq->fifo.next);

  	if (time_before(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo]))

  		rq = NULL;

  	cfq_log_cfqq(cfqd, cfqq, "fifo=%p", rq);

  	return rq;

  }

  static inline int
  cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	const int base_rq = cfqd->cfq_slice_async_rq;

  	WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

  	return 2 * (base_rq + base_rq * (CFQ_PRIO_LISTS - 1 - cfqq->ioprio));

  }

  /*

   * Select a queue for service. If we have a current active queue,
   * check whether to continue servicing it, or retrieve and set a new one.

   */

  static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)

  {

  	struct cfq_queue *cfqq, *new_cfqq = NULL;

  	cfqq = cfqd->active_queue;
  	if (!cfqq)
  		goto new_queue;

  	/*

  	 * The active queue has run out of time, expire it and select new.

  	 */

  	if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq))

  		goto expire;

  	/*

  	 * If we have a RT cfqq waiting, then we pre-empt the current non-rt
  	 * cfqq.
  	 */
  	if (!cfq_class_rt(cfqq) && cfqd->busy_rt_queues) {
  		/*
  		 * We simulate this as cfqq timed out so that it gets to bank
  		 * the remaining of its time slice.
  		 */
  		cfq_log_cfqq(cfqd, cfqq, "preempt");
  		cfq_slice_expired(cfqd, 1);
  		goto new_queue;
  	}
  
  	/*

  	 * The active queue has requests and isn't expired, allow it to
  	 * dispatch.

  	 */

  	if (!RB_EMPTY_ROOT(&cfqq->sort_list))

  		goto keep_queue;

  
  	/*

  	 * If another queue has a request waiting within our mean seek
  	 * distance, let it run.  The expire code will check for close
  	 * cooperators and put the close queue at the front of the service
  	 * tree.
  	 */
  	new_cfqq = cfq_close_cooperator(cfqd, cfqq, 0);
  	if (new_cfqq)
  		goto expire;
  
  	/*

  	 * No requests pending. If the active queue still has requests in
  	 * flight or is idling for a new request, allow either of these
  	 * conditions to happen (or time out) before selecting a new queue.
  	 */

  	if (timer_pending(&cfqd->idle_slice_timer) ||
  	    (cfqq->dispatched && cfq_cfqq_idle_window(cfqq))) {

  		cfqq = NULL;
  		goto keep_queue;

  	}

  expire:

  	cfq_slice_expired(cfqd, 0);

  new_queue:

  	cfqq = cfq_set_active_queue(cfqd, new_cfqq);

  keep_queue:

  	return cfqq;

  }

  static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)

  {
  	int dispatched = 0;
  
  	while (cfqq->next_rq) {
  		cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);
  		dispatched++;
  	}
  
  	BUG_ON(!list_empty(&cfqq->fifo));
  	return dispatched;
  }

  /*
   * Drain our current requests. Used for barriers and when switching
   * io schedulers on-the-fly.
   */

  static int cfq_forced_dispatch(struct cfq_data *cfqd)

  {

  	struct cfq_queue *cfqq;

  	int dispatched = 0;

  	while ((cfqq = cfq_rb_first(&cfqd->service_tree)) != NULL)

  		dispatched += __cfq_forced_dispatch_cfqq(cfqq);

  	cfq_slice_expired(cfqd, 0);

  
  	BUG_ON(cfqd->busy_queues);

  	cfq_log(cfqd, "forced_dispatch=%d", dispatched);

  	return dispatched;
  }

  /*
   * Dispatch a request from cfqq, moving them to the request queue
   * dispatch list.
   */
  static void cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	struct request *rq;
  
  	BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
  
  	/*
  	 * follow expired path, else get first next available
  	 */
  	rq = cfq_check_fifo(cfqq);
  	if (!rq)
  		rq = cfqq->next_rq;
  
  	/*
  	 * insert request into driver dispatch list
  	 */
  	cfq_dispatch_insert(cfqd->queue, rq);
  
  	if (!cfqd->active_cic) {
  		struct cfq_io_context *cic = RQ_CIC(rq);

  		atomic_long_inc(&cic->ioc->refcount);

  		cfqd->active_cic = cic;
  	}
  }
  
  /*
   * Find the cfqq that we need to service and move a request from that to the
   * dispatch list
   */

  static int cfq_dispatch_requests(struct request_queue *q, int force)

  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	struct cfq_queue *cfqq;

  	unsigned int max_dispatch;

  
  	if (!cfqd->busy_queues)
  		return 0;

  	if (unlikely(force))
  		return cfq_forced_dispatch(cfqd);

  	cfqq = cfq_select_queue(cfqd);
  	if (!cfqq)
  		return 0;
  
  	/*
  	 * If this is an async queue and we have sync IO in flight, let it wait
  	 */
  	if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
  		return 0;
  
  	max_dispatch = cfqd->cfq_quantum;
  	if (cfq_class_idle(cfqq))
  		max_dispatch = 1;

  	/*
  	 * Does this cfqq already have too much IO in flight?
  	 */
  	if (cfqq->dispatched >= max_dispatch) {
  		/*
  		 * idle queue must always only have a single IO in flight
  		 */

  		if (cfq_class_idle(cfqq))

  			return 0;

  		/*
  		 * We have other queues, don't allow more IO from this one
  		 */
  		if (cfqd->busy_queues > 1)
  			return 0;

  		/*
  		 * we are the only queue, allow up to 4 times of 'quantum'
  		 */
  		if (cfqq->dispatched >= 4 * max_dispatch)
  			return 0;
  	}

  	/*
  	 * Dispatch a request from this cfqq
  	 */
  	cfq_dispatch_request(cfqd, cfqq);
  	cfqq->slice_dispatch++;

  	cfq_clear_cfqq_must_dispatch(cfqq);

  	/*
  	 * expire an async queue immediately if it has used up its slice. idle
  	 * queue always expire after 1 dispatch round.
  	 */
  	if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
  	    cfqq->slice_dispatch >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
  	    cfq_class_idle(cfqq))) {
  		cfqq->slice_end = jiffies + 1;
  		cfq_slice_expired(cfqd, 0);

  	}

  	cfq_log(cfqd, "dispatched a request");
  	return 1;

  }

  /*

   * task holds one reference to the queue, dropped when task exits. each rq
   * in-flight on this queue also holds a reference, dropped when rq is freed.

   *
   * queue lock must be held here.
   */
  static void cfq_put_queue(struct cfq_queue *cfqq)
  {

  	struct cfq_data *cfqd = cfqq->cfqd;
  
  	BUG_ON(atomic_read(&cfqq->ref) <= 0);

  
  	if (!atomic_dec_and_test(&cfqq->ref))
  		return;

  	cfq_log_cfqq(cfqd, cfqq, "put_queue");

  	BUG_ON(rb_first(&cfqq->sort_list));

  	BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);

  	BUG_ON(cfq_cfqq_on_rr(cfqq));

  	if (unlikely(cfqd->active_queue == cfqq)) {

  		__cfq_slice_expired(cfqd, cfqq, 0);

  		cfq_schedule_dispatch(cfqd);
  	}

  	kmem_cache_free(cfq_pool, cfqq);
  }

  /*
   * Must always be called with the rcu_read_lock() held
   */

  static void
  __call_for_each_cic(struct io_context *ioc,
  		    void (*func)(struct io_context *, struct cfq_io_context *))
  {
  	struct cfq_io_context *cic;
  	struct hlist_node *n;
  
  	hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
  		func(ioc, cic);
  }

  /*

   * Call func for each cic attached to this ioc.

   */

  static void

  call_for_each_cic(struct io_context *ioc,
  		  void (*func)(struct io_context *, struct cfq_io_context *))

  {

  	rcu_read_lock();

  	__call_for_each_cic(ioc, func);

  	rcu_read_unlock();

  }
  
  static void cfq_cic_free_rcu(struct rcu_head *head)
  {
  	struct cfq_io_context *cic;
  
  	cic = container_of(head, struct cfq_io_context, rcu_head);
  
  	kmem_cache_free(cfq_ioc_pool, cic);
  	elv_ioc_count_dec(ioc_count);

  	if (ioc_gone) {
  		/*
  		 * CFQ scheduler is exiting, grab exit lock and check
  		 * the pending io context count. If it hits zero,
  		 * complete ioc_gone and set it back to NULL
  		 */
  		spin_lock(&ioc_gone_lock);
  		if (ioc_gone && !elv_ioc_count_read(ioc_count)) {
  			complete(ioc_gone);
  			ioc_gone = NULL;
  		}
  		spin_unlock(&ioc_gone_lock);
  	}

  }

  static void cfq_cic_free(struct cfq_io_context *cic)
  {
  	call_rcu(&cic->rcu_head, cfq_cic_free_rcu);

  }
  
  static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)
  {
  	unsigned long flags;
  
  	BUG_ON(!cic->dead_key);
  
  	spin_lock_irqsave(&ioc->lock, flags);
  	radix_tree_delete(&ioc->radix_root, cic->dead_key);

  	hlist_del_rcu(&cic->cic_list);

  	spin_unlock_irqrestore(&ioc->lock, flags);

  	cfq_cic_free(cic);

  }

  /*
   * Must be called with rcu_read_lock() held or preemption otherwise disabled.
   * Only two callers of this - ->dtor() which is called with the rcu_read_lock(),
   * and ->trim() which is called with the task lock held
   */

  static void cfq_free_io_context(struct io_context *ioc)
  {

  	/*

  	 * ioc->refcount is zero here, or we are called from elv_unregister(),
  	 * so no more cic's are allowed to be linked into this ioc.  So it
  	 * should be ok to iterate over the known list, we will see all cic's
  	 * since no new ones are added.

  	 */

  	__call_for_each_cic(ioc, cic_free_func);