block/blk-ioc.c - kernel/common - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Functions related to io context handling
  */
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/slab.h>
 #include <linux/sched/task.h>

 #include "blk.h"

 /*
  * For io context allocations
  */
 static struct kmem_cache *iocontext_cachep;

 /**
  * get_io_context - increment reference count to io_context
  * @ioc: io_context to get
  *
  * Increment reference count to @ioc.
  */
 void get_io_context(struct io_context *ioc)
 {
 	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
 	atomic_long_inc(&ioc->refcount);
 }

 static void icq_free_icq_rcu(struct rcu_head *head)
 {
 	struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);

 	kmem_cache_free(icq->__rcu_icq_cache, icq);
 }

 /*
  * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
  * and queue locked for legacy.
  */
 static void ioc_exit_icq(struct io_cq *icq)
 {
 	struct elevator_type *et = icq->q->elevator->type;

 	if (icq->flags & ICQ_EXITED)
 		return;

 	if (et->ops.exit_icq)
 		et->ops.exit_icq(icq);

 	icq->flags |= ICQ_EXITED;
 }

 /*
  * Release an icq. Called with ioc locked for blk-mq, and with both ioc
  * and queue locked for legacy.
  */
 static void ioc_destroy_icq(struct io_cq *icq)
 {
 	struct io_context *ioc = icq->ioc;
 	struct request_queue *q = icq->q;
 	struct elevator_type *et = q->elevator->type;

 	lockdep_assert_held(&ioc->lock);

 	radix_tree_delete(&ioc->icq_tree, icq->q->id);
 	hlist_del_init(&icq->ioc_node);
 	list_del_init(&icq->q_node);

 	/*
 	 * Both setting lookup hint to and clearing it from @icq are done
 	 * under queue_lock.  If it's not pointing to @icq now, it never
 	 * will.  Hint assignment itself can race safely.
 	 */
 	if (rcu_access_pointer(ioc->icq_hint) == icq)
 		rcu_assign_pointer(ioc->icq_hint, NULL);

 	ioc_exit_icq(icq);

 	/*
 	 * @icq->q might have gone away by the time RCU callback runs
 	 * making it impossible to determine icq_cache.  Record it in @icq.
 	 */
 	icq->__rcu_icq_cache = et->icq_cache;
 	icq->flags |= ICQ_DESTROYED;
 	call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
 }

 /*
  * Slow path for ioc release in put_io_context().  Performs double-lock
  * dancing to unlink all icq's and then frees ioc.
  */
 static void ioc_release_fn(struct work_struct *work)
 {
 	struct io_context *ioc = container_of(work, struct io_context,
 					      release_work);
 	spin_lock_irq(&ioc->lock);

 	while (!hlist_empty(&ioc->icq_list)) {
 		struct io_cq *icq = hlist_entry(ioc->icq_list.first,
 						struct io_cq, ioc_node);
 		struct request_queue *q = icq->q;

 		if (spin_trylock(&q->queue_lock)) {
 			ioc_destroy_icq(icq);
 			spin_unlock(&q->queue_lock);
 		} else {
 			/* Make sure q and icq cannot be freed. */
 			rcu_read_lock();

 			/* Re-acquire the locks in the correct order. */
 			spin_unlock(&ioc->lock);
 			spin_lock(&q->queue_lock);
 			spin_lock(&ioc->lock);

 			/*
 			 * The icq may have been destroyed when the ioc lock
 			 * was released.
 			 */
 			if (!(icq->flags & ICQ_DESTROYED))
 				ioc_destroy_icq(icq);

 			spin_unlock(&q->queue_lock);
 			rcu_read_unlock();
 		}
 	}

 	spin_unlock_irq(&ioc->lock);

 	kmem_cache_free(iocontext_cachep, ioc);
 }

 /**
  * put_io_context - put a reference of io_context
  * @ioc: io_context to put
  *
  * Decrement reference count of @ioc and release it if the count reaches
  * zero.
  */
 void put_io_context(struct io_context *ioc)
 {
 	unsigned long flags;
 	bool free_ioc = false;

 	if (ioc == NULL)
 		return;

 	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);

 	/*
 	 * Releasing ioc requires reverse order double locking and we may
 	 * already be holding a queue_lock.  Do it asynchronously from wq.
 	 */
 	if (atomic_long_dec_and_test(&ioc->refcount)) {
 		spin_lock_irqsave(&ioc->lock, flags);
 		if (!hlist_empty(&ioc->icq_list))
 			queue_work(system_power_efficient_wq,
 					&ioc->release_work);
 		else
 			free_ioc = true;
 		spin_unlock_irqrestore(&ioc->lock, flags);
 	}

 	if (free_ioc)
 		kmem_cache_free(iocontext_cachep, ioc);
 }

 /**
  * put_io_context_active - put active reference on ioc
  * @ioc: ioc of interest
  *
  * Undo get_io_context_active().  If active reference reaches zero after
  * put, @ioc can never issue further IOs and ioscheds are notified.
  */
 void put_io_context_active(struct io_context *ioc)
 {
 	struct io_cq *icq;

 	if (!atomic_dec_and_test(&ioc->active_ref)) {
 		put_io_context(ioc);
 		return;
 	}

 	spin_lock_irq(&ioc->lock);
 	hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
 		if (icq->flags & ICQ_EXITED)
 			continue;

 		ioc_exit_icq(icq);
 	}
 	spin_unlock_irq(&ioc->lock);

 	put_io_context(ioc);
 }

 /* Called by the exiting task */
 void exit_io_context(struct task_struct *task)
 {
 	struct io_context *ioc;

 	task_lock(task);
 	ioc = task->io_context;
 	task->io_context = NULL;
 	task_unlock(task);

 	atomic_dec(&ioc->nr_tasks);
 	put_io_context_active(ioc);
 }

 static void __ioc_clear_queue(struct list_head *icq_list)
 {
 	unsigned long flags;

 	rcu_read_lock();
 	while (!list_empty(icq_list)) {
 		struct io_cq *icq = list_entry(icq_list->next,
 						struct io_cq, q_node);
 		struct io_context *ioc = icq->ioc;

 		spin_lock_irqsave(&ioc->lock, flags);
 		if (icq->flags & ICQ_DESTROYED) {
 			spin_unlock_irqrestore(&ioc->lock, flags);
 			continue;
 		}
 		ioc_destroy_icq(icq);
 		spin_unlock_irqrestore(&ioc->lock, flags);
 	}
 	rcu_read_unlock();
 }

 /**
  * ioc_clear_queue - break any ioc association with the specified queue
  * @q: request_queue being cleared
  *
  * Walk @q->icq_list and exit all io_cq's.
  */
 void ioc_clear_queue(struct request_queue *q)
 {
 	LIST_HEAD(icq_list);

 	spin_lock_irq(&q->queue_lock);
 	list_splice_init(&q->icq_list, &icq_list);
 	spin_unlock_irq(&q->queue_lock);

 	__ioc_clear_queue(&icq_list);
 }

 int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
 {
 	struct io_context *ioc;
 	int ret;

 	ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
 				    node);
 	if (unlikely(!ioc))
 		return -ENOMEM;

 	/* initialize */
 	atomic_long_set(&ioc->refcount, 1);
 	atomic_set(&ioc->nr_tasks, 1);
 	atomic_set(&ioc->active_ref, 1);
 	spin_lock_init(&ioc->lock);
 	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
 	INIT_HLIST_HEAD(&ioc->icq_list);
 	INIT_WORK(&ioc->release_work, ioc_release_fn);

 	/*
 	 * Try to install.  ioc shouldn't be installed if someone else
 	 * already did or @task, which isn't %current, is exiting.  Note
 	 * that we need to allow ioc creation on exiting %current as exit
 	 * path may issue IOs from e.g. exit_files().  The exit path is
 	 * responsible for not issuing IO after exit_io_context().
 	 */
 	task_lock(task);
 	if (!task->io_context &&
 	    (task == current || !(task->flags & PF_EXITING)))
 		task->io_context = ioc;
 	else
 		kmem_cache_free(iocontext_cachep, ioc);

 	ret = task->io_context ? 0 : -EBUSY;

 	task_unlock(task);

 	return ret;
 }

 /**
  * get_task_io_context - get io_context of a task
  * @task: task of interest
  * @gfp_flags: allocation flags, used if allocation is necessary
  * @node: allocation node, used if allocation is necessary
  *
  * Return io_context of @task.  If it doesn't exist, it is created with
  * @gfp_flags and @node.  The returned io_context has its reference count
  * incremented.
  *
  * This function always goes through task_lock() and it's better to use
  * %current->io_context + get_io_context() for %current.
  */
 struct io_context *get_task_io_context(struct task_struct *task,
 				       gfp_t gfp_flags, int node)
 {
 	struct io_context *ioc;

 	might_sleep_if(gfpflags_allow_blocking(gfp_flags));

 	do {
 		task_lock(task);
 		ioc = task->io_context;
 		if (likely(ioc)) {
 			get_io_context(ioc);
 			task_unlock(task);
 			return ioc;
 		}
 		task_unlock(task);
 	} while (!create_task_io_context(task, gfp_flags, node));

 	return NULL;
 }

 /**
  * ioc_lookup_icq - lookup io_cq from ioc
  * @ioc: the associated io_context
  * @q: the associated request_queue
  *
  * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
  * with @q->queue_lock held.
  */
 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
 {
 	struct io_cq *icq;

 	lockdep_assert_held(&q->queue_lock);

 	/*
 	 * icq's are indexed from @ioc using radix tree and hint pointer,
 	 * both of which are protected with RCU.  All removals are done
 	 * holding both q and ioc locks, and we're holding q lock - if we
 	 * find a icq which points to us, it's guaranteed to be valid.
 	 */
 	rcu_read_lock();
 	icq = rcu_dereference(ioc->icq_hint);
 	if (icq && icq->q == q)
 		goto out;

 	icq = radix_tree_lookup(&ioc->icq_tree, q->id);
 	if (icq && icq->q == q)
 		rcu_assign_pointer(ioc->icq_hint, icq);	/* allowed to race */
 	else
 		icq = NULL;
 out:
 	rcu_read_unlock();
 	return icq;
 }
 EXPORT_SYMBOL(ioc_lookup_icq);

 /**
  * ioc_create_icq - create and link io_cq
  * @ioc: io_context of interest
  * @q: request_queue of interest
  * @gfp_mask: allocation mask
  *
  * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
  * will be created using @gfp_mask.
  *
  * The caller is responsible for ensuring @ioc won't go away and @q is
  * alive and will stay alive until this function returns.
  */
 struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
 			     gfp_t gfp_mask)
 {
 	struct elevator_type *et = q->elevator->type;
 	struct io_cq *icq;

 	/* allocate stuff */
 	icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
 				    q->node);
 	if (!icq)
 		return NULL;

 	if (radix_tree_maybe_preload(gfp_mask) < 0) {
 		kmem_cache_free(et->icq_cache, icq);
 		return NULL;
 	}

 	icq->ioc = ioc;
 	icq->q = q;
 	INIT_LIST_HEAD(&icq->q_node);
 	INIT_HLIST_NODE(&icq->ioc_node);

 	/* lock both q and ioc and try to link @icq */
 	spin_lock_irq(&q->queue_lock);
 	spin_lock(&ioc->lock);

 	if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
 		hlist_add_head(&icq->ioc_node, &ioc->icq_list);
 		list_add(&icq->q_node, &q->icq_list);
 		if (et->ops.init_icq)
 			et->ops.init_icq(icq);
 	} else {
 		kmem_cache_free(et->icq_cache, icq);
 		icq = ioc_lookup_icq(ioc, q);
 		if (!icq)
 			printk(KERN_ERR "cfq: icq link failed!\n");
 	}

 	spin_unlock(&ioc->lock);
 	spin_unlock_irq(&q->queue_lock);
 	radix_tree_preload_end();
 	return icq;
 }

 static int __init blk_ioc_init(void)
 {
 	iocontext_cachep = kmem_cache_create("blkdev_ioc",
 			sizeof(struct io_context), 0, SLAB_PANIC, NULL);
 	return 0;
 }
 subsys_initcall(blk_ioc_init);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Functions related to io context handling
	*/
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/init.h>
	#include <linux/bio.h>
	#include <linux/blkdev.h>
	#include <linux/slab.h>
	#include <linux/sched/task.h>

	#include "blk.h"

	/*
	* For io context allocations
	*/
	static struct kmem_cache *iocontext_cachep;

	/**
	* get_io_context - increment reference count to io_context
	* @ioc: io_context to get
	*
	* Increment reference count to @ioc.
	*/
	void get_io_context(struct io_context *ioc)
	{
	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
	atomic_long_inc(&ioc->refcount);
	}

	static void icq_free_icq_rcu(struct rcu_head *head)
	{
	struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);

	kmem_cache_free(icq->__rcu_icq_cache, icq);
	}

	/*
	* Exit an icq. Called with ioc locked for blk-mq, and with both ioc
	* and queue locked for legacy.
	*/
	static void ioc_exit_icq(struct io_cq *icq)
	{
	struct elevator_type *et = icq->q->elevator->type;

	if (icq->flags & ICQ_EXITED)
	return;

	if (et->ops.exit_icq)
	et->ops.exit_icq(icq);

	icq->flags \|= ICQ_EXITED;
	}

	/*
	* Release an icq. Called with ioc locked for blk-mq, and with both ioc
	* and queue locked for legacy.
	*/
	static void ioc_destroy_icq(struct io_cq *icq)
	{
	struct io_context *ioc = icq->ioc;
	struct request_queue *q = icq->q;
	struct elevator_type *et = q->elevator->type;

	lockdep_assert_held(&ioc->lock);

	radix_tree_delete(&ioc->icq_tree, icq->q->id);
	hlist_del_init(&icq->ioc_node);
	list_del_init(&icq->q_node);

	/*
	* Both setting lookup hint to and clearing it from @icq are done
	* under queue_lock. If it's not pointing to @icq now, it never
	* will. Hint assignment itself can race safely.
	*/
	if (rcu_access_pointer(ioc->icq_hint) == icq)
	rcu_assign_pointer(ioc->icq_hint, NULL);

	ioc_exit_icq(icq);

	/*
	* @icq->q might have gone away by the time RCU callback runs
	* making it impossible to determine icq_cache. Record it in @icq.
	*/
	icq->__rcu_icq_cache = et->icq_cache;
	icq->flags \|= ICQ_DESTROYED;
	call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
	}

	/*
	* Slow path for ioc release in put_io_context(). Performs double-lock
	* dancing to unlink all icq's and then frees ioc.
	*/
	static void ioc_release_fn(struct work_struct *work)
	{
	struct io_context *ioc = container_of(work, struct io_context,
	release_work);
	spin_lock_irq(&ioc->lock);

	while (!hlist_empty(&ioc->icq_list)) {
	struct io_cq *icq = hlist_entry(ioc->icq_list.first,
	struct io_cq, ioc_node);
	struct request_queue *q = icq->q;

	if (spin_trylock(&q->queue_lock)) {
	ioc_destroy_icq(icq);
	spin_unlock(&q->queue_lock);
	} else {
	/* Make sure q and icq cannot be freed. */
	rcu_read_lock();

	/* Re-acquire the locks in the correct order. */
	spin_unlock(&ioc->lock);
	spin_lock(&q->queue_lock);
	spin_lock(&ioc->lock);

	/*
	* The icq may have been destroyed when the ioc lock
	* was released.
	*/
	if (!(icq->flags & ICQ_DESTROYED))
	ioc_destroy_icq(icq);

	spin_unlock(&q->queue_lock);
	rcu_read_unlock();
	}
	}

	spin_unlock_irq(&ioc->lock);

	kmem_cache_free(iocontext_cachep, ioc);
	}

	/**
	* put_io_context - put a reference of io_context
	* @ioc: io_context to put
	*
	* Decrement reference count of @ioc and release it if the count reaches
	* zero.
	*/
	void put_io_context(struct io_context *ioc)
	{
	unsigned long flags;
	bool free_ioc = false;

	if (ioc == NULL)
	return;

	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);

	/*
	* Releasing ioc requires reverse order double locking and we may
	* already be holding a queue_lock. Do it asynchronously from wq.
	*/
	if (atomic_long_dec_and_test(&ioc->refcount)) {
	spin_lock_irqsave(&ioc->lock, flags);
	if (!hlist_empty(&ioc->icq_list))
	queue_work(system_power_efficient_wq,
	&ioc->release_work);
	else
	free_ioc = true;
	spin_unlock_irqrestore(&ioc->lock, flags);
	}

	if (free_ioc)
	kmem_cache_free(iocontext_cachep, ioc);
	}

	/**
	* put_io_context_active - put active reference on ioc
	* @ioc: ioc of interest
	*
	* Undo get_io_context_active(). If active reference reaches zero after
	* put, @ioc can never issue further IOs and ioscheds are notified.
	*/
	void put_io_context_active(struct io_context *ioc)
	{
	struct io_cq *icq;

	if (!atomic_dec_and_test(&ioc->active_ref)) {
	put_io_context(ioc);
	return;
	}

	spin_lock_irq(&ioc->lock);
	hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
	if (icq->flags & ICQ_EXITED)
	continue;

	ioc_exit_icq(icq);
	}
	spin_unlock_irq(&ioc->lock);

	put_io_context(ioc);
	}

	/* Called by the exiting task */
	void exit_io_context(struct task_struct *task)
	{
	struct io_context *ioc;

	task_lock(task);
	ioc = task->io_context;
	task->io_context = NULL;
	task_unlock(task);

	atomic_dec(&ioc->nr_tasks);
	put_io_context_active(ioc);
	}

	static void __ioc_clear_queue(struct list_head *icq_list)
	{
	unsigned long flags;

	rcu_read_lock();
	while (!list_empty(icq_list)) {
	struct io_cq *icq = list_entry(icq_list->next,
	struct io_cq, q_node);
	struct io_context *ioc = icq->ioc;

	spin_lock_irqsave(&ioc->lock, flags);
	if (icq->flags & ICQ_DESTROYED) {
	spin_unlock_irqrestore(&ioc->lock, flags);
	continue;
	}
	ioc_destroy_icq(icq);
	spin_unlock_irqrestore(&ioc->lock, flags);
	}
	rcu_read_unlock();
	}

	/**
	* ioc_clear_queue - break any ioc association with the specified queue
	* @q: request_queue being cleared
	*
	* Walk @q->icq_list and exit all io_cq's.
	*/
	void ioc_clear_queue(struct request_queue *q)
	{
	LIST_HEAD(icq_list);

	spin_lock_irq(&q->queue_lock);
	list_splice_init(&q->icq_list, &icq_list);
	spin_unlock_irq(&q->queue_lock);

	__ioc_clear_queue(&icq_list);
	}

	int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
	{
	struct io_context *ioc;
	int ret;

	ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags \| __GFP_ZERO,
	node);
	if (unlikely(!ioc))
	return -ENOMEM;

	/* initialize */
	atomic_long_set(&ioc->refcount, 1);
	atomic_set(&ioc->nr_tasks, 1);
	atomic_set(&ioc->active_ref, 1);
	spin_lock_init(&ioc->lock);
	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
	INIT_HLIST_HEAD(&ioc->icq_list);
	INIT_WORK(&ioc->release_work, ioc_release_fn);

	/*
	* Try to install. ioc shouldn't be installed if someone else
	* already did or @task, which isn't %current, is exiting. Note
	* that we need to allow ioc creation on exiting %current as exit
	* path may issue IOs from e.g. exit_files(). The exit path is
	* responsible for not issuing IO after exit_io_context().
	*/
	task_lock(task);
	if (!task->io_context &&
	(task == current \|\| !(task->flags & PF_EXITING)))
	task->io_context = ioc;
	else
	kmem_cache_free(iocontext_cachep, ioc);

	ret = task->io_context ? 0 : -EBUSY;

	task_unlock(task);

	return ret;
	}

	/**
	* get_task_io_context - get io_context of a task
	* @task: task of interest
	* @gfp_flags: allocation flags, used if allocation is necessary
	* @node: allocation node, used if allocation is necessary
	*
	* Return io_context of @task. If it doesn't exist, it is created with
	* @gfp_flags and @node. The returned io_context has its reference count
	* incremented.
	*
	* This function always goes through task_lock() and it's better to use
	* %current->io_context + get_io_context() for %current.
	*/
	struct io_context get_task_io_context(struct task_struct task,
	gfp_t gfp_flags, int node)
	{
	struct io_context *ioc;

	might_sleep_if(gfpflags_allow_blocking(gfp_flags));

	do {
	task_lock(task);
	ioc = task->io_context;
	if (likely(ioc)) {
	get_io_context(ioc);
	task_unlock(task);
	return ioc;
	}
	task_unlock(task);
	} while (!create_task_io_context(task, gfp_flags, node));

	return NULL;
	}

	/**
	* ioc_lookup_icq - lookup io_cq from ioc
	* @ioc: the associated io_context
	* @q: the associated request_queue
	*
	* Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
	* with @q->queue_lock held.
	*/
	struct io_cq ioc_lookup_icq(struct io_context ioc, struct request_queue *q)
	{
	struct io_cq *icq;

	lockdep_assert_held(&q->queue_lock);

	/*
	* icq's are indexed from @ioc using radix tree and hint pointer,
	* both of which are protected with RCU. All removals are done
	* holding both q and ioc locks, and we're holding q lock - if we
	* find a icq which points to us, it's guaranteed to be valid.
	*/
	rcu_read_lock();
	icq = rcu_dereference(ioc->icq_hint);
	if (icq && icq->q == q)
	goto out;

	icq = radix_tree_lookup(&ioc->icq_tree, q->id);
	if (icq && icq->q == q)
	rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
	else
	icq = NULL;
	out:
	rcu_read_unlock();
	return icq;
	}
	EXPORT_SYMBOL(ioc_lookup_icq);

	/**
	* ioc_create_icq - create and link io_cq
	* @ioc: io_context of interest
	* @q: request_queue of interest
	* @gfp_mask: allocation mask
	*
	* Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they
	* will be created using @gfp_mask.
	*
	* The caller is responsible for ensuring @ioc won't go away and @q is
	* alive and will stay alive until this function returns.
	*/
	struct io_cq ioc_create_icq(struct io_context ioc, struct request_queue *q,
	gfp_t gfp_mask)
	{
	struct elevator_type *et = q->elevator->type;
	struct io_cq *icq;

	/* allocate stuff */
	icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask \| __GFP_ZERO,
	q->node);
	if (!icq)
	return NULL;

	if (radix_tree_maybe_preload(gfp_mask) < 0) {
	kmem_cache_free(et->icq_cache, icq);
	return NULL;
	}

	icq->ioc = ioc;
	icq->q = q;
	INIT_LIST_HEAD(&icq->q_node);
	INIT_HLIST_NODE(&icq->ioc_node);

	/* lock both q and ioc and try to link @icq */
	spin_lock_irq(&q->queue_lock);
	spin_lock(&ioc->lock);

	if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
	hlist_add_head(&icq->ioc_node, &ioc->icq_list);
	list_add(&icq->q_node, &q->icq_list);
	if (et->ops.init_icq)
	et->ops.init_icq(icq);
	} else {
	kmem_cache_free(et->icq_cache, icq);
	icq = ioc_lookup_icq(ioc, q);
	if (!icq)
	printk(KERN_ERR "cfq: icq link failed!\n");
	}

	spin_unlock(&ioc->lock);
	spin_unlock_irq(&q->queue_lock);
	radix_tree_preload_end();
	return icq;
	}

	static int __init blk_ioc_init(void)
	{
	iocontext_cachep = kmem_cache_create("blkdev_ioc",
	sizeof(struct io_context), 0, SLAB_PANIC, NULL);
	return 0;
	}
	subsys_initcall(blk_ioc_init);