dm thin: move bio_prison code to separate module (4f81a417) · Commits · e / devices / android_kernel_xiaomi_markw

drivers/md/Kconfig

+8 −0

Original line number	Diff line number	Diff line
		@@ -216,6 +216,13 @@ config DM_BUFIO
		as a cache, holding recently-read blocks in memory and performing
		delayed writes.

		config DM_BIO_PRISON
		tristate
		depends on BLK_DEV_DM && EXPERIMENTAL
		---help---
		Some bio locking schemes used by other device-mapper targets
		including thin provisioning.

		source "drivers/md/persistent-data/Kconfig"

		config DM_CRYPT
		@@ -247,6 +254,7 @@ config DM_THIN_PROVISIONING
		tristate "Thin provisioning target (EXPERIMENTAL)"
		depends on BLK_DEV_DM && EXPERIMENTAL
		select DM_PERSISTENT_DATA
		select DM_BIO_PRISON
		---help---
		Provides thin provisioning and snapshots that share a data store.

drivers/md/Makefile

+1 −0

Original line number	Diff line number	Diff line
		@@ -29,6 +29,7 @@ obj-$(CONFIG_MD_FAULTY) += faulty.o
		obj-$(CONFIG_BLK_DEV_MD) += md-mod.o
		obj-$(CONFIG_BLK_DEV_DM) += dm-mod.o
		obj-$(CONFIG_DM_BUFIO) += dm-bufio.o
		obj-$(CONFIG_DM_BIO_PRISON) += dm-bio-prison.o
		obj-$(CONFIG_DM_CRYPT) += dm-crypt.o
		obj-$(CONFIG_DM_DELAY) += dm-delay.o
		obj-$(CONFIG_DM_FLAKEY) += dm-flakey.o

drivers/md/dm-bio-prison.c

0 → 100644

+415 −0

Original line number	Diff line number	Diff line
		/*
		* Copyright (C) 2012 Red Hat, Inc.
		*
		* This file is released under the GPL.
		*/

		#include "dm.h"
		#include "dm-bio-prison.h"

		#include <linux/spinlock.h>
		#include <linux/mempool.h>
		#include <linux/module.h>
		#include <linux/slab.h>

		/----------------------------------------------------------------/

		struct dm_bio_prison_cell {
		struct hlist_node list;
		struct dm_bio_prison *prison;
		struct dm_cell_key key;
		struct bio *holder;
		struct bio_list bios;
		};

		struct dm_bio_prison {
		spinlock_t lock;
		mempool_t *cell_pool;

		unsigned nr_buckets;
		unsigned hash_mask;
		struct hlist_head *cells;
		};

		/----------------------------------------------------------------/

		static uint32_t calc_nr_buckets(unsigned nr_cells)
		{
		uint32_t n = 128;

		nr_cells /= 4;
		nr_cells = min(nr_cells, 8192u);

		while (n < nr_cells)
		n <<= 1;

		return n;
		}

		static struct kmem_cache *_cell_cache;

		/*
		* @nr_cells should be the number of cells you want in use _concurrently_.
		* Don't confuse it with the number of distinct keys.
		*/
		struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells)
		{
		unsigned i;
		uint32_t nr_buckets = calc_nr_buckets(nr_cells);
		size_t len = sizeof(struct dm_bio_prison) +
		(sizeof(struct hlist_head) * nr_buckets);
		struct dm_bio_prison *prison = kmalloc(len, GFP_KERNEL);

		if (!prison)
		return NULL;

		spin_lock_init(&prison->lock);
		prison->cell_pool = mempool_create_slab_pool(nr_cells, _cell_cache);
		if (!prison->cell_pool) {
		kfree(prison);
		return NULL;
		}

		prison->nr_buckets = nr_buckets;
		prison->hash_mask = nr_buckets - 1;
		prison->cells = (struct hlist_head *) (prison + 1);
		for (i = 0; i < nr_buckets; i++)
		INIT_HLIST_HEAD(prison->cells + i);

		return prison;
		}
		EXPORT_SYMBOL_GPL(dm_bio_prison_create);

		void dm_bio_prison_destroy(struct dm_bio_prison *prison)
		{
		mempool_destroy(prison->cell_pool);
		kfree(prison);
		}
		EXPORT_SYMBOL_GPL(dm_bio_prison_destroy);

		static uint32_t hash_key(struct dm_bio_prison prison, struct dm_cell_key key)
		{
		const unsigned long BIG_PRIME = 4294967291UL;
		uint64_t hash = key->block * BIG_PRIME;

		return (uint32_t) (hash & prison->hash_mask);
		}

		static int keys_equal(struct dm_cell_key lhs, struct dm_cell_key rhs)
		{
		return (lhs->virtual == rhs->virtual) &&
		(lhs->dev == rhs->dev) &&
		(lhs->block == rhs->block);
		}

		static struct dm_bio_prison_cell __search_bucket(struct hlist_head bucket,
		struct dm_cell_key *key)
		{
		struct dm_bio_prison_cell *cell;
		struct hlist_node *tmp;

		hlist_for_each_entry(cell, tmp, bucket, list)
		if (keys_equal(&cell->key, key))
		return cell;

		return NULL;
		}

		/*
		* This may block if a new cell needs allocating. You must ensure that
		* cells will be unlocked even if the calling thread is blocked.
		*
		* Returns 1 if the cell was already held, 0 if @inmate is the new holder.
		*/
		int dm_bio_detain(struct dm_bio_prison prison, struct dm_cell_key key,
		struct bio inmate, struct dm_bio_prison_cell *ref)
		{
		int r = 1;
		unsigned long flags;
		uint32_t hash = hash_key(prison, key);
		struct dm_bio_prison_cell cell, cell2;

		BUG_ON(hash > prison->nr_buckets);

		spin_lock_irqsave(&prison->lock, flags);

		cell = __search_bucket(prison->cells + hash, key);
		if (cell) {
		bio_list_add(&cell->bios, inmate);
		goto out;
		}

		/*
		* Allocate a new cell
		*/
		spin_unlock_irqrestore(&prison->lock, flags);
		cell2 = mempool_alloc(prison->cell_pool, GFP_NOIO);
		spin_lock_irqsave(&prison->lock, flags);

		/*
		* We've been unlocked, so we have to double check that
		* nobody else has inserted this cell in the meantime.
		*/
		cell = __search_bucket(prison->cells + hash, key);
		if (cell) {
		mempool_free(cell2, prison->cell_pool);
		bio_list_add(&cell->bios, inmate);
		goto out;
		}

		/*
		* Use new cell.
		*/
		cell = cell2;

		cell->prison = prison;
		memcpy(&cell->key, key, sizeof(cell->key));
		cell->holder = inmate;
		bio_list_init(&cell->bios);
		hlist_add_head(&cell->list, prison->cells + hash);

		r = 0;

		out:
		spin_unlock_irqrestore(&prison->lock, flags);

		*ref = cell;

		return r;
		}
		EXPORT_SYMBOL_GPL(dm_bio_detain);

		/*
		* @inmates must have been initialised prior to this call
		*/
		static void __cell_release(struct dm_bio_prison_cell cell, struct bio_list inmates)
		{
		struct dm_bio_prison *prison = cell->prison;

		hlist_del(&cell->list);

		if (inmates) {
		bio_list_add(inmates, cell->holder);
		bio_list_merge(inmates, &cell->bios);
		}

		mempool_free(cell, prison->cell_pool);
		}

		void dm_cell_release(struct dm_bio_prison_cell cell, struct bio_list bios)
		{
		unsigned long flags;
		struct dm_bio_prison *prison = cell->prison;

		spin_lock_irqsave(&prison->lock, flags);
		__cell_release(cell, bios);
		spin_unlock_irqrestore(&prison->lock, flags);
		}
		EXPORT_SYMBOL_GPL(dm_cell_release);

		/*
		* There are a couple of places where we put a bio into a cell briefly
		* before taking it out again. In these situations we know that no other
		* bio may be in the cell. This function releases the cell, and also does
		* a sanity check.
		*/
		static void __cell_release_singleton(struct dm_bio_prison_cell cell, struct bio bio)
		{
		BUG_ON(cell->holder != bio);
		BUG_ON(!bio_list_empty(&cell->bios));

		__cell_release(cell, NULL);
		}

		void dm_cell_release_singleton(struct dm_bio_prison_cell cell, struct bio bio)
		{
		unsigned long flags;
		struct dm_bio_prison *prison = cell->prison;

		spin_lock_irqsave(&prison->lock, flags);
		__cell_release_singleton(cell, bio);
		spin_unlock_irqrestore(&prison->lock, flags);
		}
		EXPORT_SYMBOL_GPL(dm_cell_release_singleton);

		/*
		* Sometimes we don't want the holder, just the additional bios.
		*/
		static void __cell_release_no_holder(struct dm_bio_prison_cell cell, struct bio_list inmates)
		{
		struct dm_bio_prison *prison = cell->prison;

		hlist_del(&cell->list);
		bio_list_merge(inmates, &cell->bios);

		mempool_free(cell, prison->cell_pool);
		}

		void dm_cell_release_no_holder(struct dm_bio_prison_cell cell, struct bio_list inmates)
		{
		unsigned long flags;
		struct dm_bio_prison *prison = cell->prison;

		spin_lock_irqsave(&prison->lock, flags);
		__cell_release_no_holder(cell, inmates);
		spin_unlock_irqrestore(&prison->lock, flags);
		}
		EXPORT_SYMBOL_GPL(dm_cell_release_no_holder);

		void dm_cell_error(struct dm_bio_prison_cell *cell)
		{
		struct dm_bio_prison *prison = cell->prison;
		struct bio_list bios;
		struct bio *bio;
		unsigned long flags;

		bio_list_init(&bios);

		spin_lock_irqsave(&prison->lock, flags);
		__cell_release(cell, &bios);
		spin_unlock_irqrestore(&prison->lock, flags);

		while ((bio = bio_list_pop(&bios)))
		bio_io_error(bio);
		}
		EXPORT_SYMBOL_GPL(dm_cell_error);

		/----------------------------------------------------------------/

		#define DEFERRED_SET_SIZE 64

		struct dm_deferred_entry {
		struct dm_deferred_set *ds;
		unsigned count;
		struct list_head work_items;
		};

		struct dm_deferred_set {
		spinlock_t lock;
		unsigned current_entry;
		unsigned sweeper;
		struct dm_deferred_entry entries[DEFERRED_SET_SIZE];
		};

		struct dm_deferred_set *dm_deferred_set_create(void)
		{
		int i;
		struct dm_deferred_set *ds;

		ds = kmalloc(sizeof(*ds), GFP_KERNEL);
		if (!ds)
		return NULL;

		spin_lock_init(&ds->lock);
		ds->current_entry = 0;
		ds->sweeper = 0;
		for (i = 0; i < DEFERRED_SET_SIZE; i++) {
		ds->entries[i].ds = ds;
		ds->entries[i].count = 0;
		INIT_LIST_HEAD(&ds->entries[i].work_items);
		}

		return ds;
		}
		EXPORT_SYMBOL_GPL(dm_deferred_set_create);

		void dm_deferred_set_destroy(struct dm_deferred_set *ds)
		{
		kfree(ds);
		}
		EXPORT_SYMBOL_GPL(dm_deferred_set_destroy);

		struct dm_deferred_entry dm_deferred_entry_inc(struct dm_deferred_set ds)
		{
		unsigned long flags;
		struct dm_deferred_entry *entry;

		spin_lock_irqsave(&ds->lock, flags);
		entry = ds->entries + ds->current_entry;
		entry->count++;
		spin_unlock_irqrestore(&ds->lock, flags);

		return entry;
		}
		EXPORT_SYMBOL_GPL(dm_deferred_entry_inc);

		static unsigned ds_next(unsigned index)
		{
		return (index + 1) % DEFERRED_SET_SIZE;
		}

		static void __sweep(struct dm_deferred_set ds, struct list_head head)
		{
		while ((ds->sweeper != ds->current_entry) &&
		!ds->entries[ds->sweeper].count) {
		list_splice_init(&ds->entries[ds->sweeper].work_items, head);
		ds->sweeper = ds_next(ds->sweeper);
		}

		if ((ds->sweeper == ds->current_entry) && !ds->entries[ds->sweeper].count)
		list_splice_init(&ds->entries[ds->sweeper].work_items, head);
		}

		void dm_deferred_entry_dec(struct dm_deferred_entry entry, struct list_head head)
		{
		unsigned long flags;

		spin_lock_irqsave(&entry->ds->lock, flags);
		BUG_ON(!entry->count);
		--entry->count;
		__sweep(entry->ds, head);
		spin_unlock_irqrestore(&entry->ds->lock, flags);
		}
		EXPORT_SYMBOL_GPL(dm_deferred_entry_dec);

		/*
		* Returns 1 if deferred or 0 if no pending items to delay job.
		*/
		int dm_deferred_set_add_work(struct dm_deferred_set ds, struct list_head work)
		{
		int r = 1;
		unsigned long flags;
		unsigned next_entry;

		spin_lock_irqsave(&ds->lock, flags);
		if ((ds->sweeper == ds->current_entry) &&
		!ds->entries[ds->current_entry].count)
		r = 0;
		else {
		list_add(work, &ds->entries[ds->current_entry].work_items);
		next_entry = ds_next(ds->current_entry);
		if (!ds->entries[next_entry].count)
		ds->current_entry = next_entry;
		}
		spin_unlock_irqrestore(&ds->lock, flags);

		return r;
		}
		EXPORT_SYMBOL_GPL(dm_deferred_set_add_work);

		/----------------------------------------------------------------/

		static int __init dm_bio_prison_init(void)
		{
		_cell_cache = KMEM_CACHE(dm_bio_prison_cell, 0);
		if (!_cell_cache)
		return -ENOMEM;

		return 0;
		}

		static void __exit dm_bio_prison_exit(void)
		{
		kmem_cache_destroy(_cell_cache);
		_cell_cache = NULL;
		}

		/*
		* module hooks
		*/
		module_init(dm_bio_prison_init);
		module_exit(dm_bio_prison_exit);

		MODULE_DESCRIPTION(DM_NAME " bio prison");
		MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
		MODULE_LICENSE("GPL");

drivers/md/dm-bio-prison.h

0 → 100644

+72 −0

Original line number	Diff line number	Diff line
		/*
		* Copyright (C) 2011-2012 Red Hat, Inc.
		*
		* This file is released under the GPL.
		*/

		#ifndef DM_BIO_PRISON_H
		#define DM_BIO_PRISON_H

		#include "persistent-data/dm-block-manager.h" /* FIXME: for dm_block_t */
		#include "dm-thin-metadata.h" /* FIXME: for dm_thin_id */

		#include <linux/list.h>
		#include <linux/bio.h>

		/----------------------------------------------------------------/

		/*
		* Sometimes we can't deal with a bio straight away. We put them in prison
		* where they can't cause any mischief. Bios are put in a cell identified
		* by a key, multiple bios can be in the same cell. When the cell is
		* subsequently unlocked the bios become available.
		*/
		struct dm_bio_prison;
		struct dm_bio_prison_cell;

		/* FIXME: this needs to be more abstract */
		struct dm_cell_key {
		int virtual;
		dm_thin_id dev;
		dm_block_t block;
		};

		struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells);
		void dm_bio_prison_destroy(struct dm_bio_prison *prison);

		/*
		* This may block if a new cell needs allocating. You must ensure that
		* cells will be unlocked even if the calling thread is blocked.
		*
		* Returns 1 if the cell was already held, 0 if @inmate is the new holder.
		*/
		int dm_bio_detain(struct dm_bio_prison prison, struct dm_cell_key key,
		struct bio inmate, struct dm_bio_prison_cell *ref);

		void dm_cell_release(struct dm_bio_prison_cell cell, struct bio_list bios);
		void dm_cell_release_singleton(struct dm_bio_prison_cell cell, struct bio bio); // FIXME: bio arg not needed
		void dm_cell_release_no_holder(struct dm_bio_prison_cell cell, struct bio_list inmates);
		void dm_cell_error(struct dm_bio_prison_cell *cell);

		/----------------------------------------------------------------/

		/*
		* We use the deferred set to keep track of pending reads to shared blocks.
		* We do this to ensure the new mapping caused by a write isn't performed
		* until these prior reads have completed. Otherwise the insertion of the
		* new mapping could free the old block that the read bios are mapped to.
		*/

		struct dm_deferred_set;
		struct dm_deferred_entry;

		struct dm_deferred_set *dm_deferred_set_create(void);
		void dm_deferred_set_destroy(struct dm_deferred_set *ds);

		struct dm_deferred_entry dm_deferred_entry_inc(struct dm_deferred_set ds);
		void dm_deferred_entry_dec(struct dm_deferred_entry entry, struct list_head head);
		int dm_deferred_set_add_work(struct dm_deferred_set ds, struct list_head work);

		/----------------------------------------------------------------/

		#endif

drivers/md/dm-thin.c

+3 −404

Original line number	Diff line number	Diff line
		@@ -5,6 +5,7 @@
		*/

		#include "dm-thin-metadata.h"
		#include "dm-bio-prison.h"
		#include "dm.h"

		#include <linux/device-mapper.h>
		@@ -21,7 +22,6 @@
		* Tunable constants
		*/
		#define ENDIO_HOOK_POOL_SIZE 1024
		#define DEFERRED_SET_SIZE 64
		#define MAPPING_POOL_SIZE 1024
		#define PRISON_CELLS 1024
		#define COMMIT_PERIOD HZ
		@@ -98,404 +98,6 @@

		/----------------------------------------------------------------/

		/*
		* Sometimes we can't deal with a bio straight away. We put them in prison
		* where they can't cause any mischief. Bios are put in a cell identified
		* by a key, multiple bios can be in the same cell. When the cell is
		* subsequently unlocked the bios become available.
		*/
		struct dm_bio_prison;

		struct dm_cell_key {
		int virtual;
		dm_thin_id dev;
		dm_block_t block;
		};

		struct dm_bio_prison_cell {
		struct hlist_node list;
		struct dm_bio_prison *prison;
		struct dm_cell_key key;
		struct bio *holder;
		struct bio_list bios;
		};

		struct dm_bio_prison {
		spinlock_t lock;
		mempool_t *cell_pool;

		unsigned nr_buckets;
		unsigned hash_mask;
		struct hlist_head *cells;
		};

		static uint32_t calc_nr_buckets(unsigned nr_cells)
		{
		uint32_t n = 128;

		nr_cells /= 4;
		nr_cells = min(nr_cells, 8192u);

		while (n < nr_cells)
		n <<= 1;

		return n;
		}

		static struct kmem_cache *_cell_cache;

		/*
		* @nr_cells should be the number of cells you want in use _concurrently_.
		* Don't confuse it with the number of distinct keys.
		*/
		static struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells)
		{
		unsigned i;
		uint32_t nr_buckets = calc_nr_buckets(nr_cells);
		size_t len = sizeof(struct dm_bio_prison) +
		(sizeof(struct hlist_head) * nr_buckets);
		struct dm_bio_prison *prison = kmalloc(len, GFP_KERNEL);

		if (!prison)
		return NULL;

		spin_lock_init(&prison->lock);
		prison->cell_pool = mempool_create_slab_pool(nr_cells, _cell_cache);
		if (!prison->cell_pool) {
		kfree(prison);
		return NULL;
		}

		prison->nr_buckets = nr_buckets;
		prison->hash_mask = nr_buckets - 1;
		prison->cells = (struct hlist_head *) (prison + 1);
		for (i = 0; i < nr_buckets; i++)
		INIT_HLIST_HEAD(prison->cells + i);

		return prison;
		}

		static void dm_bio_prison_destroy(struct dm_bio_prison *prison)
		{
		mempool_destroy(prison->cell_pool);
		kfree(prison);
		}

		static uint32_t hash_key(struct dm_bio_prison prison, struct dm_cell_key key)
		{
		const unsigned long BIG_PRIME = 4294967291UL;
		uint64_t hash = key->block * BIG_PRIME;

		return (uint32_t) (hash & prison->hash_mask);
		}

		static int keys_equal(struct dm_cell_key lhs, struct dm_cell_key rhs)
		{
		return (lhs->virtual == rhs->virtual) &&
		(lhs->dev == rhs->dev) &&
		(lhs->block == rhs->block);
		}

		static struct dm_bio_prison_cell __search_bucket(struct hlist_head bucket,
		struct dm_cell_key *key)
		{
		struct dm_bio_prison_cell *cell;
		struct hlist_node *tmp;

		hlist_for_each_entry(cell, tmp, bucket, list)
		if (keys_equal(&cell->key, key))
		return cell;

		return NULL;
		}

		/*
		* This may block if a new cell needs allocating. You must ensure that
		* cells will be unlocked even if the calling thread is blocked.
		*
		* Returns 1 if the cell was already held, 0 if @inmate is the new holder.
		*/
		static int dm_bio_detain(struct dm_bio_prison prison, struct dm_cell_key key,
		struct bio inmate, struct dm_bio_prison_cell *ref)
		{
		int r = 1;
		unsigned long flags;
		uint32_t hash = hash_key(prison, key);
		struct dm_bio_prison_cell cell, cell2;

		BUG_ON(hash > prison->nr_buckets);

		spin_lock_irqsave(&prison->lock, flags);

		cell = __search_bucket(prison->cells + hash, key);
		if (cell) {
		bio_list_add(&cell->bios, inmate);
		goto out;
		}

		/*
		* Allocate a new cell
		*/
		spin_unlock_irqrestore(&prison->lock, flags);
		cell2 = mempool_alloc(prison->cell_pool, GFP_NOIO);
		spin_lock_irqsave(&prison->lock, flags);

		/*
		* We've been unlocked, so we have to double check that
		* nobody else has inserted this cell in the meantime.
		*/
		cell = __search_bucket(prison->cells + hash, key);
		if (cell) {
		mempool_free(cell2, prison->cell_pool);
		bio_list_add(&cell->bios, inmate);
		goto out;
		}

		/*
		* Use new cell.
		*/
		cell = cell2;

		cell->prison = prison;
		memcpy(&cell->key, key, sizeof(cell->key));
		cell->holder = inmate;
		bio_list_init(&cell->bios);
		hlist_add_head(&cell->list, prison->cells + hash);

		r = 0;

		out:
		spin_unlock_irqrestore(&prison->lock, flags);

		*ref = cell;

		return r;
		}

		/*
		* @inmates must have been initialised prior to this call
		*/
		static void __cell_release(struct dm_bio_prison_cell cell, struct bio_list inmates)
		{
		struct dm_bio_prison *prison = cell->prison;

		hlist_del(&cell->list);

		if (inmates) {
		bio_list_add(inmates, cell->holder);
		bio_list_merge(inmates, &cell->bios);
		}

		mempool_free(cell, prison->cell_pool);
		}

		static void dm_cell_release(struct dm_bio_prison_cell cell, struct bio_list bios)
		{
		unsigned long flags;
		struct dm_bio_prison *prison = cell->prison;

		spin_lock_irqsave(&prison->lock, flags);
		__cell_release(cell, bios);
		spin_unlock_irqrestore(&prison->lock, flags);
		}

		/*
		* There are a couple of places where we put a bio into a cell briefly
		* before taking it out again. In these situations we know that no other
		* bio may be in the cell. This function releases the cell, and also does
		* a sanity check.
		*/
		static void __cell_release_singleton(struct dm_bio_prison_cell cell, struct bio bio)
		{
		BUG_ON(cell->holder != bio);
		BUG_ON(!bio_list_empty(&cell->bios));

		__cell_release(cell, NULL);
		}

		static void dm_cell_release_singleton(struct dm_bio_prison_cell cell, struct bio bio)
		{
		unsigned long flags;
		struct dm_bio_prison *prison = cell->prison;

		spin_lock_irqsave(&prison->lock, flags);
		__cell_release_singleton(cell, bio);
		spin_unlock_irqrestore(&prison->lock, flags);
		}

		/*
		* Sometimes we don't want the holder, just the additional bios.
		*/
		static void __cell_release_no_holder(struct dm_bio_prison_cell *cell,
		struct bio_list *inmates)
		{
		struct dm_bio_prison *prison = cell->prison;

		hlist_del(&cell->list);
		bio_list_merge(inmates, &cell->bios);

		mempool_free(cell, prison->cell_pool);
		}

		static void dm_cell_release_no_holder(struct dm_bio_prison_cell *cell,
		struct bio_list *inmates)
		{
		unsigned long flags;
		struct dm_bio_prison *prison = cell->prison;

		spin_lock_irqsave(&prison->lock, flags);
		__cell_release_no_holder(cell, inmates);
		spin_unlock_irqrestore(&prison->lock, flags);
		}

		static void dm_cell_error(struct dm_bio_prison_cell *cell)
		{
		struct dm_bio_prison *prison = cell->prison;
		struct bio_list bios;
		struct bio *bio;
		unsigned long flags;

		bio_list_init(&bios);

		spin_lock_irqsave(&prison->lock, flags);
		__cell_release(cell, &bios);
		spin_unlock_irqrestore(&prison->lock, flags);

		while ((bio = bio_list_pop(&bios)))
		bio_io_error(bio);
		}

		/----------------------------------------------------------------/

		/*
		* We use the deferred set to keep track of pending reads to shared blocks.
		* We do this to ensure the new mapping caused by a write isn't performed
		* until these prior reads have completed. Otherwise the insertion of the
		* new mapping could free the old block that the read bios are mapped to.
		*/

		struct dm_deferred_set;
		struct dm_deferred_entry {
		struct dm_deferred_set *ds;
		unsigned count;
		struct list_head work_items;
		};

		struct dm_deferred_set {
		spinlock_t lock;
		unsigned current_entry;
		unsigned sweeper;
		struct dm_deferred_entry entries[DEFERRED_SET_SIZE];
		};

		static struct dm_deferred_set *dm_deferred_set_create(void)
		{
		int i;
		struct dm_deferred_set *ds;

		ds = kmalloc(sizeof(*ds), GFP_KERNEL);
		if (!ds)
		return NULL;

		spin_lock_init(&ds->lock);
		ds->current_entry = 0;
		ds->sweeper = 0;
		for (i = 0; i < DEFERRED_SET_SIZE; i++) {
		ds->entries[i].ds = ds;
		ds->entries[i].count = 0;
		INIT_LIST_HEAD(&ds->entries[i].work_items);
		}

		return ds;
		}

		static void dm_deferred_set_destroy(struct dm_deferred_set *ds)
		{
		kfree(ds);
		}

		static struct dm_deferred_entry dm_deferred_entry_inc(struct dm_deferred_set ds)
		{
		unsigned long flags;
		struct dm_deferred_entry *entry;

		spin_lock_irqsave(&ds->lock, flags);
		entry = ds->entries + ds->current_entry;
		entry->count++;
		spin_unlock_irqrestore(&ds->lock, flags);

		return entry;
		}

		static unsigned ds_next(unsigned index)
		{
		return (index + 1) % DEFERRED_SET_SIZE;
		}

		static void __sweep(struct dm_deferred_set ds, struct list_head head)
		{
		while ((ds->sweeper != ds->current_entry) &&
		!ds->entries[ds->sweeper].count) {
		list_splice_init(&ds->entries[ds->sweeper].work_items, head);
		ds->sweeper = ds_next(ds->sweeper);
		}

		if ((ds->sweeper == ds->current_entry) && !ds->entries[ds->sweeper].count)
		list_splice_init(&ds->entries[ds->sweeper].work_items, head);
		}

		static void dm_deferred_entry_dec(struct dm_deferred_entry entry, struct list_head head)
		{
		unsigned long flags;

		spin_lock_irqsave(&entry->ds->lock, flags);
		BUG_ON(!entry->count);
		--entry->count;
		__sweep(entry->ds, head);
		spin_unlock_irqrestore(&entry->ds->lock, flags);
		}

		/*
		* Returns 1 if deferred or 0 if no pending items to delay job.
		*/
		static int dm_deferred_set_add_work(struct dm_deferred_set ds, struct list_head work)
		{
		int r = 1;
		unsigned long flags;
		unsigned next_entry;

		spin_lock_irqsave(&ds->lock, flags);
		if ((ds->sweeper == ds->current_entry) &&
		!ds->entries[ds->current_entry].count)
		r = 0;
		else {
		list_add(work, &ds->entries[ds->current_entry].work_items);
		next_entry = ds_next(ds->current_entry);
		if (!ds->entries[next_entry].count)
		ds->current_entry = next_entry;
		}
		spin_unlock_irqrestore(&ds->lock, flags);

		return r;
		}

		static int __init dm_bio_prison_init(void)
		{
		_cell_cache = KMEM_CACHE(dm_bio_prison_cell, 0);
		if (!_cell_cache)
		return -ENOMEM;

		return 0;
		}

		static void __exit dm_bio_prison_exit(void)
		{
		kmem_cache_destroy(_cell_cache);
		_cell_cache = NULL;
		}

		/----------------------------------------------------------------/

		/*
		* Key building.
		*/
		@@ -2852,7 +2454,7 @@ static struct target_type pool_target = {
		.name = "thin-pool",
		.features = DM_TARGET_SINGLETON \| DM_TARGET_ALWAYS_WRITEABLE \|
		DM_TARGET_IMMUTABLE,
		.version = {1, 4, 0},
		.version = {1, 5, 0},
		.module = THIS_MODULE,
		.ctr = pool_ctr,
		.dtr = pool_dtr,
		@@ -3143,7 +2745,7 @@ static void thin_io_hints(struct dm_target ti, struct queue_limits limits)

		static struct target_type thin_target = {
		.name = "thin",
		.version = {1, 4, 0},
		.version = {1, 5, 0},
		.module = THIS_MODULE,
		.ctr = thin_ctr,
		.dtr = thin_dtr,
		@@ -3173,8 +2775,6 @@ static int __init dm_thin_init(void)

		r = -ENOMEM;

		dm_bio_prison_init();

		_new_mapping_cache = KMEM_CACHE(dm_thin_new_mapping, 0);
		if (!_new_mapping_cache)
		goto bad_new_mapping_cache;
		@@ -3200,7 +2800,6 @@ static void dm_thin_exit(void)
		dm_unregister_target(&thin_target);
		dm_unregister_target(&pool_target);

		dm_bio_prison_exit();
		kmem_cache_destroy(_new_mapping_cache);
		kmem_cache_destroy(_endio_hook_cache);
		}