Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2967 insertions, 0 deletions

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
new file mode 100644
index 0000000000..486e1180cc
--- /dev/null
+++ b/drivers/md/dm-bufio.c
@@ -0,0 +1,2967 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2009-2011 Red Hat, Inc.
+ *
+ * Author: Mikulas Patocka <mpatocka@redhat.com>
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/dm-bufio.h>
+
+#include <linux/device-mapper.h>
+#include <linux/dm-io.h>
+#include <linux/slab.h>
+#include <linux/sched/mm.h>
+#include <linux/jiffies.h>
+#include <linux/vmalloc.h>
+#include <linux/shrinker.h>
+#include <linux/module.h>
+#include <linux/rbtree.h>
+#include <linux/stacktrace.h>
+#include <linux/jump_label.h>
+
+#include "dm.h"
+
+#define DM_MSG_PREFIX "bufio"
+
+/*
+ * Memory management policy:
+ *	Limit the number of buffers to DM_BUFIO_MEMORY_PERCENT of main memory
+ *	or DM_BUFIO_VMALLOC_PERCENT of vmalloc memory (whichever is lower).
+ *	Always allocate at least DM_BUFIO_MIN_BUFFERS buffers.
+ *	Start background writeback when there are DM_BUFIO_WRITEBACK_PERCENT
+ *	dirty buffers.
+ */
+#define DM_BUFIO_MIN_BUFFERS		8
+
+#define DM_BUFIO_MEMORY_PERCENT		2
+#define DM_BUFIO_VMALLOC_PERCENT	25
+#define DM_BUFIO_WRITEBACK_RATIO	3
+#define DM_BUFIO_LOW_WATERMARK_RATIO	16
+
+/*
+ * Check buffer ages in this interval (seconds)
+ */
+#define DM_BUFIO_WORK_TIMER_SECS	30
+
+/*
+ * Free buffers when they are older than this (seconds)
+ */
+#define DM_BUFIO_DEFAULT_AGE_SECS	300
+
+/*
+ * The nr of bytes of cached data to keep around.
+ */
+#define DM_BUFIO_DEFAULT_RETAIN_BYTES   (256 * 1024)
+
+/*
+ * Align buffer writes to this boundary.
+ * Tests show that SSDs have the highest IOPS when using 4k writes.
+ */
+#define DM_BUFIO_WRITE_ALIGN		4096
+
+/*
+ * dm_buffer->list_mode
+ */
+#define LIST_CLEAN	0
+#define LIST_DIRTY	1
+#define LIST_SIZE	2
+
+/*--------------------------------------------------------------*/
+
+/*
+ * Rather than use an LRU list, we use a clock algorithm where entries
+ * are held in a circular list.  When an entry is 'hit' a reference bit
+ * is set.  The least recently used entry is approximated by running a
+ * cursor around the list selecting unreferenced entries. Referenced
+ * entries have their reference bit cleared as the cursor passes them.
+ */
+struct lru_entry {
+	struct list_head list;
+	atomic_t referenced;
+};
+
+struct lru_iter {
+	struct lru *lru;
+	struct list_head list;
+	struct lru_entry *stop;
+	struct lru_entry *e;
+};
+
+struct lru {
+	struct list_head *cursor;
+	unsigned long count;
+
+	struct list_head iterators;
+};
+
+/*--------------*/
+
+static void lru_init(struct lru *lru)
+{
+	lru->cursor = NULL;
+	lru->count = 0;
+	INIT_LIST_HEAD(&lru->iterators);
+}
+
+static void lru_destroy(struct lru *lru)
+{
+	WARN_ON_ONCE(lru->cursor);
+	WARN_ON_ONCE(!list_empty(&lru->iterators));
+}
+
+/*
+ * Insert a new entry into the lru.
+ */
+static void lru_insert(struct lru *lru, struct lru_entry *le)
+{
+	/*
+	 * Don't be tempted to set to 1, makes the lru aspect
+	 * perform poorly.
+	 */
+	atomic_set(&le->referenced, 0);
+
+	if (lru->cursor) {
+		list_add_tail(&le->list, lru->cursor);
+	} else {
+		INIT_LIST_HEAD(&le->list);
+		lru->cursor = &le->list;
+	}
+	lru->count++;
+}
+
+/*--------------*/
+
+/*
+ * Convert a list_head pointer to an lru_entry pointer.
+ */
+static inline struct lru_entry *to_le(struct list_head *l)
+{
+	return container_of(l, struct lru_entry, list);
+}
+
+/*
+ * Initialize an lru_iter and add it to the list of cursors in the lru.
+ */
+static void lru_iter_begin(struct lru *lru, struct lru_iter *it)
+{
+	it->lru = lru;
+	it->stop = lru->cursor ? to_le(lru->cursor->prev) : NULL;
+	it->e = lru->cursor ? to_le(lru->cursor) : NULL;
+	list_add(&it->list, &lru->iterators);
+}
+
+/*
+ * Remove an lru_iter from the list of cursors in the lru.
+ */
+static inline void lru_iter_end(struct lru_iter *it)
+{
+	list_del(&it->list);
+}
+
+/* Predicate function type to be used with lru_iter_next */
+typedef bool (*iter_predicate)(struct lru_entry *le, void *context);
+
+/*
+ * Advance the cursor to the next entry that passes the
+ * predicate, and return that entry.  Returns NULL if the
+ * iteration is complete.
+ */
+static struct lru_entry *lru_iter_next(struct lru_iter *it,
+				       iter_predicate pred, void *context)
+{
+	struct lru_entry *e;
+
+	while (it->e) {
+		e = it->e;
+
+		/* advance the cursor */
+		if (it->e == it->stop)
+			it->e = NULL;
+		else
+			it->e = to_le(it->e->list.next);
+
+		if (pred(e, context))
+			return e;
+	}
+
+	return NULL;
+}
+
+/*
+ * Invalidate a specific lru_entry and update all cursors in
+ * the lru accordingly.
+ */
+static void lru_iter_invalidate(struct lru *lru, struct lru_entry *e)
+{
+	struct lru_iter *it;
+
+	list_for_each_entry(it, &lru->iterators, list) {
+		/* Move c->e forwards if necc. */
+		if (it->e == e) {
+			it->e = to_le(it->e->list.next);
+			if (it->e == e)
+				it->e = NULL;
+		}
+
+		/* Move it->stop backwards if necc. */
+		if (it->stop == e) {
+			it->stop = to_le(it->stop->list.prev);
+			if (it->stop == e)
+				it->stop = NULL;
+		}
+	}
+}
+
+/*--------------*/
+
+/*
+ * Remove a specific entry from the lru.
+ */
+static void lru_remove(struct lru *lru, struct lru_entry *le)
+{
+	lru_iter_invalidate(lru, le);
+	if (lru->count == 1) {
+		lru->cursor = NULL;
+	} else {
+		if (lru->cursor == &le->list)
+			lru->cursor = lru->cursor->next;
+		list_del(&le->list);
+	}
+	lru->count--;
+}
+
+/*
+ * Mark as referenced.
+ */
+static inline void lru_reference(struct lru_entry *le)
+{
+	atomic_set(&le->referenced, 1);
+}
+
+/*--------------*/
+
+/*
+ * Remove the least recently used entry (approx), that passes the predicate.
+ * Returns NULL on failure.
+ */
+enum evict_result {
+	ER_EVICT,
+	ER_DONT_EVICT,
+	ER_STOP, /* stop looking for something to evict */
+};
+
+typedef enum evict_result (*le_predicate)(struct lru_entry *le, void *context);
+
+static struct lru_entry *lru_evict(struct lru *lru, le_predicate pred, void *context, bool no_sleep)
+{
+	unsigned long tested = 0;
+	struct list_head *h = lru->cursor;
+	struct lru_entry *le;
+
+	if (!h)
+		return NULL;
+	/*
+	 * In the worst case we have to loop around twice. Once to clear
+	 * the reference flags, and then again to discover the predicate
+	 * fails for all entries.
+	 */
+	while (tested < lru->count) {
+		le = container_of(h, struct lru_entry, list);
+
+		if (atomic_read(&le->referenced)) {
+			atomic_set(&le->referenced, 0);
+		} else {
+			tested++;
+			switch (pred(le, context)) {
+			case ER_EVICT:
+				/*
+				 * Adjust the cursor, so we start the next
+				 * search from here.
+				 */
+				lru->cursor = le->list.next;
+				lru_remove(lru, le);
+				return le;
+
+			case ER_DONT_EVICT:
+				break;
+
+			case ER_STOP:
+				lru->cursor = le->list.next;
+				return NULL;
+			}
+		}
+
+		h = h->next;
+
+		if (!no_sleep)
+			cond_resched();
+	}
+
+	return NULL;
+}
+
+/*--------------------------------------------------------------*/
+
+/*
+ * Buffer state bits.
+ */
+#define B_READING	0
+#define B_WRITING	1
+#define B_DIRTY		2
+
+/*
+ * Describes how the block was allocated:
+ * kmem_cache_alloc(), __get_free_pages() or vmalloc().
+ * See the comment at alloc_buffer_data.
+ */
+enum data_mode {
+	DATA_MODE_SLAB = 0,
+	DATA_MODE_GET_FREE_PAGES = 1,
+	DATA_MODE_VMALLOC = 2,
+	DATA_MODE_LIMIT = 3
+};
+
+struct dm_buffer {
+	/* protected by the locks in dm_buffer_cache */
+	struct rb_node node;
+
+	/* immutable, so don't need protecting */
+	sector_t block;
+	void *data;
+	unsigned char data_mode;		/* DATA_MODE_* */
+
+	/*
+	 * These two fields are used in isolation, so do not need
+	 * a surrounding lock.
+	 */
+	atomic_t hold_count;
+	unsigned long last_accessed;
+
+	/*
+	 * Everything else is protected by the mutex in
+	 * dm_bufio_client
+	 */
+	unsigned long state;
+	struct lru_entry lru;
+	unsigned char list_mode;		/* LIST_* */
+	blk_status_t read_error;
+	blk_status_t write_error;
+	unsigned int dirty_start;
+	unsigned int dirty_end;
+	unsigned int write_start;
+	unsigned int write_end;
+	struct list_head write_list;
+	struct dm_bufio_client *c;
+	void (*end_io)(struct dm_buffer *b, blk_status_t bs);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+#define MAX_STACK 10
+	unsigned int stack_len;
+	unsigned long stack_entries[MAX_STACK];
+#endif
+};
+
+/*--------------------------------------------------------------*/
+
+/*
+ * The buffer cache manages buffers, particularly:
+ *  - inc/dec of holder count
+ *  - setting the last_accessed field
+ *  - maintains clean/dirty state along with lru
+ *  - selecting buffers that match predicates
+ *
+ * It does *not* handle:
+ *  - allocation/freeing of buffers.
+ *  - IO
+ *  - Eviction or cache sizing.
+ *
+ * cache_get() and cache_put() are threadsafe, you do not need to
+ * protect these calls with a surrounding mutex.  All the other
+ * methods are not threadsafe; they do use locking primitives, but
+ * only enough to ensure get/put are threadsafe.
+ */
+
+struct buffer_tree {
+	union {
+		struct rw_semaphore lock;
+		rwlock_t spinlock;
+	} u;
+	struct rb_root root;
+} ____cacheline_aligned_in_smp;
+
+struct dm_buffer_cache {
+	struct lru lru[LIST_SIZE];
+	/*
+	 * We spread entries across multiple trees to reduce contention
+	 * on the locks.
+	 */
+	unsigned int num_locks;
+	bool no_sleep;
+	struct buffer_tree trees[];
+};
+
+static DEFINE_STATIC_KEY_FALSE(no_sleep_enabled);
+
+static inline unsigned int cache_index(sector_t block, unsigned int num_locks)
+{
+	return dm_hash_locks_index(block, num_locks);
+}
+
+static inline void cache_read_lock(struct dm_buffer_cache *bc, sector_t block)
+{
+	if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
+		read_lock_bh(&bc->trees[cache_index(block, bc->num_locks)].u.spinlock);
+	else
+		down_read(&bc->trees[cache_index(block, bc->num_locks)].u.lock);
+}
+
+static inline void cache_read_unlock(struct dm_buffer_cache *bc, sector_t block)
+{
+	if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
+		read_unlock_bh(&bc->trees[cache_index(block, bc->num_locks)].u.spinlock);
+	else
+		up_read(&bc->trees[cache_index(block, bc->num_locks)].u.lock);
+}
+
+static inline void cache_write_lock(struct dm_buffer_cache *bc, sector_t block)
+{
+	if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
+		write_lock_bh(&bc->trees[cache_index(block, bc->num_locks)].u.spinlock);
+	else
+		down_write(&bc->trees[cache_index(block, bc->num_locks)].u.lock);
+}
+
+static inline void cache_write_unlock(struct dm_buffer_cache *bc, sector_t block)
+{
+	if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
+		write_unlock_bh(&bc->trees[cache_index(block, bc->num_locks)].u.spinlock);
+	else
+		up_write(&bc->trees[cache_index(block, bc->num_locks)].u.lock);
+}
+
+/*
+ * Sometimes we want to repeatedly get and drop locks as part of an iteration.
+ * This struct helps avoid redundant drop and gets of the same lock.
+ */
+struct lock_history {
+	struct dm_buffer_cache *cache;
+	bool write;
+	unsigned int previous;
+	unsigned int no_previous;
+};
+
+static void lh_init(struct lock_history *lh, struct dm_buffer_cache *cache, bool write)
+{
+	lh->cache = cache;
+	lh->write = write;
+	lh->no_previous = cache->num_locks;
+	lh->previous = lh->no_previous;
+}
+
+static void __lh_lock(struct lock_history *lh, unsigned int index)
+{
+	if (lh->write) {
+		if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
+			write_lock_bh(&lh->cache->trees[index].u.spinlock);
+		else
+			down_write(&lh->cache->trees[index].u.lock);
+	} else {
+		if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
+			read_lock_bh(&lh->cache->trees[index].u.spinlock);
+		else
+			down_read(&lh->cache->trees[index].u.lock);
+	}
+}
+
+static void __lh_unlock(struct lock_history *lh, unsigned int index)
+{
+	if (lh->write) {
+		if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
+			write_unlock_bh(&lh->cache->trees[index].u.spinlock);
+		else
+			up_write(&lh->cache->trees[index].u.lock);
+	} else {
+		if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
+			read_unlock_bh(&lh->cache->trees[index].u.spinlock);
+		else
+			up_read(&lh->cache->trees[index].u.lock);
+	}
+}
+
+/*
+ * Make sure you call this since it will unlock the final lock.
+ */
+static void lh_exit(struct lock_history *lh)
+{
+	if (lh->previous != lh->no_previous) {
+		__lh_unlock(lh, lh->previous);
+		lh->previous = lh->no_previous;
+	}
+}
+
+/*
+ * Named 'next' because there is no corresponding
+ * 'up/unlock' call since it's done automatically.
+ */
+static void lh_next(struct lock_history *lh, sector_t b)
+{
+	unsigned int index = cache_index(b, lh->no_previous); /* no_previous is num_locks */
+
+	if (lh->previous != lh->no_previous) {
+		if (lh->previous != index) {
+			__lh_unlock(lh, lh->previous);
+			__lh_lock(lh, index);
+			lh->previous = index;
+		}
+	} else {
+		__lh_lock(lh, index);
+		lh->previous = index;
+	}
+}
+
+static inline struct dm_buffer *le_to_buffer(struct lru_entry *le)
+{
+	return container_of(le, struct dm_buffer, lru);
+}
+
+static struct dm_buffer *list_to_buffer(struct list_head *l)
+{
+	struct lru_entry *le = list_entry(l, struct lru_entry, list);
+
+	if (!le)
+		return NULL;
+
+	return le_to_buffer(le);
+}
+
+static void cache_init(struct dm_buffer_cache *bc, unsigned int num_locks, bool no_sleep)
+{
+	unsigned int i;
+
+	bc->num_locks = num_locks;
+	bc->no_sleep = no_sleep;
+
+	for (i = 0; i < bc->num_locks; i++) {
+		if (no_sleep)
+			rwlock_init(&bc->trees[i].u.spinlock);
+		else
+			init_rwsem(&bc->trees[i].u.lock);
+		bc->trees[i].root = RB_ROOT;
+	}
+
+	lru_init(&bc->lru[LIST_CLEAN]);
+	lru_init(&bc->lru[LIST_DIRTY]);
+}
+
+static void cache_destroy(struct dm_buffer_cache *bc)
+{
+	unsigned int i;
+
+	for (i = 0; i < bc->num_locks; i++)
+		WARN_ON_ONCE(!RB_EMPTY_ROOT(&bc->trees[i].root));
+
+	lru_destroy(&bc->lru[LIST_CLEAN]);
+	lru_destroy(&bc->lru[LIST_DIRTY]);
+}
+
+/*--------------*/
+
+/*
+ * not threadsafe, or racey depending how you look at it
+ */
+static inline unsigned long cache_count(struct dm_buffer_cache *bc, int list_mode)
+{
+	return bc->lru[list_mode].count;
+}
+
+static inline unsigned long cache_total(struct dm_buffer_cache *bc)
+{
+	return cache_count(bc, LIST_CLEAN) + cache_count(bc, LIST_DIRTY);
+}
+
+/*--------------*/
+
+/*
+ * Gets a specific buffer, indexed by block.
+ * If the buffer is found then its holder count will be incremented and
+ * lru_reference will be called.
+ *
+ * threadsafe
+ */
+static struct dm_buffer *__cache_get(const struct rb_root *root, sector_t block)
+{
+	struct rb_node *n = root->rb_node;
+	struct dm_buffer *b;
+
+	while (n) {
+		b = container_of(n, struct dm_buffer, node);
+
+		if (b->block == block)
+			return b;
+
+		n = block < b->block ? n->rb_left : n->rb_right;
+	}
+
+	return NULL;
+}
+
+static void __cache_inc_buffer(struct dm_buffer *b)
+{
+	atomic_inc(&b->hold_count);
+	WRITE_ONCE(b->last_accessed, jiffies);
+}
+
+static struct dm_buffer *cache_get(struct dm_buffer_cache *bc, sector_t block)
+{
+	struct dm_buffer *b;
+
+	cache_read_lock(bc, block);
+	b = __cache_get(&bc->trees[cache_index(block, bc->num_locks)].root, block);
+	if (b) {
+		lru_reference(&b->lru);
+		__cache_inc_buffer(b);
+	}
+	cache_read_unlock(bc, block);
+
+	return b;
+}
+
+/*--------------*/
+
+/*
+ * Returns true if the hold count hits zero.
+ * threadsafe
+ */
+static bool cache_put(struct dm_buffer_cache *bc, struct dm_buffer *b)
+{
+	bool r;
+
+	cache_read_lock(bc, b->block);
+	BUG_ON(!atomic_read(&b->hold_count));
+	r = atomic_dec_and_test(&b->hold_count);
+	cache_read_unlock(bc, b->block);
+
+	return r;
+}
+
+/*--------------*/
+
+typedef enum evict_result (*b_predicate)(struct dm_buffer *, void *);
+
+/*
+ * Evicts a buffer based on a predicate.  The oldest buffer that
+ * matches the predicate will be selected.  In addition to the
+ * predicate the hold_count of the selected buffer will be zero.
+ */
+struct evict_wrapper {
+	struct lock_history *lh;
+	b_predicate pred;
+	void *context;
+};
+
+/*
+ * Wraps the buffer predicate turning it into an lru predicate.  Adds
+ * extra test for hold_count.
+ */
+static enum evict_result __evict_pred(struct lru_entry *le, void *context)
+{
+	struct evict_wrapper *w = context;
+	struct dm_buffer *b = le_to_buffer(le);
+
+	lh_next(w->lh, b->block);
+
+	if (atomic_read(&b->hold_count))
+		return ER_DONT_EVICT;
+
+	return w->pred(b, w->context);
+}
+
+static struct dm_buffer *__cache_evict(struct dm_buffer_cache *bc, int list_mode,
+				       b_predicate pred, void *context,
+				       struct lock_history *lh)
+{
+	struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context};
+	struct lru_entry *le;
+	struct dm_buffer *b;
+
+	le = lru_evict(&bc->lru[list_mode], __evict_pred, &w, bc->no_sleep);
+	if (!le)
+		return NULL;
+
+	b = le_to_buffer(le);
+	/* __evict_pred will have locked the appropriate tree. */
+	rb_erase(&b->node, &bc->trees[cache_index(b->block, bc->num_locks)].root);
+
+	return b;
+}
+
+static struct dm_buffer *cache_evict(struct dm_buffer_cache *bc, int list_mode,
+				     b_predicate pred, void *context)
+{
+	struct dm_buffer *b;
+	struct lock_history lh;
+
+	lh_init(&lh, bc, true);
+	b = __cache_evict(bc, list_mode, pred, context, &lh);
+	lh_exit(&lh);
+
+	return b;
+}
+
+/*--------------*/
+
+/*
+ * Mark a buffer as clean or dirty. Not threadsafe.
+ */
+static void cache_mark(struct dm_buffer_cache *bc, struct dm_buffer *b, int list_mode)
+{
+	cache_write_lock(bc, b->block);
+	if (list_mode != b->list_mode) {
+		lru_remove(&bc->lru[b->list_mode], &b->lru);
+		b->list_mode = list_mode;
+		lru_insert(&bc->lru[b->list_mode], &b->lru);
+	}
+	cache_write_unlock(bc, b->block);
+}
+
+/*--------------*/
+
+/*
+ * Runs through the lru associated with 'old_mode', if the predicate matches then
+ * it moves them to 'new_mode'.  Not threadsafe.
+ */
+static void __cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode,
+			      b_predicate pred, void *context, struct lock_history *lh)
+{
+	struct lru_entry *le;
+	struct dm_buffer *b;
+	struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context};
+
+	while (true) {
+		le = lru_evict(&bc->lru[old_mode], __evict_pred, &w, bc->no_sleep);
+		if (!le)
+			break;
+
+		b = le_to_buffer(le);
+		b->list_mode = new_mode;
+		lru_insert(&bc->lru[b->list_mode], &b->lru);
+	}
+}
+
+static void cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode,
+			    b_predicate pred, void *context)
+{
+	struct lock_history lh;
+
+	lh_init(&lh, bc, true);
+	__cache_mark_many(bc, old_mode, new_mode, pred, context, &lh);
+	lh_exit(&lh);
+}
+
+/*--------------*/
+
+/*
+ * Iterates through all clean or dirty entries calling a function for each
+ * entry.  The callback may terminate the iteration early.  Not threadsafe.
+ */
+
+/*
+ * Iterator functions should return one of these actions to indicate
+ * how the iteration should proceed.
+ */
+enum it_action {
+	IT_NEXT,
+	IT_COMPLETE,
+};
+
+typedef enum it_action (*iter_fn)(struct dm_buffer *b, void *context);
+
+static void __cache_iterate(struct dm_buffer_cache *bc, int list_mode,
+			    iter_fn fn, void *context, struct lock_history *lh)
+{
+	struct lru *lru = &bc->lru[list_mode];
+	struct lru_entry *le, *first;
+
+	if (!lru->cursor)
+		return;
+
+	first = le = to_le(lru->cursor);
+	do {
+		struct dm_buffer *b = le_to_buffer(le);
+
+		lh_next(lh, b->block);
+
+		switch (fn(b, context)) {
+		case IT_NEXT:
+			break;
+
+		case IT_COMPLETE:
+			return;
+		}
+		cond_resched();
+
+		le = to_le(le->list.next);
+	} while (le != first);
+}
+
+static void cache_iterate(struct dm_buffer_cache *bc, int list_mode,
+			  iter_fn fn, void *context)
+{
+	struct lock_history lh;
+
+	lh_init(&lh, bc, false);
+	__cache_iterate(bc, list_mode, fn, context, &lh);
+	lh_exit(&lh);
+}
+
+/*--------------*/
+
+/*
+ * Passes ownership of the buffer to the cache. Returns false if the
+ * buffer was already present (in which case ownership does not pass).
+ * eg, a race with another thread.
+ *
+ * Holder count should be 1 on insertion.
+ *
+ * Not threadsafe.
+ */
+static bool __cache_insert(struct rb_root *root, struct dm_buffer *b)
+{
+	struct rb_node **new = &root->rb_node, *parent = NULL;
+	struct dm_buffer *found;
+
+	while (*new) {
+		found = container_of(*new, struct dm_buffer, node);
+
+		if (found->block == b->block)
+			return false;
+
+		parent = *new;
+		new = b->block < found->block ?
+			&found->node.rb_left : &found->node.rb_right;
+	}
+
+	rb_link_node(&b->node, parent, new);
+	rb_insert_color(&b->node, root);
+
+	return true;
+}
+
+static bool cache_insert(struct dm_buffer_cache *bc, struct dm_buffer *b)
+{
+	bool r;
+
+	if (WARN_ON_ONCE(b->list_mode >= LIST_SIZE))
+		return false;
+
+	cache_write_lock(bc, b->block);
+	BUG_ON(atomic_read(&b->hold_count) != 1);
+	r = __cache_insert(&bc->trees[cache_index(b->block, bc->num_locks)].root, b);
+	if (r)
+		lru_insert(&bc->lru[b->list_mode], &b->lru);
+	cache_write_unlock(bc, b->block);
+
+	return r;
+}
+
+/*--------------*/
+
+/*
+ * Removes buffer from cache, ownership of the buffer passes back to the caller.
+ * Fails if the hold_count is not one (ie. the caller holds the only reference).
+ *
+ * Not threadsafe.
+ */
+static bool cache_remove(struct dm_buffer_cache *bc, struct dm_buffer *b)
+{
+	bool r;
+
+	cache_write_lock(bc, b->block);
+
+	if (atomic_read(&b->hold_count) != 1) {
+		r = false;
+	} else {
+		r = true;
+		rb_erase(&b->node, &bc->trees[cache_index(b->block, bc->num_locks)].root);
+		lru_remove(&bc->lru[b->list_mode], &b->lru);
+	}
+
+	cache_write_unlock(bc, b->block);
+
+	return r;
+}
+
+/*--------------*/
+
+typedef void (*b_release)(struct dm_buffer *);
+
+static struct dm_buffer *__find_next(struct rb_root *root, sector_t block)
+{
+	struct rb_node *n = root->rb_node;
+	struct dm_buffer *b;
+	struct dm_buffer *best = NULL;
+
+	while (n) {
+		b = container_of(n, struct dm_buffer, node);
+
+		if (b->block == block)
+			return b;
+
+		if (block <= b->block) {
+			n = n->rb_left;
+			best = b;
+		} else {
+			n = n->rb_right;
+		}
+	}
+
+	return best;
+}
+
+static void __remove_range(struct dm_buffer_cache *bc,
+			   struct rb_root *root,
+			   sector_t begin, sector_t end,
+			   b_predicate pred, b_release release)
+{
+	struct dm_buffer *b;
+
+	while (true) {
+		cond_resched();
+
+		b = __find_next(root, begin);
+		if (!b || (b->block >= end))
+			break;
+
+		begin = b->block + 1;
+
+		if (atomic_read(&b->hold_count))
+			continue;
+
+		if (pred(b, NULL) == ER_EVICT) {
+			rb_erase(&b->node, root);
+			lru_remove(&bc->lru[b->list_mode], &b->lru);
+			release(b);
+		}
+	}
+}
+
+static void cache_remove_range(struct dm_buffer_cache *bc,
+			       sector_t begin, sector_t end,
+			       b_predicate pred, b_release release)
+{
+	unsigned int i;
+
+	BUG_ON(bc->no_sleep);
+	for (i = 0; i < bc->num_locks; i++) {
+		down_write(&bc->trees[i].u.lock);
+		__remove_range(bc, &bc->trees[i].root, begin, end, pred, release);
+		up_write(&bc->trees[i].u.lock);
+	}
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Linking of buffers:
+ *	All buffers are linked to buffer_cache with their node field.
+ *
+ *	Clean buffers that are not being written (B_WRITING not set)
+ *	are linked to lru[LIST_CLEAN] with their lru_list field.
+ *
+ *	Dirty and clean buffers that are being written are linked to
+ *	lru[LIST_DIRTY] with their lru_list field. When the write
+ *	finishes, the buffer cannot be relinked immediately (because we
+ *	are in an interrupt context and relinking requires process
+ *	context), so some clean-not-writing buffers can be held on
+ *	dirty_lru too.  They are later added to lru in the process
+ *	context.
+ */
+struct dm_bufio_client {
+	struct block_device *bdev;
+	unsigned int block_size;
+	s8 sectors_per_block_bits;
+
+	bool no_sleep;
+	struct mutex lock;
+	spinlock_t spinlock;
+
+	int async_write_error;
+
+	void (*alloc_callback)(struct dm_buffer *buf);
+	void (*write_callback)(struct dm_buffer *buf);
+	struct kmem_cache *slab_buffer;
+	struct kmem_cache *slab_cache;
+	struct dm_io_client *dm_io;
+
+	struct list_head reserved_buffers;
+	unsigned int need_reserved_buffers;
+
+	unsigned int minimum_buffers;
+
+	sector_t start;
+
+	struct shrinker shrinker;
+	struct work_struct shrink_work;
+	atomic_long_t need_shrink;
+
+	wait_queue_head_t free_buffer_wait;
+
+	struct list_head client_list;
+
+	/*
+	 * Used by global_cleanup to sort the clients list.
+	 */
+	unsigned long oldest_buffer;
+
+	struct dm_buffer_cache cache; /* must be last member */
+};
+
+/*----------------------------------------------------------------*/
+
+#define dm_bufio_in_request()	(!!current->bio_list)
+
+static void dm_bufio_lock(struct dm_bufio_client *c)
+{
+	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
+		spin_lock_bh(&c->spinlock);
+	else
+		mutex_lock_nested(&c->lock, dm_bufio_in_request());
+}
+
+static void dm_bufio_unlock(struct dm_bufio_client *c)
+{
+	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
+		spin_unlock_bh(&c->spinlock);
+	else
+		mutex_unlock(&c->lock);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Default cache size: available memory divided by the ratio.
+ */
+static unsigned long dm_bufio_default_cache_size;
+
+/*
+ * Total cache size set by the user.
+ */
+static unsigned long dm_bufio_cache_size;
+
+/*
+ * A copy of dm_bufio_cache_size because dm_bufio_cache_size can change
+ * at any time.  If it disagrees, the user has changed cache size.
+ */
+static unsigned long dm_bufio_cache_size_latch;
+
+static DEFINE_SPINLOCK(global_spinlock);
+
+/*
+ * Buffers are freed after this timeout
+ */
+static unsigned int dm_bufio_max_age = DM_BUFIO_DEFAULT_AGE_SECS;
+static unsigned long dm_bufio_retain_bytes = DM_BUFIO_DEFAULT_RETAIN_BYTES;
+
+static unsigned long dm_bufio_peak_allocated;
+static unsigned long dm_bufio_allocated_kmem_cache;
+static unsigned long dm_bufio_allocated_get_free_pages;
+static unsigned long dm_bufio_allocated_vmalloc;
+static unsigned long dm_bufio_current_allocated;
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The current number of clients.
+ */
+static int dm_bufio_client_count;
+
+/*
+ * The list of all clients.
+ */
+static LIST_HEAD(dm_bufio_all_clients);
+
+/*
+ * This mutex protects dm_bufio_cache_size_latch and dm_bufio_client_count
+ */
+static DEFINE_MUTEX(dm_bufio_clients_lock);
+
+static struct workqueue_struct *dm_bufio_wq;
+static struct delayed_work dm_bufio_cleanup_old_work;
+static struct work_struct dm_bufio_replacement_work;
+
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+static void buffer_record_stack(struct dm_buffer *b)
+{
+	b->stack_len = stack_trace_save(b->stack_entries, MAX_STACK, 2);
+}
+#endif
+
+/*----------------------------------------------------------------*/
+
+static void adjust_total_allocated(struct dm_buffer *b, bool unlink)
+{
+	unsigned char data_mode;
+	long diff;
+
+	static unsigned long * const class_ptr[DATA_MODE_LIMIT] = {
+		&dm_bufio_allocated_kmem_cache,
+		&dm_bufio_allocated_get_free_pages,
+		&dm_bufio_allocated_vmalloc,
+	};
+
+	data_mode = b->data_mode;
+	diff = (long)b->c->block_size;
+	if (unlink)
+		diff = -diff;
+
+	spin_lock(&global_spinlock);
+
+	*class_ptr[data_mode] += diff;
+
+	dm_bufio_current_allocated += diff;
+
+	if (dm_bufio_current_allocated > dm_bufio_peak_allocated)
+		dm_bufio_peak_allocated = dm_bufio_current_allocated;
+
+	if (!unlink) {
+		if (dm_bufio_current_allocated > dm_bufio_cache_size)
+			queue_work(dm_bufio_wq, &dm_bufio_replacement_work);
+	}
+
+	spin_unlock(&global_spinlock);
+}
+
+/*
+ * Change the number of clients and recalculate per-client limit.
+ */
+static void __cache_size_refresh(void)
+{
+	if (WARN_ON(!mutex_is_locked(&dm_bufio_clients_lock)))
+		return;
+	if (WARN_ON(dm_bufio_client_count < 0))
+		return;
+
+	dm_bufio_cache_size_latch = READ_ONCE(dm_bufio_cache_size);
+
+	/*
+	 * Use default if set to 0 and report the actual cache size used.
+	 */
+	if (!dm_bufio_cache_size_latch) {
+		(void)cmpxchg(&dm_bufio_cache_size, 0,
+			      dm_bufio_default_cache_size);
+		dm_bufio_cache_size_latch = dm_bufio_default_cache_size;
+	}
+}
+
+/*
+ * Allocating buffer data.
+ *
+ * Small buffers are allocated with kmem_cache, to use space optimally.
+ *
+ * For large buffers, we choose between get_free_pages and vmalloc.
+ * Each has advantages and disadvantages.
+ *
+ * __get_free_pages can randomly fail if the memory is fragmented.
+ * __vmalloc won't randomly fail, but vmalloc space is limited (it may be
+ * as low as 128M) so using it for caching is not appropriate.
+ *
+ * If the allocation may fail we use __get_free_pages. Memory fragmentation
+ * won't have a fatal effect here, but it just causes flushes of some other
+ * buffers and more I/O will be performed. Don't use __get_free_pages if it
+ * always fails (i.e. order > MAX_ORDER).
+ *
+ * If the allocation shouldn't fail we use __vmalloc. This is only for the
+ * initial reserve allocation, so there's no risk of wasting all vmalloc
+ * space.
+ */
+static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
+			       unsigned char *data_mode)
+{
+	if (unlikely(c->slab_cache != NULL)) {
+		*data_mode = DATA_MODE_SLAB;
+		return kmem_cache_alloc(c->slab_cache, gfp_mask);
+	}
+
+	if (c->block_size <= KMALLOC_MAX_SIZE &&
+	    gfp_mask & __GFP_NORETRY) {
+		*data_mode = DATA_MODE_GET_FREE_PAGES;
+		return (void *)__get_free_pages(gfp_mask,
+						c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
+	}
+
+	*data_mode = DATA_MODE_VMALLOC;
+
+	return __vmalloc(c->block_size, gfp_mask);
+}
+
+/*
+ * Free buffer's data.
+ */
+static void free_buffer_data(struct dm_bufio_client *c,
+			     void *data, unsigned char data_mode)
+{
+	switch (data_mode) {
+	case DATA_MODE_SLAB:
+		kmem_cache_free(c->slab_cache, data);
+		break;
+
+	case DATA_MODE_GET_FREE_PAGES:
+		free_pages((unsigned long)data,
+			   c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
+		break;
+
+	case DATA_MODE_VMALLOC:
+		vfree(data);
+		break;
+
+	default:
+		DMCRIT("dm_bufio_free_buffer_data: bad data mode: %d",
+		       data_mode);
+		BUG();
+	}
+}
+
+/*
+ * Allocate buffer and its data.
+ */
+static struct dm_buffer *alloc_buffer(struct dm_bufio_client *c, gfp_t gfp_mask)
+{
+	struct dm_buffer *b = kmem_cache_alloc(c->slab_buffer, gfp_mask);
+
+	if (!b)
+		return NULL;
+
+	b->c = c;
+
+	b->data = alloc_buffer_data(c, gfp_mask, &b->data_mode);
+	if (!b->data) {
+		kmem_cache_free(c->slab_buffer, b);
+		return NULL;
+	}
+	adjust_total_allocated(b, false);
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	b->stack_len = 0;
+#endif
+	return b;
+}
+
+/*
+ * Free buffer and its data.
+ */
+static void free_buffer(struct dm_buffer *b)
+{
+	struct dm_bufio_client *c = b->c;
+
+	adjust_total_allocated(b, true);
+	free_buffer_data(c, b->data, b->data_mode);
+	kmem_cache_free(c->slab_buffer, b);
+}
+
+/*
+ *--------------------------------------------------------------------------
+ * Submit I/O on the buffer.
+ *
+ * Bio interface is faster but it has some problems:
+ *	the vector list is limited (increasing this limit increases
+ *	memory-consumption per buffer, so it is not viable);
+ *
+ *	the memory must be direct-mapped, not vmalloced;
+ *
+ * If the buffer is small enough (up to DM_BUFIO_INLINE_VECS pages) and
+ * it is not vmalloced, try using the bio interface.
+ *
+ * If the buffer is big, if it is vmalloced or if the underlying device
+ * rejects the bio because it is too large, use dm-io layer to do the I/O.
+ * The dm-io layer splits the I/O into multiple requests, avoiding the above
+ * shortcomings.
+ *--------------------------------------------------------------------------
+ */
+
+/*
+ * dm-io completion routine. It just calls b->bio.bi_end_io, pretending
+ * that the request was handled directly with bio interface.
+ */
+static void dmio_complete(unsigned long error, void *context)
+{
+	struct dm_buffer *b = context;
+
+	b->end_io(b, unlikely(error != 0) ? BLK_STS_IOERR : 0);
+}
+
+static void use_dmio(struct dm_buffer *b, enum req_op op, sector_t sector,
+		     unsigned int n_sectors, unsigned int offset)
+{
+	int r;
+	struct dm_io_request io_req = {
+		.bi_opf = op,
+		.notify.fn = dmio_complete,
+		.notify.context = b,
+		.client = b->c->dm_io,
+	};
+	struct dm_io_region region = {
+		.bdev = b->c->bdev,
+		.sector = sector,
+		.count = n_sectors,
+	};
+
+	if (b->data_mode != DATA_MODE_VMALLOC) {
+		io_req.mem.type = DM_IO_KMEM;
+		io_req.mem.ptr.addr = (char *)b->data + offset;
+	} else {
+		io_req.mem.type = DM_IO_VMA;
+		io_req.mem.ptr.vma = (char *)b->data + offset;
+	}
+
+	r = dm_io(&io_req, 1, &region, NULL);
+	if (unlikely(r))
+		b->end_io(b, errno_to_blk_status(r));
+}
+
+static void bio_complete(struct bio *bio)
+{
+	struct dm_buffer *b = bio->bi_private;
+	blk_status_t status = bio->bi_status;
+
+	bio_uninit(bio);
+	kfree(bio);
+	b->end_io(b, status);
+}
+
+static void use_bio(struct dm_buffer *b, enum req_op op, sector_t sector,
+		    unsigned int n_sectors, unsigned int offset)
+{
+	struct bio *bio;
+	char *ptr;
+	unsigned int len;
+
+	bio = bio_kmalloc(1, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOWARN);
+	if (!bio) {
+		use_dmio(b, op, sector, n_sectors, offset);
+		return;
+	}
+	bio_init(bio, b->c->bdev, bio->bi_inline_vecs, 1, op);
+	bio->bi_iter.bi_sector = sector;
+	bio->bi_end_io = bio_complete;
+	bio->bi_private = b;
+
+	ptr = (char *)b->data + offset;
+	len = n_sectors << SECTOR_SHIFT;
+
+	__bio_add_page(bio, virt_to_page(ptr), len, offset_in_page(ptr));
+
+	submit_bio(bio);
+}
+
+static inline sector_t block_to_sector(struct dm_bufio_client *c, sector_t block)
+{
+	sector_t sector;
+
+	if (likely(c->sectors_per_block_bits >= 0))
+		sector = block << c->sectors_per_block_bits;
+	else
+		sector = block * (c->block_size >> SECTOR_SHIFT);
+	sector += c->start;
+
+	return sector;
+}
+
+static void submit_io(struct dm_buffer *b, enum req_op op,
+		      void (*end_io)(struct dm_buffer *, blk_status_t))
+{
+	unsigned int n_sectors;
+	sector_t sector;
+	unsigned int offset, end;
+
+	b->end_io = end_io;
+
+	sector = block_to_sector(b->c, b->block);
+
+	if (op != REQ_OP_WRITE) {
+		n_sectors = b->c->block_size >> SECTOR_SHIFT;
+		offset = 0;
+	} else {
+		if (b->c->write_callback)
+			b->c->write_callback(b);
+		offset = b->write_start;
+		end = b->write_end;
+		offset &= -DM_BUFIO_WRITE_ALIGN;
+		end += DM_BUFIO_WRITE_ALIGN - 1;
+		end &= -DM_BUFIO_WRITE_ALIGN;
+		if (unlikely(end > b->c->block_size))
+			end = b->c->block_size;
+
+		sector += offset >> SECTOR_SHIFT;
+		n_sectors = (end - offset) >> SECTOR_SHIFT;
+	}
+
+	if (b->data_mode != DATA_MODE_VMALLOC)
+		use_bio(b, op, sector, n_sectors, offset);
+	else
+		use_dmio(b, op, sector, n_sectors, offset);
+}
+
+/*
+ *--------------------------------------------------------------
+ * Writing dirty buffers
+ *--------------------------------------------------------------
+ */
+
+/*
+ * The endio routine for write.
+ *
+ * Set the error, clear B_WRITING bit and wake anyone who was waiting on
+ * it.
+ */
+static void write_endio(struct dm_buffer *b, blk_status_t status)
+{
+	b->write_error = status;
+	if (unlikely(status)) {
+		struct dm_bufio_client *c = b->c;
+
+		(void)cmpxchg(&c->async_write_error, 0,
+				blk_status_to_errno(status));
+	}
+
+	BUG_ON(!test_bit(B_WRITING, &b->state));
+
+	smp_mb__before_atomic();
+	clear_bit(B_WRITING, &b->state);
+	smp_mb__after_atomic();
+
+	wake_up_bit(&b->state, B_WRITING);
+}
+
+/*
+ * Initiate a write on a dirty buffer, but don't wait for it.
+ *
+ * - If the buffer is not dirty, exit.
+ * - If there some previous write going on, wait for it to finish (we can't
+ *   have two writes on the same buffer simultaneously).
+ * - Submit our write and don't wait on it. We set B_WRITING indicating
+ *   that there is a write in progress.
+ */
+static void __write_dirty_buffer(struct dm_buffer *b,
+				 struct list_head *write_list)
+{
+	if (!test_bit(B_DIRTY, &b->state))
+		return;
+
+	clear_bit(B_DIRTY, &b->state);
+	wait_on_bit_lock_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
+
+	b->write_start = b->dirty_start;
+	b->write_end = b->dirty_end;
+
+	if (!write_list)
+		submit_io(b, REQ_OP_WRITE, write_endio);
+	else
+		list_add_tail(&b->write_list, write_list);
+}
+
+static void __flush_write_list(struct list_head *write_list)
+{
+	struct blk_plug plug;
+
+	blk_start_plug(&plug);
+	while (!list_empty(write_list)) {
+		struct dm_buffer *b =
+			list_entry(write_list->next, struct dm_buffer, write_list);
+		list_del(&b->write_list);
+		submit_io(b, REQ_OP_WRITE, write_endio);
+		cond_resched();
+	}
+	blk_finish_plug(&plug);
+}
+
+/*
+ * Wait until any activity on the buffer finishes.  Possibly write the
+ * buffer if it is dirty.  When this function finishes, there is no I/O
+ * running on the buffer and the buffer is not dirty.
+ */
+static void __make_buffer_clean(struct dm_buffer *b)
+{
+	BUG_ON(atomic_read(&b->hold_count));
+
+	/* smp_load_acquire() pairs with read_endio()'s smp_mb__before_atomic() */
+	if (!smp_load_acquire(&b->state))	/* fast case */
+		return;
+
+	wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);
+	__write_dirty_buffer(b, NULL);
+	wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
+}
+
+static enum evict_result is_clean(struct dm_buffer *b, void *context)
+{
+	struct dm_bufio_client *c = context;
+
+	/* These should never happen */
+	if (WARN_ON_ONCE(test_bit(B_WRITING, &b->state)))
+		return ER_DONT_EVICT;
+	if (WARN_ON_ONCE(test_bit(B_DIRTY, &b->state)))
+		return ER_DONT_EVICT;
+	if (WARN_ON_ONCE(b->list_mode != LIST_CLEAN))
+		return ER_DONT_EVICT;
+
+	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep &&
+	    unlikely(test_bit(B_READING, &b->state)))
+		return ER_DONT_EVICT;
+
+	return ER_EVICT;
+}
+
+static enum evict_result is_dirty(struct dm_buffer *b, void *context)
+{
+	/* These should never happen */
+	if (WARN_ON_ONCE(test_bit(B_READING, &b->state)))
+		return ER_DONT_EVICT;
+	if (WARN_ON_ONCE(b->list_mode != LIST_DIRTY))
+		return ER_DONT_EVICT;
+
+	return ER_EVICT;
+}
+
+/*
+ * Find some buffer that is not held by anybody, clean it, unlink it and
+ * return it.
+ */
+static struct dm_buffer *__get_unclaimed_buffer(struct dm_bufio_client *c)
+{
+	struct dm_buffer *b;
+
+	b = cache_evict(&c->cache, LIST_CLEAN, is_clean, c);
+	if (b) {
+		/* this also waits for pending reads */
+		__make_buffer_clean(b);
+		return b;
+	}
+
+	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
+		return NULL;
+
+	b = cache_evict(&c->cache, LIST_DIRTY, is_dirty, NULL);
+	if (b) {
+		__make_buffer_clean(b);
+		return b;
+	}
+
+	return NULL;
+}
+
+/*
+ * Wait until some other threads free some buffer or release hold count on
+ * some buffer.
+ *
+ * This function is entered with c->lock held, drops it and regains it
+ * before exiting.
+ */
+static void __wait_for_free_buffer(struct dm_bufio_client *c)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	add_wait_queue(&c->free_buffer_wait, &wait);
+	set_current_state(TASK_UNINTERRUPTIBLE);
+	dm_bufio_unlock(c);
+
+	/*
+	 * It's possible to miss a wake up event since we don't always
+	 * hold c->lock when wake_up is called.  So we have a timeout here,
+	 * just in case.
+	 */
+	io_schedule_timeout(5 * HZ);
+
+	remove_wait_queue(&c->free_buffer_wait, &wait);
+
+	dm_bufio_lock(c);
+}
+
+enum new_flag {
+	NF_FRESH = 0,
+	NF_READ = 1,
+	NF_GET = 2,
+	NF_PREFETCH = 3
+};
+
+/*
+ * Allocate a new buffer. If the allocation is not possible, wait until
+ * some other thread frees a buffer.
+ *
+ * May drop the lock and regain it.
+ */
+static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c, enum new_flag nf)
+{
+	struct dm_buffer *b;
+	bool tried_noio_alloc = false;
+
+	/*
+	 * dm-bufio is resistant to allocation failures (it just keeps
+	 * one buffer reserved in cases all the allocations fail).
+	 * So set flags to not try too hard:
+	 *	GFP_NOWAIT: don't wait; if we need to sleep we'll release our
+	 *		    mutex and wait ourselves.
+	 *	__GFP_NORETRY: don't retry and rather return failure
+	 *	__GFP_NOMEMALLOC: don't use emergency reserves
+	 *	__GFP_NOWARN: don't print a warning in case of failure
+	 *
+	 * For debugging, if we set the cache size to 1, no new buffers will
+	 * be allocated.
+	 */
+	while (1) {
+		if (dm_bufio_cache_size_latch != 1) {
+			b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			if (b)
+				return b;
+		}
+
+		if (nf == NF_PREFETCH)
+			return NULL;
+
+		if (dm_bufio_cache_size_latch != 1 && !tried_noio_alloc) {
+			dm_bufio_unlock(c);
+			b = alloc_buffer(c, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			dm_bufio_lock(c);
+			if (b)
+				return b;
+			tried_noio_alloc = true;
+		}
+
+		if (!list_empty(&c->reserved_buffers)) {
+			b = list_to_buffer(c->reserved_buffers.next);
+			list_del(&b->lru.list);
+			c->need_reserved_buffers++;
+
+			return b;
+		}
+
+		b = __get_unclaimed_buffer(c);
+		if (b)
+			return b;
+
+		__wait_for_free_buffer(c);
+	}
+}
+
+static struct dm_buffer *__alloc_buffer_wait(struct dm_bufio_client *c, enum new_flag nf)
+{
+	struct dm_buffer *b = __alloc_buffer_wait_no_callback(c, nf);
+
+	if (!b)
+		return NULL;
+
+	if (c->alloc_callback)
+		c->alloc_callback(b);
+
+	return b;
+}
+
+/*
+ * Free a buffer and wake other threads waiting for free buffers.
+ */
+static void __free_buffer_wake(struct dm_buffer *b)
+{
+	struct dm_bufio_client *c = b->c;
+
+	b->block = -1;
+	if (!c->need_reserved_buffers)
+		free_buffer(b);
+	else {
+		list_add(&b->lru.list, &c->reserved_buffers);
+		c->need_reserved_buffers--;
+	}
+
+	/*
+	 * We hold the bufio lock here, so no one can add entries to the
+	 * wait queue anyway.
+	 */
+	if (unlikely(waitqueue_active(&c->free_buffer_wait)))
+		wake_up(&c->free_buffer_wait);
+}
+
+static enum evict_result cleaned(struct dm_buffer *b, void *context)
+{
+	if (WARN_ON_ONCE(test_bit(B_READING, &b->state)))
+		return ER_DONT_EVICT; /* should never happen */
+
+	if (test_bit(B_DIRTY, &b->state) || test_bit(B_WRITING, &b->state))
+		return ER_DONT_EVICT;
+	else
+		return ER_EVICT;
+}
+
+static void __move_clean_buffers(struct dm_bufio_client *c)
+{
+	cache_mark_many(&c->cache, LIST_DIRTY, LIST_CLEAN, cleaned, NULL);
+}
+
+struct write_context {
+	int no_wait;
+	struct list_head *write_list;
+};
+
+static enum it_action write_one(struct dm_buffer *b, void *context)
+{
+	struct write_context *wc = context;
+
+	if (wc->no_wait && test_bit(B_WRITING, &b->state))
+		return IT_COMPLETE;
+
+	__write_dirty_buffer(b, wc->write_list);
+	return IT_NEXT;
+}
+
+static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait,
+					struct list_head *write_list)
+{
+	struct write_context wc = {.no_wait = no_wait, .write_list = write_list};
+
+	__move_clean_buffers(c);
+	cache_iterate(&c->cache, LIST_DIRTY, write_one, &wc);
+}
+
+/*
+ * Check if we're over watermark.
+ * If we are over threshold_buffers, start freeing buffers.
+ * If we're over "limit_buffers", block until we get under the limit.
+ */
+static void __check_watermark(struct dm_bufio_client *c,
+			      struct list_head *write_list)
+{
+	if (cache_count(&c->cache, LIST_DIRTY) >
+	    cache_count(&c->cache, LIST_CLEAN) * DM_BUFIO_WRITEBACK_RATIO)
+		__write_dirty_buffers_async(c, 1, write_list);
+}
+
+/*
+ *--------------------------------------------------------------
+ * Getting a buffer
+ *--------------------------------------------------------------
+ */
+
+static void cache_put_and_wake(struct dm_bufio_client *c, struct dm_buffer *b)
+{
+	/*
+	 * Relying on waitqueue_active() is racey, but we sleep
+	 * with schedule_timeout anyway.
+	 */
+	if (cache_put(&c->cache, b) &&
+	    unlikely(waitqueue_active(&c->free_buffer_wait)))
+		wake_up(&c->free_buffer_wait);
+}
+
+/*
+ * This assumes you have already checked the cache to see if the buffer
+ * is already present (it will recheck after dropping the lock for allocation).
+ */
+static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
+				     enum new_flag nf, int *need_submit,
+				     struct list_head *write_list)
+{
+	struct dm_buffer *b, *new_b = NULL;
+
+	*need_submit = 0;
+
+	/* This can't be called with NF_GET */
+	if (WARN_ON_ONCE(nf == NF_GET))
+		return NULL;
+
+	new_b = __alloc_buffer_wait(c, nf);
+	if (!new_b)
+		return NULL;
+
+	/*
+	 * We've had a period where the mutex was unlocked, so need to
+	 * recheck the buffer tree.
+	 */
+	b = cache_get(&c->cache, block);
+	if (b) {
+		__free_buffer_wake(new_b);
+		goto found_buffer;
+	}
+
+	__check_watermark(c, write_list);
+
+	b = new_b;
+	atomic_set(&b->hold_count, 1);
+	WRITE_ONCE(b->last_accessed, jiffies);
+	b->block = block;
+	b->read_error = 0;
+	b->write_error = 0;
+	b->list_mode = LIST_CLEAN;
+
+	if (nf == NF_FRESH)
+		b->state = 0;
+	else {
+		b->state = 1 << B_READING;
+		*need_submit = 1;
+	}
+
+	/*
+	 * We mustn't insert into the cache until the B_READING state
+	 * is set.  Otherwise another thread could get it and use
+	 * it before it had been read.
+	 */
+	cache_insert(&c->cache, b);
+
+	return b;
+
+found_buffer:
+	if (nf == NF_PREFETCH) {
+		cache_put_and_wake(c, b);
+		return NULL;
+	}
+
+	/*
+	 * Note: it is essential that we don't wait for the buffer to be
+	 * read if dm_bufio_get function is used. Both dm_bufio_get and
+	 * dm_bufio_prefetch can be used in the driver request routine.
+	 * If the user called both dm_bufio_prefetch and dm_bufio_get on
+	 * the same buffer, it would deadlock if we waited.
+	 */
+	if (nf == NF_GET && unlikely(test_bit_acquire(B_READING, &b->state))) {
+		cache_put_and_wake(c, b);
+		return NULL;
+	}
+
+	return b;
+}
+
+/*
+ * The endio routine for reading: set the error, clear the bit and wake up
+ * anyone waiting on the buffer.
+ */
+static void read_endio(struct dm_buffer *b, blk_status_t status)
+{
+	b->read_error = status;
+
+	BUG_ON(!test_bit(B_READING, &b->state));
+
+	smp_mb__before_atomic();
+	clear_bit(B_READING, &b->state);
+	smp_mb__after_atomic();
+
+	wake_up_bit(&b->state, B_READING);
+}
+
+/*
+ * A common routine for dm_bufio_new and dm_bufio_read.  Operation of these
+ * functions is similar except that dm_bufio_new doesn't read the
+ * buffer from the disk (assuming that the caller overwrites all the data
+ * and uses dm_bufio_mark_buffer_dirty to write new data back).
+ */
+static void *new_read(struct dm_bufio_client *c, sector_t block,
+		      enum new_flag nf, struct dm_buffer **bp)
+{
+	int need_submit = 0;
+	struct dm_buffer *b;
+
+	LIST_HEAD(write_list);
+
+	*bp = NULL;
+
+	/*
+	 * Fast path, hopefully the block is already in the cache.  No need
+	 * to get the client lock for this.
+	 */
+	b = cache_get(&c->cache, block);
+	if (b) {
+		if (nf == NF_PREFETCH) {
+			cache_put_and_wake(c, b);
+			return NULL;
+		}
+
+		/*
+		 * Note: it is essential that we don't wait for the buffer to be
+		 * read if dm_bufio_get function is used. Both dm_bufio_get and
+		 * dm_bufio_prefetch can be used in the driver request routine.
+		 * If the user called both dm_bufio_prefetch and dm_bufio_get on
+		 * the same buffer, it would deadlock if we waited.
+		 */
+		if (nf == NF_GET && unlikely(test_bit_acquire(B_READING, &b->state))) {
+			cache_put_and_wake(c, b);
+			return NULL;
+		}
+	}
+
+	if (!b) {
+		if (nf == NF_GET)
+			return NULL;
+
+		dm_bufio_lock(c);
+		b = __bufio_new(c, block, nf, &need_submit, &write_list);
+		dm_bufio_unlock(c);
+	}
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	if (b && (atomic_read(&b->hold_count) == 1))
+		buffer_record_stack(b);
+#endif
+
+	__flush_write_list(&write_list);
+
+	if (!b)
+		return NULL;
+
+	if (need_submit)
+		submit_io(b, REQ_OP_READ, read_endio);
+
+	if (nf != NF_GET)	/* we already tested this condition above */
+		wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);
+
+	if (b->read_error) {
+		int error = blk_status_to_errno(b->read_error);
+
+		dm_bufio_release(b);
+
+		return ERR_PTR(error);
+	}
+
+	*bp = b;
+
+	return b->data;
+}
+
+void *dm_bufio_get(struct dm_bufio_client *c, sector_t block,
+		   struct dm_buffer **bp)
+{
+	return new_read(c, block, NF_GET, bp);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get);
+
+void *dm_bufio_read(struct dm_bufio_client *c, sector_t block,
+		    struct dm_buffer **bp)
+{
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return ERR_PTR(-EINVAL);
+
+	return new_read(c, block, NF_READ, bp);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_read);
+
+void *dm_bufio_new(struct dm_bufio_client *c, sector_t block,
+		   struct dm_buffer **bp)
+{
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return ERR_PTR(-EINVAL);
+
+	return new_read(c, block, NF_FRESH, bp);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_new);
+
+void dm_bufio_prefetch(struct dm_bufio_client *c,
+		       sector_t block, unsigned int n_blocks)
+{
+	struct blk_plug plug;
+
+	LIST_HEAD(write_list);
+
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return; /* should never happen */
+
+	blk_start_plug(&plug);
+
+	for (; n_blocks--; block++) {
+		int need_submit;
+		struct dm_buffer *b;
+
+		b = cache_get(&c->cache, block);
+		if (b) {
+			/* already in cache */
+			cache_put_and_wake(c, b);
+			continue;
+		}
+
+		dm_bufio_lock(c);
+		b = __bufio_new(c, block, NF_PREFETCH, &need_submit,
+				&write_list);
+		if (unlikely(!list_empty(&write_list))) {
+			dm_bufio_unlock(c);
+			blk_finish_plug(&plug);
+			__flush_write_list(&write_list);
+			blk_start_plug(&plug);
+			dm_bufio_lock(c);
+		}
+		if (unlikely(b != NULL)) {
+			dm_bufio_unlock(c);
+
+			if (need_submit)
+				submit_io(b, REQ_OP_READ, read_endio);
+			dm_bufio_release(b);
+
+			cond_resched();
+
+			if (!n_blocks)
+				goto flush_plug;
+			dm_bufio_lock(c);
+		}
+		dm_bufio_unlock(c);
+	}
+
+flush_plug:
+	blk_finish_plug(&plug);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_prefetch);
+
+void dm_bufio_release(struct dm_buffer *b)
+{
+	struct dm_bufio_client *c = b->c;
+
+	/*
+	 * If there were errors on the buffer, and the buffer is not
+	 * to be written, free the buffer. There is no point in caching
+	 * invalid buffer.
+	 */
+	if ((b->read_error || b->write_error) &&
+	    !test_bit_acquire(B_READING, &b->state) &&
+	    !test_bit(B_WRITING, &b->state) &&
+	    !test_bit(B_DIRTY, &b->state)) {
+		dm_bufio_lock(c);
+
+		/* cache remove can fail if there are other holders */
+		if (cache_remove(&c->cache, b)) {
+			__free_buffer_wake(b);
+			dm_bufio_unlock(c);
+			return;
+		}
+
+		dm_bufio_unlock(c);
+	}
+
+	cache_put_and_wake(c, b);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_release);
+
+void dm_bufio_mark_partial_buffer_dirty(struct dm_buffer *b,
+					unsigned int start, unsigned int end)
+{
+	struct dm_bufio_client *c = b->c;
+
+	BUG_ON(start >= end);
+	BUG_ON(end > b->c->block_size);
+
+	dm_bufio_lock(c);
+
+	BUG_ON(test_bit(B_READING, &b->state));
+
+	if (!test_and_set_bit(B_DIRTY, &b->state)) {
+		b->dirty_start = start;
+		b->dirty_end = end;
+		cache_mark(&c->cache, b, LIST_DIRTY);
+	} else {
+		if (start < b->dirty_start)
+			b->dirty_start = start;
+		if (end > b->dirty_end)
+			b->dirty_end = end;
+	}
+
+	dm_bufio_unlock(c);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_mark_partial_buffer_dirty);
+
+void dm_bufio_mark_buffer_dirty(struct dm_buffer *b)
+{
+	dm_bufio_mark_partial_buffer_dirty(b, 0, b->c->block_size);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_mark_buffer_dirty);
+
+void dm_bufio_write_dirty_buffers_async(struct dm_bufio_client *c)
+{
+	LIST_HEAD(write_list);
+
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return; /* should never happen */
+
+	dm_bufio_lock(c);
+	__write_dirty_buffers_async(c, 0, &write_list);
+	dm_bufio_unlock(c);
+	__flush_write_list(&write_list);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers_async);
+
+/*
+ * For performance, it is essential that the buffers are written asynchronously
+ * and simultaneously (so that the block layer can merge the writes) and then
+ * waited upon.
+ *
+ * Finally, we flush hardware disk cache.
+ */
+static bool is_writing(struct lru_entry *e, void *context)
+{
+	struct dm_buffer *b = le_to_buffer(e);
+
+	return test_bit(B_WRITING, &b->state);
+}
+
+int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c)
+{
+	int a, f;
+	unsigned long nr_buffers;
+	struct lru_entry *e;
+	struct lru_iter it;
+
+	LIST_HEAD(write_list);
+
+	dm_bufio_lock(c);
+	__write_dirty_buffers_async(c, 0, &write_list);
+	dm_bufio_unlock(c);
+	__flush_write_list(&write_list);
+	dm_bufio_lock(c);
+
+	nr_buffers = cache_count(&c->cache, LIST_DIRTY);
+	lru_iter_begin(&c->cache.lru[LIST_DIRTY], &it);
+	while ((e = lru_iter_next(&it, is_writing, c))) {
+		struct dm_buffer *b = le_to_buffer(e);
+		__cache_inc_buffer(b);
+
+		BUG_ON(test_bit(B_READING, &b->state));
+
+		if (nr_buffers) {
+			nr_buffers--;
+			dm_bufio_unlock(c);
+			wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
+			dm_bufio_lock(c);
+		} else {
+			wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
+		}
+
+		if (!test_bit(B_DIRTY, &b->state) && !test_bit(B_WRITING, &b->state))
+			cache_mark(&c->cache, b, LIST_CLEAN);
+
+		cache_put_and_wake(c, b);
+
+		cond_resched();
+	}
+	lru_iter_end(&it);
+
+	wake_up(&c->free_buffer_wait);
+	dm_bufio_unlock(c);
+
+	a = xchg(&c->async_write_error, 0);
+	f = dm_bufio_issue_flush(c);
+	if (a)
+		return a;
+
+	return f;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers);
+
+/*
+ * Use dm-io to send an empty barrier to flush the device.
+ */
+int dm_bufio_issue_flush(struct dm_bufio_client *c)
+{
+	struct dm_io_request io_req = {
+		.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC,
+		.mem.type = DM_IO_KMEM,
+		.mem.ptr.addr = NULL,
+		.client = c->dm_io,
+	};
+	struct dm_io_region io_reg = {
+		.bdev = c->bdev,
+		.sector = 0,
+		.count = 0,
+	};
+
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return -EINVAL;
+
+	return dm_io(&io_req, 1, &io_reg, NULL);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_issue_flush);
+
+/*
+ * Use dm-io to send a discard request to flush the device.
+ */
+int dm_bufio_issue_discard(struct dm_bufio_client *c, sector_t block, sector_t count)
+{
+	struct dm_io_request io_req = {
+		.bi_opf = REQ_OP_DISCARD | REQ_SYNC,
+		.mem.type = DM_IO_KMEM,
+		.mem.ptr.addr = NULL,
+		.client = c->dm_io,
+	};
+	struct dm_io_region io_reg = {
+		.bdev = c->bdev,
+		.sector = block_to_sector(c, block),
+		.count = block_to_sector(c, count),
+	};
+
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return -EINVAL; /* discards are optional */
+
+	return dm_io(&io_req, 1, &io_reg, NULL);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_issue_discard);
+
+static bool forget_buffer(struct dm_bufio_client *c, sector_t block)
+{
+	struct dm_buffer *b;
+
+	b = cache_get(&c->cache, block);
+	if (b) {
+		if (likely(!smp_load_acquire(&b->state))) {
+			if (cache_remove(&c->cache, b))
+				__free_buffer_wake(b);
+			else
+				cache_put_and_wake(c, b);
+		} else {
+			cache_put_and_wake(c, b);
+		}
+	}
+
+	return b ? true : false;
+}
+
+/*
+ * Free the given buffer.
+ *
+ * This is just a hint, if the buffer is in use or dirty, this function
+ * does nothing.
+ */
+void dm_bufio_forget(struct dm_bufio_client *c, sector_t block)
+{
+	dm_bufio_lock(c);
+	forget_buffer(c, block);
+	dm_bufio_unlock(c);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_forget);
+
+static enum evict_result idle(struct dm_buffer *b, void *context)
+{
+	return b->state ? ER_DONT_EVICT : ER_EVICT;
+}
+
+void dm_bufio_forget_buffers(struct dm_bufio_client *c, sector_t block, sector_t n_blocks)
+{
+	dm_bufio_lock(c);
+	cache_remove_range(&c->cache, block, block + n_blocks, idle, __free_buffer_wake);
+	dm_bufio_unlock(c);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_forget_buffers);
+
+void dm_bufio_set_minimum_buffers(struct dm_bufio_client *c, unsigned int n)
+{
+	c->minimum_buffers = n;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_set_minimum_buffers);
+
+unsigned int dm_bufio_get_block_size(struct dm_bufio_client *c)
+{
+	return c->block_size;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_block_size);
+
+sector_t dm_bufio_get_device_size(struct dm_bufio_client *c)
+{
+	sector_t s = bdev_nr_sectors(c->bdev);
+
+	if (s >= c->start)
+		s -= c->start;
+	else
+		s = 0;
+	if (likely(c->sectors_per_block_bits >= 0))
+		s >>= c->sectors_per_block_bits;
+	else
+		sector_div(s, c->block_size >> SECTOR_SHIFT);
+	return s;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_device_size);
+
+struct dm_io_client *dm_bufio_get_dm_io_client(struct dm_bufio_client *c)
+{
+	return c->dm_io;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_dm_io_client);
+
+sector_t dm_bufio_get_block_number(struct dm_buffer *b)
+{
+	return b->block;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_block_number);
+
+void *dm_bufio_get_block_data(struct dm_buffer *b)
+{
+	return b->data;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_block_data);
+
+void *dm_bufio_get_aux_data(struct dm_buffer *b)
+{
+	return b + 1;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_aux_data);
+
+struct dm_bufio_client *dm_bufio_get_client(struct dm_buffer *b)
+{
+	return b->c;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_client);
+
+static enum it_action warn_leak(struct dm_buffer *b, void *context)
+{
+	bool *warned = context;
+
+	WARN_ON(!(*warned));
+	*warned = true;
+	DMERR("leaked buffer %llx, hold count %u, list %d",
+	      (unsigned long long)b->block, atomic_read(&b->hold_count), b->list_mode);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	stack_trace_print(b->stack_entries, b->stack_len, 1);
+	/* mark unclaimed to avoid WARN_ON at end of drop_buffers() */
+	atomic_set(&b->hold_count, 0);
+#endif
+	return IT_NEXT;
+}
+
+static void drop_buffers(struct dm_bufio_client *c)
+{
+	int i;
+	struct dm_buffer *b;
+
+	if (WARN_ON(dm_bufio_in_request()))
+		return; /* should never happen */
+
+	/*
+	 * An optimization so that the buffers are not written one-by-one.
+	 */
+	dm_bufio_write_dirty_buffers_async(c);
+
+	dm_bufio_lock(c);
+
+	while ((b = __get_unclaimed_buffer(c)))
+		__free_buffer_wake(b);
+
+	for (i = 0; i < LIST_SIZE; i++) {
+		bool warned = false;
+
+		cache_iterate(&c->cache, i, warn_leak, &warned);
+	}
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	while ((b = __get_unclaimed_buffer(c)))
+		__free_buffer_wake(b);
+#endif
+
+	for (i = 0; i < LIST_SIZE; i++)
+		WARN_ON(cache_count(&c->cache, i));
+
+	dm_bufio_unlock(c);
+}
+
+static unsigned long get_retain_buffers(struct dm_bufio_client *c)
+{
+	unsigned long retain_bytes = READ_ONCE(dm_bufio_retain_bytes);
+
+	if (likely(c->sectors_per_block_bits >= 0))
+		retain_bytes >>= c->sectors_per_block_bits + SECTOR_SHIFT;
+	else
+		retain_bytes /= c->block_size;
+
+	return retain_bytes;
+}
+
+static void __scan(struct dm_bufio_client *c)
+{
+	int l;
+	struct dm_buffer *b;
+	unsigned long freed = 0;
+	unsigned long retain_target = get_retain_buffers(c);
+	unsigned long count = cache_total(&c->cache);
+
+	for (l = 0; l < LIST_SIZE; l++) {
+		while (true) {
+			if (count - freed <= retain_target)
+				atomic_long_set(&c->need_shrink, 0);
+			if (!atomic_long_read(&c->need_shrink))
+				break;
+
+			b = cache_evict(&c->cache, l,
+					l == LIST_CLEAN ? is_clean : is_dirty, c);
+			if (!b)
+				break;
+
+			__make_buffer_clean(b);
+			__free_buffer_wake(b);
+
+			atomic_long_dec(&c->need_shrink);
+			freed++;
+			cond_resched();
+		}
+	}
+}
+
+static void shrink_work(struct work_struct *w)
+{
+	struct dm_bufio_client *c = container_of(w, struct dm_bufio_client, shrink_work);
+
+	dm_bufio_lock(c);
+	__scan(c);
+	dm_bufio_unlock(c);
+}
+
+static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+	struct dm_bufio_client *c;
+
+	c = container_of(shrink, struct dm_bufio_client, shrinker);
+	atomic_long_add(sc->nr_to_scan, &c->need_shrink);
+	queue_work(dm_bufio_wq, &c->shrink_work);
+
+	return sc->nr_to_scan;
+}
+
+static unsigned long dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
+{
+	struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
+	unsigned long count = cache_total(&c->cache);
+	unsigned long retain_target = get_retain_buffers(c);
+	unsigned long queued_for_cleanup = atomic_long_read(&c->need_shrink);
+
+	if (unlikely(count < retain_target))
+		count = 0;
+	else
+		count -= retain_target;
+
+	if (unlikely(count < queued_for_cleanup))
+		count = 0;
+	else
+		count -= queued_for_cleanup;
+
+	return count;
+}
+
+/*
+ * Create the buffering interface
+ */
+struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsigned int block_size,
+					       unsigned int reserved_buffers, unsigned int aux_size,
+					       void (*alloc_callback)(struct dm_buffer *),
+					       void (*write_callback)(struct dm_buffer *),
+					       unsigned int flags)
+{
+	int r;
+	unsigned int num_locks;
+	struct dm_bufio_client *c;
+	char slab_name[27];
+
+	if (!block_size || block_size & ((1 << SECTOR_SHIFT) - 1)) {
+		DMERR("%s: block size not specified or is not multiple of 512b", __func__);
+		r = -EINVAL;
+		goto bad_client;
+	}
+
+	num_locks = dm_num_hash_locks();
+	c = kzalloc(sizeof(*c) + (num_locks * sizeof(struct buffer_tree)), GFP_KERNEL);
+	if (!c) {
+		r = -ENOMEM;
+		goto bad_client;
+	}
+	cache_init(&c->cache, num_locks, (flags & DM_BUFIO_CLIENT_NO_SLEEP) != 0);
+
+	c->bdev = bdev;
+	c->block_size = block_size;
+	if (is_power_of_2(block_size))
+		c->sectors_per_block_bits = __ffs(block_size) - SECTOR_SHIFT;
+	else
+		c->sectors_per_block_bits = -1;
+
+	c->alloc_callback = alloc_callback;
+	c->write_callback = write_callback;
+
+	if (flags & DM_BUFIO_CLIENT_NO_SLEEP) {
+		c->no_sleep = true;
+		static_branch_inc(&no_sleep_enabled);
+	}
+
+	mutex_init(&c->lock);
+	spin_lock_init(&c->spinlock);
+	INIT_LIST_HEAD(&c->reserved_buffers);
+	c->need_reserved_buffers = reserved_buffers;
+
+	dm_bufio_set_minimum_buffers(c, DM_BUFIO_MIN_BUFFERS);
+
+	init_waitqueue_head(&c->free_buffer_wait);
+	c->async_write_error = 0;
+
+	c->dm_io = dm_io_client_create();
+	if (IS_ERR(c->dm_io)) {
+		r = PTR_ERR(c->dm_io);
+		goto bad_dm_io;
+	}
+
+	if (block_size <= KMALLOC_MAX_SIZE &&
+	    (block_size < PAGE_SIZE || !is_power_of_2(block_size))) {
+		unsigned int align = min(1U << __ffs(block_size), (unsigned int)PAGE_SIZE);
+
+		snprintf(slab_name, sizeof(slab_name), "dm_bufio_cache-%u", block_size);
+		c->slab_cache = kmem_cache_create(slab_name, block_size, align,
+						  SLAB_RECLAIM_ACCOUNT, NULL);
+		if (!c->slab_cache) {
+			r = -ENOMEM;
+			goto bad;
+		}
+	}
+	if (aux_size)
+		snprintf(slab_name, sizeof(slab_name), "dm_bufio_buffer-%u", aux_size);
+	else
+		snprintf(slab_name, sizeof(slab_name), "dm_bufio_buffer");
+	c->slab_buffer = kmem_cache_create(slab_name, sizeof(struct dm_buffer) + aux_size,
+					   0, SLAB_RECLAIM_ACCOUNT, NULL);
+	if (!c->slab_buffer) {
+		r = -ENOMEM;
+		goto bad;
+	}
+
+	while (c->need_reserved_buffers) {
+		struct dm_buffer *b = alloc_buffer(c, GFP_KERNEL);
+
+		if (!b) {
+			r = -ENOMEM;
+			goto bad;
+		}
+		__free_buffer_wake(b);
+	}
+
+	INIT_WORK(&c->shrink_work, shrink_work);
+	atomic_long_set(&c->need_shrink, 0);
+
+	c->shrinker.count_objects = dm_bufio_shrink_count;
+	c->shrinker.scan_objects = dm_bufio_shrink_scan;
+	c->shrinker.seeks = 1;
+	c->shrinker.batch = 0;
+	r = register_shrinker(&c->shrinker, "dm-bufio:(%u:%u)",
+			      MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
+	if (r)
+		goto bad;
+
+	mutex_lock(&dm_bufio_clients_lock);
+	dm_bufio_client_count++;
+	list_add(&c->client_list, &dm_bufio_all_clients);
+	__cache_size_refresh();
+	mutex_unlock(&dm_bufio_clients_lock);
+
+	return c;
+
+bad:
+	while (!list_empty(&c->reserved_buffers)) {
+		struct dm_buffer *b = list_to_buffer(c->reserved_buffers.next);
+
+		list_del(&b->lru.list);
+		free_buffer(b);
+	}
+	kmem_cache_destroy(c->slab_cache);
+	kmem_cache_destroy(c->slab_buffer);
+	dm_io_client_destroy(c->dm_io);
+bad_dm_io:
+	mutex_destroy(&c->lock);
+	if (c->no_sleep)
+		static_branch_dec(&no_sleep_enabled);
+	kfree(c);
+bad_client:
+	return ERR_PTR(r);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_client_create);
+
+/*
+ * Free the buffering interface.
+ * It is required that there are no references on any buffers.
+ */
+void dm_bufio_client_destroy(struct dm_bufio_client *c)
+{
+	unsigned int i;
+
+	drop_buffers(c);
+
+	unregister_shrinker(&c->shrinker);
+	flush_work(&c->shrink_work);
+
+	mutex_lock(&dm_bufio_clients_lock);
+
+	list_del(&c->client_list);
+	dm_bufio_client_count--;
+	__cache_size_refresh();
+
+	mutex_unlock(&dm_bufio_clients_lock);
+
+	WARN_ON(c->need_reserved_buffers);
+
+	while (!list_empty(&c->reserved_buffers)) {
+		struct dm_buffer *b = list_to_buffer(c->reserved_buffers.next);
+
+		list_del(&b->lru.list);
+		free_buffer(b);
+	}
+
+	for (i = 0; i < LIST_SIZE; i++)
+		if (cache_count(&c->cache, i))
+			DMERR("leaked buffer count %d: %lu", i, cache_count(&c->cache, i));
+
+	for (i = 0; i < LIST_SIZE; i++)
+		WARN_ON(cache_count(&c->cache, i));
+
+	cache_destroy(&c->cache);
+	kmem_cache_destroy(c->slab_cache);
+	kmem_cache_destroy(c->slab_buffer);
+	dm_io_client_destroy(c->dm_io);
+	mutex_destroy(&c->lock);
+	if (c->no_sleep)
+		static_branch_dec(&no_sleep_enabled);
+	kfree(c);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_client_destroy);
+
+void dm_bufio_client_reset(struct dm_bufio_client *c)
+{
+	drop_buffers(c);
+	flush_work(&c->shrink_work);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_client_reset);
+
+void dm_bufio_set_sector_offset(struct dm_bufio_client *c, sector_t start)
+{
+	c->start = start;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_set_sector_offset);
+
+/*--------------------------------------------------------------*/
+
+static unsigned int get_max_age_hz(void)
+{
+	unsigned int max_age = READ_ONCE(dm_bufio_max_age);
+
+	if (max_age > UINT_MAX / HZ)
+		max_age = UINT_MAX / HZ;
+
+	return max_age * HZ;
+}
+
+static bool older_than(struct dm_buffer *b, unsigned long age_hz)
+{
+	return time_after_eq(jiffies, READ_ONCE(b->last_accessed) + age_hz);
+}
+
+struct evict_params {
+	gfp_t gfp;
+	unsigned long age_hz;
+
+	/*
+	 * This gets updated with the largest last_accessed (ie. most
+	 * recently used) of the evicted buffers.  It will not be reinitialised
+	 * by __evict_many(), so you can use it across multiple invocations.
+	 */
+	unsigned long last_accessed;
+};
+
+/*
+ * We may not be able to evict this buffer if IO pending or the client
+ * is still using it.
+ *
+ * And if GFP_NOFS is used, we must not do any I/O because we hold
+ * dm_bufio_clients_lock and we would risk deadlock if the I/O gets
+ * rerouted to different bufio client.
+ */
+static enum evict_result select_for_evict(struct dm_buffer *b, void *context)
+{
+	struct evict_params *params = context;
+
+	if (!(params->gfp & __GFP_FS) ||
+	    (static_branch_unlikely(&no_sleep_enabled) && b->c->no_sleep)) {
+		if (test_bit_acquire(B_READING, &b->state) ||
+		    test_bit(B_WRITING, &b->state) ||
+		    test_bit(B_DIRTY, &b->state))
+			return ER_DONT_EVICT;
+	}
+
+	return older_than(b, params->age_hz) ? ER_EVICT : ER_STOP;
+}
+
+static unsigned long __evict_many(struct dm_bufio_client *c,
+				  struct evict_params *params,
+				  int list_mode, unsigned long max_count)
+{
+	unsigned long count;
+	unsigned long last_accessed;
+	struct dm_buffer *b;
+
+	for (count = 0; count < max_count; count++) {
+		b = cache_evict(&c->cache, list_mode, select_for_evict, params);
+		if (!b)
+			break;
+
+		last_accessed = READ_ONCE(b->last_accessed);
+		if (time_after_eq(params->last_accessed, last_accessed))
+			params->last_accessed = last_accessed;
+
+		__make_buffer_clean(b);
+		__free_buffer_wake(b);
+
+		cond_resched();
+	}
+
+	return count;
+}
+
+static void evict_old_buffers(struct dm_bufio_client *c, unsigned long age_hz)
+{
+	struct evict_params params = {.gfp = 0, .age_hz = age_hz, .last_accessed = 0};
+	unsigned long retain = get_retain_buffers(c);
+	unsigned long count;
+	LIST_HEAD(write_list);
+
+	dm_bufio_lock(c);
+
+	__check_watermark(c, &write_list);
+	if (unlikely(!list_empty(&write_list))) {
+		dm_bufio_unlock(c);
+		__flush_write_list(&write_list);
+		dm_bufio_lock(c);
+	}
+
+	count = cache_total(&c->cache);
+	if (count > retain)
+		__evict_many(c, &params, LIST_CLEAN, count - retain);
+
+	dm_bufio_unlock(c);
+}
+
+static void cleanup_old_buffers(void)
+{
+	unsigned long max_age_hz = get_max_age_hz();
+	struct dm_bufio_client *c;
+
+	mutex_lock(&dm_bufio_clients_lock);
+
+	__cache_size_refresh();
+
+	list_for_each_entry(c, &dm_bufio_all_clients, client_list)
+		evict_old_buffers(c, max_age_hz);
+
+	mutex_unlock(&dm_bufio_clients_lock);
+}
+
+static void work_fn(struct work_struct *w)
+{
+	cleanup_old_buffers();
+
+	queue_delayed_work(dm_bufio_wq, &dm_bufio_cleanup_old_work,
+			   DM_BUFIO_WORK_TIMER_SECS * HZ);
+}
+
+/*--------------------------------------------------------------*/
+
+/*
+ * Global cleanup tries to evict the oldest buffers from across _all_
+ * the clients.  It does this by repeatedly evicting a few buffers from
+ * the client that holds the oldest buffer.  It's approximate, but hopefully
+ * good enough.
+ */
+static struct dm_bufio_client *__pop_client(void)
+{
+	struct list_head *h;
+
+	if (list_empty(&dm_bufio_all_clients))
+		return NULL;
+
+	h = dm_bufio_all_clients.next;
+	list_del(h);
+	return container_of(h, struct dm_bufio_client, client_list);
+}
+
+/*
+ * Inserts the client in the global client list based on its
+ * 'oldest_buffer' field.
+ */
+static void __insert_client(struct dm_bufio_client *new_client)
+{
+	struct dm_bufio_client *c;
+	struct list_head *h = dm_bufio_all_clients.next;
+
+	while (h != &dm_bufio_all_clients) {
+		c = container_of(h, struct dm_bufio_client, client_list);
+		if (time_after_eq(c->oldest_buffer, new_client->oldest_buffer))
+			break;
+		h = h->next;
+	}
+
+	list_add_tail(&new_client->client_list, h);
+}
+
+static unsigned long __evict_a_few(unsigned long nr_buffers)
+{
+	unsigned long count;
+	struct dm_bufio_client *c;
+	struct evict_params params = {
+		.gfp = GFP_KERNEL,
+		.age_hz = 0,
+		/* set to jiffies in case there are no buffers in this client */
+		.last_accessed = jiffies
+	};
+
+	c = __pop_client();
+	if (!c)
+		return 0;
+
+	dm_bufio_lock(c);
+	count = __evict_many(c, &params, LIST_CLEAN, nr_buffers);
+	dm_bufio_unlock(c);
+
+	if (count)
+		c->oldest_buffer = params.last_accessed;
+	__insert_client(c);
+
+	return count;
+}
+
+static void check_watermarks(void)
+{
+	LIST_HEAD(write_list);
+	struct dm_bufio_client *c;
+
+	mutex_lock(&dm_bufio_clients_lock);
+	list_for_each_entry(c, &dm_bufio_all_clients, client_list) {
+		dm_bufio_lock(c);
+		__check_watermark(c, &write_list);
+		dm_bufio_unlock(c);
+	}
+	mutex_unlock(&dm_bufio_clients_lock);
+
+	__flush_write_list(&write_list);
+}
+
+static void evict_old(void)
+{
+	unsigned long threshold = dm_bufio_cache_size -
+		dm_bufio_cache_size / DM_BUFIO_LOW_WATERMARK_RATIO;
+
+	mutex_lock(&dm_bufio_clients_lock);
+	while (dm_bufio_current_allocated > threshold) {
+		if (!__evict_a_few(64))
+			break;
+		cond_resched();
+	}
+	mutex_unlock(&dm_bufio_clients_lock);
+}
+
+static void do_global_cleanup(struct work_struct *w)
+{
+	check_watermarks();
+	evict_old();
+}
+
+/*
+ *--------------------------------------------------------------
+ * Module setup
+ *--------------------------------------------------------------
+ */
+
+/*
+ * This is called only once for the whole dm_bufio module.
+ * It initializes memory limit.
+ */
+static int __init dm_bufio_init(void)
+{
+	__u64 mem;
+
+	dm_bufio_allocated_kmem_cache = 0;
+	dm_bufio_allocated_get_free_pages = 0;
+	dm_bufio_allocated_vmalloc = 0;
+	dm_bufio_current_allocated = 0;
+
+	mem = (__u64)mult_frac(totalram_pages() - totalhigh_pages(),
+			       DM_BUFIO_MEMORY_PERCENT, 100) << PAGE_SHIFT;
+
+	if (mem > ULONG_MAX)
+		mem = ULONG_MAX;
+
+#ifdef CONFIG_MMU
+	if (mem > mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100))
+		mem = mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100);
+#endif
+
+	dm_bufio_default_cache_size = mem;
+
+	mutex_lock(&dm_bufio_clients_lock);
+	__cache_size_refresh();
+	mutex_unlock(&dm_bufio_clients_lock);
+
+	dm_bufio_wq = alloc_workqueue("dm_bufio_cache", WQ_MEM_RECLAIM, 0);
+	if (!dm_bufio_wq)
+		return -ENOMEM;
+
+	INIT_DELAYED_WORK(&dm_bufio_cleanup_old_work, work_fn);
+	INIT_WORK(&dm_bufio_replacement_work, do_global_cleanup);
+	queue_delayed_work(dm_bufio_wq, &dm_bufio_cleanup_old_work,
+			   DM_BUFIO_WORK_TIMER_SECS * HZ);
+
+	return 0;
+}
+
+/*
+ * This is called once when unloading the dm_bufio module.
+ */
+static void __exit dm_bufio_exit(void)
+{
+	int bug = 0;
+
+	cancel_delayed_work_sync(&dm_bufio_cleanup_old_work);
+	destroy_workqueue(dm_bufio_wq);
+
+	if (dm_bufio_client_count) {
+		DMCRIT("%s: dm_bufio_client_count leaked: %d",
+			__func__, dm_bufio_client_count);
+		bug = 1;
+	}
+
+	if (dm_bufio_current_allocated) {
+		DMCRIT("%s: dm_bufio_current_allocated leaked: %lu",
+			__func__, dm_bufio_current_allocated);
+		bug = 1;
+	}
+
+	if (dm_bufio_allocated_get_free_pages) {
+		DMCRIT("%s: dm_bufio_allocated_get_free_pages leaked: %lu",
+		       __func__, dm_bufio_allocated_get_free_pages);
+		bug = 1;
+	}
+
+	if (dm_bufio_allocated_vmalloc) {
+		DMCRIT("%s: dm_bufio_vmalloc leaked: %lu",
+		       __func__, dm_bufio_allocated_vmalloc);
+		bug = 1;
+	}
+
+	WARN_ON(bug); /* leaks are not worth crashing the system */
+}
+
+module_init(dm_bufio_init)
+module_exit(dm_bufio_exit)
+
+module_param_named(max_cache_size_bytes, dm_bufio_cache_size, ulong, 0644);
+MODULE_PARM_DESC(max_cache_size_bytes, "Size of metadata cache");
+
+module_param_named(max_age_seconds, dm_bufio_max_age, uint, 0644);
+MODULE_PARM_DESC(max_age_seconds, "Max age of a buffer in seconds");
+
+module_param_named(retain_bytes, dm_bufio_retain_bytes, ulong, 0644);
+MODULE_PARM_DESC(retain_bytes, "Try to keep at least this many bytes cached in memory");
+
+module_param_named(peak_allocated_bytes, dm_bufio_peak_allocated, ulong, 0644);
+MODULE_PARM_DESC(peak_allocated_bytes, "Tracks the maximum allocated memory");
+
+module_param_named(allocated_kmem_cache_bytes, dm_bufio_allocated_kmem_cache, ulong, 0444);
+MODULE_PARM_DESC(allocated_kmem_cache_bytes, "Memory allocated with kmem_cache_alloc");
+
+module_param_named(allocated_get_free_pages_bytes, dm_bufio_allocated_get_free_pages, ulong, 0444);
+MODULE_PARM_DESC(allocated_get_free_pages_bytes, "Memory allocated with get_free_pages");
+
+module_param_named(allocated_vmalloc_bytes, dm_bufio_allocated_vmalloc, ulong, 0444);
+MODULE_PARM_DESC(allocated_vmalloc_bytes, "Memory allocated with vmalloc");
+
+module_param_named(current_allocated_bytes, dm_bufio_current_allocated, ulong, 0444);
+MODULE_PARM_DESC(current_allocated_bytes, "Memory currently used by the cache");
+
+MODULE_AUTHOR("Mikulas Patocka <dm-devel@redhat.com>");
+MODULE_DESCRIPTION(DM_NAME " buffered I/O library");
+MODULE_LICENSE("GPL");