md/dm-pcache/cache_key.c

// SPDX-License-Identifier: GPL-2.0-or-later
#include "cache.h"
#include "backing_dev.h"
#include "cache_dev.h"
#include "dm_pcache.h"

struct pcache_cache_kset_onmedia pcache_empty_kset = { 0 };

void cache_key_init(struct pcache_cache_tree *cache_tree, struct pcache_cache_key *key)
{
	kref_init(&key->ref);
	key->cache_tree = cache_tree;
	INIT_LIST_HEAD(&key->list_node);
	RB_CLEAR_NODE(&key->rb_node);
}

struct pcache_cache_key *cache_key_alloc(struct pcache_cache_tree *cache_tree, gfp_t gfp_mask)
{
	struct pcache_cache_key *key;

	key = mempool_alloc(&cache_tree->key_pool, gfp_mask);
	if (!key)
		return NULL;

	memset(key, 0, sizeof(struct pcache_cache_key));
	cache_key_init(cache_tree, key);

	return key;
}

/**
 * cache_key_get - Increment the reference count of a cache key.
 * @key: Pointer to the pcache_cache_key structure.
 *
 * This function increments the reference count of the specified cache key,
 * ensuring that it is not freed while still in use.
 */
void cache_key_get(struct pcache_cache_key *key)
{
	kref_get(&key->ref);
}

/**
 * cache_key_destroy - Free a cache key structure when its reference count drops to zero.
 * @ref: Pointer to the kref structure.
 *
 * This function is called when the reference count of the cache key reaches zero.
 * It frees the allocated cache key back to the slab cache.
 */
static void cache_key_destroy(struct kref *ref)
{
	struct pcache_cache_key *key = container_of(ref, struct pcache_cache_key, ref);
	struct pcache_cache_tree *cache_tree = key->cache_tree;

	mempool_free(key, &cache_tree->key_pool);
}

void cache_key_put(struct pcache_cache_key *key)
{
	kref_put(&key->ref, cache_key_destroy);
}

void cache_pos_advance(struct pcache_cache_pos *pos, u32 len)
{
	/* Ensure enough space remains in the current segment */
	BUG_ON(cache_seg_remain(pos) < len);

	pos->seg_off += len;
}

static void cache_key_encode(struct pcache_cache *cache,
			     struct pcache_cache_key_onmedia *key_onmedia,
			     struct pcache_cache_key *key)
{
	key_onmedia->off = key->off;
	key_onmedia->len = key->len;

	key_onmedia->cache_seg_id = key->cache_pos.cache_seg->cache_seg_id;
	key_onmedia->cache_seg_off = key->cache_pos.seg_off;

	key_onmedia->seg_gen = key->seg_gen;
	key_onmedia->flags = key->flags;

	if (cache_data_crc_on(cache))
		key_onmedia->data_crc = cache_key_data_crc(key);
}

int cache_key_decode(struct pcache_cache *cache,
			struct pcache_cache_key_onmedia *key_onmedia,
			struct pcache_cache_key *key)
{
	struct dm_pcache *pcache = CACHE_TO_PCACHE(cache);
	u64 dev_bytes = (u64)cache->dev_size << SECTOR_SHIFT;

	key->off = key_onmedia->off;
	key->len = key_onmedia->len;

	if (key_onmedia->len == 0 ||
	    key_onmedia->len > dev_bytes ||
	    key_onmedia->off > dev_bytes - key_onmedia->len) {
		pcache_dev_err(pcache, "key off %llu + len %u exceeds device size\n",
				key_onmedia->off, key_onmedia->len);
		return -EIO;
	}

	if (!cache_seg_id_valid(cache, key_onmedia->cache_seg_id)) {
		pcache_dev_err(pcache, "invalid cache_seg_id %u in cache key (n_segs %u)\n",
				key_onmedia->cache_seg_id, cache->n_segs);
		return -EIO;
	}

	key->cache_pos.cache_seg = &cache->segments[key_onmedia->cache_seg_id];
	key->cache_pos.seg_off = key_onmedia->cache_seg_off;

	if ((u64)key->cache_pos.seg_off + key->len >
			key->cache_pos.cache_seg->segment.data_size) {
		pcache_dev_err(pcache, "key seg_off %u + len %u exceeds segment data size %u\n",
				key->cache_pos.seg_off, key->len,
				key->cache_pos.cache_seg->segment.data_size);
		return -EIO;
	}

	key->seg_gen = key_onmedia->seg_gen;
	key->flags = key_onmedia->flags;

	if (cache_data_crc_on(cache) &&
			key_onmedia->data_crc != cache_key_data_crc(key)) {
		pcache_dev_err(pcache, "key: %llu:%u seg %u:%u data_crc error: %x, expected: %x\n",
				key->off, key->len, key->cache_pos.cache_seg->cache_seg_id,
				key->cache_pos.seg_off, cache_key_data_crc(key), key_onmedia->data_crc);
		return -EIO;
	}

	return 0;
}

static void append_last_kset(struct pcache_cache *cache, u32 next_seg)
{
	struct pcache_cache_kset_onmedia kset_onmedia = { 0 };

	kset_onmedia.flags |= PCACHE_KSET_FLAGS_LAST;
	kset_onmedia.next_cache_seg_id = next_seg;
	kset_onmedia.magic = PCACHE_KSET_MAGIC;
	kset_onmedia.crc = cache_kset_crc(&kset_onmedia);

	memcpy_flushcache(get_key_head_addr(cache), &kset_onmedia, sizeof(struct pcache_cache_kset_onmedia));
	pmem_wmb();
	cache_pos_advance(&cache->key_head, sizeof(struct pcache_cache_kset_onmedia));
}

int cache_kset_close(struct pcache_cache *cache, struct pcache_cache_kset *kset)
{
	struct pcache_cache_kset_onmedia *kset_onmedia;
	u32 kset_onmedia_size;
	int ret;

	kset_onmedia = &kset->kset_onmedia;

	if (!kset_onmedia->key_num)
		return 0;

	kset_onmedia_size = struct_size(kset_onmedia, data, kset_onmedia->key_num);

	spin_lock(&cache->key_head_lock);
again:
	/* Reserve space for the last kset */
	if (cache_seg_remain(&cache->key_head) < kset_onmedia_size + sizeof(struct pcache_cache_kset_onmedia)) {
		struct pcache_cache_segment *next_seg;

		next_seg = get_cache_segment(cache);
		if (!next_seg) {
			ret = -EBUSY;
			goto out;
		}

		/* clear outdated kset in next seg */
		memcpy_flushcache(next_seg->segment.data, &pcache_empty_kset,
					sizeof(struct pcache_cache_kset_onmedia));
		append_last_kset(cache, next_seg->cache_seg_id);
		cache->key_head.cache_seg = next_seg;
		cache->key_head.seg_off = 0;
		goto again;
	}

	kset_onmedia->magic = PCACHE_KSET_MAGIC;
	kset_onmedia->crc = cache_kset_crc(kset_onmedia);

	/* clear outdated kset after current kset */
	memcpy_flushcache(get_key_head_addr(cache) + kset_onmedia_size, &pcache_empty_kset,
				sizeof(struct pcache_cache_kset_onmedia));
	/* write current kset into segment */
	memcpy_flushcache(get_key_head_addr(cache), kset_onmedia, kset_onmedia_size);
	pmem_wmb();

	/* reset kset_onmedia */
	memset(kset_onmedia, 0, sizeof(struct pcache_cache_kset_onmedia));
	cache_pos_advance(&cache->key_head, kset_onmedia_size);

	ret = 0;
out:
	spin_unlock(&cache->key_head_lock);

	return ret;
}

/**
 * cache_key_append - Append a cache key to the related kset.
 * @cache: Pointer to the pcache_cache structure.
 * @key: Pointer to the cache key structure to append.
 * @force_close: Need to close current kset if true.
 *
 * This function appends a cache key to the appropriate kset. If the kset
 * is full, it closes the kset. If not, it queues a flush work to write
 * the kset to media.
 *
 * Returns 0 on success, or a negative error code on failure.
 */
int cache_key_append(struct pcache_cache *cache, struct pcache_cache_key *key, bool force_close)
{
	struct pcache_cache_kset *kset;
	struct pcache_cache_kset_onmedia *kset_onmedia;
	struct pcache_cache_key_onmedia *key_onmedia;
	u32 kset_id = get_kset_id(cache, key->off);
	int ret = 0;

	kset = get_kset(cache, kset_id);
	kset_onmedia = &kset->kset_onmedia;

	spin_lock(&kset->kset_lock);
	key_onmedia = &kset_onmedia->data[kset_onmedia->key_num];
	cache_key_encode(cache, key_onmedia, key);

	/* Check if the current kset has reached the maximum number of keys */
	if (++kset_onmedia->key_num == PCACHE_KSET_KEYS_MAX || force_close) {
		/* If full, close the kset */
		ret = cache_kset_close(cache, kset);
		if (ret) {
			kset_onmedia->key_num--;
			goto out;
		}
	} else {
		/* If not full, queue a delayed work to flush the kset */
		queue_delayed_work(cache_get_wq(cache), &kset->flush_work, 1 * HZ);
	}
out:
	spin_unlock(&kset->kset_lock);

	return ret;
}

/**
 * cache_subtree_walk - Traverse the cache tree.
 * @ctx: Pointer to the context structure for traversal.
 *
 * This function traverses the cache tree starting from the specified node.
 * It calls the appropriate callback functions based on the relationships
 * between the keys in the cache tree.
 *
 * Returns 0 on success, or a negative error code on failure.
 */
int cache_subtree_walk(struct pcache_cache_subtree_walk_ctx *ctx)
{
	struct pcache_cache_key *key_tmp, *key;
	struct rb_node *node_tmp;
	int ret = SUBTREE_WALK_RET_OK;

	key = ctx->key;
	node_tmp = ctx->start_node;

	while (node_tmp) {
		if (ctx->walk_done && ctx->walk_done(ctx))
			break;

		key_tmp = CACHE_KEY(node_tmp);
		/*
		 * If key_tmp ends before the start of key, continue to the next node.
		 * |----------|
		 *              |=====|
		 */
		if (cache_key_lend(key_tmp) <= cache_key_lstart(key)) {
			if (ctx->after) {
				ret = ctx->after(key, key_tmp, ctx);
				if (ret)
					goto out;
			}
			goto next;
		}

		/*
		 * If key_tmp starts after the end of key, stop traversing.
		 *        |--------|
		 * |====|
		 */
		if (cache_key_lstart(key_tmp) >= cache_key_lend(key)) {
			if (ctx->before) {
				ret = ctx->before(key, key_tmp, ctx);
				if (ret)
					goto out;
			}
			break;
		}

		/* Handle overlapping keys */
		if (cache_key_lstart(key_tmp) >= cache_key_lstart(key)) {
			/*
			 * If key_tmp encompasses key.
			 *     |----------------|	key_tmp
			 * |===========|		key
			 */
			if (cache_key_lend(key_tmp) >= cache_key_lend(key)) {
				if (ctx->overlap_tail) {
					ret = ctx->overlap_tail(key, key_tmp, ctx);
					if (ret)
						goto out;
				}
				break;
			}

			/*
			 * If key_tmp is contained within key.
			 *    |----|		key_tmp
			 * |==========|		key
			 */
			if (ctx->overlap_contain) {
				ret = ctx->overlap_contain(key, key_tmp, ctx);
				if (ret)
					goto out;
			}

			goto next;
		}

		/*
		 * If key_tmp starts before key ends but ends after key.
		 * |-----------|	key_tmp
		 *   |====|		key
		 */
		if (cache_key_lend(key_tmp) > cache_key_lend(key)) {
			if (ctx->overlap_contained) {
				ret = ctx->overlap_contained(key, key_tmp, ctx);
				if (ret)
					goto out;
			}
			break;
		}

		/*
		 * If key_tmp starts before key and ends within key.
		 * |--------|		key_tmp
		 *   |==========|	key
		 */
		if (ctx->overlap_head) {
			ret = ctx->overlap_head(key, key_tmp, ctx);
			if (ret)
				goto out;
		}
next:
		node_tmp = rb_next(node_tmp);
	}

out:
	if (ctx->walk_finally)
		ret = ctx->walk_finally(ctx, ret);

	return ret;
}

/**
 * cache_subtree_search - Search for a key in the cache tree.
 * @cache_subtree: Pointer to the cache tree structure.
 * @key: Pointer to the cache key to search for.
 * @parentp: Pointer to store the parent node of the found node.
 * @newp: Pointer to store the location where the new node should be inserted.
 * @delete_key_list: List to collect invalid keys for deletion.
 *
 * This function searches the cache tree for a specific key and returns
 * the node that is the predecessor of the key, or first node if the key is
 * less than all keys in the tree. If any invalid keys are found during
 * the search, they are added to the delete_key_list for later cleanup.
 *
 * Returns a pointer to the previous node.
 */
struct rb_node *cache_subtree_search(struct pcache_cache_subtree *cache_subtree, struct pcache_cache_key *key,
				  struct rb_node **parentp, struct rb_node ***newp,
				  struct list_head *delete_key_list)
{
	struct rb_node **new, *parent = NULL;
	struct pcache_cache_key *key_tmp;
	struct rb_node *prev_node = NULL;

	new = &(cache_subtree->root.rb_node);
	while (*new) {
		key_tmp = container_of(*new, struct pcache_cache_key, rb_node);
		if (cache_key_invalid(key_tmp))
			list_add(&key_tmp->list_node, delete_key_list);

		parent = *new;
		if (key_tmp->off >= key->off) {
			new = &((*new)->rb_left);
		} else {
			prev_node = *new;
			new = &((*new)->rb_right);
		}
	}

	if (!prev_node)
		prev_node = rb_first(&cache_subtree->root);

	if (parentp)
		*parentp = parent;

	if (newp)
		*newp = new;

	return prev_node;
}

static struct pcache_cache_key *get_pre_alloc_key(struct pcache_cache_subtree_walk_ctx *ctx)
{
	struct pcache_cache_key *key;

	if (ctx->pre_alloc_key) {
		key = ctx->pre_alloc_key;
		ctx->pre_alloc_key = NULL;

		return key;
	}

	return cache_key_alloc(ctx->cache_tree, GFP_NOWAIT);
}

/**
 * fixup_overlap_tail - Adjust the key when it overlaps at the tail.
 * @key: Pointer to the new cache key being inserted.
 * @key_tmp: Pointer to the existing key that overlaps.
 * @ctx: Pointer to the context for walking the cache tree.
 *
 * This function modifies the existing key (key_tmp) when there is an
 * overlap at the tail with the new key. If the modified key becomes
 * empty, it is deleted.
 */
static int fixup_overlap_tail(struct pcache_cache_key *key,
			       struct pcache_cache_key *key_tmp,
			       struct pcache_cache_subtree_walk_ctx *ctx)
{
	/*
	 *     |----------------|	key_tmp
	 * |===========|		key
	 */
	BUG_ON(cache_key_empty(key));
	if (cache_key_empty(key_tmp)) {
		cache_key_delete(key_tmp);
		return SUBTREE_WALK_RET_RESEARCH;
	}

	cache_key_cutfront(key_tmp, cache_key_lend(key) - cache_key_lstart(key_tmp));
	if (key_tmp->len == 0) {
		cache_key_delete(key_tmp);
		return SUBTREE_WALK_RET_RESEARCH;
	}

	return SUBTREE_WALK_RET_OK;
}

/**
 * fixup_overlap_contain - Handle case where new key completely contains an existing key.
 * @key: Pointer to the new cache key being inserted.
 * @key_tmp: Pointer to the existing key that is being contained.
 * @ctx: Pointer to the context for walking the cache tree.
 *
 * This function deletes the existing key (key_tmp) when the new key
 * completely contains it. It returns SUBTREE_WALK_RET_RESEARCH to indicate that the
 * tree structure may have changed, necessitating a re-insertion of
 * the new key.
 */
static int fixup_overlap_contain(struct pcache_cache_key *key,
				  struct pcache_cache_key *key_tmp,
				  struct pcache_cache_subtree_walk_ctx *ctx)
{
	/*
	 *    |----|			key_tmp
	 * |==========|			key
	 */
	BUG_ON(cache_key_empty(key));
	cache_key_delete(key_tmp);

	return SUBTREE_WALK_RET_RESEARCH;
}

/**
 * fixup_overlap_contained - Handle overlap when a new key is contained in an existing key.
 * @key: The new cache key being inserted.
 * @key_tmp: The existing cache key that overlaps with the new key.
 * @ctx: Context for the cache tree walk.
 *
 * This function adjusts the existing key if the new key is contained
 * within it. If the existing key is empty, it indicates a placeholder key
 * that was inserted during a miss read. This placeholder will later be
 * updated with real data from the backing_dev, making it no longer an empty key.
 *
 * If we delete key or insert a key, the structure of the entire cache tree may change,
 * requiring a full research of the tree to find a new insertion point.
 */
static int fixup_overlap_contained(struct pcache_cache_key *key,
	struct pcache_cache_key *key_tmp, struct pcache_cache_subtree_walk_ctx *ctx)
{
	struct pcache_cache_tree *cache_tree = ctx->cache_tree;

	/*
	 * |-----------|		key_tmp
	 *   |====|			key
	 */
	BUG_ON(cache_key_empty(key));
	if (cache_key_empty(key_tmp)) {
		/* If key_tmp is empty, don't split it;
		 * it's a placeholder key for miss reads that will be updated later.
		 */
		cache_key_cutback(key_tmp, cache_key_lend(key_tmp) - cache_key_lstart(key));
		if (key_tmp->len == 0) {
			cache_key_delete(key_tmp);
			return SUBTREE_WALK_RET_RESEARCH;
		}
	} else {
		struct pcache_cache_key *key_fixup;
		bool need_research = false;

		key_fixup = get_pre_alloc_key(ctx);
		if (!key_fixup)
			return SUBTREE_WALK_RET_NEED_KEY;

		cache_key_copy(key_fixup, key_tmp);

		/* Split key_tmp based on the new key's range */
		cache_key_cutback(key_tmp, cache_key_lend(key_tmp) - cache_key_lstart(key));
		if (key_tmp->len == 0) {
			cache_key_delete(key_tmp);
			need_research = true;
		}

		/* Create a new portion for key_fixup */
		cache_key_cutfront(key_fixup, cache_key_lend(key) - cache_key_lstart(key_tmp));
		if (key_fixup->len == 0) {
			cache_key_put(key_fixup);
		} else {
			/* Insert the new key into the cache */
			cache_key_insert(cache_tree, key_fixup, false);
			need_research = true;
		}

		if (need_research)
			return SUBTREE_WALK_RET_RESEARCH;
	}

	return SUBTREE_WALK_RET_OK;
}

/**
 * fixup_overlap_head - Handle overlap when a new key overlaps with the head of an existing key.
 * @key: The new cache key being inserted.
 * @key_tmp: The existing cache key that overlaps with the new key.
 * @ctx: Context for the cache tree walk.
 *
 * This function adjusts the existing key if the new key overlaps
 * with the beginning of it. If the resulting key length is zero
 * after the adjustment, the key is deleted. This indicates that
 * the key no longer holds valid data and requires the tree to be
 * re-researched for a new insertion point.
 */
static int fixup_overlap_head(struct pcache_cache_key *key,
	struct pcache_cache_key *key_tmp, struct pcache_cache_subtree_walk_ctx *ctx)
{
	/*
	 * |--------|		key_tmp
	 *   |==========|	key
	 */
	BUG_ON(cache_key_empty(key));
	/* Adjust key_tmp by cutting back based on the new key's start */
	cache_key_cutback(key_tmp, cache_key_lend(key_tmp) - cache_key_lstart(key));
	if (key_tmp->len == 0) {
		/* If the adjusted key_tmp length is zero, delete it */
		cache_key_delete(key_tmp);
		return SUBTREE_WALK_RET_RESEARCH;
	}

	return SUBTREE_WALK_RET_OK;
}

/**
 * cache_key_insert - Insert a new cache key into the cache tree.
 * @cache_tree: Pointer to the cache_tree structure.
 * @key: The cache key to insert.
 * @fixup: Indicates if this is a new key being inserted.
 *
 * This function searches for the appropriate location to insert
 * a new cache key into the cache tree. It handles key overlaps
 * and ensures any invalid keys are removed before insertion.
 */
void cache_key_insert(struct pcache_cache_tree *cache_tree, struct pcache_cache_key *key, bool fixup)
{
	struct pcache_cache *cache = cache_tree->cache;
	struct pcache_cache_subtree_walk_ctx walk_ctx = { 0 };
	struct rb_node **new, *parent = NULL;
	struct pcache_cache_subtree *cache_subtree;
	struct pcache_cache_key *key_tmp = NULL, *key_next;
	struct rb_node *prev_node = NULL;
	LIST_HEAD(delete_key_list);
	int ret;

	cache_subtree = get_subtree(cache_tree, key->off);
	key->cache_subtree = cache_subtree;
search:
	prev_node = cache_subtree_search(cache_subtree, key, &parent, &new, &delete_key_list);
	if (!list_empty(&delete_key_list)) {
		/* Remove invalid keys from the delete list */
		list_for_each_entry_safe(key_tmp, key_next, &delete_key_list, list_node) {
			list_del_init(&key_tmp->list_node);
			cache_key_delete(key_tmp);
		}
		goto search;
	}

	if (fixup) {
		/* Set up the context with the cache, start node, and new key */
		walk_ctx.cache_tree = cache_tree;
		walk_ctx.start_node = prev_node;
		walk_ctx.key = key;

		/* Assign overlap handling functions for different scenarios */
		walk_ctx.overlap_tail = fixup_overlap_tail;
		walk_ctx.overlap_head = fixup_overlap_head;
		walk_ctx.overlap_contain = fixup_overlap_contain;
		walk_ctx.overlap_contained = fixup_overlap_contained;

		ret = cache_subtree_walk(&walk_ctx);
		switch (ret) {
		case SUBTREE_WALK_RET_OK:
			break;
		case SUBTREE_WALK_RET_RESEARCH:
			goto search;
		case SUBTREE_WALK_RET_NEED_KEY:
			spin_unlock(&cache_subtree->tree_lock);
			pcache_dev_debug(CACHE_TO_PCACHE(cache), "allocate pre_alloc_key with GFP_NOIO");
			walk_ctx.pre_alloc_key = cache_key_alloc(cache_tree, GFP_NOIO);
			spin_lock(&cache_subtree->tree_lock);
			goto search;
		default:
			BUG();
		}
	}

	if (walk_ctx.pre_alloc_key)
		cache_key_put(walk_ctx.pre_alloc_key);

	/* Link and insert the new key into the red-black tree */
	rb_link_node(&key->rb_node, parent, new);
	rb_insert_color(&key->rb_node, &cache_subtree->root);
}

/**
 * clean_fn - Cleanup function to remove invalid keys from the cache tree.
 * @work: Pointer to the work_struct associated with the cleanup.
 *
 * This function cleans up invalid keys from the cache tree in the background
 * after a cache segment has been invalidated during cache garbage collection.
 * It processes a maximum of PCACHE_CLEAN_KEYS_MAX keys per iteration and holds
 * the tree lock to ensure thread safety.
 */
void clean_fn(struct work_struct *work)
{
	struct pcache_cache *cache = container_of(work, struct pcache_cache, clean_work);
	struct pcache_cache_subtree *cache_subtree;
	struct rb_node *node;
	struct pcache_cache_key *key;
	int i, count;

	for (i = 0; i < cache->req_key_tree.n_subtrees; i++) {
		cache_subtree = &cache->req_key_tree.subtrees[i];

again:
		if (pcache_is_stopping(CACHE_TO_PCACHE(cache)))
			return;

		/* Delete up to PCACHE_CLEAN_KEYS_MAX keys in one iteration */
		count = 0;
		spin_lock(&cache_subtree->tree_lock);
		node = rb_first(&cache_subtree->root);
		while (node) {
			key = CACHE_KEY(node);
			node = rb_next(node);
			if (cache_key_invalid(key)) {
				count++;
				cache_key_delete(key);
			}

			if (count >= PCACHE_CLEAN_KEYS_MAX) {
				/* Unlock and pause before continuing cleanup */
				spin_unlock(&cache_subtree->tree_lock);
				usleep_range(1000, 2000);
				goto again;
			}
		}
		spin_unlock(&cache_subtree->tree_lock);
	}
}

/*
 * kset_flush_fn - Flush work for a cache kset.
 *
 * This function is called when a kset flush work is queued from
 * cache_key_append(). If the kset is full, it will be closed
 * immediately. If not, the flush work will be queued for later closure.
 *
 * If cache_kset_close detects that a new segment is required to store
 * the kset and there are no available segments, it will return an error.
 * In this scenario, a retry will be attempted.
 */
void kset_flush_fn(struct work_struct *work)
{
	struct pcache_cache_kset *kset = container_of(work, struct pcache_cache_kset, flush_work.work);
	struct pcache_cache *cache = kset->cache;
	int ret;

	if (pcache_is_stopping(CACHE_TO_PCACHE(cache)))
		return;

	spin_lock(&kset->kset_lock);
	ret = cache_kset_close(cache, kset);
	spin_unlock(&kset->kset_lock);

	if (ret) {
		/* Failed to flush kset, schedule a retry. */
		queue_delayed_work(cache_get_wq(cache), &kset->flush_work, msecs_to_jiffies(100));
	}
}

static int kset_replay(struct pcache_cache *cache, struct pcache_cache_kset_onmedia *kset_onmedia)
{
	struct pcache_cache_key_onmedia *key_onmedia;
	struct pcache_cache_subtree *cache_subtree;
	struct pcache_cache_key *key;
	int ret;
	int i;

	for (i = 0; i < kset_onmedia->key_num; i++) {
		key_onmedia = &kset_onmedia->data[i];

		key = cache_key_alloc(&cache->req_key_tree, GFP_NOIO);
		ret = cache_key_decode(cache, key_onmedia, key);
		if (ret) {
			cache_key_put(key);
			goto err;
		}

		/* Check if the segment generation is valid for insertion. */
		if (key->seg_gen < key->cache_pos.cache_seg->gen) {
			cache_key_put(key);
			continue;
		}

		__set_bit(key->cache_pos.cache_seg->cache_seg_id, cache->seg_map);
		cache_subtree = get_subtree(&cache->req_key_tree, key->off);
		spin_lock(&cache_subtree->tree_lock);
		cache_key_insert(&cache->req_key_tree, key, true);
		spin_unlock(&cache_subtree->tree_lock);
		cache_seg_get(key->cache_pos.cache_seg);
	}

	return 0;
err:
	return ret;
}

int cache_replay(struct pcache_cache *cache)
{
	struct dm_pcache *pcache = CACHE_TO_PCACHE(cache);
	struct pcache_cache_pos pos_tail;
	struct pcache_cache_pos *pos;
	struct pcache_cache_kset_onmedia *kset_onmedia;
	u32 to_copy, count = 0, last_hops = 0;
	int ret = 0;

	kset_onmedia = kzalloc(PCACHE_KSET_ONMEDIA_SIZE_MAX, GFP_KERNEL);
	if (!kset_onmedia)
		return -ENOMEM;

	cache_pos_copy(&pos_tail, &cache->key_tail);
	pos = &pos_tail;

	/*
	 * In cache replaying stage, there is no other one will access
	 * cache->seg_map, so we can set bit here without cache->seg_map_lock.
	 */
	__set_bit(pos->cache_seg->cache_seg_id, cache->seg_map);

	while (true) {
		to_copy = min(PCACHE_KSET_ONMEDIA_SIZE_MAX, cache_seg_remain(pos));
		ret = copy_mc_to_kernel(kset_onmedia, cache_pos_addr(pos), to_copy);
		if (ret) {
			ret = -EIO;
			goto out;
		}

		if (!kset_onmedia_valid(kset_onmedia) ||
				kset_onmedia->crc != cache_kset_crc(kset_onmedia)) {
			break;
		}

		/* Process the last kset and prepare for the next segment. */
		if (kset_onmedia->flags & PCACHE_KSET_FLAGS_LAST) {
			struct pcache_cache_segment *next_seg;

			pcache_dev_debug(pcache, "last kset replay, next: %u\n", kset_onmedia->next_cache_seg_id);

			if (!cache_seg_id_valid(cache, kset_onmedia->next_cache_seg_id)) {
				ret = -EIO;
				goto out;
			}

			if (++last_hops > cache->n_segs) {
				ret = -EIO;
				goto out;
			}

			next_seg = &cache->segments[kset_onmedia->next_cache_seg_id];

			pos->cache_seg = next_seg;
			pos->seg_off = 0;

			__set_bit(pos->cache_seg->cache_seg_id, cache->seg_map);
			continue;
		}

		/* Replay the kset and check for errors. */
		if (get_kset_onmedia_size(kset_onmedia) > cache_seg_remain(pos)) {
			ret = -EIO;
			goto out;
		}

		ret = kset_replay(cache, kset_onmedia);
		if (ret)
			goto out;

		/* Advance the position after processing the kset. */
		cache_pos_advance(pos, get_kset_onmedia_size(kset_onmedia));
		if (++count > 512) {
			cond_resched();
			count = 0;
		}
	}

	/* Update the key_head position after replaying. */
	spin_lock(&cache->key_head_lock);
	cache_pos_copy(&cache->key_head, pos);
	spin_unlock(&cache->key_head_lock);
out:
	kfree(kset_onmedia);
	return ret;
}

/*
 * cache_verify_dirty_tail - reject a persisted dirty_tail whose last-kset
 * chain does not terminate.
 *
 * dirty_tail is decoded independently of the key_tail chain cache_replay()
 * walks, so replay's hop cap does not cover it. A crafted chain that loops
 * back on itself makes the writeback worker re-arm forever; walk it once here
 * with the same cap and fail the load if it does not end within n_segs hops.
 */
int cache_verify_dirty_tail(struct pcache_cache *cache)
{
	struct pcache_cache_pos pos;
	struct pcache_cache_kset_onmedia *kset_onmedia;
	u32 to_copy, last_hops = 0, count = 0;
	int ret = 0;

	kset_onmedia = kzalloc(PCACHE_KSET_ONMEDIA_SIZE_MAX, GFP_KERNEL);
	if (!kset_onmedia)
		return -ENOMEM;

	cache_pos_copy(&pos, &cache->dirty_tail);

	while (true) {
		to_copy = min(PCACHE_KSET_ONMEDIA_SIZE_MAX, cache_seg_remain(&pos));
		ret = copy_mc_to_kernel(kset_onmedia, cache_pos_addr(&pos), to_copy);
		if (ret) {
			ret = -EIO;
			goto out;
		}

		/* A missing, short or corrupt kset is the normal end of the chain. */
		if (!kset_onmedia_valid(kset_onmedia) ||
		    kset_onmedia->crc != cache_kset_crc(kset_onmedia)) {
			ret = 0;
			goto out;
		}

		if (kset_onmedia->flags & PCACHE_KSET_FLAGS_LAST) {
			if (!cache_seg_id_valid(cache, kset_onmedia->next_cache_seg_id)) {
				ret = -EIO;
				goto out;
			}

			if (++last_hops > cache->n_segs) {
				ret = -EIO;
				goto out;
			}

			pos.cache_seg = &cache->segments[kset_onmedia->next_cache_seg_id];
			pos.seg_off = 0;
			continue;
		}

		if (get_kset_onmedia_size(kset_onmedia) > cache_seg_remain(&pos)) {
			ret = -EIO;
			goto out;
		}

		cache_pos_advance(&pos, get_kset_onmedia_size(kset_onmedia));
		if (++count > 512) {
			cond_resched();
			count = 0;
		}
	}
out:
	kfree(kset_onmedia);
	return ret;
}

int cache_tree_init(struct pcache_cache *cache, struct pcache_cache_tree *cache_tree, u32 n_subtrees)
{
	int ret;
	u32 i;

	cache_tree->cache = cache;
	cache_tree->n_subtrees = n_subtrees;

	ret = mempool_init_slab_pool(&cache_tree->key_pool, 1024, key_cache);
	if (ret)
		goto err;

	/*
	 * Allocate and initialize the subtrees array.
	 * Each element is a cache tree structure that contains
	 * an RB tree root and a spinlock for protecting its contents.
	 */
	cache_tree->subtrees = kvzalloc_objs(struct pcache_cache_subtree,
					     cache_tree->n_subtrees);
	if (!cache_tree->subtrees) {
		ret = -ENOMEM;
		goto key_pool_exit;
	}

	for (i = 0; i < cache_tree->n_subtrees; i++) {
		struct pcache_cache_subtree *cache_subtree = &cache_tree->subtrees[i];

		cache_subtree->root = RB_ROOT;
		spin_lock_init(&cache_subtree->tree_lock);
	}

	return 0;

key_pool_exit:
	mempool_exit(&cache_tree->key_pool);
err:
	return ret;
}

void cache_tree_clear(struct pcache_cache_tree *cache_tree)
{
	struct pcache_cache_subtree *cache_subtree;
	struct rb_node *node;
	struct pcache_cache_key *key;
	u32 i;

	for (i = 0; i < cache_tree->n_subtrees; i++) {
		cache_subtree = &cache_tree->subtrees[i];

		spin_lock(&cache_subtree->tree_lock);
		node = rb_first(&cache_subtree->root);
		while (node) {
			key = CACHE_KEY(node);
			node = rb_next(node);

			cache_key_delete(key);
		}
		spin_unlock(&cache_subtree->tree_lock);
	}
}

void cache_tree_exit(struct pcache_cache_tree *cache_tree)
{
	cache_tree_clear(cache_tree);
	kvfree(cache_tree->subtrees);
	mempool_exit(&cache_tree->key_pool);
}