/* SPDX-License-Identifier: GPL-2.0+ */
#ifndef _LINUX_MAPLE_TREE_H
#define _LINUX_MAPLE_TREE_H
/*
 * Maple Tree - An RCU-safe adaptive tree for storing ranges
 * Copyright (c) 2018-2022 Oracle
 * Authors:     Liam R. Howlett <Liam.Howlett@Oracle.com>
 *              Matthew Wilcox <willy@infradead.org>
 */

#include <linux/kernel.h>
#include <linux/rcupdate.h>
#include <linux/spinlock.h>
/* #define CONFIG_MAPLE_RCU_DISABLED */
/* #define CONFIG_DEBUG_MAPLE_TREE_VERBOSE */

/*
 * Allocated nodes are mutable until they have been inserted into the tree,
 * at which time they cannot change their type until they have been removed
 * from the tree and an RCU grace period has passed.
 *
 * Removed nodes have their ->parent set to point to themselves.  RCU readers
 * check ->parent before relying on the value that they loaded from the
 * slots array.  This lets us reuse the slots array for the RCU head.
 *
 * Nodes in the tree point to their parent unless bit 0 is set.
 */
#if defined(CONFIG_64BIT) || defined(BUILD_VDSO32_64)
/* 64bit sizes */
#define MAPLE_NODE_SLOTS	31	/* 256 bytes including ->parent */
#define MAPLE_RANGE64_SLOTS	16	/* 256 bytes */
#define MAPLE_ARANGE64_SLOTS	10	/* 240 bytes */
#define MAPLE_ARANGE64_META_MAX	15	/* Out of range for metadata */
#define MAPLE_ALLOC_SLOTS	(MAPLE_NODE_SLOTS - 1)
#else
/* 32bit sizes */
#define MAPLE_NODE_SLOTS	63	/* 256 bytes including ->parent */
#define MAPLE_RANGE64_SLOTS	32	/* 256 bytes */
#define MAPLE_ARANGE64_SLOTS	21	/* 240 bytes */
#define MAPLE_ARANGE64_META_MAX	31	/* Out of range for metadata */
#define MAPLE_ALLOC_SLOTS	(MAPLE_NODE_SLOTS - 2)
#endif /* defined(CONFIG_64BIT) || defined(BUILD_VDSO32_64) */

#define MAPLE_NODE_MASK		255UL

/*
 * The node->parent of the root node has bit 0 set and the rest of the pointer
 * is a pointer to the tree itself.  No more bits are available in this pointer
 * (on m68k, the data structure may only be 2-byte aligned).
 *
 * Internal non-root nodes can only have maple_range_* nodes as parents.  The
 * parent pointer is 256B aligned like all other tree nodes.  When storing a 32
 * or 64 bit values, the offset can fit into 4 bits.  The 16 bit values need an
 * extra bit to store the offset.  This extra bit comes from a reuse of the last
 * bit in the node type.  This is possible by using bit 1 to indicate if bit 2
 * is part of the type or the slot.
 *
 * Once the type is decided, the decision of an allocation range type or a range
 * type is done by examining the immutable tree flag for the MAPLE_ALLOC_RANGE
 * flag.
 *
 *  Node types:
 *   0x??1 = Root
 *   0x?00 = 16 bit nodes
 *   0x010 = 32 bit nodes
 *   0x110 = 64 bit nodes
 *
 *  Slot size and location in the parent pointer:
 *   type  : slot location
 *   0x??1 : Root
 *   0x?00 : 16 bit values, type in 0-1, slot in 2-6
 *   0x010 : 32 bit values, type in 0-2, slot in 3-6
 *   0x110 : 64 bit values, type in 0-2, slot in 3-6
 */

/*
 * This metadata is used to optimize the gap updating code and in reverse
 * searching for gaps or any other code that needs to find the end of the data.
 */
struct maple_metadata {
	unsigned char end;
	unsigned char gap;
};

/*
 * Leaf nodes do not store pointers to nodes, they store user data.  Users may
 * store almost any bit pattern.  As noted above, the optimisation of storing an
 * entry at 0 in the root pointer cannot be done for data which have the bottom
 * two bits set to '10'.  We also reserve values with the bottom two bits set to
 * '10' which are below 4096 (ie 2, 6, 10 .. 4094) for internal use.  Some APIs
 * return errnos as a negative errno shifted right by two bits and the bottom
 * two bits set to '10', and while choosing to store these values in the array
 * is not an error, it may lead to confusion if you're testing for an error with
 * mas_is_err().
 *
 * Non-leaf nodes store the type of the node pointed to (enum maple_type in bits
 * 3-6), bit 2 is reserved.  That leaves bits 0-1 unused for now.
 *
 * In regular B-Tree terms, pivots are called keys.  The term pivot is used to
 * indicate that the tree is specifying ranges,  Pivots may appear in the
 * subtree with an entry attached to the value whereas keys are unique to a
 * specific position of a B-tree.  Pivot values are inclusive of the slot with
 * the same index.
 */

struct maple_range_64 {
	struct maple_pnode *parent;
	unsigned long pivot[MAPLE_RANGE64_SLOTS - 1];
	union {
		void __rcu *slot[MAPLE_RANGE64_SLOTS];
		struct {
			void __rcu *pad[MAPLE_RANGE64_SLOTS - 1];
			struct maple_metadata meta;
		};
	};
};

/*
 * At tree creation time, the user can specify that they're willing to trade off
 * storing fewer entries in a tree in return for storing more information in
 * each node.
 *
 * The maple tree supports recording the largest range of NULL entries available
 * in this node, also called gaps.  This optimises the tree for allocating a
 * range.
 */
struct maple_arange_64 {
	struct maple_pnode *parent;
	unsigned long pivot[MAPLE_ARANGE64_SLOTS - 1];
	void __rcu *slot[MAPLE_ARANGE64_SLOTS];
	unsigned long gap[MAPLE_ARANGE64_SLOTS];
	struct maple_metadata meta;
};

struct maple_alloc {
	unsigned long total;
	unsigned char node_count;
	unsigned int request_count;
	struct maple_alloc *slot[MAPLE_ALLOC_SLOTS];
};

struct maple_topiary {
	struct maple_pnode *parent;
	struct maple_enode *next; /* Overlaps the pivot */
};

enum maple_type {
	maple_dense,
	maple_leaf_64,
	maple_range_64,
	maple_arange_64,
};


/**
 * DOC: Maple tree flags
 *
 * * MT_FLAGS_ALLOC_RANGE	- Track gaps in this tree
 * * MT_FLAGS_USE_RCU		- Operate in RCU mode
 * * MT_FLAGS_HEIGHT_OFFSET	- The position of the tree height in the flags
 * * MT_FLAGS_HEIGHT_MASK	- The mask for the maple tree height value
 * * MT_FLAGS_LOCK_MASK		- How the mt_lock is used
 * * MT_FLAGS_LOCK_IRQ		- Acquired irq-safe
 * * MT_FLAGS_LOCK_BH		- Acquired bh-safe
 * * MT_FLAGS_LOCK_EXTERN	- mt_lock is not used
 *
 * MAPLE_HEIGHT_MAX	The largest height that can be stored
 */
#define MT_FLAGS_ALLOC_RANGE	0x01
#define MT_FLAGS_USE_RCU	0x02
#define MT_FLAGS_HEIGHT_OFFSET	0x02
#define MT_FLAGS_HEIGHT_MASK	0x7C
#define MT_FLAGS_LOCK_MASK	0x300
#define MT_FLAGS_LOCK_IRQ	0x100
#define MT_FLAGS_LOCK_BH	0x200
#define MT_FLAGS_LOCK_EXTERN	0x300

#define MAPLE_HEIGHT_MAX	31


#define MAPLE_NODE_TYPE_MASK	0x0F
#define MAPLE_NODE_TYPE_SHIFT	0x03

#define MAPLE_RESERVED_RANGE	4096

#ifdef CONFIG_LOCKDEP
typedef struct lockdep_map *lockdep_map_p;
#define mt_lock_is_held(mt)	lock_is_held(mt->ma_external_lock)
#define mt_set_external_lock(mt, lock)					\
	(mt)->ma_external_lock = &(lock)->dep_map
#else
typedef struct { /* nothing */ } lockdep_map_p;
#define mt_lock_is_held(mt)	1
#define mt_set_external_lock(mt, lock)	do { } while (0)
#endif

/*
 * If the tree contains a single entry at index 0, it is usually stored in
 * tree->ma_root.  To optimise for the page cache, an entry which ends in '00',
 * '01' or '11' is stored in the root, but an entry which ends in '10' will be
 * stored in a node.  Bits 3-6 are used to store enum maple_type.
 *
 * The flags are used both to store some immutable information about this tree
 * (set at tree creation time) and dynamic information set under the spinlock.
 *
 * Another use of flags are to indicate global states of the tree.  This is the
 * case with the MAPLE_USE_RCU flag, which indicates the tree is currently in
 * RCU mode.  This mode was added to allow the tree to reuse nodes instead of
 * re-allocating and RCU freeing nodes when there is a single user.
 */
struct maple_tree {
	union {
		spinlock_t	ma_lock;
		lockdep_map_p	ma_external_lock;
	};
	void __rcu      *ma_root;
	unsigned int	ma_flags;
};

/**
 * MTREE_INIT() - Initialize a maple tree
 * @name: The maple tree name
 * @__flags: The maple tree flags
 *
 */
#define MTREE_INIT(name, __flags) {					\
	.ma_lock = __SPIN_LOCK_UNLOCKED((name).ma_lock),		\
	.ma_flags = __flags,						\
	.ma_root = NULL,						\
}

/**
 * MTREE_INIT_EXT() - Initialize a maple tree with an external lock.
 * @name: The tree name
 * @__flags: The maple tree flags
 * @__lock: The external lock
 */
#ifdef CONFIG_LOCKDEP
#define MTREE_INIT_EXT(name, __flags, __lock) {				\
	.ma_external_lock = &(__lock).dep_map,				\
	.ma_flags = (__flags),						\
	.ma_root = NULL,						\
}
#else
#define MTREE_INIT_EXT(name, __flags, __lock)	MTREE_INIT(name, __flags)
#endif

#define DEFINE_MTREE(name)						\
	struct maple_tree name = MTREE_INIT(name, 0)

#define mtree_lock(mt)		spin_lock((&(mt)->ma_lock))
#define mtree_lock_nested(mas, subclass) \
		spin_lock_nested((&(mt)->ma_lock), subclass)
#define mtree_unlock(mt)	spin_unlock((&(mt)->ma_lock))

/*
 * The Maple Tree squeezes various bits in at various points which aren't
 * necessarily obvious.  Usually, this is done by observing that pointers are
 * N-byte aligned and thus the bottom log_2(N) bits are available for use.  We
 * don't use the high bits of pointers to store additional information because
 * we don't know what bits are unused on any given architecture.
 *
 * Nodes are 256 bytes in size and are also aligned to 256 bytes, giving us 8
 * low bits for our own purposes.  Nodes are currently of 4 types:
 * 1. Single pointer (Range is 0-0)
 * 2. Non-leaf Allocation Range nodes
 * 3. Non-leaf Range nodes
 * 4. Leaf Range nodes All nodes consist of a number of node slots,
 *    pivots, and a parent pointer.
 */

struct maple_node {
	union {
		struct {
			struct maple_pnode *parent;
			void __rcu *slot[MAPLE_NODE_SLOTS];
		};
		struct {
			void *pad;
			struct rcu_head rcu;
			struct maple_enode *piv_parent;
			unsigned char parent_slot;
			enum maple_type type;
			unsigned char slot_len;
			unsigned int ma_flags;
		};
		struct maple_range_64 mr64;
		struct maple_arange_64 ma64;
		struct maple_alloc alloc;
	};
};

/*
 * More complicated stores can cause two nodes to become one or three and
 * potentially alter the height of the tree.  Either half of the tree may need
 * to be rebalanced against the other.  The ma_topiary struct is used to track
 * which nodes have been 'cut' from the tree so that the change can be done
 * safely at a later date.  This is done to support RCU.
 */
struct ma_topiary {
	struct maple_enode *head;
	struct maple_enode *tail;
	struct maple_tree *mtree;
};

void *mtree_load(struct maple_tree *mt, unsigned long index);

int mtree_insert(struct maple_tree *mt, unsigned long index,
		void *entry, gfp_t gfp);
int mtree_insert_range(struct maple_tree *mt, unsigned long first,
		unsigned long last, void *entry, gfp_t gfp);
int mtree_alloc_range(struct maple_tree *mt, unsigned long *startp,
		void *entry, unsigned long size, unsigned long min,
		unsigned long max, gfp_t gfp);
int mtree_alloc_rrange(struct maple_tree *mt, unsigned long *startp,
		void *entry, unsigned long size, unsigned long min,
		unsigned long max, gfp_t gfp);

int mtree_store_range(struct maple_tree *mt, unsigned long first,
		      unsigned long last, void *entry, gfp_t gfp);
int mtree_store(struct maple_tree *mt, unsigned long index,
		void *entry, gfp_t gfp);
void *mtree_erase(struct maple_tree *mt, unsigned long index);

int mtree_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp);
int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp);

void mtree_destroy(struct maple_tree *mt);
void __mt_destroy(struct maple_tree *mt);

/**
 * mtree_empty() - Determine if a tree has any present entries.
 * @mt: Maple Tree.
 *
 * Context: Any context.
 * Return: %true if the tree contains only NULL pointers.
 */
static inline bool mtree_empty(const struct maple_tree *mt)
{
	return mt->ma_root == NULL;
}

/* Advanced API */

/*
 * The maple state is defined in the struct ma_state and is used to keep track
 * of information during operations, and even between operations when using the
 * advanced API.
 *
 * If state->node has bit 0 set then it references a tree location which is not
 * a node (eg the root).  If bit 1 is set, the rest of the bits are a negative
 * errno.  Bit 2 (the 'unallocated slots' bit) is clear.  Bits 3-6 indicate the
 * node type.
 *
 * state->alloc either has a request number of nodes or an allocated node.  If
 * stat->alloc has a requested number of nodes, the first bit will be set (0x1)
 * and the remaining bits are the value.  If state->alloc is a node, then the
 * node will be of type maple_alloc.  maple_alloc has MAPLE_NODE_SLOTS - 1 for
 * storing more allocated nodes, a total number of nodes allocated, and the
 * node_count in this node.  node_count is the number of allocated nodes in this
 * node.  The scaling beyond MAPLE_NODE_SLOTS - 1 is handled by storing further
 * nodes into state->alloc->slot[0]'s node.  Nodes are taken from state->alloc
 * by removing a node from the state->alloc node until state->alloc->node_count
 * is 1, when state->alloc is returned and the state->alloc->slot[0] is promoted
 * to state->alloc.  Nodes are pushed onto state->alloc by putting the current
 * state->alloc into the pushed node's slot[0].
 *
 * The state also contains the implied min/max of the state->node, the depth of
 * this search, and the offset. The implied min/max are either from the parent
 * node or are 0-oo for the root node.  The depth is incremented or decremented
 * every time a node is walked down or up.  The offset is the slot/pivot of
 * interest in the node - either for reading or writing.
 *
 * When returning a value the maple state index and last respectively contain
 * the start and end of the range for the entry.  Ranges are inclusive in the
 * Maple Tree.
 */
struct ma_state {
	struct maple_tree *tree;	/* The tree we're operating in */
	unsigned long index;		/* The index we're operating on - range start */
	unsigned long last;		/* The last index we're operating on - range end */
	struct maple_enode *node;	/* The node containing this entry */
	unsigned long min;		/* The minimum index of this node - implied pivot min */
	unsigned long max;		/* The maximum index of this node - implied pivot max */
	struct maple_alloc *alloc;	/* Allocated nodes for this operation */
	unsigned char depth;		/* depth of tree descent during write */
	unsigned char offset;
	unsigned char mas_flags;
};

struct ma_wr_state {
	struct ma_state *mas;
	struct maple_node *node;	/* Decoded mas->node */
	unsigned long r_min;		/* range min */
	unsigned long r_max;		/* range max */
	enum maple_type type;		/* mas->node type */
	unsigned char offset_end;	/* The offset where the write ends */
	unsigned char node_end;		/* mas->node end */
	unsigned long *pivots;		/* mas->node->pivots pointer */
	unsigned long end_piv;		/* The pivot at the offset end */
	void __rcu **slots;		/* mas->node->slots pointer */
	void *entry;			/* The entry to write */
	void *content;			/* The existing entry that is being overwritten */
};

#define mas_lock(mas)           spin_lock(&((mas)->tree->ma_lock))
#define mas_lock_nested(mas, subclass) \
		spin_lock_nested(&((mas)->tree->ma_lock), subclass)
#define mas_unlock(mas)         spin_unlock(&((mas)->tree->ma_lock))


/*
 * Special values for ma_state.node.
 * MAS_START means we have not searched the tree.
 * MAS_ROOT means we have searched the tree and the entry we found lives in
 * the root of the tree (ie it has index 0, length 1 and is the only entry in
 * the tree).
 * MAS_NONE means we have searched the tree and there is no node in the
 * tree for this entry.  For example, we searched for index 1 in an empty
 * tree.  Or we have a tree which points to a full leaf node and we
 * searched for an entry which is larger than can be contained in that
 * leaf node.
 * MA_ERROR represents an errno.  After dropping the lock and attempting
 * to resolve the error, the walk would have to be restarted from the
 * top of the tree as the tree may have been modified.
 */
#define MAS_START	((struct maple_enode *)1UL)
#define MAS_ROOT	((struct maple_enode *)5UL)
#define MAS_NONE	((struct maple_enode *)9UL)
#define MAS_PAUSE	((struct maple_enode *)17UL)
#define MA_ERROR(err) \
		((struct maple_enode *)(((unsigned long)err << 2) | 2UL))

#define MA_STATE(name, mt, first, end)					\
	struct ma_state name = {					\
		.tree = mt,						\
		.index = first,						\
		.last = end,						\
		.node = MAS_START,					\
		.min = 0,						\
		.max = ULONG_MAX,					\
		.alloc = NULL,						\
	}

#define MA_WR_STATE(name, ma_state, wr_entry)				\
	struct ma_wr_state name = {					\
		.mas = ma_state,					\
		.content = NULL,					\
		.entry = wr_entry,					\
	}

#define MA_TOPIARY(name, tree)						\
	struct ma_topiary name = {					\
		.head = NULL,						\
		.tail = NULL,						\
		.mtree = tree,						\
	}

void *mas_walk(struct ma_state *mas);
void *mas_store(struct ma_state *mas, void *entry);
void *mas_erase(struct ma_state *mas);
int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp);
void mas_store_prealloc(struct ma_state *mas, void *entry);
void *mas_find(struct ma_state *mas, unsigned long max);
void *mas_find_range(struct ma_state *mas, unsigned long max);
void *mas_find_rev(struct ma_state *mas, unsigned long min);
void *mas_find_range_rev(struct ma_state *mas, unsigned long max);
int mas_preallocate(struct ma_state *mas, void *entry, gfp_t gfp);
bool mas_is_err(struct ma_state *mas);

bool mas_nomem(struct ma_state *mas, gfp_t gfp);
void mas_pause(struct ma_state *mas);
void maple_tree_init(void);
void mas_destroy(struct ma_state *mas);
int mas_expected_entries(struct ma_state *mas, unsigned long nr_entries);

void *mas_prev(struct ma_state *mas, unsigned long min);
void *mas_prev_range(struct ma_state *mas, unsigned long max);
void *mas_next(struct ma_state *mas, unsigned long max);
void *mas_next_range(struct ma_state *mas, unsigned long max);

int mas_empty_area(struct ma_state *mas, unsigned long min, unsigned long max,
		   unsigned long size);

/* Checks if a mas has not found anything */
static inline bool mas_is_none(struct ma_state *mas)
{
	return mas->node == MAS_NONE;
}

/* Checks if a mas has been paused */
static inline bool mas_is_paused(struct ma_state *mas)
{
	return mas->node == MAS_PAUSE;
}

void mas_dup_tree(struct ma_state *oldmas, struct ma_state *mas);
void mas_dup_store(struct ma_state *mas, void *entry);

/*
 * This finds an empty area from the highest address to the lowest.
 * AKA "Topdown" version,
 */
int mas_empty_area_rev(struct ma_state *mas, unsigned long min,
		       unsigned long max, unsigned long size);
/**
 * mas_reset() - Reset a Maple Tree operation state.
 * @mas: Maple Tree operation state.
 *
 * Resets the error or walk state of the @mas so future walks of the
 * array will start from the root.  Use this if you have dropped the
 * lock and want to reuse the ma_state.
 *
 * Context: Any context.
 */
static inline void mas_reset(struct ma_state *mas)
{
	mas->node = MAS_START;
}

/**
 * mas_for_each() - Iterate over a range of the maple tree.
 * @__mas: Maple Tree operation state (maple_state)
 * @__entry: Entry retrieved from the tree
 * @__max: maximum index to retrieve from the tree
 *
 * When returned, mas->index and mas->last will hold the entire range for the
 * entry.
 *
 * Note: may return the zero entry.
 *
 */
#define mas_for_each(__mas, __entry, __max) \
	while (((__entry) = mas_find((__mas), (__max))) != NULL)
/**
 * __mas_set_range() - Set up Maple Tree operation state to a sub-range of the
 * current location.
 * @mas: Maple Tree operation state.
 * @start: New start of range in the Maple Tree.
 * @last: New end of range in the Maple Tree.
 *
 * set the internal maple state values to a sub-range.
 * Please use mas_set_range() if you do not know where you are in the tree.
 */
static inline void __mas_set_range(struct ma_state *mas, unsigned long start,
		unsigned long last)
{
	mas->index = start;
	mas->last = last;
}

/**
 * mas_set_range() - Set up Maple Tree operation state for a different index.
 * @mas: Maple Tree operation state.
 * @start: New start of range in the Maple Tree.
 * @last: New end of range in the Maple Tree.
 *
 * Move the operation state to refer to a different range.  This will
 * have the effect of starting a walk from the top; see mas_next()
 * to move to an adjacent index.
 */
static inline
void mas_set_range(struct ma_state *mas, unsigned long start, unsigned long last)
{
	__mas_set_range(mas, start, last);
	mas->node = MAS_START;
}

/**
 * mas_set() - Set up Maple Tree operation state for a different index.
 * @mas: Maple Tree operation state.
 * @index: New index into the Maple Tree.
 *
 * Move the operation state to refer to a different index.  This will
 * have the effect of starting a walk from the top; see mas_next()
 * to move to an adjacent index.
 */
static inline void mas_set(struct ma_state *mas, unsigned long index)
{

	mas_set_range(mas, index, index);
}

static inline bool mt_external_lock(const struct maple_tree *mt)
{
	return (mt->ma_flags & MT_FLAGS_LOCK_MASK) == MT_FLAGS_LOCK_EXTERN;
}

/**
 * mt_init_flags() - Initialise an empty maple tree with flags.
 * @mt: Maple Tree
 * @flags: maple tree flags.
 *
 * If you need to initialise a Maple Tree with special flags (eg, an
 * allocation tree), use this function.
 *
 * Context: Any context.
 */
static inline void mt_init_flags(struct maple_tree *mt, unsigned int flags)
{
	mt->ma_flags = flags;
	if (!mt_external_lock(mt))
		spin_lock_init(&mt->ma_lock);
	rcu_assign_pointer(mt->ma_root, NULL);
}

/**
 * mt_init() - Initialise an empty maple tree.
 * @mt: Maple Tree
 *
 * An empty Maple Tree.
 *
 * Context: Any context.
 */
static inline void mt_init(struct maple_tree *mt)
{
	mt_init_flags(mt, 0);
}

static inline bool mt_in_rcu(struct maple_tree *mt)
{
#ifdef CONFIG_MAPLE_RCU_DISABLED
	return false;
#endif
	return mt->ma_flags & MT_FLAGS_USE_RCU;
}

/**
 * mt_clear_in_rcu() - Switch the tree to non-RCU mode.
 * @mt: The Maple Tree
 */
static inline void mt_clear_in_rcu(struct maple_tree *mt)
{
	if (!mt_in_rcu(mt))
		return;

	if (mt_external_lock(mt)) {
		BUG_ON(!mt_lock_is_held(mt));
		mt->ma_flags &= ~MT_FLAGS_USE_RCU;
	} else {
		mtree_lock(mt);
		mt->ma_flags &= ~MT_FLAGS_USE_RCU;
		mtree_unlock(mt);
	}
}

/**
 * mt_set_in_rcu() - Switch the tree to RCU safe mode.
 * @mt: The Maple Tree
 */
static inline void mt_set_in_rcu(struct maple_tree *mt)
{
	if (mt_in_rcu(mt))
		return;

	if (mt_external_lock(mt)) {
		BUG_ON(!mt_lock_is_held(mt));
		mt->ma_flags |= MT_FLAGS_USE_RCU;
	} else {
		mtree_lock(mt);
		mt->ma_flags |= MT_FLAGS_USE_RCU;
		mtree_unlock(mt);
	}
}

static inline unsigned int mt_height(const struct maple_tree *mt)

{
	return (mt->ma_flags & MT_FLAGS_HEIGHT_MASK) >> MT_FLAGS_HEIGHT_OFFSET;
}

void *mt_find(struct maple_tree *mt, unsigned long *index, unsigned long max);
void *mt_find_after(struct maple_tree *mt, unsigned long *index,
		    unsigned long max);
void *mt_prev(struct maple_tree *mt, unsigned long index,  unsigned long min);
void *mt_next(struct maple_tree *mt, unsigned long index, unsigned long max);

/**
 * mt_for_each - Iterate over each entry starting at index until max.
 * @__tree: The Maple Tree
 * @__entry: The current entry
 * @__index: The index to update to track the location in the tree
 * @__max: The maximum limit for @index
 *
 * Note: Will not return the zero entry.
 */
#define mt_for_each(__tree, __entry, __index, __max) \
	for (__entry = mt_find(__tree, &(__index), __max); \
		__entry; __entry = mt_find_after(__tree, &(__index), __max))


#ifdef CONFIG_DEBUG_MAPLE_TREE
extern atomic_t maple_tree_tests_run;
extern atomic_t maple_tree_tests_passed;

void mt_dump(const struct maple_tree *mt);
void mt_validate(struct maple_tree *mt);
void mt_cache_shrink(void);
#define MT_BUG_ON(__tree, __x) do {					\
	atomic_inc(&maple_tree_tests_run);				\
	if (__x) {							\
		pr_info("BUG at %s:%d (%u)\n",				\
		__func__, __LINE__, __x);				\
		mt_dump(__tree);					\
		pr_info("Pass: %u Run:%u\n",				\
			atomic_read(&maple_tree_tests_passed),		\
			atomic_read(&maple_tree_tests_run));		\
		dump_stack();						\
	} else {							\
		atomic_inc(&maple_tree_tests_passed);			\
	}								\
} while (0)
#else
#define MT_BUG_ON(__tree, __x) BUG_ON(__x)
#endif /* CONFIG_DEBUG_MAPLE_TREE */

#endif /*_LINUX_MAPLE_TREE_H */