/*
   * Copyright (C) 2001 Momchil Velikov
   * Portions Copyright (C) 2001 Christoph Hellwig

   * Copyright (C) 2005 SGI, Christoph Lameter

   * Copyright (C) 2006 Nick Piggin

   * Copyright (C) 2012 Konstantin Khlebnikov

   * Copyright (C) 2016 Intel, Matthew Wilcox
   * Copyright (C) 2016 Intel, Ross Zwisler

   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as
   * published by the Free Software Foundation; either version 2, or (at
   * your option) any later version.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   */

  #include <linux/cpu.h>

  #include <linux/errno.h>
  #include <linux/init.h>
  #include <linux/kernel.h>

  #include <linux/export.h>

  #include <linux/radix-tree.h>
  #include <linux/percpu.h>
  #include <linux/slab.h>

  #include <linux/kmemleak.h>

  #include <linux/cpu.h>

  #include <linux/string.h>
  #include <linux/bitops.h>

  #include <linux/rcupdate.h>

  #include <linux/preempt.h>		/* in_interrupt() */

  /* Number of nodes in fully populated tree of given height */
  static unsigned long height_to_maxnodes[RADIX_TREE_MAX_PATH + 1] __read_mostly;

  /*

   * Radix tree node cache.
   */

  static struct kmem_cache *radix_tree_node_cachep;

  
  /*

   * The radix tree is variable-height, so an insert operation not only has
   * to build the branch to its corresponding item, it also has to build the
   * branch to existing items if the size has to be increased (by
   * radix_tree_extend).
   *
   * The worst case is a zero height tree with just a single item at index 0,
   * and then inserting an item at index ULONG_MAX. This requires 2 new branches
   * of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
   * Hence:
   */
  #define RADIX_TREE_PRELOAD_SIZE (RADIX_TREE_MAX_PATH * 2 - 1)
  
  /*

   * Per-cpu pool of preloaded nodes
   */
  struct radix_tree_preload {

  	unsigned nr;

  	/* nodes->private_data points to next preallocated node */
  	struct radix_tree_node *nodes;

  };

  static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };

  static inline struct radix_tree_node *entry_to_node(void *ptr)
  {
  	return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
  }

  static inline void *node_to_entry(void *ptr)

  {

  	return (void *)((unsigned long)ptr | RADIX_TREE_INTERNAL_NODE);

  }

  #define RADIX_TREE_RETRY	node_to_entry(NULL)

  #ifdef CONFIG_RADIX_TREE_MULTIORDER
  /* Sibling slots point directly to another slot in the same node */
  static inline bool is_sibling_entry(struct radix_tree_node *parent, void *node)
  {
  	void **ptr = node;
  	return (parent->slots <= ptr) &&
  			(ptr < parent->slots + RADIX_TREE_MAP_SIZE);
  }
  #else
  static inline bool is_sibling_entry(struct radix_tree_node *parent, void *node)
  {
  	return false;
  }
  #endif
  
  static inline unsigned long get_slot_offset(struct radix_tree_node *parent,
  						 void **slot)
  {
  	return slot - parent->slots;
  }

  static unsigned int radix_tree_descend(struct radix_tree_node *parent,
  			struct radix_tree_node **nodep, unsigned long index)

  {

  	unsigned int offset = (index >> parent->shift) & RADIX_TREE_MAP_MASK;

  	void **entry = rcu_dereference_raw(parent->slots[offset]);
  
  #ifdef CONFIG_RADIX_TREE_MULTIORDER

  	if (radix_tree_is_internal_node(entry)) {

  		if (is_sibling_entry(parent, entry)) {
  			void **sibentry = (void **) entry_to_node(entry);
  			offset = get_slot_offset(parent, sibentry);
  			entry = rcu_dereference_raw(*sibentry);

  		}
  	}
  #endif
  
  	*nodep = (void *)entry;
  	return offset;
  }

  static inline gfp_t root_gfp_mask(struct radix_tree_root *root)
  {
  	return root->gfp_mask & __GFP_BITS_MASK;
  }

  static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
  		int offset)
  {
  	__set_bit(offset, node->tags[tag]);
  }
  
  static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
  		int offset)
  {
  	__clear_bit(offset, node->tags[tag]);
  }
  
  static inline int tag_get(struct radix_tree_node *node, unsigned int tag,
  		int offset)
  {
  	return test_bit(offset, node->tags[tag]);
  }
  
  static inline void root_tag_set(struct radix_tree_root *root, unsigned int tag)
  {
  	root->gfp_mask |= (__force gfp_t)(1 << (tag + __GFP_BITS_SHIFT));
  }

  static inline void root_tag_clear(struct radix_tree_root *root, unsigned tag)

  {
  	root->gfp_mask &= (__force gfp_t)~(1 << (tag + __GFP_BITS_SHIFT));
  }
  
  static inline void root_tag_clear_all(struct radix_tree_root *root)
  {
  	root->gfp_mask &= __GFP_BITS_MASK;
  }
  
  static inline int root_tag_get(struct radix_tree_root *root, unsigned int tag)
  {

  	return (__force int)root->gfp_mask & (1 << (tag + __GFP_BITS_SHIFT));

  }

  static inline unsigned root_tags_get(struct radix_tree_root *root)
  {
  	return (__force unsigned)root->gfp_mask >> __GFP_BITS_SHIFT;
  }

  /*
   * Returns 1 if any slot in the node has this tag set.
   * Otherwise returns 0.
   */
  static inline int any_tag_set(struct radix_tree_node *node, unsigned int tag)
  {

  	unsigned idx;

  	for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
  		if (node->tags[tag][idx])
  			return 1;
  	}
  	return 0;
  }

  
  /**
   * radix_tree_find_next_bit - find the next set bit in a memory region
   *
   * @addr: The address to base the search on
   * @size: The bitmap size in bits
   * @offset: The bitnumber to start searching at
   *
   * Unrollable variant of find_next_bit() for constant size arrays.
   * Tail bits starting from size to roundup(size, BITS_PER_LONG) must be zero.
   * Returns next bit offset, or size if nothing found.
   */
  static __always_inline unsigned long

  radix_tree_find_next_bit(struct radix_tree_node *node, unsigned int tag,
  			 unsigned long offset)

  {

  	const unsigned long *addr = node->tags[tag];

  	if (offset < RADIX_TREE_MAP_SIZE) {

  		unsigned long tmp;
  
  		addr += offset / BITS_PER_LONG;
  		tmp = *addr >> (offset % BITS_PER_LONG);
  		if (tmp)
  			return __ffs(tmp) + offset;
  		offset = (offset + BITS_PER_LONG) & ~(BITS_PER_LONG - 1);

  		while (offset < RADIX_TREE_MAP_SIZE) {

  			tmp = *++addr;
  			if (tmp)
  				return __ffs(tmp) + offset;
  			offset += BITS_PER_LONG;
  		}
  	}

  	return RADIX_TREE_MAP_SIZE;

  }

  static unsigned int iter_offset(const struct radix_tree_iter *iter)
  {
  	return (iter->index >> iter_shift(iter)) & RADIX_TREE_MAP_MASK;
  }

  /*
   * The maximum index which can be stored in a radix tree
   */
  static inline unsigned long shift_maxindex(unsigned int shift)
  {
  	return (RADIX_TREE_MAP_SIZE << shift) - 1;
  }
  
  static inline unsigned long node_maxindex(struct radix_tree_node *node)
  {
  	return shift_maxindex(node->shift);
  }

  #ifndef __KERNEL__

  static void dump_node(struct radix_tree_node *node, unsigned long index)

  {

  	unsigned long i;

  	pr_debug("radix node: %p offset %d indices %lu-%lu parent %p tags %lx %lx %lx shift %d count %d exceptional %d
  ",
  		node, node->offset, index, index | node_maxindex(node),
  		node->parent,

  		node->tags[0][0], node->tags[1][0], node->tags[2][0],

  		node->shift, node->count, node->exceptional);

  
  	for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {

  		unsigned long first = index | (i << node->shift);
  		unsigned long last = first | ((1UL << node->shift) - 1);

  		void *entry = node->slots[i];
  		if (!entry)
  			continue;

  		if (entry == RADIX_TREE_RETRY) {
  			pr_debug("radix retry offset %ld indices %lu-%lu parent %p
  ",
  					i, first, last, node);

  		} else if (!radix_tree_is_internal_node(entry)) {

  			pr_debug("radix entry %p offset %ld indices %lu-%lu parent %p
  ",
  					entry, i, first, last, node);
  		} else if (is_sibling_entry(node, entry)) {
  			pr_debug("radix sblng %p offset %ld indices %lu-%lu parent %p val %p
  ",
  					entry, i, first, last, node,
  					*(void **)entry_to_node(entry));

  		} else {

  			dump_node(entry_to_node(entry), first);

  		}
  	}

  }
  
  /* For debug */
  static void radix_tree_dump(struct radix_tree_root *root)
  {

  	pr_debug("radix root: %p rnode %p tags %x
  ",
  			root, root->rnode,

  			root->gfp_mask >> __GFP_BITS_SHIFT);

  	if (!radix_tree_is_internal_node(root->rnode))

  		return;

  	dump_node(entry_to_node(root->rnode), 0);

  }
  #endif

  /*
   * This assumes that the caller has performed appropriate preallocation, and
   * that the caller has pinned this thread of control to the current CPU.
   */
  static struct radix_tree_node *

  radix_tree_node_alloc(struct radix_tree_root *root,
  			struct radix_tree_node *parent,
  			unsigned int shift, unsigned int offset,
  			unsigned int count, unsigned int exceptional)

  {

  	struct radix_tree_node *ret = NULL;

  	gfp_t gfp_mask = root_gfp_mask(root);

  	/*

  	 * Preload code isn't irq safe and it doesn't make sense to use
  	 * preloading during an interrupt anyway as all the allocations have
  	 * to be atomic. So just do normal allocation when in interrupt.

  	 */

  	if (!gfpflags_allow_blocking(gfp_mask) && !in_interrupt()) {

  		struct radix_tree_preload *rtp;

  		/*

  		 * Even if the caller has preloaded, try to allocate from the

  		 * cache first for the new node to get accounted to the memory
  		 * cgroup.

  		 */
  		ret = kmem_cache_alloc(radix_tree_node_cachep,

  				       gfp_mask | __GFP_NOWARN);

  		if (ret)
  			goto out;
  
  		/*

  		 * Provided the caller has preloaded here, we will always
  		 * succeed in getting a node here (and never reach
  		 * kmem_cache_alloc)
  		 */

  		rtp = this_cpu_ptr(&radix_tree_preloads);

  		if (rtp->nr) {

  			ret = rtp->nodes;
  			rtp->nodes = ret->private_data;
  			ret->private_data = NULL;

  			rtp->nr--;
  		}

  		/*
  		 * Update the allocation stack trace as this is more useful
  		 * for debugging.
  		 */
  		kmemleak_update_trace(ret);

  		goto out;

  	}

  	ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);

  out:

  	BUG_ON(radix_tree_is_internal_node(ret));

  	if (ret) {
  		ret->parent = parent;
  		ret->shift = shift;
  		ret->offset = offset;
  		ret->count = count;
  		ret->exceptional = exceptional;
  	}

  	return ret;
  }

  static void radix_tree_node_rcu_free(struct rcu_head *head)
  {
  	struct radix_tree_node *node =
  			container_of(head, struct radix_tree_node, rcu_head);

  
  	/*

  	 * Must only free zeroed nodes into the slab.  We can be left with
  	 * non-NULL entries by radix_tree_free_nodes, so clear the entries
  	 * and tags here.

  	 */

  	memset(node->slots, 0, sizeof(node->slots));
  	memset(node->tags, 0, sizeof(node->tags));

  	INIT_LIST_HEAD(&node->private_list);

  	kmem_cache_free(radix_tree_node_cachep, node);
  }

  static inline void
  radix_tree_node_free(struct radix_tree_node *node)
  {

  	call_rcu(&node->rcu_head, radix_tree_node_rcu_free);

  }
  
  /*
   * Load up this CPU's radix_tree_node buffer with sufficient objects to
   * ensure that the addition of a single element in the tree cannot fail.  On
   * success, return zero, with preemption disabled.  On error, return -ENOMEM
   * with preemption not disabled.

   *
   * To make use of this facility, the radix tree must be initialised without

   * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().

   */

  static int __radix_tree_preload(gfp_t gfp_mask, unsigned nr)

  {
  	struct radix_tree_preload *rtp;
  	struct radix_tree_node *node;
  	int ret = -ENOMEM;

  	/*
  	 * Nodes preloaded by one cgroup can be be used by another cgroup, so
  	 * they should never be accounted to any particular memory cgroup.
  	 */
  	gfp_mask &= ~__GFP_ACCOUNT;

  	preempt_disable();

  	rtp = this_cpu_ptr(&radix_tree_preloads);

  	while (rtp->nr < nr) {

  		preempt_enable();

  		node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);

  		if (node == NULL)
  			goto out;
  		preempt_disable();

  		rtp = this_cpu_ptr(&radix_tree_preloads);

  		if (rtp->nr < nr) {

  			node->private_data = rtp->nodes;
  			rtp->nodes = node;
  			rtp->nr++;
  		} else {

  			kmem_cache_free(radix_tree_node_cachep, node);

  		}

  	}
  	ret = 0;
  out:
  	return ret;
  }

  
  /*
   * Load up this CPU's radix_tree_node buffer with sufficient objects to
   * ensure that the addition of a single element in the tree cannot fail.  On
   * success, return zero, with preemption disabled.  On error, return -ENOMEM
   * with preemption not disabled.
   *
   * To make use of this facility, the radix tree must be initialised without

   * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().

   */
  int radix_tree_preload(gfp_t gfp_mask)
  {
  	/* Warn on non-sensical use... */

  	WARN_ON_ONCE(!gfpflags_allow_blocking(gfp_mask));

  	return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);

  }

  EXPORT_SYMBOL(radix_tree_preload);

  /*

   * The same as above function, except we don't guarantee preloading happens.
   * We do it, if we decide it helps. On success, return zero with preemption
   * disabled. On error, return -ENOMEM with preemption not disabled.
   */
  int radix_tree_maybe_preload(gfp_t gfp_mask)
  {

  	if (gfpflags_allow_blocking(gfp_mask))

  		return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);

  	/* Preloading doesn't help anything with this gfp mask, skip it */
  	preempt_disable();
  	return 0;
  }
  EXPORT_SYMBOL(radix_tree_maybe_preload);

  #ifdef CONFIG_RADIX_TREE_MULTIORDER
  /*
   * Preload with enough objects to ensure that we can split a single entry
   * of order @old_order into many entries of size @new_order
   */
  int radix_tree_split_preload(unsigned int old_order, unsigned int new_order,
  							gfp_t gfp_mask)
  {
  	unsigned top = 1 << (old_order % RADIX_TREE_MAP_SHIFT);
  	unsigned layers = (old_order / RADIX_TREE_MAP_SHIFT) -
  				(new_order / RADIX_TREE_MAP_SHIFT);
  	unsigned nr = 0;
  
  	WARN_ON_ONCE(!gfpflags_allow_blocking(gfp_mask));
  	BUG_ON(new_order >= old_order);
  
  	while (layers--)
  		nr = nr * RADIX_TREE_MAP_SIZE + 1;
  	return __radix_tree_preload(gfp_mask, top * nr);
  }
  #endif

  /*

   * The same as function above, but preload number of nodes required to insert
   * (1 << order) continuous naturally-aligned elements.
   */
  int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order)
  {
  	unsigned long nr_subtrees;
  	int nr_nodes, subtree_height;
  
  	/* Preloading doesn't help anything with this gfp mask, skip it */
  	if (!gfpflags_allow_blocking(gfp_mask)) {
  		preempt_disable();
  		return 0;
  	}
  
  	/*
  	 * Calculate number and height of fully populated subtrees it takes to
  	 * store (1 << order) elements.
  	 */
  	nr_subtrees = 1 << order;
  	for (subtree_height = 0; nr_subtrees > RADIX_TREE_MAP_SIZE;
  			subtree_height++)
  		nr_subtrees >>= RADIX_TREE_MAP_SHIFT;
  
  	/*
  	 * The worst case is zero height tree with a single item at index 0 and
  	 * then inserting items starting at ULONG_MAX - (1 << order).
  	 *
  	 * This requires RADIX_TREE_MAX_PATH nodes to build branch from root to
  	 * 0-index item.
  	 */
  	nr_nodes = RADIX_TREE_MAX_PATH;
  
  	/* Plus branch to fully populated subtrees. */
  	nr_nodes += RADIX_TREE_MAX_PATH - subtree_height;
  
  	/* Root node is shared. */
  	nr_nodes--;
  
  	/* Plus nodes required to build subtrees. */
  	nr_nodes += nr_subtrees * height_to_maxnodes[subtree_height];
  
  	return __radix_tree_preload(gfp_mask, nr_nodes);
  }

  static unsigned radix_tree_load_root(struct radix_tree_root *root,
  		struct radix_tree_node **nodep, unsigned long *maxindex)
  {
  	struct radix_tree_node *node = rcu_dereference_raw(root->rnode);
  
  	*nodep = node;

  	if (likely(radix_tree_is_internal_node(node))) {

  		node = entry_to_node(node);

  		*maxindex = node_maxindex(node);

  		return node->shift + RADIX_TREE_MAP_SHIFT;

  	}
  
  	*maxindex = 0;
  	return 0;
  }

  /*
   *	Extend a radix tree so it can store key @index.
   */

  static int radix_tree_extend(struct radix_tree_root *root,

  				unsigned long index, unsigned int shift)

  {

  	struct radix_tree_node *slot;

  	unsigned int maxshift;

  	int tag;

  	/* Figure out what the shift should be.  */
  	maxshift = shift;
  	while (index > shift_maxindex(maxshift))
  		maxshift += RADIX_TREE_MAP_SHIFT;

  	slot = root->rnode;
  	if (!slot)

  		goto out;

  	do {

  		struct radix_tree_node *node = radix_tree_node_alloc(root,
  							NULL, shift, 0, 1, 0);

  		if (!node)

  			return -ENOMEM;

  		/* Propagate the aggregated tag info into the new root */

  		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {

  			if (root_tag_get(root, tag))

  				tag_set(node, tag, 0);
  		}

  		BUG_ON(shift > BITS_PER_LONG);

  		if (radix_tree_is_internal_node(slot)) {

  			entry_to_node(slot)->parent = node;

  		} else if (radix_tree_exceptional_entry(slot)) {

  			/* Moving an exceptional root->rnode to a node */

  			node->exceptional = 1;

  		}

  		node->slots[0] = slot;

  		slot = node_to_entry(node);
  		rcu_assign_pointer(root->rnode, slot);

  		shift += RADIX_TREE_MAP_SHIFT;

  	} while (shift <= maxshift);

  out:

  	return maxshift + RADIX_TREE_MAP_SHIFT;

  }
  
  /**

   *	radix_tree_shrink    -    shrink radix tree to minimum height
   *	@root		radix tree root
   */

  static inline void radix_tree_shrink(struct radix_tree_root *root,

  				     radix_tree_update_node_t update_node,
  				     void *private)

  {

  	for (;;) {
  		struct radix_tree_node *node = root->rnode;
  		struct radix_tree_node *child;
  
  		if (!radix_tree_is_internal_node(node))
  			break;
  		node = entry_to_node(node);
  
  		/*
  		 * The candidate node has more than one child, or its child
  		 * is not at the leftmost slot, or the child is a multiorder
  		 * entry, we cannot shrink.
  		 */
  		if (node->count != 1)
  			break;
  		child = node->slots[0];
  		if (!child)
  			break;
  		if (!radix_tree_is_internal_node(child) && node->shift)
  			break;
  
  		if (radix_tree_is_internal_node(child))
  			entry_to_node(child)->parent = NULL;
  
  		/*
  		 * We don't need rcu_assign_pointer(), since we are simply
  		 * moving the node from one part of the tree to another: if it
  		 * was safe to dereference the old pointer to it
  		 * (node->slots[0]), it will be safe to dereference the new
  		 * one (root->rnode) as far as dependent read barriers go.
  		 */
  		root->rnode = child;
  
  		/*
  		 * We have a dilemma here. The node's slot[0] must not be
  		 * NULLed in case there are concurrent lookups expecting to
  		 * find the item. However if this was a bottom-level node,
  		 * then it may be subject to the slot pointer being visible
  		 * to callers dereferencing it. If item corresponding to
  		 * slot[0] is subsequently deleted, these callers would expect
  		 * their slot to become empty sooner or later.
  		 *
  		 * For example, lockless pagecache will look up a slot, deref
  		 * the page pointer, and if the page has 0 refcount it means it
  		 * was concurrently deleted from pagecache so try the deref
  		 * again. Fortunately there is already a requirement for logic
  		 * to retry the entire slot lookup -- the indirect pointer
  		 * problem (replacing direct root node with an indirect pointer
  		 * also results in a stale slot). So tag the slot as indirect
  		 * to force callers to retry.
  		 */

  		node->count = 0;
  		if (!radix_tree_is_internal_node(child)) {

  			node->slots[0] = RADIX_TREE_RETRY;

  			if (update_node)
  				update_node(node, private);
  		}

  
  		radix_tree_node_free(node);

  	}

  }

  static void delete_node(struct radix_tree_root *root,

  			struct radix_tree_node *node,
  			radix_tree_update_node_t update_node, void *private)

  {

  	do {
  		struct radix_tree_node *parent;
  
  		if (node->count) {
  			if (node == entry_to_node(root->rnode))

  				radix_tree_shrink(root, update_node, private);
  			return;

  		}
  
  		parent = node->parent;
  		if (parent) {
  			parent->slots[node->offset] = NULL;
  			parent->count--;
  		} else {
  			root_tag_clear_all(root);
  			root->rnode = NULL;
  		}
  
  		radix_tree_node_free(node);

  
  		node = parent;
  	} while (node);

  }
  
  /**

   *	__radix_tree_create	-	create a slot in a radix tree

   *	@root:		radix tree root
   *	@index:		index key

   *	@order:		index occupies 2^order aligned slots

   *	@nodep:		returns node
   *	@slotp:		returns slot

   *

   *	Create, if necessary, and return the node and slot for an item
   *	at position @index in the radix tree @root.
   *
   *	Until there is more than one item in the tree, no nodes are
   *	allocated and @root->rnode is used as a direct slot instead of
   *	pointing to a node, in which case *@nodep will be NULL.
   *
   *	Returns -ENOMEM, or 0 for success.

   */

  int __radix_tree_create(struct radix_tree_root *root, unsigned long index,

  			unsigned order, struct radix_tree_node **nodep,
  			void ***slotp)

  {

  	struct radix_tree_node *node = NULL, *child;
  	void **slot = (void **)&root->rnode;

  	unsigned long maxindex;

  	unsigned int shift, offset = 0;

  	unsigned long max = index | ((1UL << order) - 1);

  	shift = radix_tree_load_root(root, &child, &maxindex);

  
  	/* Make sure the tree is high enough.  */

  	if (order > 0 && max == ((1UL << order) - 1))
  		max++;

  	if (max > maxindex) {

  		int error = radix_tree_extend(root, max, shift);

  		if (error < 0)

  			return error;

  		shift = error;

  		child = root->rnode;

  	}

  	while (shift > order) {

  		shift -= RADIX_TREE_MAP_SHIFT;

  		if (child == NULL) {

  			/* Have to add a child node.  */

  			child = radix_tree_node_alloc(root, node, shift,
  							offset, 0, 0);

  			if (!child)

  				return -ENOMEM;

  			rcu_assign_pointer(*slot, node_to_entry(child));
  			if (node)

  				node->count++;

  		} else if (!radix_tree_is_internal_node(child))

  			break;

  
  		/* Go a level down */

  		node = entry_to_node(child);

  		offset = radix_tree_descend(node, &child, index);

  		slot = &node->slots[offset];

  	}

  	if (nodep)
  		*nodep = node;
  	if (slotp)
  		*slotp = slot;
  	return 0;
  }

  #ifdef CONFIG_RADIX_TREE_MULTIORDER

  /*
   * Free any nodes below this node.  The tree is presumed to not need
   * shrinking, and any user data in the tree is presumed to not need a
   * destructor called on it.  If we need to add a destructor, we can
   * add that functionality later.  Note that we may not clear tags or
   * slots from the tree as an RCU walker may still have a pointer into
   * this subtree.  We could replace the entries with RADIX_TREE_RETRY,
   * but we'll still have to clear those in rcu_free.
   */
  static void radix_tree_free_nodes(struct radix_tree_node *node)
  {
  	unsigned offset = 0;
  	struct radix_tree_node *child = entry_to_node(node);
  
  	for (;;) {
  		void *entry = child->slots[offset];
  		if (radix_tree_is_internal_node(entry) &&
  					!is_sibling_entry(child, entry)) {
  			child = entry_to_node(entry);
  			offset = 0;
  			continue;
  		}
  		offset++;
  		while (offset == RADIX_TREE_MAP_SIZE) {
  			struct radix_tree_node *old = child;
  			offset = child->offset + 1;
  			child = child->parent;
  			radix_tree_node_free(old);
  			if (old == entry_to_node(node))
  				return;
  		}
  	}
  }
  
  static inline int insert_entries(struct radix_tree_node *node, void **slot,
  				void *item, unsigned order, bool replace)
  {
  	struct radix_tree_node *child;
  	unsigned i, n, tag, offset, tags = 0;
  
  	if (node) {

  		if (order > node->shift)
  			n = 1 << (order - node->shift);
  		else
  			n = 1;

  		offset = get_slot_offset(node, slot);
  	} else {
  		n = 1;
  		offset = 0;
  	}
  
  	if (n > 1) {

  		offset = offset & ~(n - 1);

  		slot = &node->slots[offset];

  	}
  	child = node_to_entry(slot);
  
  	for (i = 0; i < n; i++) {
  		if (slot[i]) {
  			if (replace) {
  				node->count--;
  				for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  					if (tag_get(node, tag, offset + i))
  						tags |= 1 << tag;
  			} else

  				return -EEXIST;
  		}

  	}

  	for (i = 0; i < n; i++) {
  		struct radix_tree_node *old = slot[i];
  		if (i) {

  			rcu_assign_pointer(slot[i], child);

  			for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  				if (tags & (1 << tag))
  					tag_clear(node, tag, offset + i);
  		} else {
  			rcu_assign_pointer(slot[i], item);
  			for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  				if (tags & (1 << tag))
  					tag_set(node, tag, offset);

  		}

  		if (radix_tree_is_internal_node(old) &&

  					!is_sibling_entry(node, old) &&
  					(old != RADIX_TREE_RETRY))

  			radix_tree_free_nodes(old);
  		if (radix_tree_exceptional_entry(old))
  			node->exceptional--;

  	}

  	if (node) {
  		node->count += n;
  		if (radix_tree_exceptional_entry(item))
  			node->exceptional += n;
  	}
  	return n;

  }

  #else
  static inline int insert_entries(struct radix_tree_node *node, void **slot,
  				void *item, unsigned order, bool replace)
  {
  	if (*slot)
  		return -EEXIST;
  	rcu_assign_pointer(*slot, item);
  	if (node) {
  		node->count++;
  		if (radix_tree_exceptional_entry(item))
  			node->exceptional++;
  	}
  	return 1;
  }
  #endif

  
  /**

   *	__radix_tree_insert    -    insert into a radix tree

   *	@root:		radix tree root
   *	@index:		index key

   *	@order:		key covers the 2^order indices around index

   *	@item:		item to insert
   *
   *	Insert an item into the radix tree at position @index.
   */

  int __radix_tree_insert(struct radix_tree_root *root, unsigned long index,
  			unsigned order, void *item)

  {
  	struct radix_tree_node *node;
  	void **slot;
  	int error;

  	BUG_ON(radix_tree_is_internal_node(item));

  	error = __radix_tree_create(root, index, order, &node, &slot);

  	if (error)
  		return error;

  
  	error = insert_entries(node, slot, item, order, false);
  	if (error < 0)
  		return error;

  	if (node) {

  		unsigned offset = get_slot_offset(node, slot);

  		BUG_ON(tag_get(node, 0, offset));
  		BUG_ON(tag_get(node, 1, offset));
  		BUG_ON(tag_get(node, 2, offset));

  	} else {

  		BUG_ON(root_tags_get(root));

  	}

  	return 0;
  }

  EXPORT_SYMBOL(__radix_tree_insert);

  /**
   *	__radix_tree_lookup	-	lookup an item in a radix tree
   *	@root:		radix tree root
   *	@index:		index key
   *	@nodep:		returns node
   *	@slotp:		returns slot
   *
   *	Lookup and return the item at position @index in the radix
   *	tree @root.
   *
   *	Until there is more than one item in the tree, no nodes are
   *	allocated and @root->rnode is used as a direct slot instead of
   *	pointing to a node, in which case *@nodep will be NULL.

   */

  void *__radix_tree_lookup(struct radix_tree_root *root, unsigned long index,
  			  struct radix_tree_node **nodep, void ***slotp)

  {

  	struct radix_tree_node *node, *parent;

  	unsigned long maxindex;

  	void **slot;

   restart:
  	parent = NULL;
  	slot = (void **)&root->rnode;

  	radix_tree_load_root(root, &node, &maxindex);

  	if (index > maxindex)

  		return NULL;

  	while (radix_tree_is_internal_node(node)) {

  		unsigned offset;

  		if (node == RADIX_TREE_RETRY)
  			goto restart;

  		parent = entry_to_node(node);

  		offset = radix_tree_descend(parent, &node, index);

  		slot = parent->slots + offset;
  	}

  	if (nodep)
  		*nodep = parent;
  	if (slotp)
  		*slotp = slot;
  	return node;

  }
  
  /**
   *	radix_tree_lookup_slot    -    lookup a slot in a radix tree
   *	@root:		radix tree root
   *	@index:		index key
   *
   *	Returns:  the slot corresponding to the position @index in the
   *	radix tree @root. This is useful for update-if-exists operations.
   *
   *	This function can be called under rcu_read_lock iff the slot is not
   *	modified by radix_tree_replace_slot, otherwise it must be called
   *	exclusive from other writers. Any dereference of the slot must be done
   *	using radix_tree_deref_slot.
   */
  void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
  {

  	void **slot;
  
  	if (!__radix_tree_lookup(root, index, NULL, &slot))
  		return NULL;
  	return slot;

  }

  EXPORT_SYMBOL(radix_tree_lookup_slot);
  
  /**
   *	radix_tree_lookup    -    perform lookup operation on a radix tree
   *	@root:		radix tree root
   *	@index:		index key
   *
   *	Lookup the item at the position @index in the radix tree @root.

   *
   *	This function can be called under rcu_read_lock, however the caller
   *	must manage lifetimes of leaf nodes (eg. RCU may also be used to free
   *	them safely). No RCU barriers are required to access or modify the
   *	returned item, however.

   */
  void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
  {

  	return __radix_tree_lookup(root, index, NULL, NULL);

  }
  EXPORT_SYMBOL(radix_tree_lookup);

  static inline int slot_count(struct radix_tree_node *node,
  						void **slot)
  {
  	int n = 1;
  #ifdef CONFIG_RADIX_TREE_MULTIORDER
  	void *ptr = node_to_entry(slot);
  	unsigned offset = get_slot_offset(node, slot);
  	int i;
  
  	for (i = 1; offset + i < RADIX_TREE_MAP_SIZE; i++) {
  		if (node->slots[offset + i] != ptr)
  			break;
  		n++;
  	}
  #endif
  	return n;
  }

  static void replace_slot(struct radix_tree_root *root,
  			 struct radix_tree_node *node,
  			 void **slot, void *item,
  			 bool warn_typeswitch)

  {
  	void *old = rcu_dereference_raw(*slot);

  	int count, exceptional;

  
  	WARN_ON_ONCE(radix_tree_is_internal_node(item));

  	count = !!item - !!old;

  	exceptional = !!radix_tree_exceptional_entry(item) -
  		      !!radix_tree_exceptional_entry(old);

  	WARN_ON_ONCE(warn_typeswitch && (count || exceptional));

  	if (node) {
  		node->count += count;

  		if (exceptional) {
  			exceptional *= slot_count(node, slot);
  			node->exceptional += exceptional;
  		}

  	}

  
  	rcu_assign_pointer(*slot, item);
  }

  static inline void delete_sibling_entries(struct radix_tree_node *node,
  						void **slot)
  {
  #ifdef CONFIG_RADIX_TREE_MULTIORDER
  	bool exceptional = radix_tree_exceptional_entry(*slot);
  	void *ptr = node_to_entry(slot);
  	unsigned offset = get_slot_offset(node, slot);
  	int i;
  
  	for (i = 1; offset + i < RADIX_TREE_MAP_SIZE; i++) {
  		if (node->slots[offset + i] != ptr)
  			break;
  		node->slots[offset + i] = NULL;
  		node->count--;
  		if (exceptional)
  			node->exceptional--;
  	}
  #endif
  }

  /**

   * __radix_tree_replace		- replace item in a slot

   * @root:		radix tree root
   * @node:		pointer to tree node
   * @slot:		pointer to slot in @node
   * @item:		new item to store in the slot.
   * @update_node:	callback for changing leaf nodes
   * @private:		private data to pass to @update_node

   *
   * For use with __radix_tree_lookup().  Caller must hold tree write locked
   * across slot lookup and replacement.
   */
  void __radix_tree_replace(struct radix_tree_root *root,
  			  struct radix_tree_node *node,

  			  void **slot, void *item,
  			  radix_tree_update_node_t update_node, void *private)

  {

  	if (!item)
  		delete_sibling_entries(node, slot);

  	/*

  	 * This function supports replacing exceptional entries and
  	 * deleting entries, but that needs accounting against the
  	 * node unless the slot is root->rnode.

  	 */
  	replace_slot(root, node, slot, item,
  		     !node && slot != (void **)&root->rnode);

  	if (!node)
  		return;
  
  	if (update_node)
  		update_node(node, private);
  
  	delete_node(root, node, update_node, private);

  }
  
  /**
   * radix_tree_replace_slot	- replace item in a slot
   * @root:	radix tree root
   * @slot:	pointer to slot
   * @item:	new item to store in the slot.
   *
   * For use with radix_tree_lookup_slot(), radix_tree_gang_lookup_slot(),
   * radix_tree_gang_lookup_tag_slot().  Caller must hold tree write locked
   * across slot lookup and replacement.
   *
   * NOTE: This cannot be used to switch between non-entries (empty slots),
   * regular entries, and exceptional entries, as that requires accounting

   * inside the radix tree node. When switching from one type of entry or

   * deleting, use __radix_tree_lookup() and __radix_tree_replace() or
   * radix_tree_iter_replace().

   */
  void radix_tree_replace_slot(struct radix_tree_root *root,
  			     void **slot, void *item)
  {
  	replace_slot(root, NULL, slot, item, true);
  }

  /**
   * radix_tree_iter_replace - replace item in a slot
   * @root:	radix tree root
   * @slot:	pointer to slot
   * @item:	new item to store in the slot.
   *
   * For use with radix_tree_split() and radix_tree_for_each_slot().
   * Caller must hold tree write locked across split and replacement.
   */
  void radix_tree_iter_replace(struct radix_tree_root *root,
  		const struct radix_tree_iter *iter, void **slot, void *item)
  {
  	__radix_tree_replace(root, iter->node, slot, item, NULL, NULL);
  }

  #ifdef CONFIG_RADIX_TREE_MULTIORDER
  /**
   * radix_tree_join - replace multiple entries with one multiorder entry
   * @root: radix tree root
   * @index: an index inside the new entry
   * @order: order of the new entry
   * @item: new entry
   *
   * Call this function to replace several entries with one larger entry.
   * The existing entries are presumed to not need freeing as a result of
   * this call.
   *
   * The replacement entry will have all the tags set on it that were set
   * on any of the entries it is replacing.
   */
  int radix_tree_join(struct radix_tree_root *root, unsigned long index,
  			unsigned order, void *item)
  {
  	struct radix_tree_node *node;
  	void **slot;
  	int error;
  
  	BUG_ON(radix_tree_is_internal_node(item));
  
  	error = __radix_tree_create(root, index, order, &node, &slot);
  	if (!error)
  		error = insert_entries(node, slot, item, order, true);
  	if (error > 0)
  		error = 0;
  
  	return error;
  }

  
  /**
   * radix_tree_split - Split an entry into smaller entries
   * @root: radix tree root
   * @index: An index within the large entry
   * @order: Order of new entries
   *
   * Call this function as the first step in replacing a multiorder entry
   * with several entries of lower order.  After this function returns,
   * loop over the relevant portion of the tree using radix_tree_for_each_slot()
   * and call radix_tree_iter_replace() to set up each new entry.
   *
   * The tags from this entry are replicated to all the new entries.
   *
   * The radix tree should be locked against modification during the entire
   * replacement operation.  Lock-free lookups will see RADIX_TREE_RETRY which
   * should prompt RCU walkers to restart the lookup from the root.
   */
  int radix_tree_split(struct radix_tree_root *root, unsigned long index,
  				unsigned order)
  {
  	struct radix_tree_node *parent, *node, *child;
  	void **slot;
  	unsigned int offset, end;
  	unsigned n, tag, tags = 0;
  
  	if (!__radix_tree_lookup(root, index, &parent, &slot))
  		return -ENOENT;
  	if (!parent)
  		return -ENOENT;
  
  	offset = get_slot_offset(parent, slot);
  
  	for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  		if (tag_get(parent, tag, offset))
  			tags |= 1 << tag;
  
  	for (end = offset + 1; end < RADIX_TREE_MAP_SIZE; end++) {
  		if (!is_sibling_entry(parent, parent->slots[end]))
  			break;
  		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  			if (tags & (1 << tag))
  				tag_set(parent, tag, end);
  		/* rcu_assign_pointer ensures tags are set before RETRY */
  		rcu_assign_pointer(parent->slots[end], RADIX_TREE_RETRY);
  	}
  	rcu_assign_pointer(parent->slots[offset], RADIX_TREE_RETRY);
  	parent->exceptional -= (end - offset);
  
  	if (order == parent->shift)
  		return 0;
  	if (order > parent->shift) {
  		while (offset < end)
  			offset += insert_entries(parent, &parent->slots[offset],
  					RADIX_TREE_RETRY, order, true);
  		return 0;
  	}
  
  	node = parent;
  
  	for (;;) {
  		if (node->shift > order) {

  			child = radix_tree_node_alloc(root, node,
  					node->shift - RADIX_TREE_MAP_SHIFT,
  					offset, 0, 0);

  			if (!child)
  				goto nomem;

  			if (node != parent) {
  				node->count++;
  				node->slots[offset] = node_to_entry(child);
  				for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  					if (tags & (1 << tag))
  						tag_set(node, tag, offset);
  			}
  
  			node = child;
  			offset = 0;
  			continue;
  		}
  
  		n = insert_entries(node, &node->slots[offset],
  					RADIX_TREE_RETRY, order, false);
  		BUG_ON(n > RADIX_TREE_MAP_SIZE);
  
  		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  			if (tags & (1 << tag))
  				tag_set(node, tag, offset);
  		offset += n;
  
  		while (offset == RADIX_TREE_MAP_SIZE) {
  			if (node == parent)
  				break;
  			offset = node->offset;
  			child = node;
  			node = node->parent;
  			rcu_assign_pointer(node->slots[offset],
  						node_to_entry(child));
  			offset++;
  		}
  		if ((node == parent) && (offset == end))
  			return 0;
  	}
  
   nomem:
  	/* Shouldn't happen; did user forget to preload? */
  	/* TODO: free all the allocated nodes */
  	WARN_ON(1);
  	return -ENOMEM;
  }

  #endif

  /**
   *	radix_tree_tag_set - set a tag on a radix tree node
   *	@root:		radix tree root
   *	@index:		index key

   *	@tag:		tag index

   *

   *	Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
   *	corresponding to @index in the radix tree.  From

   *	the root all the way down to the leaf node.
   *

   *	Returns the address of the tagged item.  Setting a tag on a not-present

   *	item is a bug.
   */
  void *radix_tree_tag_set(struct radix_tree_root *root,

  			unsigned long index, unsigned int tag)

  {

  	struct radix_tree_node *node, *parent;
  	unsigned long maxindex;

  	radix_tree_load_root(root, &node, &maxindex);

  	BUG_ON(index > maxindex);

  	while (radix_tree_is_internal_node(node)) {

  		unsigned offset;

  		parent = entry_to_node(node);

  		offset = radix_tree_descend(parent, &node, index);

  		BUG_ON(!node);
  
  		if (!tag_get(parent, tag, offset))
  			tag_set(parent, tag, offset);

  	}

  	/* set the root's tag bit */

  	if (!root_tag_get(root, tag))

  		root_tag_set(root, tag);

  	return node;

  }
  EXPORT_SYMBOL(radix_tree_tag_set);

  static void node_tag_clear(struct radix_tree_root *root,
  				struct radix_tree_node *node,
  				unsigned int tag, unsigned int offset)
  {
  	while (node) {
  		if (!tag_get(node, tag, offset))
  			return;
  		tag_clear(node, tag, offset);
  		if (any_tag_set(node, tag))
  			return;
  
  		offset = node->offset;
  		node = node->parent;
  	}
  
  	/* clear the root's tag bit */
  	if (root_tag_get(root, tag))
  		root_tag_clear(root, tag);
  }

  static void node_tag_set(struct radix_tree_root *root,
  				struct radix_tree_node *node,
  				unsigned int tag, unsigned int offset)
  {
  	while (node) {
  		if (tag_get(node, tag, offset))
  			return;
  		tag_set(node, tag, offset);
  		offset = node->offset;
  		node = node->parent;
  	}
  
  	if (!root_tag_get(root, tag))
  		root_tag_set(root, tag);
  }

  /**

   * radix_tree_iter_tag_set - set a tag on the current iterator entry
   * @root:	radix tree root
   * @iter:	iterator state
   * @tag:	tag to set
   */
  void radix_tree_iter_tag_set(struct radix_tree_root *root,
  			const struct radix_tree_iter *iter, unsigned int tag)
  {
  	node_tag_set(root, iter->node, tag, iter_offset(iter));
  }
  
  /**

   *	radix_tree_tag_clear - clear a tag on a radix tree node
   *	@root:		radix tree root
   *	@index:		index key

   *	@tag:		tag index

   *

   *	Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)

   *	corresponding to @index in the radix tree.  If this causes
   *	the leaf node to have no tags set then clear the tag in the

   *	next-to-leaf node, etc.
   *
   *	Returns the address of the tagged item on success, else NULL.  ie:
   *	has the same return value and semantics as radix_tree_lookup().
   */
  void *radix_tree_tag_clear(struct radix_tree_root *root,

  			unsigned long index, unsigned int tag)

  {

  	struct radix_tree_node *node, *parent;
  	unsigned long maxindex;

  	int uninitialized_var(offset);

  	radix_tree_load_root(root, &node, &maxindex);

  	if (index > maxindex)
  		return NULL;

  	parent = NULL;

  	while (radix_tree_is_internal_node(node)) {

  		parent = entry_to_node(node);

  		offset = radix_tree_descend(parent, &node, index);

  	}

  	if (node)
  		node_tag_clear(root, parent, tag, offset);

  	return node;

  }
  EXPORT_SYMBOL(radix_tree_tag_clear);

  /**

   * radix_tree_tag_get - get a tag on a radix tree node
   * @root:		radix tree root
   * @index:		index key

   * @tag:		tag index (< RADIX_TREE_MAX_TAGS)

   *

   * Return values:

   *

   *  0: tag not present or not set
   *  1: tag set

   *
   * Note that the return value of this function may not be relied on, even if
   * the RCU lock is held, unless tag modification and node deletion are excluded
   * from concurrency.

   */
  int radix_tree_tag_get(struct radix_tree_root *root,

  			unsigned long index, unsigned int tag)

  {

  	struct radix_tree_node *node, *parent;
  	unsigned long maxindex;

  	if (!root_tag_get(root, tag))
  		return 0;

  	radix_tree_load_root(root, &node, &maxindex);

  	if (index > maxindex)
  		return 0;

  	if (node == NULL)
  		return 0;

  	while (radix_tree_is_internal_node(node)) {

  		unsigned offset;

  		parent = entry_to_node(node);

  		offset = radix_tree_descend(parent, &node, index);

  		if (!node)

  			return 0;

  		if (!tag_get(parent, tag, offset))

  			return 0;

  		if (node == RADIX_TREE_RETRY)
  			break;

  	}

  
  	return 1;

  }
  EXPORT_SYMBOL(radix_tree_tag_get);

  static inline void __set_iter_shift(struct radix_tree_iter *iter,
  					unsigned int shift)
  {
  #ifdef CONFIG_RADIX_TREE_MULTIORDER
  	iter->shift = shift;
  #endif
  }

  /* Construct iter->tags bit-mask from node->tags[tag] array */
  static void set_iter_tags(struct radix_tree_iter *iter,
  				struct radix_tree_node *node, unsigned offset,
  				unsigned tag)
  {
  	unsigned tag_long = offset / BITS_PER_LONG;
  	unsigned tag_bit  = offset % BITS_PER_LONG;
  
  	iter->tags = node->tags[tag][tag_long] >> tag_bit;
  
  	/* This never happens if RADIX_TREE_TAG_LONGS == 1 */
  	if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
  		/* Pick tags from next element */
  		if (tag_bit)
  			iter->tags |= node->tags[tag][tag_long + 1] <<
  						(BITS_PER_LONG - tag_bit);
  		/* Clip chunk size, here only BITS_PER_LONG tags */
  		iter->next_index = __radix_tree_iter_add(iter, BITS_PER_LONG);
  	}
  }
  
  #ifdef CONFIG_RADIX_TREE_MULTIORDER
  static void **skip_siblings(struct radix_tree_node **nodep,
  			void **slot, struct radix_tree_iter *iter)
  {
  	void *sib = node_to_entry(slot - 1);
  
  	while (iter->index < iter->next_index) {
  		*nodep = rcu_dereference_raw(*slot);
  		if (*nodep && *nodep != sib)
  			return slot;
  		slot++;
  		iter->index = __radix_tree_iter_add(iter, 1);
  		iter->tags >>= 1;
  	}
  
  	*nodep = NULL;
  	return NULL;
  }
  
  void ** __radix_tree_next_slot(void **slot, struct radix_tree_iter *iter,
  					unsigned flags)
  {
  	unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;
  	struct radix_tree_node *node = rcu_dereference_raw(*slot);
  
  	slot = skip_siblings(&node, slot, iter);
  
  	while (radix_tree_is_internal_node(node)) {
  		unsigned offset;
  		unsigned long next_index;
  
  		if (node == RADIX_TREE_RETRY)
  			return slot;
  		node = entry_to_node(node);

  		iter->node = node;

  		iter->shift = node->shift;
  
  		if (flags & RADIX_TREE_ITER_TAGGED) {
  			offset = radix_tree_find_next_bit(node, tag, 0);
  			if (offset == RADIX_TREE_MAP_SIZE)
  				return NULL;
  			slot = &node->slots[offset];
  			iter->index = __radix_tree_iter_add(iter, offset);
  			set_iter_tags(iter, node, offset, tag);
  			node = rcu_dereference_raw(*slot);
  		} else {
  			offset = 0;
  			slot = &node->slots[0];
  			for (;;) {
  				node = rcu_dereference_raw(*slot);
  				if (node)
  					break;
  				slot++;
  				offset++;
  				if (offset == RADIX_TREE_MAP_SIZE)
  					return NULL;
  			}
  			iter->index = __radix_tree_iter_add(iter, offset);
  		}
  		if ((flags & RADIX_TREE_ITER_CONTIG) && (offset > 0))
  			goto none;
  		next_index = (iter->index | shift_maxindex(iter->shift)) + 1;
  		if (next_index < iter->next_index)
  			iter->next_index = next_index;
  	}
  
  	return slot;
   none:
  	iter->next_index = 0;
  	return NULL;
  }
  EXPORT_SYMBOL(__radix_tree_next_slot);
  #else
  static void **skip_siblings(struct radix_tree_node **nodep,
  			void **slot, struct radix_tree_iter *iter)
  {
  	return slot;
  }
  #endif
  
  void **radix_tree_iter_resume(void **slot, struct radix_tree_iter *iter)
  {
  	struct radix_tree_node *node;
  
  	slot++;
  	iter->index = __radix_tree_iter_add(iter, 1);
  	node = rcu_dereference_raw(*slot);
  	skip_siblings(&node, slot, iter);
  	iter->next_index = iter->index;
  	iter->tags = 0;
  	return NULL;
  }
  EXPORT_SYMBOL(radix_tree_iter_resume);

  /**

   * radix_tree_next_chunk - find next chunk of slots for iteration
   *
   * @root:	radix tree root
   * @iter:	iterator state
   * @flags:	RADIX_TREE_ITER_* flags and tag index
   * Returns:	pointer to chunk first slot, or NULL if iteration is over
   */
  void **radix_tree_next_chunk(struct radix_tree_root *root,
  			     struct radix_tree_iter *iter, unsigned flags)
  {

  	unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;

  	struct radix_tree_node *node, *child;

  	unsigned long index, offset, maxindex;

  
  	if ((flags & RADIX_TREE_ITER_TAGGED) && !root_tag_get(root, tag))
  		return NULL;
  
  	/*
  	 * Catch next_index overflow after ~0UL. iter->index never overflows
  	 * during iterating; it can be zero only at the beginning.
  	 * And we cannot overflow iter->next_index in a single step,
  	 * because RADIX_TREE_MAP_SHIFT < BITS_PER_LONG.

  	 *
  	 * This condition also used by radix_tree_next_slot() to stop

  	 * contiguous iterating, and forbid switching to the next chunk.

  	 */
  	index = iter->next_index;
  	if (!index && iter->index)
  		return NULL;

   restart:

  	radix_tree_load_root(root, &child, &maxindex);

  	if (index > maxindex)
  		return NULL;

  	if (!child)
  		return NULL;

  	if (!radix_tree_is_internal_node(child)) {

  		/* Single-slot tree */

  		iter->index = index;
  		iter->next_index = maxindex + 1;

  		iter->tags = 1;

  		iter->node = NULL;

  		__set_iter_shift(iter, 0);

  		return (void **)&root->rnode;

  	}

  	do {
  		node = entry_to_node(child);

  		offset = radix_tree_descend(node, &child, index);

  		if ((flags & RADIX_TREE_ITER_TAGGED) ?

  				!tag_get(node, tag, offset) : !child) {

  			/* Hole detected */
  			if (flags & RADIX_TREE_ITER_CONTIG)
  				return NULL;
  
  			if (flags & RADIX_TREE_ITER_TAGGED)

  				offset = radix_tree_find_next_bit(node, tag,

  						offset + 1);
  			else
  				while (++offset	< RADIX_TREE_MAP_SIZE) {

  					void *slot = node->slots[offset];
  					if (is_sibling_entry(node, slot))
  						continue;
  					if (slot)

  						break;
  				}

  			index &= ~node_maxindex(node);

  			index += offset << node->shift;

  			/* Overflow after ~0UL */
  			if (!index)
  				return NULL;
  			if (offset == RADIX_TREE_MAP_SIZE)
  				goto restart;

  			child = rcu_dereference_raw(node->slots[offset]);

  		}

  		if (!child)

  			goto restart;

  		if (child == RADIX_TREE_RETRY)
  			break;

  	} while (radix_tree_is_internal_node(child));

  
  	/* Update the iterator state */

  	iter->index = (index &~ node_maxindex(node)) | (offset << node->shift);
  	iter->next_index = (index | node_maxindex(node)) + 1;

  	iter->node = node;

  	__set_iter_shift(iter, node->shift);

  	if (flags & RADIX_TREE_ITER_TAGGED)
  		set_iter_tags(iter, node, offset, tag);

  
  	return node->slots + offset;
  }
  EXPORT_SYMBOL(radix_tree_next_chunk);
  
  /**

   *	radix_tree_gang_lookup - perform multiple lookup on a radix tree
   *	@root:		radix tree root
   *	@results:	where the results of the lookup are placed
   *	@first_index:	start the lookup from this key
   *	@max_items:	place up to this many items at *results
   *
   *	Performs an index-ascending scan of the tree for present items.  Places
   *	them at *@results and returns the number of items which were placed at
   *	*@results.
   *
   *	The implementation is naive.

   *
   *	Like radix_tree_lookup, radix_tree_gang_lookup may be called under
   *	rcu_read_lock. In this case, rather than the returned results being

   *	an atomic snapshot of the tree at a single point in time, the
   *	semantics of an RCU protected gang lookup are as though multiple
   *	radix_tree_lookups have been issued in individual locks, and results
   *	stored in 'results'.

   */
  unsigned int
  radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
  			unsigned long first_index, unsigned int max_items)
  {

  	struct radix_tree_iter iter;
  	void **slot;
  	unsigned int ret = 0;

  	if (unlikely(!max_items))

  		return 0;

  	radix_tree_for_each_slot(slot, root, &iter, first_index) {

  		results[ret] = rcu_dereference_raw(*slot);

  		if (!results[ret])
  			continue;

  		if (radix_tree_is_internal_node(results[ret])) {

  			slot = radix_tree_iter_retry(&iter);
  			continue;
  		}

  		if (++ret == max_items)

  			break;

  	}

  	return ret;
  }
  EXPORT_SYMBOL(radix_tree_gang_lookup);

  /**
   *	radix_tree_gang_lookup_slot - perform multiple slot lookup on radix tree
   *	@root:		radix tree root
   *	@results:	where the results of the lookup are placed

   *	@indices:	where their indices should be placed (but usually NULL)

   *	@first_index:	start the lookup from this key
   *	@max_items:	place up to this many items at *results
   *
   *	Performs an index-ascending scan of the tree for present items.  Places
   *	their slots at *@results and returns the number of items which were
   *	placed at *@results.
   *
   *	The implementation is naive.
   *
   *	Like radix_tree_gang_lookup as far as RCU and locking goes. Slots must
   *	be dereferenced with radix_tree_deref_slot, and if using only RCU
   *	protection, radix_tree_deref_slot may fail requiring a retry.
   */
  unsigned int

  radix_tree_gang_lookup_slot(struct radix_tree_root *root,
  			void ***results, unsigned long *indices,

  			unsigned long first_index, unsigned int max_items)
  {

  	struct radix_tree_iter iter;
  	void **slot;
  	unsigned int ret = 0;

  	if (unlikely(!max_items))

  		return 0;

  	radix_tree_for_each_slot(slot, root, &iter, first_index) {
  		results[ret] = slot;

  		if (indices)

  			indices[ret] = iter.index;
  		if (++ret == max_items)

  			break;

  	}
  
  	return ret;
  }
  EXPORT_SYMBOL(radix_tree_gang_lookup_slot);

  /**
   *	radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
   *	                             based on a tag
   *	@root:		radix tree root
   *	@results:	where the results of the lookup are placed
   *	@first_index:	start the lookup from this key
   *	@max_items:	place up to this many items at *results

   *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)

   *
   *	Performs an index-ascending scan of the tree for present items which
   *	have the tag indexed by @tag set.  Places the items at *@results and
   *	returns the number of items which were placed at *@results.
   */
  unsigned int
  radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,

  		unsigned long first_index, unsigned int max_items,
  		unsigned int tag)

  {

  	struct radix_tree_iter iter;
  	void **slot;
  	unsigned int ret = 0;

  	if (unlikely(!max_items))

  		return 0;

  	radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {

  		results[ret] = rcu_dereference_raw(*slot);

  		if (!results[ret])
  			continue;

  		if (radix_tree_is_internal_node(results[ret])) {

  			slot = radix_tree_iter_retry(&iter);
  			continue;
  		}

  		if (++ret == max_items)

  			break;

  	}

  	return ret;
  }
  EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
  
  /**

   *	radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
   *					  radix tree based on a tag
   *	@root:		radix tree root
   *	@results:	where the results of the lookup are placed
   *	@first_index:	start the lookup from this key
   *	@max_items:	place up to this many items at *results
   *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
   *
   *	Performs an index-ascending scan of the tree for present items which
   *	have the tag indexed by @tag set.  Places the slots at *@results and
   *	returns the number of slots which were placed at *@results.
   */
  unsigned int
  radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
  		unsigned long first_index, unsigned int max_items,
  		unsigned int tag)
  {

  	struct radix_tree_iter iter;
  	void **slot;
  	unsigned int ret = 0;

  	if (unlikely(!max_items))

  		return 0;

  	radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
  		results[ret] = slot;
  		if (++ret == max_items)

  			break;

  	}
  
  	return ret;
  }
  EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);

  /**

   *	__radix_tree_delete_node    -    try to free node after clearing a slot
   *	@root:		radix tree root

   *	@node:		node containing @index
   *
   *	After clearing the slot at @index in @node from radix tree
   *	rooted at @root, call this function to attempt freeing the
   *	node and shrinking the tree.

   */

  void __radix_tree_delete_node(struct radix_tree_root *root,

  			      struct radix_tree_node *node)
  {

  	delete_node(root, node, NULL, NULL);

  }
  
  /**

   *	radix_tree_delete_item    -    delete an item from a radix tree

   *	@root:		radix tree root
   *	@index:		index key

   *	@item:		expected item

   *

   *	Remove @item at @index from the radix tree rooted at @root.

   *

   *	Returns the address of the deleted item, or NULL if it was not present
   *	or the entry at the given @index was not @item.

   */

  void *radix_tree_delete_item(struct radix_tree_root *root,
  			     unsigned long index, void *item)

  {

  	struct radix_tree_node *node;

  	unsigned int offset;

  	void **slot;
  	void *entry;

  	int tag;

  	entry = __radix_tree_lookup(root, index, &node, &slot);
  	if (!entry)
  		return NULL;

  	if (item && entry != item)
  		return NULL;
  
  	if (!node) {

  		root_tag_clear_all(root);
  		root->rnode = NULL;

  		return entry;

  	}

  	offset = get_slot_offset(node, slot);

  	/* Clear all tags associated with the item to be deleted.  */
  	for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  		node_tag_clear(root, node, tag, offset);

  	__radix_tree_replace(root, node, slot, NULL, NULL, NULL);

  	return entry;

  }

  EXPORT_SYMBOL(radix_tree_delete_item);
  
  /**
   *	radix_tree_delete    -    delete an item from a radix tree
   *	@root:		radix tree root
   *	@index:		index key
   *
   *	Remove the item at @index from the radix tree rooted at @root.
   *
   *	Returns the address of the deleted item, or NULL if it was not present.
   */
  void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
  {
  	return radix_tree_delete_item(root, index, NULL);
  }

  EXPORT_SYMBOL(radix_tree_delete);

  void radix_tree_clear_tags(struct radix_tree_root *root,
  			   struct radix_tree_node *node,
  			   void **slot)

  {

  	if (node) {
  		unsigned int tag, offset = get_slot_offset(node, slot);
  		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
  			node_tag_clear(root, node, tag, offset);
  	} else {
  		/* Clear root node tags */
  		root->gfp_mask &= __GFP_BITS_MASK;
  	}

  }

  /**
   *	radix_tree_tagged - test whether any items in the tree are tagged
   *	@root:		radix tree root
   *	@tag:		tag to test
   */

  int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)

  {

  	return root_tag_get(root, tag);

  }
  EXPORT_SYMBOL(radix_tree_tagged);
  
  static void

  radix_tree_node_ctor(void *arg)

  {

  	struct radix_tree_node *node = arg;
  
  	memset(node, 0, sizeof(*node));
  	INIT_LIST_HEAD(&node->private_list);

  }

  static __init unsigned long __maxindex(unsigned int height)
  {
  	unsigned int width = height * RADIX_TREE_MAP_SHIFT;
  	int shift = RADIX_TREE_INDEX_BITS - width;
  
  	if (shift < 0)
  		return ~0UL;
  	if (shift >= BITS_PER_LONG)
  		return 0UL;
  	return ~0UL >> shift;
  }
  
  static __init void radix_tree_init_maxnodes(void)
  {
  	unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH + 1];
  	unsigned int i, j;
  
  	for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
  		height_to_maxindex[i] = __maxindex(i);
  	for (i = 0; i < ARRAY_SIZE(height_to_maxnodes); i++) {
  		for (j = i; j > 0; j--)
  			height_to_maxnodes[i] += height_to_maxindex[j - 1] + 1;
  	}
  }

  static int radix_tree_cpu_dead(unsigned int cpu)

  {

  	struct radix_tree_preload *rtp;
  	struct radix_tree_node *node;
  
  	/* Free per-cpu pool of preloaded nodes */

  	rtp = &per_cpu(radix_tree_preloads, cpu);
  	while (rtp->nr) {
  		node = rtp->nodes;
  		rtp->nodes = node->private_data;
  		kmem_cache_free(radix_tree_node_cachep, node);
  		rtp->nr--;

  	}

  	return 0;

  }

  
  void __init radix_tree_init(void)
  {

  	int ret;

  	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
  			sizeof(struct radix_tree_node), 0,

  			SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
  			radix_tree_node_ctor);

  	radix_tree_init_maxnodes();

  	ret = cpuhp_setup_state_nocalls(CPUHP_RADIX_DEAD, "lib/radix:dead",
  					NULL, radix_tree_cpu_dead);
  	WARN_ON(ret < 0);

  }