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 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * 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
  */
 
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
 #include <linux/bug.h>
 #include <linux/cpu.h>
 #include <linux/errno.h>
 #include <linux/export.h>
 #include <linux/idr.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/kmemleak.h>
 #include <linux/percpu.h>
 #include <linux/preempt.h>      /* in_interrupt() */
 #include <linux/radix-tree.h>
 #include <linux/rcupdate.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/xarray.h>
 
 /*
  * Radix tree node cache.
  */
 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)
 
 /*
  * The IDR does not have to be as high as the radix tree since it uses
  * signed integers, not unsigned longs.
  */
 #define IDR_INDEX_BITS      (8 /* CHAR_BIT */ * sizeof(int) - 1)
 #define IDR_MAX_PATH        (DIV_ROUND_UP(IDR_INDEX_BITS, \
                         RADIX_TREE_MAP_SHIFT))
 #define IDR_PRELOAD_SIZE    (IDR_MAX_PATH * 2 - 1)
 
 /*
  * Per-cpu pool of preloaded nodes
  */
 DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = {
     .lock = INIT_LOCAL_LOCK(lock),
 };
 EXPORT_PER_CPU_SYMBOL_GPL(radix_tree_preloads);
 
 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    XA_RETRY_ENTRY
 
 static inline unsigned long
 get_slot_offset(const struct radix_tree_node *parent, void __rcu **slot)
 {
     return parent ? slot - parent->slots : 0;
 }
 
 static unsigned int radix_tree_descend(const struct radix_tree_node *parent,
             struct radix_tree_node **nodep, unsigned long index)
 {
     unsigned int offset = (index >> parent->shift) & RADIX_TREE_MAP_MASK;
     void __rcu **entry = rcu_dereference_raw(parent->slots[offset]);
 
     *nodep = (void *)entry;
     return offset;
 }
 
 static inline gfp_t root_gfp_mask(const struct radix_tree_root *root)
 {
     return root->xa_flags & (__GFP_BITS_MASK & ~GFP_ZONEMASK);
 }
 
 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(const 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 tag)
 {
     root->xa_flags |= (__force gfp_t)(1 << (tag + ROOT_TAG_SHIFT));
 }
 
 static inline void root_tag_clear(struct radix_tree_root *root, unsigned tag)
 {
     root->xa_flags &= (__force gfp_t)~(1 << (tag + ROOT_TAG_SHIFT));
 }
 
 static inline void root_tag_clear_all(struct radix_tree_root *root)
 {
     root->xa_flags &= (__force gfp_t)((1 << ROOT_TAG_SHIFT) - 1);
 }
 
 static inline int root_tag_get(const struct radix_tree_root *root, unsigned tag)
 {
     return (__force int)root->xa_flags & (1 << (tag + ROOT_TAG_SHIFT));
 }
 
 static inline unsigned root_tags_get(const struct radix_tree_root *root)
 {
     return (__force unsigned)root->xa_flags >> ROOT_TAG_SHIFT;
 }
 
 static inline bool is_idr(const struct radix_tree_root *root)
 {
     return !!(root->xa_flags & ROOT_IS_IDR);
 }
 
 /*
  * Returns 1 if any slot in the node has this tag set.
  * Otherwise returns 0.
  */
 static inline int any_tag_set(const 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;
 }
 
 static inline void all_tag_set(struct radix_tree_node *node, unsigned int tag)
 {
     bitmap_fill(node->tags[tag], RADIX_TREE_MAP_SIZE);
 }
 
 /**
  * radix_tree_find_next_bit - find the next set bit in a memory region
  *
  * @node: where to begin the search
  * @tag: the tag index
  * @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 & 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(const struct radix_tree_node *node)
 {
     return shift_maxindex(node->shift);
 }
 
 static unsigned long next_index(unsigned long index,
                 const struct radix_tree_node *node,
                 unsigned long offset)
 {
     return (index & ~node_maxindex(node)) + (offset << node->shift);
 }
 
 /*
  * 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(gfp_t gfp_mask, struct radix_tree_node *parent,
             struct radix_tree_root *root,
             unsigned int shift, unsigned int offset,
             unsigned int count, unsigned int nr_values)
 {
     struct radix_tree_node *ret = NULL;
 
     /*
      * 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->parent;
             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->shift = shift;
         ret->offset = offset;
         ret->count = count;
         ret->nr_values = nr_values;
         ret->parent = parent;
         ret->array = root;
     }
     return ret;
 }
 
 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 __must_check 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 used by another cgroup, so
      * they should never be accounted to any particular memory cgroup.
      */
     gfp_mask &= ~__GFP_ACCOUNT;
 
     local_lock(&radix_tree_preloads.lock);
     rtp = this_cpu_ptr(&radix_tree_preloads);
     while (rtp->nr < nr) {
         local_unlock(&radix_tree_preloads.lock);
         node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
         if (node == NULL)
             goto out;
         local_lock(&radix_tree_preloads.lock);
         rtp = this_cpu_ptr(&radix_tree_preloads);
         if (rtp->nr < nr) {
             node->parent = 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 */
     local_lock(&radix_tree_preloads.lock);
     return 0;
 }
 EXPORT_SYMBOL(radix_tree_maybe_preload);
 
 static unsigned radix_tree_load_root(const struct radix_tree_root *root,
         struct radix_tree_node **nodep, unsigned long *maxindex)
 {
     struct radix_tree_node *node = rcu_dereference_raw(root->xa_head);
 
     *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, gfp_t gfp,
                 unsigned long index, unsigned int shift)
 {
     void *entry;
     unsigned int maxshift;
     int tag;
 
     /* Figure out what the shift should be.  */
     maxshift = shift;
     while (index > shift_maxindex(maxshift))
         maxshift += RADIX_TREE_MAP_SHIFT;
 
     entry = rcu_dereference_raw(root->xa_head);
     if (!entry && (!is_idr(root) || root_tag_get(root, IDR_FREE)))
         goto out;
 
     do {
         struct radix_tree_node *node = radix_tree_node_alloc(gfp, NULL,
                             root, shift, 0, 1, 0);
         if (!node)
             return -ENOMEM;
 
         if (is_idr(root)) {
             all_tag_set(node, IDR_FREE);
             if (!root_tag_get(root, IDR_FREE)) {
                 tag_clear(node, IDR_FREE, 0);
                 root_tag_set(root, IDR_FREE);
             }
         } else {
             /* Propagate the aggregated tag info to the new child */
             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(entry)) {
             entry_to_node(entry)->parent = node;
         } else if (xa_is_value(entry)) {
             /* Moving a value entry root->xa_head to a node */
             node->nr_values = 1;
         }
         /*
          * entry was already in the radix tree, so we do not need
          * rcu_assign_pointer here
          */
         node->slots[0] = (void __rcu *)entry;
         entry = node_to_entry(node);
         rcu_assign_pointer(root->xa_head, entry);
         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 bool radix_tree_shrink(struct radix_tree_root *root)
 {
     bool shrunk = false;
 
     for (;;) {
         struct radix_tree_node *node = rcu_dereference_raw(root->xa_head);
         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, we cannot shrink.
          */
         if (node->count != 1)
             break;
         child = rcu_dereference_raw(node->slots[0]);
         if (!child)
             break;
 
         /*
          * For an IDR, we must not shrink entry 0 into the root in
          * case somebody calls idr_replace() with a pointer that
          * appears to be an internal entry
          */
         if (!node->shift && is_idr(root))
             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->xa_head) as far as dependent read barriers go.
          */
         root->xa_head = (void __rcu *)child;
         if (is_idr(root) && !tag_get(node, IDR_FREE, 0))
             root_tag_clear(root, IDR_FREE);
 
         /*
          * 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] = (void __rcu *)RADIX_TREE_RETRY;
         }
 
         WARN_ON_ONCE(!list_empty(&node->private_list));
         radix_tree_node_free(node);
         shrunk = true;
     }
 
     return shrunk;
 }
 
 static bool delete_node(struct radix_tree_root *root,
             struct radix_tree_node *node)
 {
     bool deleted = false;
 
     do {
         struct radix_tree_node *parent;
 
         if (node->count) {
             if (node_to_entry(node) ==
                     rcu_dereference_raw(root->xa_head))
                 deleted |= radix_tree_shrink(root);
             return deleted;
         }
 
         parent = node->parent;
         if (parent) {
             parent->slots[node->offset] = NULL;
             parent->count--;
         } else {
             /*
              * Shouldn't the tags already have all been cleared
              * by the caller?
              */
             if (!is_idr(root))
                 root_tag_clear_all(root);
             root->xa_head = NULL;
         }
 
         WARN_ON_ONCE(!list_empty(&node->private_list));
         radix_tree_node_free(node);
         deleted = true;
 
         node = parent;
     } while (node);
 
     return deleted;
 }
 
 /**
  *  __radix_tree_create -   create a slot in a radix tree
  *  @root:      radix tree root
  *  @index:     index key
  *  @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->xa_head 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.
  */
 static int __radix_tree_create(struct radix_tree_root *root,
         unsigned long index, struct radix_tree_node **nodep,
         void __rcu ***slotp)
 {
     struct radix_tree_node *node = NULL, *child;
     void __rcu **slot = (void __rcu **)&root->xa_head;
     unsigned long maxindex;
     unsigned int shift, offset = 0;
     unsigned long max = index;
     gfp_t gfp = root_gfp_mask(root);
 
     shift = radix_tree_load_root(root, &child, &maxindex);
 
     /* Make sure the tree is high enough.  */
     if (max > maxindex) {
         int error = radix_tree_extend(root, gfp, max, shift);
         if (error < 0)
             return error;
         shift = error;
         child = rcu_dereference_raw(root->xa_head);
     }
 
     while (shift > 0) {
         shift -= RADIX_TREE_MAP_SHIFT;
         if (child == NULL) {
             /* Have to add a child node.  */
             child = radix_tree_node_alloc(gfp, node, root, 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;
 }
 
 /*
  * 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 = rcu_dereference_raw(child->slots[offset]);
         if (xa_is_node(entry) && child->shift) {
             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;
             WARN_ON_ONCE(!list_empty(&old->private_list));
             radix_tree_node_free(old);
             if (old == entry_to_node(node))
                 return;
         }
     }
 }
 
 static inline int insert_entries(struct radix_tree_node *node,
         void __rcu **slot, void *item)
 {
     if (*slot)
         return -EEXIST;
     rcu_assign_pointer(*slot, item);
     if (node) {
         node->count++;
         if (xa_is_value(item))
             node->nr_values++;
     }
     return 1;
 }
 
 /**
  *  radix_tree_insert    -    insert into a radix tree
  *  @root:      radix tree root
  *  @index:     index key
  *  @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,
             void *item)
 {
     struct radix_tree_node *node;
     void __rcu **slot;
     int error;
 
     BUG_ON(radix_tree_is_internal_node(item));
 
     error = __radix_tree_create(root, index, &node, &slot);
     if (error)
         return error;
 
     error = insert_entries(node, slot, item);
     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->xa_head is used as a direct slot instead of
  *  pointing to a node, in which case *@nodep will be NULL.
  */
 void *__radix_tree_lookup(const struct radix_tree_root *root,
               unsigned long index, struct radix_tree_node **nodep,
               void __rcu ***slotp)
 {
     struct radix_tree_node *node, *parent;
     unsigned long maxindex;
     void __rcu **slot;
 
  restart:
     parent = NULL;
     slot = (void __rcu **)&root->xa_head;
     radix_tree_load_root(root, &node, &maxindex);
     if (index > maxindex)
         return NULL;
 
     while (radix_tree_is_internal_node(node)) {
         unsigned offset;
 
         parent = entry_to_node(node);
         offset = radix_tree_descend(parent, &node, index);
         slot = parent->slots + offset;
         if (node == RADIX_TREE_RETRY)
             goto restart;
         if (parent->shift == 0)
             break;
     }
 
     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 __rcu **radix_tree_lookup_slot(const struct radix_tree_root *root,
                 unsigned long index)
 {
     void __rcu **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(const struct radix_tree_root *root, unsigned long index)
 {
     return __radix_tree_lookup(root, index, NULL, NULL);
 }
 EXPORT_SYMBOL(radix_tree_lookup);
 
 static void replace_slot(void __rcu **slot, void *item,
         struct radix_tree_node *node, int count, int values)
 {
     if (node && (count || values)) {
         node->count += count;
         node->nr_values += values;
     }
 
     rcu_assign_pointer(*slot, item);
 }
 
 static bool node_tag_get(const struct radix_tree_root *root,
                 const struct radix_tree_node *node,
                 unsigned int tag, unsigned int offset)
 {
     if (node)
         return tag_get(node, tag, offset);
     return root_tag_get(root, tag);
 }
 
 /*
  * IDR users want to be able to store NULL in the tree, so if the slot isn't
  * free, don't adjust the count, even if it's transitioning between NULL and
  * non-NULL.  For the IDA, we mark slots as being IDR_FREE while they still
  * have empty bits, but it only stores NULL in slots when they're being
  * deleted.
  */
 static int calculate_count(struct radix_tree_root *root,
                 struct radix_tree_node *node, void __rcu **slot,
                 void *item, void *old)
 {
     if (is_idr(root)) {
         unsigned offset = get_slot_offset(node, slot);
         bool free = node_tag_get(root, node, IDR_FREE, offset);
         if (!free)
             return 0;
         if (!old)
             return 1;
     }
     return !!item - !!old;
 }
 
 /**
  * __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.
  *
  * 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 __rcu **slot, void *item)
 {
     void *old = rcu_dereference_raw(*slot);
     int values = !!xa_is_value(item) - !!xa_is_value(old);
     int count = calculate_count(root, node, slot, item, old);
 
     /*
      * This function supports replacing value entries and
      * deleting entries, but that needs accounting against the
      * node unless the slot is root->xa_head.
      */
     WARN_ON_ONCE(!node && (slot != (void __rcu **)&root->xa_head) &&
             (count || values));
     replace_slot(slot, item, node, count, values);
 
     if (!node)
         return;
 
     delete_node(root, node);
 }
 
 /**
  * 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() and
  * 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 value 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 __rcu **slot, void *item)
 {
     __radix_tree_replace(root, NULL, slot, item);
 }
 EXPORT_SYMBOL(radix_tree_replace_slot);
 
 /**
  * radix_tree_iter_replace - replace item in a slot
  * @root:   radix tree root
  * @iter:   iterator state
  * @slot:   pointer to slot
  * @item:   new item to store in the slot.
  *
  * For use with radix_tree_for_each_slot().
  * Caller must hold tree write locked.
  */
 void radix_tree_iter_replace(struct radix_tree_root *root,
                 const struct radix_tree_iter *iter,
                 void __rcu **slot, void *item)
 {
     __radix_tree_replace(root, iter->node, slot, item);
 }
 
 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_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);
 }
 
 /**
  *  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 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_iter_tag_clear - clear a tag on the current iterator entry
   * @root: radix tree root
   * @iter: iterator state
   * @tag: tag to clear
   */
 void radix_tree_iter_tag_clear(struct radix_tree_root *root,
             const struct radix_tree_iter *iter, unsigned int tag)
 {
     node_tag_clear(root, iter->node, tag, iter_offset(iter));
 }
 
 /**
  * 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(const 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;
 
     while (radix_tree_is_internal_node(node)) {
         unsigned offset;
 
         parent = entry_to_node(node);
         offset = radix_tree_descend(parent, &node, index);
 
         if (!tag_get(parent, tag, offset))
             return 0;
         if (node == RADIX_TREE_RETRY)
             break;
     }
 
     return 1;
 }
 EXPORT_SYMBOL(radix_tree_tag_get);
 
 /* 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;
 
     if (!node) {
         iter->tags = 1;
         return;
     }
 
     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);
     }
 }
 
 void __rcu **radix_tree_iter_resume(void __rcu **slot,
                     struct radix_tree_iter *iter)
 {
     slot++;
     iter->index = __radix_tree_iter_add(iter, 1);
     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 __rcu **radix_tree_next_chunk(const 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;
         return (void __rcu **)&root->xa_head;
     }
 
     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 = rcu_dereference_raw(
                             node->slots[offset]);
                     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 (node->shift && radix_tree_is_internal_node(child));
 
     /* Update the iterator state */
     iter->index = (index &~ node_maxindex(node)) | offset;
     iter->next_index = (index | node_maxindex(node)) + 1;
     iter->node = node;
 
     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(const struct radix_tree_root *root, void **results,
             unsigned long first_index, unsigned int max_items)
 {
     struct radix_tree_iter iter;
     void __rcu **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_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(const struct radix_tree_root *root, void **results,
         unsigned long first_index, unsigned int max_items,
         unsigned int tag)
 {
     struct radix_tree_iter iter;
     void __rcu **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(const struct radix_tree_root *root,
         void __rcu ***results, unsigned long first_index,
         unsigned int max_items, unsigned int tag)
 {
     struct radix_tree_iter iter;
     void __rcu **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);
 
 static bool __radix_tree_delete(struct radix_tree_root *root,
                 struct radix_tree_node *node, void __rcu **slot)
 {
     void *old = rcu_dereference_raw(*slot);
     int values = xa_is_value(old) ? -1 : 0;
     unsigned offset = get_slot_offset(node, slot);
     int tag;
 
     if (is_idr(root))
         node_tag_set(root, node, IDR_FREE, offset);
     else
         for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
             node_tag_clear(root, node, tag, offset);
 
     replace_slot(slot, NULL, node, -1, values);
     return node && delete_node(root, node);
 }
 
 /**
  * radix_tree_iter_delete - delete the entry at this iterator position
  * @root: radix tree root
  * @iter: iterator state
  * @slot: pointer to slot
  *
  * Delete the entry at the position currently pointed to by the iterator.
  * This may result in the current node being freed; if it is, the iterator
  * is advanced so that it will not reference the freed memory.  This
  * function may be called without any locking if there are no other threads
  * which can access this tree.
  */
 void radix_tree_iter_delete(struct radix_tree_root *root,
                 struct radix_tree_iter *iter, void __rcu **slot)
 {
     if (__radix_tree_delete(root, iter->node, slot))
         iter->index = iter->next_index;
 }
 EXPORT_SYMBOL(radix_tree_iter_delete);
 
 /**
  * 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.
  *
  * Return: the deleted entry, 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 = NULL;
     void __rcu **slot = NULL;
     void *entry;
 
     entry = __radix_tree_lookup(root, index, &node, &slot);
     if (!slot)
         return NULL;
     if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE,
                         get_slot_offset(node, slot))))
         return NULL;
 
     if (item && entry != item)
         return NULL;
 
     __radix_tree_delete(root, node, slot);
 
     return entry;
 }
 EXPORT_SYMBOL(radix_tree_delete_item);
 
 /**
  * radix_tree_delete - delete an entry from a radix tree
  * @root: radix tree root
  * @index: index key
  *
  * Remove the entry at @index from the radix tree rooted at @root.
  *
  * Return: The deleted entry, 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);
 
 /**
  *  radix_tree_tagged - test whether any items in the tree are tagged
  *  @root:      radix tree root
  *  @tag:       tag to test
  */
 int radix_tree_tagged(const struct radix_tree_root *root, unsigned int tag)
 {
     return root_tag_get(root, tag);
 }
 EXPORT_SYMBOL(radix_tree_tagged);
 
 /**
  * idr_preload - preload for idr_alloc()
  * @gfp_mask: allocation mask to use for preloading
  *
  * Preallocate memory to use for the next call to idr_alloc().  This function
  * returns with preemption disabled.  It will be enabled by idr_preload_end().
  */
 void idr_preload(gfp_t gfp_mask)
 {
     if (__radix_tree_preload(gfp_mask, IDR_PRELOAD_SIZE))
         local_lock(&radix_tree_preloads.lock);
 }
 EXPORT_SYMBOL(idr_preload);
 
 void __rcu **idr_get_free(struct radix_tree_root *root,
                   struct radix_tree_iter *iter, gfp_t gfp,
                   unsigned long max)
 {
     struct radix_tree_node *node = NULL, *child;
     void __rcu **slot = (void __rcu **)&root->xa_head;
     unsigned long maxindex, start = iter->next_index;
     unsigned int shift, offset = 0;
 
  grow:
     shift = radix_tree_load_root(root, &child, &maxindex);
     if (!radix_tree_tagged(root, IDR_FREE))
         start = max(start, maxindex + 1);
     if (start > max)
         return ERR_PTR(-ENOSPC);
 
     if (start > maxindex) {
         int error = radix_tree_extend(root, gfp, start, shift);
         if (error < 0)
             return ERR_PTR(error);
         shift = error;
         child = rcu_dereference_raw(root->xa_head);
     }
     if (start == 0 && shift == 0)
         shift = RADIX_TREE_MAP_SHIFT;
 
     while (shift) {
         shift -= RADIX_TREE_MAP_SHIFT;
         if (child == NULL) {
             /* Have to add a child node.  */
             child = radix_tree_node_alloc(gfp, node, root, shift,
                             offset, 0, 0);
             if (!child)
                 return ERR_PTR(-ENOMEM);
             all_tag_set(child, IDR_FREE);
             rcu_assign_pointer(*slot, node_to_entry(child));
             if (node)
                 node->count++;
         } else if (!radix_tree_is_internal_node(child))
             break;
 
         node = entry_to_node(child);
         offset = radix_tree_descend(node, &child, start);
         if (!tag_get(node, IDR_FREE, offset)) {
             offset = radix_tree_find_next_bit(node, IDR_FREE,
                             offset + 1);
             start = next_index(start, node, offset);
             if (start > max || start == 0)
                 return ERR_PTR(-ENOSPC);
             while (offset == RADIX_TREE_MAP_SIZE) {
                 offset = node->offset + 1;
                 node = node->parent;
                 if (!node)
                     goto grow;
                 shift = node->shift;
             }
             child = rcu_dereference_raw(node->slots[offset]);
         }
         slot = &node->slots[offset];
     }
 
     iter->index = start;
     if (node)
         iter->next_index = 1 + min(max, (start | node_maxindex(node)));
     else
         iter->next_index = 1;
     iter->node = node;
     set_iter_tags(iter, node, offset, IDR_FREE);
 
     return slot;
 }
 
 /**
  * idr_destroy - release all internal memory from an IDR
  * @idr: idr handle
  *
  * After this function is called, the IDR is empty, and may be reused or
  * the data structure containing it may be freed.
  *
  * A typical clean-up sequence for objects stored in an idr tree will use
  * idr_for_each() to free all objects, if necessary, then idr_destroy() to
  * free the memory used to keep track of those objects.
  */
 void idr_destroy(struct idr *idr)
 {
     struct radix_tree_node *node = rcu_dereference_raw(idr->idr_rt.xa_head);
     if (radix_tree_is_internal_node(node))
         radix_tree_free_nodes(node);
     idr->idr_rt.xa_head = NULL;
     root_tag_set(&idr->idr_rt, IDR_FREE);
 }
 EXPORT_SYMBOL(idr_destroy);
 
 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 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->parent;
         kmem_cache_free(radix_tree_node_cachep, node);
         rtp->nr--;
     }
     return 0;
 }
 
 void __init radix_tree_init(void)
 {
     int ret;
 
     BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32);
     BUILD_BUG_ON(ROOT_IS_IDR & ~GFP_ZONEMASK);
     BUILD_BUG_ON(XA_CHUNK_SIZE > 255);
     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);
     ret = cpuhp_setup_state_nocalls(CPUHP_RADIX_DEAD, "lib/radix:dead",
                     NULL, radix_tree_cpu_dead);
     WARN_ON(ret < 0);
 }

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