radix-tree.c

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/*
 * 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
 *
 * 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/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/notifier.h>
#include <linux/cpu.h>
#include <linux/string.h>
#include <linux/bitops.h>
#include <linux/rcupdate.h>


#ifdef __KERNEL__
#define RADIX_TREE_MAP_SHIFT    (CONFIG_BASE_SMALL ? 4 : 6)
#else
#define RADIX_TREE_MAP_SHIFT    3   /* For more stressful testing */
#endif

#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
#define RADIX_TREE_MAP_MASK (RADIX_TREE_MAP_SIZE-1)

#define RADIX_TREE_TAG_LONGS    \
    ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)

struct radix_tree_node {
    unsigned int    height;     /* Height from the bottom */
    unsigned int    count;
    union {
        struct radix_tree_node *parent; /* Used when ascending tree */
        struct rcu_head rcu_head;   /* Used when freeing node */
    };
    void __rcu  *slots[RADIX_TREE_MAP_SIZE];
    unsigned long   tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
};

#define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
#define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
                      RADIX_TREE_MAP_SHIFT))

/*
 * The height_to_maxindex array needs to be one deeper than the maximum
 * path as height 0 holds only 1 entry.
 */
static unsigned long height_to_maxindex[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 {
    int nr;
    struct radix_tree_node *nodes[RADIX_TREE_PRELOAD_SIZE];
};
static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };

static inline void *ptr_to_indirect(void *ptr)
{
    return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR);
}

static inline void *indirect_to_ptr(void *ptr)
{
    return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
}

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 int 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 unsigned)root->gfp_mask & (1 << (tag + __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)
{
    int idx;
    for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
        if (node->tags[tag][idx])
            return 1;
    }
    return 0;
}

static __always_inline unsigned long
radix_tree_find_next_bit(const unsigned long *addr,
             unsigned long size, unsigned long offset)
{
    if (!__builtin_constant_p(size))
        return find_next_bit(addr, size, offset);

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

/*
 * 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 *ret = NULL;
    gfp_t gfp_mask = root_gfp_mask(root);

    if (!(gfp_mask & __GFP_WAIT)) {
        struct radix_tree_preload *rtp;

        /*
         * Provided the caller has preloaded here, we will always
         * succeed in getting a node here (and never reach
         * kmem_cache_alloc)
         */
        rtp = &__get_cpu_var(radix_tree_preloads);
        if (rtp->nr) {
            ret = rtp->nodes[rtp->nr - 1];
            rtp->nodes[rtp->nr - 1] = NULL;
            rtp->nr--;
        }
    }
    if (ret == NULL)
        ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);

    BUG_ON(radix_tree_is_indirect_ptr(ret));
    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);
    int i;

    /*
     * must only free zeroed nodes into the slab. radix_tree_shrink
     * can leave us with a non-NULL entry in the first slot, so clear
     * that here to make sure.
     */
    for (i = 0; i < RADIX_TREE_MAX_TAGS; i++)
        tag_clear(node, i, 0);

    node->slots[0] = NULL;
    node->count = 0;

    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_WAIT being passed to INIT_RADIX_TREE().
 */
int radix_tree_preload(gfp_t gfp_mask)
{
    struct radix_tree_preload *rtp;
    struct radix_tree_node *node;
    int ret = -ENOMEM;

    preempt_disable();
    rtp = &__get_cpu_var(radix_tree_preloads);
    while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {
        preempt_enable();
        node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
        if (node == NULL)
            goto out;
        preempt_disable();
        rtp = &__get_cpu_var(radix_tree_preloads);
        if (rtp->nr < ARRAY_SIZE(rtp->nodes))
            rtp->nodes[rtp->nr++] = node;
        else
            kmem_cache_free(radix_tree_node_cachep, node);
    }
    ret = 0;
out:
    return ret;
}
EXPORT_SYMBOL(radix_tree_preload);

/*
 *  Return the maximum key which can be store into a
 *  radix tree with height HEIGHT.
 */
static inline unsigned long radix_tree_maxindex(unsigned int height)
{
    return height_to_maxindex[height];
}

/*
 *  Extend a radix tree so it can store key @index.
 */
static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
{
    struct radix_tree_node *node;
    struct radix_tree_node *slot;
    unsigned int height;
    int tag;

    /* Figure out what the height should be.  */
    height = root->height + 1;
    while (index > radix_tree_maxindex(height))
        height++;

    if (root->rnode == NULL) {
        root->height = height;
        goto out;
    }

    do {
        unsigned int newheight;
        if (!(node = radix_tree_node_alloc(root)))
            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);
        }

        /* Increase the height.  */
        newheight = root->height+1;
        node->height = newheight;
        node->count = 1;
        node->parent = NULL;
        slot = root->rnode;
        if (newheight > 1) {
            slot = indirect_to_ptr(slot);
            slot->parent = node;
        }
        node->slots[0] = slot;
        node = ptr_to_indirect(node);
        rcu_assign_pointer(root->rnode, node);
        root->height = newheight;
    } while (height > root->height);
out:
    return 0;
}

int radix_tree_insert(struct radix_tree_root *root,
            unsigned long index, void *item)
{
    struct radix_tree_node *node = NULL, *slot;
    unsigned int height, shift;
    int offset;
    int error;

    BUG_ON(radix_tree_is_indirect_ptr(item));

    /* Make sure the tree is high enough.  */
    if (index > radix_tree_maxindex(root->height)) {
        error = radix_tree_extend(root, index);
        if (error)
            return error;
    }

    slot = indirect_to_ptr(root->rnode);

    height = root->height;
    shift = (height-1) * RADIX_TREE_MAP_SHIFT;

    offset = 0;         /* uninitialised var warning */
    while (height > 0) {
        if (slot == NULL) {
            /* Have to add a child node.  */
            if (!(slot = radix_tree_node_alloc(root)))
                return -ENOMEM;
            slot->height = height;
            slot->parent = node;
            if (node) {
                rcu_assign_pointer(node->slots[offset], slot);
                node->count++;
            } else
                rcu_assign_pointer(root->rnode, ptr_to_indirect(slot));
        }

        /* Go a level down */
        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
        node = slot;
        slot = node->slots[offset];
        shift -= RADIX_TREE_MAP_SHIFT;
        height--;
    }

    if (slot != NULL)
        return -EEXIST;

    if (node) {
        node->count++;
        rcu_assign_pointer(node->slots[offset], item);
        BUG_ON(tag_get(node, 0, offset));
        BUG_ON(tag_get(node, 1, offset));
    } else {
        rcu_assign_pointer(root->rnode, item);
        BUG_ON(root_tag_get(root, 0));
        BUG_ON(root_tag_get(root, 1));
    }

    return 0;
}
EXPORT_SYMBOL(radix_tree_insert);

/*
 * is_slot == 1 : search for the slot.
 * is_slot == 0 : search for the node.
 */
static void *radix_tree_lookup_element(struct radix_tree_root *root,
                unsigned long index, int is_slot)
{
    unsigned int height, shift;
    struct radix_tree_node *node, **slot;

    node = rcu_dereference_raw(root->rnode);
    if (node == NULL)
        return NULL;

    if (!radix_tree_is_indirect_ptr(node)) {
        if (index > 0)
            return NULL;
        return is_slot ? (void *)&root->rnode : node;
    }
    node = indirect_to_ptr(node);

    height = node->height;
    if (index > radix_tree_maxindex(height))
        return NULL;

    shift = (height-1) * RADIX_TREE_MAP_SHIFT;

    do {
        slot = (struct radix_tree_node **)
            (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
        node = rcu_dereference_raw(*slot);
        if (node == NULL)
            return NULL;

        shift -= RADIX_TREE_MAP_SHIFT;
        height--;
    } while (height > 0);

    return is_slot ? (void *)slot : indirect_to_ptr(node);
}

void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
{
    return (void **)radix_tree_lookup_element(root, index, 1);
}
EXPORT_SYMBOL(radix_tree_lookup_slot);

void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
{
    return radix_tree_lookup_element(root, index, 0);
}
EXPORT_SYMBOL(radix_tree_lookup);

void *radix_tree_tag_set(struct radix_tree_root *root,
            unsigned long index, unsigned int tag)
{
    unsigned int height, shift;
    struct radix_tree_node *slot;

    height = root->height;
    BUG_ON(index > radix_tree_maxindex(height));

    slot = indirect_to_ptr(root->rnode);
    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;

    while (height > 0) {
        int offset;

        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
        if (!tag_get(slot, tag, offset))
            tag_set(slot, tag, offset);
        slot = slot->slots[offset];
        BUG_ON(slot == NULL);
        shift -= RADIX_TREE_MAP_SHIFT;
        height--;
    }

    /* set the root's tag bit */
    if (slot && !root_tag_get(root, tag))
        root_tag_set(root, tag);

    return slot;
}
EXPORT_SYMBOL(radix_tree_tag_set);

void *radix_tree_tag_clear(struct radix_tree_root *root,
            unsigned long index, unsigned int tag)
{
    struct radix_tree_node *node = NULL;
    struct radix_tree_node *slot = NULL;
    unsigned int height, shift;
    int uninitialized_var(offset);

    height = root->height;
    if (index > radix_tree_maxindex(height))
        goto out;

    shift = height * RADIX_TREE_MAP_SHIFT;
    slot = indirect_to_ptr(root->rnode);

    while (shift) {
        if (slot == NULL)
            goto out;

        shift -= RADIX_TREE_MAP_SHIFT;
        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
        node = slot;
        slot = slot->slots[offset];
    }

    if (slot == NULL)
        goto out;

    while (node) {
        if (!tag_get(node, tag, offset))
            goto out;
        tag_clear(node, tag, offset);
        if (any_tag_set(node, tag))
            goto out;

        index >>= RADIX_TREE_MAP_SHIFT;
        offset = index & RADIX_TREE_MAP_MASK;
        node = node->parent;
    }

    /* clear the root's tag bit */
    if (root_tag_get(root, tag))
        root_tag_clear(root, tag);

out:
    return slot;
}
EXPORT_SYMBOL(radix_tree_tag_clear);

int radix_tree_tag_get(struct radix_tree_root *root,
            unsigned long index, unsigned int tag)
{
    unsigned int height, shift;
    struct radix_tree_node *node;

    /* check the root's tag bit */
    if (!root_tag_get(root, tag))
        return 0;

    node = rcu_dereference_raw(root->rnode);
    if (node == NULL)
        return 0;

    if (!radix_tree_is_indirect_ptr(node))
        return (index == 0);
    node = indirect_to_ptr(node);

    height = node->height;
    if (index > radix_tree_maxindex(height))
        return 0;

    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;

    for ( ; ; ) {
        int offset;

        if (node == NULL)
            return 0;

        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
        if (!tag_get(node, tag, offset))
            return 0;
        if (height == 1)
            return 1;
        node = rcu_dereference_raw(node->slots[offset]);
        shift -= RADIX_TREE_MAP_SHIFT;
        height--;
    }
}
EXPORT_SYMBOL(radix_tree_tag_get);

void **radix_tree_next_chunk(struct radix_tree_root *root,
                 struct radix_tree_iter *iter, unsigned flags)
{
    unsigned shift, tag = flags & RADIX_TREE_ITER_TAG_MASK;
    struct radix_tree_node *rnode, *node;
    unsigned long index, offset;

    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 swithing to the next chunk.
     */
    index = iter->next_index;
    if (!index && iter->index)
        return NULL;

    rnode = rcu_dereference_raw(root->rnode);
    if (radix_tree_is_indirect_ptr(rnode)) {
        rnode = indirect_to_ptr(rnode);
    } else if (rnode && !index) {
        /* Single-slot tree */
        iter->index = 0;
        iter->next_index = 1;
        iter->tags = 1;
        return (void **)&root->rnode;
    } else
        return NULL;

restart:
    shift = (rnode->height - 1) * RADIX_TREE_MAP_SHIFT;
    offset = index >> shift;

    /* Index outside of the tree */
    if (offset >= RADIX_TREE_MAP_SIZE)
        return NULL;

    node = rnode;
    while (1) {
        if ((flags & RADIX_TREE_ITER_TAGGED) ?
                !test_bit(offset, node->tags[tag]) :
                !node->slots[offset]) {
            /* Hole detected */
            if (flags & RADIX_TREE_ITER_CONTIG)
                return NULL;

            if (flags & RADIX_TREE_ITER_TAGGED)
                offset = radix_tree_find_next_bit(
                        node->tags[tag],
                        RADIX_TREE_MAP_SIZE,
                        offset + 1);
            else
                while (++offset < RADIX_TREE_MAP_SIZE) {
                    if (node->slots[offset])
                        break;
                }
            index &= ~((RADIX_TREE_MAP_SIZE << shift) - 1);
            index += offset << shift;
            /* Overflow after ~0UL */
            if (!index)
                return NULL;
            if (offset == RADIX_TREE_MAP_SIZE)
                goto restart;
        }

        /* This is leaf-node */
        if (!shift)
            break;

        node = rcu_dereference_raw(node->slots[offset]);
        if (node == NULL)
            goto restart;
        shift -= RADIX_TREE_MAP_SHIFT;
        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
    }

    /* Update the iterator state */
    iter->index = index;
    iter->next_index = (index | RADIX_TREE_MAP_MASK) + 1;

    /* Construct iter->tags bit-mask from node->tags[tag] array */
    if (flags & RADIX_TREE_ITER_TAGGED) {
        unsigned tag_long, tag_bit;

        tag_long = offset / BITS_PER_LONG;
        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 = index + BITS_PER_LONG;
        }
    }

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

unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
        unsigned long *first_indexp, unsigned long last_index,
        unsigned long nr_to_tag,
        unsigned int iftag, unsigned int settag)
{
    unsigned int height = root->height;
    struct radix_tree_node *node = NULL;
    struct radix_tree_node *slot;
    unsigned int shift;
    unsigned long tagged = 0;
    unsigned long index = *first_indexp;

    last_index = min(last_index, radix_tree_maxindex(height));
    if (index > last_index)
        return 0;
    if (!nr_to_tag)
        return 0;
    if (!root_tag_get(root, iftag)) {
        *first_indexp = last_index + 1;
        return 0;
    }
    if (height == 0) {
        *first_indexp = last_index + 1;
        root_tag_set(root, settag);
        return 1;
    }

    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
    slot = indirect_to_ptr(root->rnode);

    for (;;) {
        unsigned long upindex;
        int offset;

        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
        if (!slot->slots[offset])
            goto next;
        if (!tag_get(slot, iftag, offset))
            goto next;
        if (shift) {
            /* Go down one level */
            shift -= RADIX_TREE_MAP_SHIFT;
            node = slot;
            slot = slot->slots[offset];
            continue;
        }

        /* tag the leaf */
        tagged++;
        tag_set(slot, settag, offset);

        /* walk back up the path tagging interior nodes */
        upindex = index;
        while (node) {
            upindex >>= RADIX_TREE_MAP_SHIFT;
            offset = upindex & RADIX_TREE_MAP_MASK;

            /* stop if we find a node with the tag already set */
            if (tag_get(node, settag, offset))
                break;
            tag_set(node, settag, offset);
            node = node->parent;
        }

        /*
         * Small optimization: now clear that node pointer.
         * Since all of this slot's ancestors now have the tag set
         * from setting it above, we have no further need to walk
         * back up the tree setting tags, until we update slot to
         * point to another radix_tree_node.
         */
        node = NULL;

next:
        /* Go to next item at level determined by 'shift' */
        index = ((index >> shift) + 1) << shift;
        /* Overflow can happen when last_index is ~0UL... */
        if (index > last_index || !index)
            break;
        if (tagged >= nr_to_tag)
            break;
        while (((index >> shift) & RADIX_TREE_MAP_MASK) == 0) {
            /*
             * We've fully scanned this node. Go up. Because
             * last_index is guaranteed to be in the tree, what
             * we do below cannot wander astray.
             */
            slot = slot->parent;
            shift += RADIX_TREE_MAP_SHIFT;
        }
    }
    /*
     * We need not to tag the root tag if there is no tag which is set with
     * settag within the range from *first_indexp to last_index.
     */
    if (tagged > 0)
        root_tag_set(root, settag);
    *first_indexp = index;

    return tagged;
}
EXPORT_SYMBOL(radix_tree_range_tag_if_tagged);


unsigned long radix_tree_next_hole(struct radix_tree_root *root,
                unsigned long index, unsigned long max_scan)
{
    unsigned long i;

    for (i = 0; i < max_scan; i++) {
        if (!radix_tree_lookup(root, index))
            break;
        index++;
        if (index == 0)
            break;
    }

    return index;
}
EXPORT_SYMBOL(radix_tree_next_hole);

unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
                   unsigned long index, unsigned long max_scan)
{
    unsigned long i;

    for (i = 0; i < max_scan; i++) {
        if (!radix_tree_lookup(root, index))
            break;
        index--;
        if (index == ULONG_MAX)
            break;
    }

    return index;
}
EXPORT_SYMBOL(radix_tree_prev_hole);

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] = indirect_to_ptr(rcu_dereference_raw(*slot));
        if (!results[ret])
            continue;
        if (++ret == max_items)
            break;
    }

    return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup);

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);

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] = indirect_to_ptr(rcu_dereference_raw(*slot));
        if (!results[ret])
            continue;
        if (++ret == max_items)
            break;
    }

    return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup_tag);

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);

#if defined(CONFIG_SHMEM) && defined(CONFIG_SWAP)
#include <linux/sched.h> /* for cond_resched() */

/*
 * This linear search is at present only useful to shmem_unuse_inode().
 */
static unsigned long __locate(struct radix_tree_node *slot, void *item,
                  unsigned long index, unsigned long *found_index)
{
    unsigned int shift, height;
    unsigned long i;

    height = slot->height;
    shift = (height-1) * RADIX_TREE_MAP_SHIFT;

    for ( ; height > 1; height--) {
        i = (index >> shift) & RADIX_TREE_MAP_MASK;
        for (;;) {
            if (slot->slots[i] != NULL)
                break;
            index &= ~((1UL << shift) - 1);
            index += 1UL << shift;
            if (index == 0)
                goto out;   /* 32-bit wraparound */
            i++;
            if (i == RADIX_TREE_MAP_SIZE)
                goto out;
        }

        shift -= RADIX_TREE_MAP_SHIFT;
        slot = rcu_dereference_raw(slot->slots[i]);
        if (slot == NULL)
            goto out;
    }

    /* Bottom level: check items */
    for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
        if (slot->slots[i] == item) {
            *found_index = index + i;
            index = 0;
            goto out;
        }
    }
    index += RADIX_TREE_MAP_SIZE;
out:
    return index;
}

unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
{
    struct radix_tree_node *node;
    unsigned long max_index;
    unsigned long cur_index = 0;
    unsigned long found_index = -1;

    do {
        rcu_read_lock();
        node = rcu_dereference_raw(root->rnode);
        if (!radix_tree_is_indirect_ptr(node)) {
            rcu_read_unlock();
            if (node == item)
                found_index = 0;
            break;
        }

        node = indirect_to_ptr(node);
        max_index = radix_tree_maxindex(node->height);
        if (cur_index > max_index)
            break;

        cur_index = __locate(node, item, cur_index, &found_index);
        rcu_read_unlock();
        cond_resched();
    } while (cur_index != 0 && cur_index <= max_index);

    return found_index;
}
#else
unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
{
    return -1;
}
#endif /* CONFIG_SHMEM && CONFIG_SWAP */

static inline void radix_tree_shrink(struct radix_tree_root *root)
{
    /* try to shrink tree height */
    while (root->height > 0) {
        struct radix_tree_node *to_free = root->rnode;
        struct radix_tree_node *slot;

        BUG_ON(!radix_tree_is_indirect_ptr(to_free));
        to_free = indirect_to_ptr(to_free);

        /*
         * The candidate node has more than one child, or its child
         * is not at the leftmost slot, we cannot shrink.
         */
        if (to_free->count != 1)
            break;
        if (!to_free->slots[0])
            break;

        /*
         * 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
         * (to_free->slots[0]), it will be safe to dereference the new
         * one (root->rnode) as far as dependent read barriers go.
         */
        slot = to_free->slots[0];
        if (root->height > 1) {
            slot->parent = NULL;
            slot = ptr_to_indirect(slot);
        }
        root->rnode = slot;
        root->height--;

        /*
         * 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 is 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.
         */
        if (root->height == 0)
            *((unsigned long *)&to_free->slots[0]) |=
                        RADIX_TREE_INDIRECT_PTR;

        radix_tree_node_free(to_free);
    }
}

void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
{
    struct radix_tree_node *node = NULL;
    struct radix_tree_node *slot = NULL;
    struct radix_tree_node *to_free;
    unsigned int height, shift;
    int tag;
    int uninitialized_var(offset);

    height = root->height;
    if (index > radix_tree_maxindex(height))
        goto out;

    slot = root->rnode;
    if (height == 0) {
        root_tag_clear_all(root);
        root->rnode = NULL;
        goto out;
    }
    slot = indirect_to_ptr(slot);
    shift = height * RADIX_TREE_MAP_SHIFT;

    do {
        if (slot == NULL)
            goto out;

        shift -= RADIX_TREE_MAP_SHIFT;
        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
        node = slot;
        slot = slot->slots[offset];
    } while (shift);

    if (slot == NULL)
        goto out;

    /*
     * Clear all tags associated with the item to be deleted.
     * This way of doing it would be inefficient, but seldom is any set.
     */
    for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
        if (tag_get(node, tag, offset))
            radix_tree_tag_clear(root, index, tag);
    }

    to_free = NULL;
    /* Now free the nodes we do not need anymore */
    while (node) {
        node->slots[offset] = NULL;
        node->count--;
        /*
         * Queue the node for deferred freeing after the
         * last reference to it disappears (set NULL, above).
         */
        if (to_free)
            radix_tree_node_free(to_free);

        if (node->count) {
            if (node == indirect_to_ptr(root->rnode))
                radix_tree_shrink(root);
            goto out;
        }

        /* Node with zero slots in use so free it */
        to_free = node;

        index >>= RADIX_TREE_MAP_SHIFT;
        offset = index & RADIX_TREE_MAP_MASK;
        node = node->parent;
    }

    root_tag_clear_all(root);
    root->height = 0;
    root->rnode = NULL;
    if (to_free)
        radix_tree_node_free(to_free);

out:
    return slot;
}
EXPORT_SYMBOL(radix_tree_delete);

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 *node)
{
    memset(node, 0, sizeof(struct radix_tree_node));
}

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_maxindex(void)
{
    unsigned int i;

    for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
        height_to_maxindex[i] = __maxindex(i);
}

static int radix_tree_callback(struct notifier_block *nfb,
                            unsigned long action,
                            void *hcpu)
{
       int cpu = (long)hcpu;
       struct radix_tree_preload *rtp;

       /* Free per-cpu pool of perloaded nodes */
       if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
               rtp = &per_cpu(radix_tree_preloads, cpu);
               while (rtp->nr) {
                       kmem_cache_free(radix_tree_node_cachep,
                                       rtp->nodes[rtp->nr-1]);
                       rtp->nodes[rtp->nr-1] = NULL;
                       rtp->nr--;
               }
       }
       return NOTIFY_OK;
}

void __init radix_tree_init(void)
{
    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_maxindex();
    hotcpu_notifier(radix_tree_callback, 0);
}