Merge tag 'for-linus-2020-03-07' of gitolite.kernel.org:pub/scm/linux/kernel/git...

[linux-2.6-microblaze.git] / lib / xarray.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * XArray implementation
 * Copyright (c) 2017-2018 Microsoft Corporation
 * Copyright (c) 2018-2020 Oracle
 * Author: Matthew Wilcox <willy@infradead.org>
 */

#include <linux/bitmap.h>
#include <linux/export.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/xarray.h>

/*
 * Coding conventions in this file:
 *
 * @xa is used to refer to the entire xarray.
 * @xas is the 'xarray operation state'.  It may be either a pointer to
 * an xa_state, or an xa_state stored on the stack.  This is an unfortunate
 * ambiguity.
 * @index is the index of the entry being operated on
 * @mark is an xa_mark_t; a small number indicating one of the mark bits.
 * @node refers to an xa_node; usually the primary one being operated on by
 * this function.
 * @offset is the index into the slots array inside an xa_node.
 * @parent refers to the @xa_node closer to the head than @node.
 * @entry refers to something stored in a slot in the xarray
 */

static inline unsigned int xa_lock_type(const struct xarray *xa)
{
        return (__force unsigned int)xa->xa_flags & 3;
}

static inline void xas_lock_type(struct xa_state *xas, unsigned int lock_type)
{
        if (lock_type == XA_LOCK_IRQ)
                xas_lock_irq(xas);
        else if (lock_type == XA_LOCK_BH)
                xas_lock_bh(xas);
        else
                xas_lock(xas);
}

static inline void xas_unlock_type(struct xa_state *xas, unsigned int lock_type)
{
        if (lock_type == XA_LOCK_IRQ)
                xas_unlock_irq(xas);
        else if (lock_type == XA_LOCK_BH)
                xas_unlock_bh(xas);
        else
                xas_unlock(xas);
}

static inline bool xa_track_free(const struct xarray *xa)
{
        return xa->xa_flags & XA_FLAGS_TRACK_FREE;
}

static inline bool xa_zero_busy(const struct xarray *xa)
{
        return xa->xa_flags & XA_FLAGS_ZERO_BUSY;
}

static inline void xa_mark_set(struct xarray *xa, xa_mark_t mark)
{
        if (!(xa->xa_flags & XA_FLAGS_MARK(mark)))
                xa->xa_flags |= XA_FLAGS_MARK(mark);
}

static inline void xa_mark_clear(struct xarray *xa, xa_mark_t mark)
{
        if (xa->xa_flags & XA_FLAGS_MARK(mark))
                xa->xa_flags &= ~(XA_FLAGS_MARK(mark));
}

static inline unsigned long *node_marks(struct xa_node *node, xa_mark_t mark)
{
        return node->marks[(__force unsigned)mark];
}

static inline bool node_get_mark(struct xa_node *node,
                unsigned int offset, xa_mark_t mark)
{
        return test_bit(offset, node_marks(node, mark));
}

/* returns true if the bit was set */
static inline bool node_set_mark(struct xa_node *node, unsigned int offset,
                                xa_mark_t mark)
{
        return __test_and_set_bit(offset, node_marks(node, mark));
}

/* returns true if the bit was set */
static inline bool node_clear_mark(struct xa_node *node, unsigned int offset,
                                xa_mark_t mark)
{
        return __test_and_clear_bit(offset, node_marks(node, mark));
}

static inline bool node_any_mark(struct xa_node *node, xa_mark_t mark)
{
        return !bitmap_empty(node_marks(node, mark), XA_CHUNK_SIZE);
}

static inline void node_mark_all(struct xa_node *node, xa_mark_t mark)
{
        bitmap_fill(node_marks(node, mark), XA_CHUNK_SIZE);
}

#define mark_inc(mark) do { \
        mark = (__force xa_mark_t)((__force unsigned)(mark) + 1); \
} while (0)

/*
 * xas_squash_marks() - Merge all marks to the first entry
 * @xas: Array operation state.
 *
 * Set a mark on the first entry if any entry has it set.  Clear marks on
 * all sibling entries.
 */
static void xas_squash_marks(const struct xa_state *xas)
{
        unsigned int mark = 0;
        unsigned int limit = xas->xa_offset + xas->xa_sibs + 1;

        if (!xas->xa_sibs)
                return;

        do {
                unsigned long *marks = xas->xa_node->marks[mark];
                if (find_next_bit(marks, limit, xas->xa_offset + 1) == limit)
                        continue;
                __set_bit(xas->xa_offset, marks);
                bitmap_clear(marks, xas->xa_offset + 1, xas->xa_sibs);
        } while (mark++ != (__force unsigned)XA_MARK_MAX);
}

/* extracts the offset within this node from the index */
static unsigned int get_offset(unsigned long index, struct xa_node *node)
{
        return (index >> node->shift) & XA_CHUNK_MASK;
}

static void xas_set_offset(struct xa_state *xas)
{
        xas->xa_offset = get_offset(xas->xa_index, xas->xa_node);
}

/* move the index either forwards (find) or backwards (sibling slot) */
static void xas_move_index(struct xa_state *xas, unsigned long offset)
{
        unsigned int shift = xas->xa_node->shift;
        xas->xa_index &= ~XA_CHUNK_MASK << shift;
        xas->xa_index += offset << shift;
}

static void xas_advance(struct xa_state *xas)
{
        xas->xa_offset++;
        xas_move_index(xas, xas->xa_offset);
}

static void *set_bounds(struct xa_state *xas)
{
        xas->xa_node = XAS_BOUNDS;
        return NULL;
}

/*
 * Starts a walk.  If the @xas is already valid, we assume that it's on
 * the right path and just return where we've got to.  If we're in an
 * error state, return NULL.  If the index is outside the current scope
 * of the xarray, return NULL without changing @xas->xa_node.  Otherwise
 * set @xas->xa_node to NULL and return the current head of the array.
 */
static void *xas_start(struct xa_state *xas)
{
        void *entry;

        if (xas_valid(xas))
                return xas_reload(xas);
        if (xas_error(xas))
                return NULL;

        entry = xa_head(xas->xa);
        if (!xa_is_node(entry)) {
                if (xas->xa_index)
                        return set_bounds(xas);
        } else {
                if ((xas->xa_index >> xa_to_node(entry)->shift) > XA_CHUNK_MASK)
                        return set_bounds(xas);
        }

        xas->xa_node = NULL;
        return entry;
}

static void *xas_descend(struct xa_state *xas, struct xa_node *node)
{
        unsigned int offset = get_offset(xas->xa_index, node);
        void *entry = xa_entry(xas->xa, node, offset);

        xas->xa_node = node;
        if (xa_is_sibling(entry)) {
                offset = xa_to_sibling(entry);
                entry = xa_entry(xas->xa, node, offset);
        }

        xas->xa_offset = offset;
        return entry;
}

/**
 * xas_load() - Load an entry from the XArray (advanced).
 * @xas: XArray operation state.
 *
 * Usually walks the @xas to the appropriate state to load the entry
 * stored at xa_index.  However, it will do nothing and return %NULL if
 * @xas is in an error state.  xas_load() will never expand the tree.
 *
 * If the xa_state is set up to operate on a multi-index entry, xas_load()
 * may return %NULL or an internal entry, even if there are entries
 * present within the range specified by @xas.
 *
 * Context: Any context.  The caller should hold the xa_lock or the RCU lock.
 * Return: Usually an entry in the XArray, but see description for exceptions.
 */
void *xas_load(struct xa_state *xas)
{
        void *entry = xas_start(xas);

        while (xa_is_node(entry)) {
                struct xa_node *node = xa_to_node(entry);

                if (xas->xa_shift > node->shift)
                        break;
                entry = xas_descend(xas, node);
                if (node->shift == 0)
                        break;
        }
        return entry;
}
EXPORT_SYMBOL_GPL(xas_load);

/* Move the radix tree node cache here */
extern struct kmem_cache *radix_tree_node_cachep;
extern void radix_tree_node_rcu_free(struct rcu_head *head);

#define XA_RCU_FREE     ((struct xarray *)1)

static void xa_node_free(struct xa_node *node)
{
        XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
        node->array = XA_RCU_FREE;
        call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
}

/*
 * xas_destroy() - Free any resources allocated during the XArray operation.
 * @xas: XArray operation state.
 *
 * This function is now internal-only.
 */
static void xas_destroy(struct xa_state *xas)
{
        struct xa_node *node = xas->xa_alloc;

        if (!node)
                return;
        XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
        kmem_cache_free(radix_tree_node_cachep, node);
        xas->xa_alloc = NULL;
}

/**
 * xas_nomem() - Allocate memory if needed.
 * @xas: XArray operation state.
 * @gfp: Memory allocation flags.
 *
 * If we need to add new nodes to the XArray, we try to allocate memory
 * with GFP_NOWAIT while holding the lock, which will usually succeed.
 * If it fails, @xas is flagged as needing memory to continue.  The caller
 * should drop the lock and call xas_nomem().  If xas_nomem() succeeds,
 * the caller should retry the operation.
 *
 * Forward progress is guaranteed as one node is allocated here and
 * stored in the xa_state where it will be found by xas_alloc().  More
 * nodes will likely be found in the slab allocator, but we do not tie
 * them up here.
 *
 * Return: true if memory was needed, and was successfully allocated.
 */
bool xas_nomem(struct xa_state *xas, gfp_t gfp)
{
        if (xas->xa_node != XA_ERROR(-ENOMEM)) {
                xas_destroy(xas);
                return false;
        }
        if (xas->xa->xa_flags & XA_FLAGS_ACCOUNT)
                gfp |= __GFP_ACCOUNT;
        xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp);
        if (!xas->xa_alloc)
                return false;
        XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
        xas->xa_node = XAS_RESTART;
        return true;
}
EXPORT_SYMBOL_GPL(xas_nomem);

/*
 * __xas_nomem() - Drop locks and allocate memory if needed.
 * @xas: XArray operation state.
 * @gfp: Memory allocation flags.
 *
 * Internal variant of xas_nomem().
 *
 * Return: true if memory was needed, and was successfully allocated.
 */
static bool __xas_nomem(struct xa_state *xas, gfp_t gfp)
        __must_hold(xas->xa->xa_lock)
{
        unsigned int lock_type = xa_lock_type(xas->xa);

        if (xas->xa_node != XA_ERROR(-ENOMEM)) {
                xas_destroy(xas);
                return false;
        }
        if (xas->xa->xa_flags & XA_FLAGS_ACCOUNT)
                gfp |= __GFP_ACCOUNT;
        if (gfpflags_allow_blocking(gfp)) {
                xas_unlock_type(xas, lock_type);
                xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp);
                xas_lock_type(xas, lock_type);
        } else {
                xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp);
        }
        if (!xas->xa_alloc)
                return false;
        XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
        xas->xa_node = XAS_RESTART;
        return true;
}

static void xas_update(struct xa_state *xas, struct xa_node *node)
{
        if (xas->xa_update)
                xas->xa_update(node);
        else
                XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
}

static void *xas_alloc(struct xa_state *xas, unsigned int shift)
{
        struct xa_node *parent = xas->xa_node;
        struct xa_node *node = xas->xa_alloc;

        if (xas_invalid(xas))
                return NULL;

        if (node) {
                xas->xa_alloc = NULL;
        } else {
                gfp_t gfp = GFP_NOWAIT | __GFP_NOWARN;

                if (xas->xa->xa_flags & XA_FLAGS_ACCOUNT)
                        gfp |= __GFP_ACCOUNT;

                node = kmem_cache_alloc(radix_tree_node_cachep, gfp);
                if (!node) {
                        xas_set_err(xas, -ENOMEM);
                        return NULL;
                }
        }

        if (parent) {
                node->offset = xas->xa_offset;
                parent->count++;
                XA_NODE_BUG_ON(node, parent->count > XA_CHUNK_SIZE);
                xas_update(xas, parent);
        }
        XA_NODE_BUG_ON(node, shift > BITS_PER_LONG);
        XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
        node->shift = shift;
        node->count = 0;
        node->nr_values = 0;
        RCU_INIT_POINTER(node->parent, xas->xa_node);
        node->array = xas->xa;

        return node;
}

#ifdef CONFIG_XARRAY_MULTI
/* Returns the number of indices covered by a given xa_state */
static unsigned long xas_size(const struct xa_state *xas)
{
        return (xas->xa_sibs + 1UL) << xas->xa_shift;
}
#endif

/*
 * Use this to calculate the maximum index that will need to be created
 * in order to add the entry described by @xas.  Because we cannot store a
 * multiple-index entry at index 0, the calculation is a little more complex
 * than you might expect.
 */
static unsigned long xas_max(struct xa_state *xas)
{
        unsigned long max = xas->xa_index;

#ifdef CONFIG_XARRAY_MULTI
        if (xas->xa_shift || xas->xa_sibs) {
                unsigned long mask = xas_size(xas) - 1;
                max |= mask;
                if (mask == max)
                        max++;
        }
#endif

        return max;
}

/* The maximum index that can be contained in the array without expanding it */
static unsigned long max_index(void *entry)
{
        if (!xa_is_node(entry))
                return 0;
        return (XA_CHUNK_SIZE << xa_to_node(entry)->shift) - 1;
}

static void xas_shrink(struct xa_state *xas)
{
        struct xarray *xa = xas->xa;
        struct xa_node *node = xas->xa_node;

        for (;;) {
                void *entry;

                XA_NODE_BUG_ON(node, node->count > XA_CHUNK_SIZE);
                if (node->count != 1)
                        break;
                entry = xa_entry_locked(xa, node, 0);
                if (!entry)
                        break;
                if (!xa_is_node(entry) && node->shift)
                        break;
                if (xa_is_zero(entry) && xa_zero_busy(xa))
                        entry = NULL;
                xas->xa_node = XAS_BOUNDS;

                RCU_INIT_POINTER(xa->xa_head, entry);
                if (xa_track_free(xa) && !node_get_mark(node, 0, XA_FREE_MARK))
                        xa_mark_clear(xa, XA_FREE_MARK);

                node->count = 0;
                node->nr_values = 0;
                if (!xa_is_node(entry))
                        RCU_INIT_POINTER(node->slots[0], XA_RETRY_ENTRY);
                xas_update(xas, node);
                xa_node_free(node);
                if (!xa_is_node(entry))
                        break;
                node = xa_to_node(entry);
                node->parent = NULL;
        }
}

/*
 * xas_delete_node() - Attempt to delete an xa_node
 * @xas: Array operation state.
 *
 * Attempts to delete the @xas->xa_node.  This will fail if xa->node has
 * a non-zero reference count.
 */
static void xas_delete_node(struct xa_state *xas)
{
        struct xa_node *node = xas->xa_node;

        for (;;) {
                struct xa_node *parent;

                XA_NODE_BUG_ON(node, node->count > XA_CHUNK_SIZE);
                if (node->count)
                        break;

                parent = xa_parent_locked(xas->xa, node);
                xas->xa_node = parent;
                xas->xa_offset = node->offset;
                xa_node_free(node);

                if (!parent) {
                        xas->xa->xa_head = NULL;
                        xas->xa_node = XAS_BOUNDS;
                        return;
                }

                parent->slots[xas->xa_offset] = NULL;
                parent->count--;
                XA_NODE_BUG_ON(parent, parent->count > XA_CHUNK_SIZE);
                node = parent;
                xas_update(xas, node);
        }

        if (!node->parent)
                xas_shrink(xas);
}

/**
 * xas_free_nodes() - Free this node and all nodes that it references
 * @xas: Array operation state.
 * @top: Node to free
 *
 * This node has been removed from the tree.  We must now free it and all
 * of its subnodes.  There may be RCU walkers with references into the tree,
 * so we must replace all entries with retry markers.
 */
static void xas_free_nodes(struct xa_state *xas, struct xa_node *top)
{
        unsigned int offset = 0;
        struct xa_node *node = top;

        for (;;) {
                void *entry = xa_entry_locked(xas->xa, node, offset);

                if (node->shift && xa_is_node(entry)) {
                        node = xa_to_node(entry);
                        offset = 0;
                        continue;
                }
                if (entry)
                        RCU_INIT_POINTER(node->slots[offset], XA_RETRY_ENTRY);
                offset++;
                while (offset == XA_CHUNK_SIZE) {
                        struct xa_node *parent;

                        parent = xa_parent_locked(xas->xa, node);
                        offset = node->offset + 1;
                        node->count = 0;
                        node->nr_values = 0;
                        xas_update(xas, node);
                        xa_node_free(node);
                        if (node == top)
                                return;
                        node = parent;
                }
        }
}

/*
 * xas_expand adds nodes to the head of the tree until it has reached
 * sufficient height to be able to contain @xas->xa_index
 */
static int xas_expand(struct xa_state *xas, void *head)
{
        struct xarray *xa = xas->xa;
        struct xa_node *node = NULL;
        unsigned int shift = 0;
        unsigned long max = xas_max(xas);

        if (!head) {
                if (max == 0)
                        return 0;
                while ((max >> shift) >= XA_CHUNK_SIZE)
                        shift += XA_CHUNK_SHIFT;
                return shift + XA_CHUNK_SHIFT;
        } else if (xa_is_node(head)) {
                node = xa_to_node(head);
                shift = node->shift + XA_CHUNK_SHIFT;
        }
        xas->xa_node = NULL;

        while (max > max_index(head)) {
                xa_mark_t mark = 0;

                XA_NODE_BUG_ON(node, shift > BITS_PER_LONG);
                node = xas_alloc(xas, shift);
                if (!node)
                        return -ENOMEM;

                node->count = 1;
                if (xa_is_value(head))
                        node->nr_values = 1;
                RCU_INIT_POINTER(node->slots[0], head);

                /* Propagate the aggregated mark info to the new child */
                for (;;) {
                        if (xa_track_free(xa) && mark == XA_FREE_MARK) {
                                node_mark_all(node, XA_FREE_MARK);
                                if (!xa_marked(xa, XA_FREE_MARK)) {
                                        node_clear_mark(node, 0, XA_FREE_MARK);
                                        xa_mark_set(xa, XA_FREE_MARK);
                                }
                        } else if (xa_marked(xa, mark)) {
                                node_set_mark(node, 0, mark);
                        }
                        if (mark == XA_MARK_MAX)
                                break;
                        mark_inc(mark);
                }

                /*
                 * Now that the new node is fully initialised, we can add
                 * it to the tree
                 */
                if (xa_is_node(head)) {
                        xa_to_node(head)->offset = 0;
                        rcu_assign_pointer(xa_to_node(head)->parent, node);
                }
                head = xa_mk_node(node);
                rcu_assign_pointer(xa->xa_head, head);
                xas_update(xas, node);

                shift += XA_CHUNK_SHIFT;
        }

        xas->xa_node = node;
        return shift;
}

/*
 * xas_create() - Create a slot to store an entry in.
 * @xas: XArray operation state.
 * @allow_root: %true if we can store the entry in the root directly
 *
 * Most users will not need to call this function directly, as it is called
 * by xas_store().  It is useful for doing conditional store operations
 * (see the xa_cmpxchg() implementation for an example).
 *
 * Return: If the slot already existed, returns the contents of this slot.
 * If the slot was newly created, returns %NULL.  If it failed to create the
 * slot, returns %NULL and indicates the error in @xas.
 */
static void *xas_create(struct xa_state *xas, bool allow_root)
{
        struct xarray *xa = xas->xa;
        void *entry;
        void __rcu **slot;
        struct xa_node *node = xas->xa_node;
        int shift;
        unsigned int order = xas->xa_shift;

        if (xas_top(node)) {
                entry = xa_head_locked(xa);
                xas->xa_node = NULL;
                if (!entry && xa_zero_busy(xa))
                        entry = XA_ZERO_ENTRY;
                shift = xas_expand(xas, entry);
                if (shift < 0)
                        return NULL;
                if (!shift && !allow_root)
                        shift = XA_CHUNK_SHIFT;
                entry = xa_head_locked(xa);
                slot = &xa->xa_head;
        } else if (xas_error(xas)) {
                return NULL;
        } else if (node) {
                unsigned int offset = xas->xa_offset;

                shift = node->shift;
                entry = xa_entry_locked(xa, node, offset);
                slot = &node->slots[offset];
        } else {
                shift = 0;
                entry = xa_head_locked(xa);
                slot = &xa->xa_head;
        }

        while (shift > order) {
                shift -= XA_CHUNK_SHIFT;
                if (!entry) {
                        node = xas_alloc(xas, shift);
                        if (!node)
                                break;
                        if (xa_track_free(xa))
                                node_mark_all(node, XA_FREE_MARK);
                        rcu_assign_pointer(*slot, xa_mk_node(node));
                } else if (xa_is_node(entry)) {
                        node = xa_to_node(entry);
                } else {
                        break;
                }
                entry = xas_descend(xas, node);
                slot = &node->slots[xas->xa_offset];
        }

        return entry;
}

/**
 * xas_create_range() - Ensure that stores to this range will succeed
 * @xas: XArray operation state.
 *
 * Creates all of the slots in the range covered by @xas.  Sets @xas to
 * create single-index entries and positions it at the beginning of the
 * range.  This is for the benefit of users which have not yet been
 * converted to use multi-index entries.
 */
void xas_create_range(struct xa_state *xas)
{
        unsigned long index = xas->xa_index;
        unsigned char shift = xas->xa_shift;
        unsigned char sibs = xas->xa_sibs;

        xas->xa_index |= ((sibs + 1) << shift) - 1;
        if (xas_is_node(xas) && xas->xa_node->shift == xas->xa_shift)
                xas->xa_offset |= sibs;
        xas->xa_shift = 0;
        xas->xa_sibs = 0;

        for (;;) {
                xas_create(xas, true);
                if (xas_error(xas))
                        goto restore;
                if (xas->xa_index <= (index | XA_CHUNK_MASK))
                        goto success;
                xas->xa_index -= XA_CHUNK_SIZE;

                for (;;) {
                        struct xa_node *node = xas->xa_node;
                        xas->xa_node = xa_parent_locked(xas->xa, node);
                        xas->xa_offset = node->offset - 1;
                        if (node->offset != 0)
                                break;
                }
        }

restore:
        xas->xa_shift = shift;
        xas->xa_sibs = sibs;
        xas->xa_index = index;
        return;
success:
        xas->xa_index = index;
        if (xas->xa_node)
                xas_set_offset(xas);
}
EXPORT_SYMBOL_GPL(xas_create_range);

static void update_node(struct xa_state *xas, struct xa_node *node,
                int count, int values)
{
        if (!node || (!count && !values))
                return;

        node->count += count;
        node->nr_values += values;
        XA_NODE_BUG_ON(node, node->count > XA_CHUNK_SIZE);
        XA_NODE_BUG_ON(node, node->nr_values > XA_CHUNK_SIZE);
        xas_update(xas, node);
        if (count < 0)
                xas_delete_node(xas);
}

/**
 * xas_store() - Store this entry in the XArray.
 * @xas: XArray operation state.
 * @entry: New entry.
 *
 * If @xas is operating on a multi-index entry, the entry returned by this
 * function is essentially meaningless (it may be an internal entry or it
 * may be %NULL, even if there are non-NULL entries at some of the indices
 * covered by the range).  This is not a problem for any current users,
 * and can be changed if needed.
 *
 * Return: The old entry at this index.
 */
void *xas_store(struct xa_state *xas, void *entry)
{
        struct xa_node *node;
        void __rcu **slot = &xas->xa->xa_head;
        unsigned int offset, max;
        int count = 0;
        int values = 0;
        void *first, *next;
        bool value = xa_is_value(entry);

        if (entry) {
                bool allow_root = !xa_is_node(entry) && !xa_is_zero(entry);
                first = xas_create(xas, allow_root);
        } else {
                first = xas_load(xas);
        }

        if (xas_invalid(xas))
                return first;
        node = xas->xa_node;
        if (node && (xas->xa_shift < node->shift))
                xas->xa_sibs = 0;
        if ((first == entry) && !xas->xa_sibs)
                return first;

        next = first;
        offset = xas->xa_offset;
        max = xas->xa_offset + xas->xa_sibs;
        if (node) {
                slot = &node->slots[offset];
                if (xas->xa_sibs)
                        xas_squash_marks(xas);
        }
        if (!entry)
                xas_init_marks(xas);

        for (;;) {
                /*
                 * Must clear the marks before setting the entry to NULL,
                 * otherwise xas_for_each_marked may find a NULL entry and
                 * stop early.  rcu_assign_pointer contains a release barrier
                 * so the mark clearing will appear to happen before the
                 * entry is set to NULL.
                 */
                rcu_assign_pointer(*slot, entry);
                if (xa_is_node(next) && (!node || node->shift))
                        xas_free_nodes(xas, xa_to_node(next));
                if (!node)
                        break;
                count += !next - !entry;
                values += !xa_is_value(first) - !value;
                if (entry) {
                        if (offset == max)
                                break;
                        if (!xa_is_sibling(entry))
                                entry = xa_mk_sibling(xas->xa_offset);
                } else {
                        if (offset == XA_CHUNK_MASK)
                                break;
                }
                next = xa_entry_locked(xas->xa, node, ++offset);
                if (!xa_is_sibling(next)) {
                        if (!entry && (offset > max))
                                break;
                        first = next;
                }
                slot++;
        }

        update_node(xas, node, count, values);
        return first;
}
EXPORT_SYMBOL_GPL(xas_store);

/**
 * xas_get_mark() - Returns the state of this mark.
 * @xas: XArray operation state.
 * @mark: Mark number.
 *
 * Return: true if the mark is set, false if the mark is clear or @xas
 * is in an error state.
 */
bool xas_get_mark(const struct xa_state *xas, xa_mark_t mark)
{
        if (xas_invalid(xas))
                return false;
        if (!xas->xa_node)
                return xa_marked(xas->xa, mark);
        return node_get_mark(xas->xa_node, xas->xa_offset, mark);
}
EXPORT_SYMBOL_GPL(xas_get_mark);

/**
 * xas_set_mark() - Sets the mark on this entry and its parents.
 * @xas: XArray operation state.
 * @mark: Mark number.
 *
 * Sets the specified mark on this entry, and walks up the tree setting it
 * on all the ancestor entries.  Does nothing if @xas has not been walked to
 * an entry, or is in an error state.
 */
void xas_set_mark(const struct xa_state *xas, xa_mark_t mark)
{
        struct xa_node *node = xas->xa_node;
        unsigned int offset = xas->xa_offset;

        if (xas_invalid(xas))
                return;

        while (node) {
                if (node_set_mark(node, offset, mark))
                        return;
                offset = node->offset;
                node = xa_parent_locked(xas->xa, node);
        }

        if (!xa_marked(xas->xa, mark))
                xa_mark_set(xas->xa, mark);
}
EXPORT_SYMBOL_GPL(xas_set_mark);

/**
 * xas_clear_mark() - Clears the mark on this entry and its parents.
 * @xas: XArray operation state.
 * @mark: Mark number.
 *
 * Clears the specified mark on this entry, and walks back to the head
 * attempting to clear it on all the ancestor entries.  Does nothing if
 * @xas has not been walked to an entry, or is in an error state.
 */
void xas_clear_mark(const struct xa_state *xas, xa_mark_t mark)
{
        struct xa_node *node = xas->xa_node;
        unsigned int offset = xas->xa_offset;

        if (xas_invalid(xas))
                return;

        while (node) {
                if (!node_clear_mark(node, offset, mark))
                        return;
                if (node_any_mark(node, mark))
                        return;

                offset = node->offset;
                node = xa_parent_locked(xas->xa, node);
        }

        if (xa_marked(xas->xa, mark))
                xa_mark_clear(xas->xa, mark);
}
EXPORT_SYMBOL_GPL(xas_clear_mark);

/**
 * xas_init_marks() - Initialise all marks for the entry
 * @xas: Array operations state.
 *
 * Initialise all marks for the entry specified by @xas.  If we're tracking
 * free entries with a mark, we need to set it on all entries.  All other
 * marks are cleared.
 *
 * This implementation is not as efficient as it could be; we may walk
 * up the tree multiple times.
 */
void xas_init_marks(const struct xa_state *xas)
{
        xa_mark_t mark = 0;

        for (;;) {
                if (xa_track_free(xas->xa) && mark == XA_FREE_MARK)
                        xas_set_mark(xas, mark);
                else
                        xas_clear_mark(xas, mark);
                if (mark == XA_MARK_MAX)
                        break;
                mark_inc(mark);
        }
}
EXPORT_SYMBOL_GPL(xas_init_marks);

/**
 * xas_pause() - Pause a walk to drop a lock.
 * @xas: XArray operation state.
 *
 * Some users need to pause a walk and drop the lock they're holding in
 * order to yield to a higher priority thread or carry out an operation
 * on an entry.  Those users should call this function before they drop
 * the lock.  It resets the @xas to be suitable for the next iteration
 * of the loop after the user has reacquired the lock.  If most entries
 * found during a walk require you to call xas_pause(), the xa_for_each()
 * iterator may be more appropriate.
 *
 * Note that xas_pause() only works for forward iteration.  If a user needs
 * to pause a reverse iteration, we will need a xas_pause_rev().
 */
void xas_pause(struct xa_state *xas)
{
        struct xa_node *node = xas->xa_node;

        if (xas_invalid(xas))
                return;

        xas->xa_node = XAS_RESTART;
        if (node) {
                unsigned int offset = xas->xa_offset;
                while (++offset < XA_CHUNK_SIZE) {
                        if (!xa_is_sibling(xa_entry(xas->xa, node, offset)))
                                break;
                }
                xas->xa_index += (offset - xas->xa_offset) << node->shift;
                if (xas->xa_index == 0)
                        xas->xa_node = XAS_BOUNDS;
        } else {
                xas->xa_index++;
        }
}
EXPORT_SYMBOL_GPL(xas_pause);

/*
 * __xas_prev() - Find the previous entry in the XArray.
 * @xas: XArray operation state.
 *
 * Helper function for xas_prev() which handles all the complex cases
 * out of line.
 */
void *__xas_prev(struct xa_state *xas)
{
        void *entry;

        if (!xas_frozen(xas->xa_node))
                xas->xa_index--;
        if (!xas->xa_node)
                return set_bounds(xas);
        if (xas_not_node(xas->xa_node))
                return xas_load(xas);

        if (xas->xa_offset != get_offset(xas->xa_index, xas->xa_node))
                xas->xa_offset--;

        while (xas->xa_offset == 255) {
                xas->xa_offset = xas->xa_node->offset - 1;
                xas->xa_node = xa_parent(xas->xa, xas->xa_node);
                if (!xas->xa_node)
                        return set_bounds(xas);
        }

        for (;;) {
                entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
                if (!xa_is_node(entry))
                        return entry;

                xas->xa_node = xa_to_node(entry);
                xas_set_offset(xas);
        }
}
EXPORT_SYMBOL_GPL(__xas_prev);

/*
 * __xas_next() - Find the next entry in the XArray.
 * @xas: XArray operation state.
 *
 * Helper function for xas_next() which handles all the complex cases
 * out of line.
 */
void *__xas_next(struct xa_state *xas)
{
        void *entry;

        if (!xas_frozen(xas->xa_node))
                xas->xa_index++;
        if (!xas->xa_node)
                return set_bounds(xas);
        if (xas_not_node(xas->xa_node))
                return xas_load(xas);

        if (xas->xa_offset != get_offset(xas->xa_index, xas->xa_node))
                xas->xa_offset++;

        while (xas->xa_offset == XA_CHUNK_SIZE) {
                xas->xa_offset = xas->xa_node->offset + 1;
                xas->xa_node = xa_parent(xas->xa, xas->xa_node);
                if (!xas->xa_node)
                        return set_bounds(xas);
        }

        for (;;) {
                entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
                if (!xa_is_node(entry))
                        return entry;

                xas->xa_node = xa_to_node(entry);
                xas_set_offset(xas);
        }
}
EXPORT_SYMBOL_GPL(__xas_next);

/**
 * xas_find() - Find the next present entry in the XArray.
 * @xas: XArray operation state.
 * @max: Highest index to return.
 *
 * If the @xas has not yet been walked to an entry, return the entry
 * which has an index >= xas.xa_index.  If it has been walked, the entry
 * currently being pointed at has been processed, and so we move to the
 * next entry.
 *
 * If no entry is found and the array is smaller than @max, the iterator
 * is set to the smallest index not yet in the array.  This allows @xas
 * to be immediately passed to xas_store().
 *
 * Return: The entry, if found, otherwise %NULL.
 */
void *xas_find(struct xa_state *xas, unsigned long max)
{
        void *entry;

        if (xas_error(xas) || xas->xa_node == XAS_BOUNDS)
                return NULL;
        if (xas->xa_index > max)
                return set_bounds(xas);

        if (!xas->xa_node) {
                xas->xa_index = 1;
                return set_bounds(xas);
        } else if (xas->xa_node == XAS_RESTART) {
                entry = xas_load(xas);
                if (entry || xas_not_node(xas->xa_node))
                        return entry;
        } else if (!xas->xa_node->shift &&
                    xas->xa_offset != (xas->xa_index & XA_CHUNK_MASK)) {
                xas->xa_offset = ((xas->xa_index - 1) & XA_CHUNK_MASK) + 1;
        }

        xas_advance(xas);

        while (xas->xa_node && (xas->xa_index <= max)) {
                if (unlikely(xas->xa_offset == XA_CHUNK_SIZE)) {
                        xas->xa_offset = xas->xa_node->offset + 1;
                        xas->xa_node = xa_parent(xas->xa, xas->xa_node);
                        continue;
                }

                entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
                if (xa_is_node(entry)) {
                        xas->xa_node = xa_to_node(entry);
                        xas->xa_offset = 0;
                        continue;
                }
                if (entry && !xa_is_sibling(entry))
                        return entry;

                xas_advance(xas);
        }

        if (!xas->xa_node)
                xas->xa_node = XAS_BOUNDS;
        return NULL;
}
EXPORT_SYMBOL_GPL(xas_find);

/**
 * xas_find_marked() - Find the next marked entry in the XArray.
 * @xas: XArray operation state.
 * @max: Highest index to return.
 * @mark: Mark number to search for.
 *
 * If the @xas has not yet been walked to an entry, return the marked entry
 * which has an index >= xas.xa_index.  If it has been walked, the entry
 * currently being pointed at has been processed, and so we return the
 * first marked entry with an index > xas.xa_index.
 *
 * If no marked entry is found and the array is smaller than @max, @xas is
 * set to the bounds state and xas->xa_index is set to the smallest index
 * not yet in the array.  This allows @xas to be immediately passed to
 * xas_store().
 *
 * If no entry is found before @max is reached, @xas is set to the restart
 * state.
 *
 * Return: The entry, if found, otherwise %NULL.
 */
void *xas_find_marked(struct xa_state *xas, unsigned long max, xa_mark_t mark)
{
        bool advance = true;
        unsigned int offset;
        void *entry;

        if (xas_error(xas))
                return NULL;
        if (xas->xa_index > max)
                goto max;

        if (!xas->xa_node) {
                xas->xa_index = 1;
                goto out;
        } else if (xas_top(xas->xa_node)) {
                advance = false;
                entry = xa_head(xas->xa);
                xas->xa_node = NULL;
                if (xas->xa_index > max_index(entry))
                        goto out;
                if (!xa_is_node(entry)) {
                        if (xa_marked(xas->xa, mark))
                                return entry;
                        xas->xa_index = 1;
                        goto out;
                }
                xas->xa_node = xa_to_node(entry);
                xas->xa_offset = xas->xa_index >> xas->xa_node->shift;
        }

        while (xas->xa_index <= max) {
                if (unlikely(xas->xa_offset == XA_CHUNK_SIZE)) {
                        xas->xa_offset = xas->xa_node->offset + 1;
                        xas->xa_node = xa_parent(xas->xa, xas->xa_node);
                        if (!xas->xa_node)
                                break;
                        advance = false;
                        continue;
                }

                if (!advance) {
                        entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
                        if (xa_is_sibling(entry)) {
                                xas->xa_offset = xa_to_sibling(entry);
                                xas_move_index(xas, xas->xa_offset);
                        }
                }

                offset = xas_find_chunk(xas, advance, mark);
                if (offset > xas->xa_offset) {
                        advance = false;
                        xas_move_index(xas, offset);
                        /* Mind the wrap */
                        if ((xas->xa_index - 1) >= max)
                                goto max;
                        xas->xa_offset = offset;
                        if (offset == XA_CHUNK_SIZE)
                                continue;
                }

                entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
                if (!xa_is_node(entry))
                        return entry;
                xas->xa_node = xa_to_node(entry);
                xas_set_offset(xas);
        }

out:
        if (xas->xa_index > max)
                goto max;
        return set_bounds(xas);
max:
        xas->xa_node = XAS_RESTART;
        return NULL;
}
EXPORT_SYMBOL_GPL(xas_find_marked);

/**
 * xas_find_conflict() - Find the next present entry in a range.
 * @xas: XArray operation state.
 *
 * The @xas describes both a range and a position within that range.
 *
 * Context: Any context.  Expects xa_lock to be held.
 * Return: The next entry in the range covered by @xas or %NULL.
 */
void *xas_find_conflict(struct xa_state *xas)
{
        void *curr;

        if (xas_error(xas))
                return NULL;

        if (!xas->xa_node)
                return NULL;

        if (xas_top(xas->xa_node)) {
                curr = xas_start(xas);
                if (!curr)
                        return NULL;
                while (xa_is_node(curr)) {
                        struct xa_node *node = xa_to_node(curr);
                        curr = xas_descend(xas, node);
                }
                if (curr)
                        return curr;
        }

        if (xas->xa_node->shift > xas->xa_shift)
                return NULL;

        for (;;) {
                if (xas->xa_node->shift == xas->xa_shift) {
                        if ((xas->xa_offset & xas->xa_sibs) == xas->xa_sibs)
                                break;
                } else if (xas->xa_offset == XA_CHUNK_MASK) {
                        xas->xa_offset = xas->xa_node->offset;
                        xas->xa_node = xa_parent_locked(xas->xa, xas->xa_node);
                        if (!xas->xa_node)
                                break;
                        continue;
                }
                curr = xa_entry_locked(xas->xa, xas->xa_node, ++xas->xa_offset);
                if (xa_is_sibling(curr))
                        continue;
                while (xa_is_node(curr)) {
                        xas->xa_node = xa_to_node(curr);
                        xas->xa_offset = 0;
                        curr = xa_entry_locked(xas->xa, xas->xa_node, 0);
                }
                if (curr)
                        return curr;
        }
        xas->xa_offset -= xas->xa_sibs;
        return NULL;
}
EXPORT_SYMBOL_GPL(xas_find_conflict);

/**
 * xa_load() - Load an entry from an XArray.
 * @xa: XArray.
 * @index: index into array.
 *
 * Context: Any context.  Takes and releases the RCU lock.
 * Return: The entry at @index in @xa.
 */
void *xa_load(struct xarray *xa, unsigned long index)
{
        XA_STATE(xas, xa, index);
        void *entry;

        rcu_read_lock();
        do {
                entry = xas_load(&xas);
                if (xa_is_zero(entry))
                        entry = NULL;
        } while (xas_retry(&xas, entry));
        rcu_read_unlock();

        return entry;
}
EXPORT_SYMBOL(xa_load);

static void *xas_result(struct xa_state *xas, void *curr)
{
        if (xa_is_zero(curr))
                return NULL;
        if (xas_error(xas))
                curr = xas->xa_node;
        return curr;
}

/**
 * __xa_erase() - Erase this entry from the XArray while locked.
 * @xa: XArray.
 * @index: Index into array.
 *
 * After this function returns, loading from @index will return %NULL.
 * If the index is part of a multi-index entry, all indices will be erased
 * and none of the entries will be part of a multi-index entry.
 *
 * Context: Any context.  Expects xa_lock to be held on entry.
 * Return: The entry which used to be at this index.
 */
void *__xa_erase(struct xarray *xa, unsigned long index)
{
        XA_STATE(xas, xa, index);
        return xas_result(&xas, xas_store(&xas, NULL));
}
EXPORT_SYMBOL(__xa_erase);

/**
 * xa_erase() - Erase this entry from the XArray.
 * @xa: XArray.
 * @index: Index of entry.
 *
 * After this function returns, loading from @index will return %NULL.
 * If the index is part of a multi-index entry, all indices will be erased
 * and none of the entries will be part of a multi-index entry.
 *
 * Context: Any context.  Takes and releases the xa_lock.
 * Return: The entry which used to be at this index.
 */
void *xa_erase(struct xarray *xa, unsigned long index)
{
        void *entry;

        xa_lock(xa);
        entry = __xa_erase(xa, index);
        xa_unlock(xa);

        return entry;
}
EXPORT_SYMBOL(xa_erase);

/**
 * __xa_store() - Store this entry in the XArray.
 * @xa: XArray.
 * @index: Index into array.
 * @entry: New entry.
 * @gfp: Memory allocation flags.
 *
 * You must already be holding the xa_lock when calling this function.
 * It will drop the lock if needed to allocate memory, and then reacquire
 * it afterwards.
 *
 * Context: Any context.  Expects xa_lock to be held on entry.  May
 * release and reacquire xa_lock if @gfp flags permit.
 * Return: The old entry at this index or xa_err() if an error happened.
 */
void *__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
{
        XA_STATE(xas, xa, index);
        void *curr;

        if (WARN_ON_ONCE(xa_is_advanced(entry)))
                return XA_ERROR(-EINVAL);
        if (xa_track_free(xa) && !entry)
                entry = XA_ZERO_ENTRY;

        do {
                curr = xas_store(&xas, entry);
                if (xa_track_free(xa))
                        xas_clear_mark(&xas, XA_FREE_MARK);
        } while (__xas_nomem(&xas, gfp));

        return xas_result(&xas, curr);
}
EXPORT_SYMBOL(__xa_store);

/**
 * xa_store() - Store this entry in the XArray.
 * @xa: XArray.
 * @index: Index into array.
 * @entry: New entry.
 * @gfp: Memory allocation flags.
 *
 * After this function returns, loads from this index will return @entry.
 * Storing into an existing multislot entry updates the entry of every index.
 * The marks associated with @index are unaffected unless @entry is %NULL.
 *
 * Context: Any context.  Takes and releases the xa_lock.
 * May sleep if the @gfp flags permit.
 * Return: The old entry at this index on success, xa_err(-EINVAL) if @entry
 * cannot be stored in an XArray, or xa_err(-ENOMEM) if memory allocation
 * failed.
 */
void *xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
{
        void *curr;

        xa_lock(xa);
        curr = __xa_store(xa, index, entry, gfp);
        xa_unlock(xa);

        return curr;
}
EXPORT_SYMBOL(xa_store);

/**
 * __xa_cmpxchg() - Store this entry in the XArray.
 * @xa: XArray.
 * @index: Index into array.
 * @old: Old value to test against.
 * @entry: New entry.
 * @gfp: Memory allocation flags.
 *
 * You must already be holding the xa_lock when calling this function.
 * It will drop the lock if needed to allocate memory, and then reacquire
 * it afterwards.
 *
 * Context: Any context.  Expects xa_lock to be held on entry.  May
 * release and reacquire xa_lock if @gfp flags permit.
 * Return: The old entry at this index or xa_err() if an error happened.
 */
void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
                        void *old, void *entry, gfp_t gfp)
{
        XA_STATE(xas, xa, index);
        void *curr;

        if (WARN_ON_ONCE(xa_is_advanced(entry)))
                return XA_ERROR(-EINVAL);

        do {
                curr = xas_load(&xas);
                if (curr == old) {
                        xas_store(&xas, entry);
                        if (xa_track_free(xa) && entry && !curr)
                                xas_clear_mark(&xas, XA_FREE_MARK);
                }
        } while (__xas_nomem(&xas, gfp));

        return xas_result(&xas, curr);
}
EXPORT_SYMBOL(__xa_cmpxchg);

/**
 * __xa_insert() - Store this entry in the XArray if no entry is present.
 * @xa: XArray.
 * @index: Index into array.
 * @entry: New entry.
 * @gfp: Memory allocation flags.
 *
 * Inserting a NULL entry will store a reserved entry (like xa_reserve())
 * if no entry is present.  Inserting will fail if a reserved entry is
 * present, even though loading from this index will return NULL.
 *
 * Context: Any context.  Expects xa_lock to be held on entry.  May
 * release and reacquire xa_lock if @gfp flags permit.
 * Return: 0 if the store succeeded.  -EBUSY if another entry was present.
 * -ENOMEM if memory could not be allocated.
 */
int __xa_insert(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
{
        XA_STATE(xas, xa, index);
        void *curr;

        if (WARN_ON_ONCE(xa_is_advanced(entry)))
                return -EINVAL;
        if (!entry)
                entry = XA_ZERO_ENTRY;

        do {
                curr = xas_load(&xas);
                if (!curr) {
                        xas_store(&xas, entry);
                        if (xa_track_free(xa))
                                xas_clear_mark(&xas, XA_FREE_MARK);
                } else {
                        xas_set_err(&xas, -EBUSY);
                }
        } while (__xas_nomem(&xas, gfp));

        return xas_error(&xas);
}
EXPORT_SYMBOL(__xa_insert);

#ifdef CONFIG_XARRAY_MULTI
static void xas_set_range(struct xa_state *xas, unsigned long first,
                unsigned long last)
{
        unsigned int shift = 0;
        unsigned long sibs = last - first;
        unsigned int offset = XA_CHUNK_MASK;

        xas_set(xas, first);

        while ((first & XA_CHUNK_MASK) == 0) {
                if (sibs < XA_CHUNK_MASK)
                        break;
                if ((sibs == XA_CHUNK_MASK) && (offset < XA_CHUNK_MASK))
                        break;
                shift += XA_CHUNK_SHIFT;
                if (offset == XA_CHUNK_MASK)
                        offset = sibs & XA_CHUNK_MASK;
                sibs >>= XA_CHUNK_SHIFT;
                first >>= XA_CHUNK_SHIFT;
        }

        offset = first & XA_CHUNK_MASK;
        if (offset + sibs > XA_CHUNK_MASK)
                sibs = XA_CHUNK_MASK - offset;
        if ((((first + sibs + 1) << shift) - 1) > last)
                sibs -= 1;

        xas->xa_shift = shift;
        xas->xa_sibs = sibs;
}

/**
 * xa_store_range() - Store this entry at a range of indices in the XArray.
 * @xa: XArray.
 * @first: First index to affect.
 * @last: Last index to affect.
 * @entry: New entry.
 * @gfp: Memory allocation flags.
 *
 * After this function returns, loads from any index between @first and @last,
 * inclusive will return @entry.
 * Storing into an existing multislot entry updates the entry of every index.
 * The marks associated with @index are unaffected unless @entry is %NULL.
 *
 * Context: Process context.  Takes and releases the xa_lock.  May sleep
 * if the @gfp flags permit.
 * Return: %NULL on success, xa_err(-EINVAL) if @entry cannot be stored in
 * an XArray, or xa_err(-ENOMEM) if memory allocation failed.
 */
void *xa_store_range(struct xarray *xa, unsigned long first,
                unsigned long last, void *entry, gfp_t gfp)
{
        XA_STATE(xas, xa, 0);

        if (WARN_ON_ONCE(xa_is_internal(entry)))
                return XA_ERROR(-EINVAL);
        if (last < first)
                return XA_ERROR(-EINVAL);

        do {
                xas_lock(&xas);
                if (entry) {
                        unsigned int order = BITS_PER_LONG;
                        if (last + 1)
                                order = __ffs(last + 1);
                        xas_set_order(&xas, last, order);
                        xas_create(&xas, true);
                        if (xas_error(&xas))
                                goto unlock;
                }
                do {
                        xas_set_range(&xas, first, last);
                        xas_store(&xas, entry);
                        if (xas_error(&xas))
                                goto unlock;
                        first += xas_size(&xas);
                } while (first <= last);
unlock:
                xas_unlock(&xas);
        } while (xas_nomem(&xas, gfp));

        return xas_result(&xas, NULL);
}
EXPORT_SYMBOL(xa_store_range);
#endif /* CONFIG_XARRAY_MULTI */

/**
 * __xa_alloc() - Find somewhere to store this entry in the XArray.
 * @xa: XArray.
 * @id: Pointer to ID.
 * @limit: Range for allocated ID.
 * @entry: New entry.
 * @gfp: Memory allocation flags.
 *
 * Finds an empty entry in @xa between @limit.min and @limit.max,
 * stores the index into the @id pointer, then stores the entry at
 * that index.  A concurrent lookup will not see an uninitialised @id.
 *
 * Context: Any context.  Expects xa_lock to be held on entry.  May
 * release and reacquire xa_lock if @gfp flags permit.
 * Return: 0 on success, -ENOMEM if memory could not be allocated or
 * -EBUSY if there are no free entries in @limit.
 */
int __xa_alloc(struct xarray *xa, u32 *id, void *entry,
                struct xa_limit limit, gfp_t gfp)
{
        XA_STATE(xas, xa, 0);

        if (WARN_ON_ONCE(xa_is_advanced(entry)))
                return -EINVAL;
        if (WARN_ON_ONCE(!xa_track_free(xa)))
                return -EINVAL;

        if (!entry)
                entry = XA_ZERO_ENTRY;

        do {
                xas.xa_index = limit.min;
                xas_find_marked(&xas, limit.max, XA_FREE_MARK);
                if (xas.xa_node == XAS_RESTART)
                        xas_set_err(&xas, -EBUSY);
                else
                        *id = xas.xa_index;
                xas_store(&xas, entry);
                xas_clear_mark(&xas, XA_FREE_MARK);
        } while (__xas_nomem(&xas, gfp));

        return xas_error(&xas);
}
EXPORT_SYMBOL(__xa_alloc);

/**
 * __xa_alloc_cyclic() - Find somewhere to store this entry in the XArray.
 * @xa: XArray.
 * @id: Pointer to ID.
 * @entry: New entry.
 * @limit: Range of allocated ID.
 * @next: Pointer to next ID to allocate.
 * @gfp: Memory allocation flags.
 *
 * Finds an empty entry in @xa between @limit.min and @limit.max,
 * stores the index into the @id pointer, then stores the entry at
 * that index.  A concurrent lookup will not see an uninitialised @id.
 * The search for an empty entry will start at @next and will wrap
 * around if necessary.
 *
 * Context: Any context.  Expects xa_lock to be held on entry.  May
 * release and reacquire xa_lock if @gfp flags permit.
 * Return: 0 if the allocation succeeded without wrapping.  1 if the
 * allocation succeeded after wrapping, -ENOMEM if memory could not be
 * allocated or -EBUSY if there are no free entries in @limit.
 */
int __xa_alloc_cyclic(struct xarray *xa, u32 *id, void *entry,
                struct xa_limit limit, u32 *next, gfp_t gfp)
{
        u32 min = limit.min;
        int ret;

        limit.min = max(min, *next);
        ret = __xa_alloc(xa, id, entry, limit, gfp);
        if ((xa->xa_flags & XA_FLAGS_ALLOC_WRAPPED) && ret == 0) {
                xa->xa_flags &= ~XA_FLAGS_ALLOC_WRAPPED;
                ret = 1;
        }

        if (ret < 0 && limit.min > min) {
                limit.min = min;
                ret = __xa_alloc(xa, id, entry, limit, gfp);
                if (ret == 0)
                        ret = 1;
        }

        if (ret >= 0) {
                *next = *id + 1;
                if (*next == 0)
                        xa->xa_flags |= XA_FLAGS_ALLOC_WRAPPED;
        }
        return ret;
}
EXPORT_SYMBOL(__xa_alloc_cyclic);

/**
 * __xa_set_mark() - Set this mark on this entry while locked.
 * @xa: XArray.
 * @index: Index of entry.
 * @mark: Mark number.
 *
 * Attempting to set a mark on a %NULL entry does not succeed.
 *
 * Context: Any context.  Expects xa_lock to be held on entry.
 */
void __xa_set_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
{
        XA_STATE(xas, xa, index);
        void *entry = xas_load(&xas);

        if (entry)
                xas_set_mark(&xas, mark);
}
EXPORT_SYMBOL(__xa_set_mark);

/**
 * __xa_clear_mark() - Clear this mark on this entry while locked.
 * @xa: XArray.
 * @index: Index of entry.
 * @mark: Mark number.
 *
 * Context: Any context.  Expects xa_lock to be held on entry.
 */
void __xa_clear_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
{
        XA_STATE(xas, xa, index);
        void *entry = xas_load(&xas);

        if (entry)
                xas_clear_mark(&xas, mark);
}
EXPORT_SYMBOL(__xa_clear_mark);

/**
 * xa_get_mark() - Inquire whether this mark is set on this entry.
 * @xa: XArray.
 * @index: Index of entry.
 * @mark: Mark number.
 *
 * This function uses the RCU read lock, so the result may be out of date
 * by the time it returns.  If you need the result to be stable, use a lock.
 *
 * Context: Any context.  Takes and releases the RCU lock.
 * Return: True if the entry at @index has this mark set, false if it doesn't.
 */
bool xa_get_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
{
        XA_STATE(xas, xa, index);
        void *entry;

        rcu_read_lock();
        entry = xas_start(&xas);
        while (xas_get_mark(&xas, mark)) {
                if (!xa_is_node(entry))
                        goto found;
                entry = xas_descend(&xas, xa_to_node(entry));
        }
        rcu_read_unlock();
        return false;
 found:
        rcu_read_unlock();
        return true;
}
EXPORT_SYMBOL(xa_get_mark);

/**
 * xa_set_mark() - Set this mark on this entry.
 * @xa: XArray.
 * @index: Index of entry.
 * @mark: Mark number.
 *
 * Attempting to set a mark on a %NULL entry does not succeed.
 *
 * Context: Process context.  Takes and releases the xa_lock.
 */
void xa_set_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
{
        xa_lock(xa);
        __xa_set_mark(xa, index, mark);
        xa_unlock(xa);
}
EXPORT_SYMBOL(xa_set_mark);

/**
 * xa_clear_mark() - Clear this mark on this entry.
 * @xa: XArray.
 * @index: Index of entry.
 * @mark: Mark number.
 *
 * Clearing a mark always succeeds.
 *
 * Context: Process context.  Takes and releases the xa_lock.
 */
void xa_clear_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)
{
        xa_lock(xa);
        __xa_clear_mark(xa, index, mark);
        xa_unlock(xa);
}
EXPORT_SYMBOL(xa_clear_mark);

/**
 * xa_find() - Search the XArray for an entry.
 * @xa: XArray.
 * @indexp: Pointer to an index.
 * @max: Maximum index to search to.
 * @filter: Selection criterion.
 *
 * Finds the entry in @xa which matches the @filter, and has the lowest
 * index that is at least @indexp and no more than @max.
 * If an entry is found, @indexp is updated to be the index of the entry.
 * This function is protected by the RCU read lock, so it may not find
 * entries which are being simultaneously added.  It will not return an
 * %XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
 *
 * Context: Any context.  Takes and releases the RCU lock.
 * Return: The entry, if found, otherwise %NULL.
 */
void *xa_find(struct xarray *xa, unsigned long *indexp,
                        unsigned long max, xa_mark_t filter)
{
        XA_STATE(xas, xa, *indexp);
        void *entry;

        rcu_read_lock();
        do {
                if ((__force unsigned int)filter < XA_MAX_MARKS)
                        entry = xas_find_marked(&xas, max, filter);
                else
                        entry = xas_find(&xas, max);
        } while (xas_retry(&xas, entry));
        rcu_read_unlock();

        if (entry)
                *indexp = xas.xa_index;
        return entry;
}
EXPORT_SYMBOL(xa_find);

static bool xas_sibling(struct xa_state *xas)
{
        struct xa_node *node = xas->xa_node;
        unsigned long mask;

        if (!node)
                return false;
        mask = (XA_CHUNK_SIZE << node->shift) - 1;
        return (xas->xa_index & mask) > (xas->xa_offset << node->shift);
}

/**
 * xa_find_after() - Search the XArray for a present entry.
 * @xa: XArray.
 * @indexp: Pointer to an index.
 * @max: Maximum index to search to.
 * @filter: Selection criterion.
 *
 * Finds the entry in @xa which matches the @filter and has the lowest
 * index that is above @indexp and no more than @max.
 * If an entry is found, @indexp is updated to be the index of the entry.
 * This function is protected by the RCU read lock, so it may miss entries
 * which are being simultaneously added.  It will not return an
 * %XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
 *
 * Context: Any context.  Takes and releases the RCU lock.
 * Return: The pointer, if found, otherwise %NULL.
 */
void *xa_find_after(struct xarray *xa, unsigned long *indexp,
                        unsigned long max, xa_mark_t filter)
{
        XA_STATE(xas, xa, *indexp + 1);
        void *entry;

        if (xas.xa_index == 0)
                return NULL;

        rcu_read_lock();
        for (;;) {
                if ((__force unsigned int)filter < XA_MAX_MARKS)
                        entry = xas_find_marked(&xas, max, filter);
                else
                        entry = xas_find(&xas, max);

                if (xas_invalid(&xas))
                        break;
                if (xas_sibling(&xas))
                        continue;
                if (!xas_retry(&xas, entry))
                        break;
        }
        rcu_read_unlock();

        if (entry)
                *indexp = xas.xa_index;
        return entry;
}
EXPORT_SYMBOL(xa_find_after);

static unsigned int xas_extract_present(struct xa_state *xas, void **dst,
                        unsigned long max, unsigned int n)
{
        void *entry;
        unsigned int i = 0;

        rcu_read_lock();
        xas_for_each(xas, entry, max) {
                if (xas_retry(xas, entry))
                        continue;
                dst[i++] = entry;
                if (i == n)
                        break;
        }
        rcu_read_unlock();

        return i;
}

static unsigned int xas_extract_marked(struct xa_state *xas, void **dst,
                        unsigned long max, unsigned int n, xa_mark_t mark)
{
        void *entry;
        unsigned int i = 0;

        rcu_read_lock();
        xas_for_each_marked(xas, entry, max, mark) {
                if (xas_retry(xas, entry))
                        continue;
                dst[i++] = entry;
                if (i == n)
                        break;
        }
        rcu_read_unlock();

        return i;
}

/**
 * xa_extract() - Copy selected entries from the XArray into a normal array.
 * @xa: The source XArray to copy from.
 * @dst: The buffer to copy entries into.
 * @start: The first index in the XArray eligible to be selected.
 * @max: The last index in the XArray eligible to be selected.
 * @n: The maximum number of entries to copy.
 * @filter: Selection criterion.
 *
 * Copies up to @n entries that match @filter from the XArray.  The
 * copied entries will have indices between @start and @max, inclusive.
 *
 * The @filter may be an XArray mark value, in which case entries which are
 * marked with that mark will be copied.  It may also be %XA_PRESENT, in
 * which case all entries which are not %NULL will be copied.
 *
 * The entries returned may not represent a snapshot of the XArray at a
 * moment in time.  For example, if another thread stores to index 5, then
 * index 10, calling xa_extract() may return the old contents of index 5
 * and the new contents of index 10.  Indices not modified while this
 * function is running will not be skipped.
 *
 * If you need stronger guarantees, holding the xa_lock across calls to this
 * function will prevent concurrent modification.
 *
 * Context: Any context.  Takes and releases the RCU lock.
 * Return: The number of entries copied.
 */
unsigned int xa_extract(struct xarray *xa, void **dst, unsigned long start,
                        unsigned long max, unsigned int n, xa_mark_t filter)
{
        XA_STATE(xas, xa, start);

        if (!n)
                return 0;

        if ((__force unsigned int)filter < XA_MAX_MARKS)
                return xas_extract_marked(&xas, dst, max, n, filter);
        return xas_extract_present(&xas, dst, max, n);
}
EXPORT_SYMBOL(xa_extract);

/**
 * xa_destroy() - Free all internal data structures.
 * @xa: XArray.
 *
 * After calling this function, the XArray is empty and has freed all memory
 * allocated for its internal data structures.  You are responsible for
 * freeing the objects referenced by the XArray.
 *
 * Context: Any context.  Takes and releases the xa_lock, interrupt-safe.
 */
void xa_destroy(struct xarray *xa)
{
        XA_STATE(xas, xa, 0);
        unsigned long flags;
        void *entry;

        xas.xa_node = NULL;
        xas_lock_irqsave(&xas, flags);
        entry = xa_head_locked(xa);
        RCU_INIT_POINTER(xa->xa_head, NULL);
        xas_init_marks(&xas);
        if (xa_zero_busy(xa))
                xa_mark_clear(xa, XA_FREE_MARK);
        /* lockdep checks we're still holding the lock in xas_free_nodes() */
        if (xa_is_node(entry))
                xas_free_nodes(&xas, xa_to_node(entry));
        xas_unlock_irqrestore(&xas, flags);
}
EXPORT_SYMBOL(xa_destroy);

#ifdef XA_DEBUG
void xa_dump_node(const struct xa_node *node)
{
        unsigned i, j;

        if (!node)
                return;
        if ((unsigned long)node & 3) {
                pr_cont("node %px\n", node);
                return;
        }

        pr_cont("node %px %s %d parent %px shift %d count %d values %d "
                "array %px list %px %px marks",
                node, node->parent ? "offset" : "max", node->offset,
                node->parent, node->shift, node->count, node->nr_values,
                node->array, node->private_list.prev, node->private_list.next);
        for (i = 0; i < XA_MAX_MARKS; i++)
                for (j = 0; j < XA_MARK_LONGS; j++)
                        pr_cont(" %lx", node->marks[i][j]);
        pr_cont("\n");
}

void xa_dump_index(unsigned long index, unsigned int shift)
{
        if (!shift)
                pr_info("%lu: ", index);
        else if (shift >= BITS_PER_LONG)
                pr_info("0-%lu: ", ~0UL);
        else
                pr_info("%lu-%lu: ", index, index | ((1UL << shift) - 1));
}

void xa_dump_entry(const void *entry, unsigned long index, unsigned long shift)
{
        if (!entry)
                return;

        xa_dump_index(index, shift);

        if (xa_is_node(entry)) {
                if (shift == 0) {
                        pr_cont("%px\n", entry);
                } else {
                        unsigned long i;
                        struct xa_node *node = xa_to_node(entry);
                        xa_dump_node(node);
                        for (i = 0; i < XA_CHUNK_SIZE; i++)
                                xa_dump_entry(node->slots[i],
                                      index + (i << node->shift), node->shift);
                }
        } else if (xa_is_value(entry))
                pr_cont("value %ld (0x%lx) [%px]\n", xa_to_value(entry),
                                                xa_to_value(entry), entry);
        else if (!xa_is_internal(entry))
                pr_cont("%px\n", entry);
        else if (xa_is_retry(entry))
                pr_cont("retry (%ld)\n", xa_to_internal(entry));
        else if (xa_is_sibling(entry))
                pr_cont("sibling (slot %ld)\n", xa_to_sibling(entry));
        else if (xa_is_zero(entry))
                pr_cont("zero (%ld)\n", xa_to_internal(entry));
        else
                pr_cont("UNKNOWN ENTRY (%px)\n", entry);
}

void xa_dump(const struct xarray *xa)
{
        void *entry = xa->xa_head;
        unsigned int shift = 0;

        pr_info("xarray: %px head %px flags %x marks %d %d %d\n", xa, entry,
                        xa->xa_flags, xa_marked(xa, XA_MARK_0),
                        xa_marked(xa, XA_MARK_1), xa_marked(xa, XA_MARK_2));
        if (xa_is_node(entry))
                shift = xa_to_node(entry)->shift + XA_CHUNK_SHIFT;
        xa_dump_entry(entry, 0, shift);
}
#endif