Merge tag 'v4.20-rc5' into sched/core, to pick up fixes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 2017 insertions, 0 deletions

diff --git a/lib/xarray.c b/lib/xarray.c
new file mode 100644
index 000000000000..bbacca576593
--- /dev/null
+++ b/lib/xarray.c
@@ -0,0 +1,2017 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * XArray implementation
+ * Copyright (c) 2017 Microsoft Corporation
+ * 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 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);
+	}
+	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;
+	}
+	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 (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 {
+		node = kmem_cache_alloc(radix_tree_node_cachep,
+					GFP_NOWAIT | __GFP_NOWARN);
+		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;
+		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 (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.
+ *
+ * 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)
+{
+	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;
+		shift = xas_expand(xas, entry);
+		if (shift < 0)
+			return NULL;
+		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);
+		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)
+		first = xas_create(xas);
+	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))
+			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;
+
+	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;
+	} else {
+		xas->xa_index++;
+	}
+	xas->xa_node = XAS_RESTART;
+}
+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_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_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))
+		return NULL;
+
+	if (!xas->xa_node) {
+		xas->xa_index = 1;
+		return set_bounds(xas);
+	} else if (xas_top(xas->xa_node)) {
+		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_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 bounds;
+		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 (!max)
+		goto max;
+bounds:
+	xas->xa_node = XAS_BOUNDS;
+	return NULL;
+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_init_flags() - Initialise an empty XArray with flags.
+ * @xa: XArray.
+ * @flags: XA_FLAG values.
+ *
+ * If you need to initialise an XArray with special flags (eg you need
+ * to take the lock from interrupt context), use this function instead
+ * of xa_init().
+ *
+ * Context: Any context.
+ */
+void xa_init_flags(struct xarray *xa, gfp_t flags)
+{
+	unsigned int lock_type;
+	static struct lock_class_key xa_lock_irq;
+	static struct lock_class_key xa_lock_bh;
+
+	spin_lock_init(&xa->xa_lock);
+	xa->xa_flags = flags;
+	xa->xa_head = NULL;
+
+	lock_type = xa_lock_type(xa);
+	if (lock_type == XA_LOCK_IRQ)
+		lockdep_set_class(&xa->xa_lock, &xa_lock_irq);
+	else if (lock_type == XA_LOCK_BH)
+		lockdep_set_class(&xa->xa_lock, &xa_lock_bh);
+}
+EXPORT_SYMBOL(xa_init_flags);
+
+/**
+ * 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;
+	XA_NODE_BUG_ON(xas->xa_node, xa_is_internal(curr));
+	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.
+ *
+ * If the entry at this index is a multi-index entry then all indices will
+ * be erased, and the entry will no longer be a multi-index entry.
+ * This function expects the xa_lock to be held on entry.
+ *
+ * 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.
+ */
+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.
+ *
+ * This function is the equivalent of calling xa_store() with %NULL as
+ * the third argument.  The XArray does not need to allocate memory, so
+ * the user does not need to provide GFP flags.
+ *
+ * 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_internal(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_internal(entry)))
+		return XA_ERROR(-EINVAL);
+	if (xa_track_free(xa) && !entry)
+		entry = XA_ZERO_ENTRY;
+
+	do {
+		curr = xas_load(&xas);
+		if (curr == XA_ZERO_ENTRY)
+			curr = NULL;
+		if (curr == old) {
+			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_cmpxchg);
+
+/**
+ * __xa_reserve() - Reserve this index in the XArray.
+ * @xa: XArray.
+ * @index: Index into array.
+ * @gfp: Memory allocation flags.
+ *
+ * Ensures there is somewhere to store an entry at @index in the array.
+ * If there is already something stored at @index, this function does
+ * nothing.  If there was nothing there, the entry is marked as reserved.
+ * Loading from a reserved entry returns a %NULL pointer.
+ *
+ * If you do not use the entry that you have reserved, call xa_release()
+ * or xa_erase() to free any unnecessary memory.
+ *
+ * Context: Any context.  Expects the xa_lock to be held on entry.  May
+ * release the lock, sleep and reacquire the lock if the @gfp flags permit.
+ * Return: 0 if the reservation succeeded or -ENOMEM if it failed.
+ */
+int __xa_reserve(struct xarray *xa, unsigned long index, gfp_t gfp)
+{
+	XA_STATE(xas, xa, index);
+	void *curr;
+
+	do {
+		curr = xas_load(&xas);
+		if (!curr) {
+			xas_store(&xas, XA_ZERO_ENTRY);
+			if (xa_track_free(xa))
+				xas_clear_mark(&xas, XA_FREE_MARK);
+		}
+	} while (__xas_nomem(&xas, gfp));
+
+	return xas_error(&xas);
+}
+EXPORT_SYMBOL(__xa_reserve);
+
+#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);
+			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.
+ * @max: Maximum ID to allocate (inclusive).
+ * @entry: New entry.
+ * @gfp: Memory allocation flags.
+ *
+ * Allocates an unused ID in the range specified by @id and @max.
+ * Updates the @id pointer with the index, 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 allocation fails or -ENOSPC if
+ * there is no more space in the XArray.
+ */
+int __xa_alloc(struct xarray *xa, u32 *id, u32 max, void *entry, gfp_t gfp)
+{
+	XA_STATE(xas, xa, 0);
+	int err;
+
+	if (WARN_ON_ONCE(xa_is_internal(entry)))
+		return -EINVAL;
+	if (WARN_ON_ONCE(!xa_track_free(xa)))
+		return -EINVAL;
+
+	if (!entry)
+		entry = XA_ZERO_ENTRY;
+
+	do {
+		xas.xa_index = *id;
+		xas_find_marked(&xas, max, XA_FREE_MARK);
+		if (xas.xa_node == XAS_RESTART)
+			xas_set_err(&xas, -ENOSPC);
+		xas_store(&xas, entry);
+		xas_clear_mark(&xas, XA_FREE_MARK);
+	} while (__xas_nomem(&xas, gfp));
+
+	err = xas_error(&xas);
+	if (!err)
+		*id = xas.xa_index;
+	return err;
+}
+EXPORT_SYMBOL(__xa_alloc);
+
+/**
+ * __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);
+
+/**
+ * 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;
+
+	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.xa_node == XAS_BOUNDS)
+			break;
+		if (xas.xa_shift) {
+			if (xas.xa_index & ((1UL << xas.xa_shift) - 1))
+				continue;
+		} else {
+			if (xas.xa_offset < (xas.xa_index & XA_CHUNK_MASK))
+				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);
+	/* 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