Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2288 insertions, 0 deletions

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
new file mode 100644
index 000000000..e5cab5c4e
--- /dev/null
+++ b/lib/radix-tree.c
@@ -0,0 +1,2288 @@
+/*
+ * Copyright (C) 2001 Momchil Velikov
+ * Portions Copyright (C) 2001 Christoph Hellwig
+ * Copyright (C) 2005 SGI, Christoph Lameter
+ * Copyright (C) 2006 Nick Piggin
+ * Copyright (C) 2012 Konstantin Khlebnikov
+ * Copyright (C) 2016 Intel, Matthew Wilcox
+ * Copyright (C) 2016 Intel, Ross Zwisler
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <linux/bitmap.h>
+#include <linux/bitops.h>
+#include <linux/bug.h>
+#include <linux/cpu.h>
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <linux/idr.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/kmemleak.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>		/* in_interrupt() */
+#include <linux/radix-tree.h>
+#include <linux/rcupdate.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+
+/* Number of nodes in fully populated tree of given height */
+static unsigned long height_to_maxnodes[RADIX_TREE_MAX_PATH + 1] __read_mostly;
+
+/*
+ * Radix tree node cache.
+ */
+static struct kmem_cache *radix_tree_node_cachep;
+
+/*
+ * The radix tree is variable-height, so an insert operation not only has
+ * to build the branch to its corresponding item, it also has to build the
+ * branch to existing items if the size has to be increased (by
+ * radix_tree_extend).
+ *
+ * The worst case is a zero height tree with just a single item at index 0,
+ * and then inserting an item at index ULONG_MAX. This requires 2 new branches
+ * of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
+ * Hence:
+ */
+#define RADIX_TREE_PRELOAD_SIZE (RADIX_TREE_MAX_PATH * 2 - 1)
+
+/*
+ * The IDR does not have to be as high as the radix tree since it uses
+ * signed integers, not unsigned longs.
+ */
+#define IDR_INDEX_BITS		(8 /* CHAR_BIT */ * sizeof(int) - 1)
+#define IDR_MAX_PATH		(DIV_ROUND_UP(IDR_INDEX_BITS, \
+						RADIX_TREE_MAP_SHIFT))
+#define IDR_PRELOAD_SIZE	(IDR_MAX_PATH * 2 - 1)
+
+/*
+ * The IDA is even shorter since it uses a bitmap at the last level.
+ */
+#define IDA_INDEX_BITS		(8 * sizeof(int) - 1 - ilog2(IDA_BITMAP_BITS))
+#define IDA_MAX_PATH		(DIV_ROUND_UP(IDA_INDEX_BITS, \
+						RADIX_TREE_MAP_SHIFT))
+#define IDA_PRELOAD_SIZE	(IDA_MAX_PATH * 2 - 1)
+
+/*
+ * Per-cpu pool of preloaded nodes
+ */
+struct radix_tree_preload {
+	unsigned nr;
+	/* nodes->parent points to next preallocated node */
+	struct radix_tree_node *nodes;
+};
+static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
+
+static inline struct radix_tree_node *entry_to_node(void *ptr)
+{
+	return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
+}
+
+static inline void *node_to_entry(void *ptr)
+{
+	return (void *)((unsigned long)ptr | RADIX_TREE_INTERNAL_NODE);
+}
+
+#define RADIX_TREE_RETRY	node_to_entry(NULL)
+
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+/* Sibling slots point directly to another slot in the same node */
+static inline
+bool is_sibling_entry(const struct radix_tree_node *parent, void *node)
+{
+	void __rcu **ptr = node;
+	return (parent->slots <= ptr) &&
+			(ptr < parent->slots + RADIX_TREE_MAP_SIZE);
+}
+#else
+static inline
+bool is_sibling_entry(const struct radix_tree_node *parent, void *node)
+{
+	return false;
+}
+#endif
+
+static inline unsigned long
+get_slot_offset(const struct radix_tree_node *parent, void __rcu **slot)
+{
+	return parent ? slot - parent->slots : 0;
+}
+
+static unsigned int radix_tree_descend(const struct radix_tree_node *parent,
+			struct radix_tree_node **nodep, unsigned long index)
+{
+	unsigned int offset = (index >> parent->shift) & RADIX_TREE_MAP_MASK;
+	void __rcu **entry = rcu_dereference_raw(parent->slots[offset]);
+
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+	if (radix_tree_is_internal_node(entry)) {
+		if (is_sibling_entry(parent, entry)) {
+			void __rcu **sibentry;
+			sibentry = (void __rcu **) entry_to_node(entry);
+			offset = get_slot_offset(parent, sibentry);
+			entry = rcu_dereference_raw(*sibentry);
+		}
+	}
+#endif
+
+	*nodep = (void *)entry;
+	return offset;
+}
+
+static inline gfp_t root_gfp_mask(const struct radix_tree_root *root)
+{
+	return root->gfp_mask & (__GFP_BITS_MASK & ~GFP_ZONEMASK);
+}
+
+static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
+		int offset)
+{
+	__set_bit(offset, node->tags[tag]);
+}
+
+static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
+		int offset)
+{
+	__clear_bit(offset, node->tags[tag]);
+}
+
+static inline int tag_get(const struct radix_tree_node *node, unsigned int tag,
+		int offset)
+{
+	return test_bit(offset, node->tags[tag]);
+}
+
+static inline void root_tag_set(struct radix_tree_root *root, unsigned tag)
+{
+	root->gfp_mask |= (__force gfp_t)(1 << (tag + ROOT_TAG_SHIFT));
+}
+
+static inline void root_tag_clear(struct radix_tree_root *root, unsigned tag)
+{
+	root->gfp_mask &= (__force gfp_t)~(1 << (tag + ROOT_TAG_SHIFT));
+}
+
+static inline void root_tag_clear_all(struct radix_tree_root *root)
+{
+	root->gfp_mask &= (1 << ROOT_TAG_SHIFT) - 1;
+}
+
+static inline int root_tag_get(const struct radix_tree_root *root, unsigned tag)
+{
+	return (__force int)root->gfp_mask & (1 << (tag + ROOT_TAG_SHIFT));
+}
+
+static inline unsigned root_tags_get(const struct radix_tree_root *root)
+{
+	return (__force unsigned)root->gfp_mask >> ROOT_TAG_SHIFT;
+}
+
+static inline bool is_idr(const struct radix_tree_root *root)
+{
+	return !!(root->gfp_mask & ROOT_IS_IDR);
+}
+
+/*
+ * Returns 1 if any slot in the node has this tag set.
+ * Otherwise returns 0.
+ */
+static inline int any_tag_set(const struct radix_tree_node *node,
+							unsigned int tag)
+{
+	unsigned idx;
+	for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
+		if (node->tags[tag][idx])
+			return 1;
+	}
+	return 0;
+}
+
+static inline void all_tag_set(struct radix_tree_node *node, unsigned int tag)
+{
+	bitmap_fill(node->tags[tag], RADIX_TREE_MAP_SIZE);
+}
+
+/**
+ * radix_tree_find_next_bit - find the next set bit in a memory region
+ *
+ * @addr: The address to base the search on
+ * @size: The bitmap size in bits
+ * @offset: The bitnumber to start searching at
+ *
+ * Unrollable variant of find_next_bit() for constant size arrays.
+ * Tail bits starting from size to roundup(size, BITS_PER_LONG) must be zero.
+ * Returns next bit offset, or size if nothing found.
+ */
+static __always_inline unsigned long
+radix_tree_find_next_bit(struct radix_tree_node *node, unsigned int tag,
+			 unsigned long offset)
+{
+	const unsigned long *addr = node->tags[tag];
+
+	if (offset < RADIX_TREE_MAP_SIZE) {
+		unsigned long tmp;
+
+		addr += offset / BITS_PER_LONG;
+		tmp = *addr >> (offset % BITS_PER_LONG);
+		if (tmp)
+			return __ffs(tmp) + offset;
+		offset = (offset + BITS_PER_LONG) & ~(BITS_PER_LONG - 1);
+		while (offset < RADIX_TREE_MAP_SIZE) {
+			tmp = *++addr;
+			if (tmp)
+				return __ffs(tmp) + offset;
+			offset += BITS_PER_LONG;
+		}
+	}
+	return RADIX_TREE_MAP_SIZE;
+}
+
+static unsigned int iter_offset(const struct radix_tree_iter *iter)
+{
+	return (iter->index >> iter_shift(iter)) & RADIX_TREE_MAP_MASK;
+}
+
+/*
+ * The maximum index which can be stored in a radix tree
+ */
+static inline unsigned long shift_maxindex(unsigned int shift)
+{
+	return (RADIX_TREE_MAP_SIZE << shift) - 1;
+}
+
+static inline unsigned long node_maxindex(const struct radix_tree_node *node)
+{
+	return shift_maxindex(node->shift);
+}
+
+static unsigned long next_index(unsigned long index,
+				const struct radix_tree_node *node,
+				unsigned long offset)
+{
+	return (index & ~node_maxindex(node)) + (offset << node->shift);
+}
+
+#ifndef __KERNEL__
+static void dump_node(struct radix_tree_node *node, unsigned long index)
+{
+	unsigned long i;
+
+	pr_debug("radix node: %p offset %d indices %lu-%lu parent %p tags %lx %lx %lx shift %d count %d exceptional %d\n",
+		node, node->offset, index, index | node_maxindex(node),
+		node->parent,
+		node->tags[0][0], node->tags[1][0], node->tags[2][0],
+		node->shift, node->count, node->exceptional);
+
+	for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
+		unsigned long first = index | (i << node->shift);
+		unsigned long last = first | ((1UL << node->shift) - 1);
+		void *entry = node->slots[i];
+		if (!entry)
+			continue;
+		if (entry == RADIX_TREE_RETRY) {
+			pr_debug("radix retry offset %ld indices %lu-%lu parent %p\n",
+					i, first, last, node);
+		} else if (!radix_tree_is_internal_node(entry)) {
+			pr_debug("radix entry %p offset %ld indices %lu-%lu parent %p\n",
+					entry, i, first, last, node);
+		} else if (is_sibling_entry(node, entry)) {
+			pr_debug("radix sblng %p offset %ld indices %lu-%lu parent %p val %p\n",
+					entry, i, first, last, node,
+					*(void **)entry_to_node(entry));
+		} else {
+			dump_node(entry_to_node(entry), first);
+		}
+	}
+}
+
+/* For debug */
+static void radix_tree_dump(struct radix_tree_root *root)
+{
+	pr_debug("radix root: %p rnode %p tags %x\n",
+			root, root->rnode,
+			root->gfp_mask >> ROOT_TAG_SHIFT);
+	if (!radix_tree_is_internal_node(root->rnode))
+		return;
+	dump_node(entry_to_node(root->rnode), 0);
+}
+
+static void dump_ida_node(void *entry, unsigned long index)
+{
+	unsigned long i;
+
+	if (!entry)
+		return;
+
+	if (radix_tree_is_internal_node(entry)) {
+		struct radix_tree_node *node = entry_to_node(entry);
+
+		pr_debug("ida node: %p offset %d indices %lu-%lu parent %p free %lx shift %d count %d\n",
+			node, node->offset, index * IDA_BITMAP_BITS,
+			((index | node_maxindex(node)) + 1) *
+				IDA_BITMAP_BITS - 1,
+			node->parent, node->tags[0][0], node->shift,
+			node->count);
+		for (i = 0; i < RADIX_TREE_MAP_SIZE; i++)
+			dump_ida_node(node->slots[i],
+					index | (i << node->shift));
+	} else if (radix_tree_exceptional_entry(entry)) {
+		pr_debug("ida excp: %p offset %d indices %lu-%lu data %lx\n",
+				entry, (int)(index & RADIX_TREE_MAP_MASK),
+				index * IDA_BITMAP_BITS,
+				index * IDA_BITMAP_BITS + BITS_PER_LONG -
+					RADIX_TREE_EXCEPTIONAL_SHIFT,
+				(unsigned long)entry >>
+					RADIX_TREE_EXCEPTIONAL_SHIFT);
+	} else {
+		struct ida_bitmap *bitmap = entry;
+
+		pr_debug("ida btmp: %p offset %d indices %lu-%lu data", bitmap,
+				(int)(index & RADIX_TREE_MAP_MASK),
+				index * IDA_BITMAP_BITS,
+				(index + 1) * IDA_BITMAP_BITS - 1);
+		for (i = 0; i < IDA_BITMAP_LONGS; i++)
+			pr_cont(" %lx", bitmap->bitmap[i]);
+		pr_cont("\n");
+	}
+}
+
+static void ida_dump(struct ida *ida)
+{
+	struct radix_tree_root *root = &ida->ida_rt;
+	pr_debug("ida: %p node %p free %d\n", ida, root->rnode,
+				root->gfp_mask >> ROOT_TAG_SHIFT);
+	dump_ida_node(root->rnode, 0);
+}
+#endif
+
+/*
+ * This assumes that the caller has performed appropriate preallocation, and
+ * that the caller has pinned this thread of control to the current CPU.
+ */
+static struct radix_tree_node *
+radix_tree_node_alloc(gfp_t gfp_mask, struct radix_tree_node *parent,
+			struct radix_tree_root *root,
+			unsigned int shift, unsigned int offset,
+			unsigned int count, unsigned int exceptional)
+{
+	struct radix_tree_node *ret = NULL;
+
+	/*
+	 * Preload code isn't irq safe and it doesn't make sense to use
+	 * preloading during an interrupt anyway as all the allocations have
+	 * to be atomic. So just do normal allocation when in interrupt.
+	 */
+	if (!gfpflags_allow_blocking(gfp_mask) && !in_interrupt()) {
+		struct radix_tree_preload *rtp;
+
+		/*
+		 * Even if the caller has preloaded, try to allocate from the
+		 * cache first for the new node to get accounted to the memory
+		 * cgroup.
+		 */
+		ret = kmem_cache_alloc(radix_tree_node_cachep,
+				       gfp_mask | __GFP_NOWARN);
+		if (ret)
+			goto out;
+
+		/*
+		 * Provided the caller has preloaded here, we will always
+		 * succeed in getting a node here (and never reach
+		 * kmem_cache_alloc)
+		 */
+		rtp = this_cpu_ptr(&radix_tree_preloads);
+		if (rtp->nr) {
+			ret = rtp->nodes;
+			rtp->nodes = ret->parent;
+			rtp->nr--;
+		}
+		/*
+		 * Update the allocation stack trace as this is more useful
+		 * for debugging.
+		 */
+		kmemleak_update_trace(ret);
+		goto out;
+	}
+	ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
+out:
+	BUG_ON(radix_tree_is_internal_node(ret));
+	if (ret) {
+		ret->shift = shift;
+		ret->offset = offset;
+		ret->count = count;
+		ret->exceptional = exceptional;
+		ret->parent = parent;
+		ret->root = root;
+	}
+	return ret;
+}
+
+static void radix_tree_node_rcu_free(struct rcu_head *head)
+{
+	struct radix_tree_node *node =
+			container_of(head, struct radix_tree_node, rcu_head);
+
+	/*
+	 * Must only free zeroed nodes into the slab.  We can be left with
+	 * non-NULL entries by radix_tree_free_nodes, so clear the entries
+	 * and tags here.
+	 */
+	memset(node->slots, 0, sizeof(node->slots));
+	memset(node->tags, 0, sizeof(node->tags));
+	INIT_LIST_HEAD(&node->private_list);
+
+	kmem_cache_free(radix_tree_node_cachep, node);
+}
+
+static inline void
+radix_tree_node_free(struct radix_tree_node *node)
+{
+	call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
+}
+
+/*
+ * Load up this CPU's radix_tree_node buffer with sufficient objects to
+ * ensure that the addition of a single element in the tree cannot fail.  On
+ * success, return zero, with preemption disabled.  On error, return -ENOMEM
+ * with preemption not disabled.
+ *
+ * To make use of this facility, the radix tree must be initialised without
+ * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
+ */
+static __must_check int __radix_tree_preload(gfp_t gfp_mask, unsigned nr)
+{
+	struct radix_tree_preload *rtp;
+	struct radix_tree_node *node;
+	int ret = -ENOMEM;
+
+	/*
+	 * Nodes preloaded by one cgroup can be be used by another cgroup, so
+	 * they should never be accounted to any particular memory cgroup.
+	 */
+	gfp_mask &= ~__GFP_ACCOUNT;
+
+	preempt_disable();
+	rtp = this_cpu_ptr(&radix_tree_preloads);
+	while (rtp->nr < nr) {
+		preempt_enable();
+		node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
+		if (node == NULL)
+			goto out;
+		preempt_disable();
+		rtp = this_cpu_ptr(&radix_tree_preloads);
+		if (rtp->nr < nr) {
+			node->parent = rtp->nodes;
+			rtp->nodes = node;
+			rtp->nr++;
+		} else {
+			kmem_cache_free(radix_tree_node_cachep, node);
+		}
+	}
+	ret = 0;
+out:
+	return ret;
+}
+
+/*
+ * Load up this CPU's radix_tree_node buffer with sufficient objects to
+ * ensure that the addition of a single element in the tree cannot fail.  On
+ * success, return zero, with preemption disabled.  On error, return -ENOMEM
+ * with preemption not disabled.
+ *
+ * To make use of this facility, the radix tree must be initialised without
+ * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
+ */
+int radix_tree_preload(gfp_t gfp_mask)
+{
+	/* Warn on non-sensical use... */
+	WARN_ON_ONCE(!gfpflags_allow_blocking(gfp_mask));
+	return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
+}
+EXPORT_SYMBOL(radix_tree_preload);
+
+/*
+ * The same as above function, except we don't guarantee preloading happens.
+ * We do it, if we decide it helps. On success, return zero with preemption
+ * disabled. On error, return -ENOMEM with preemption not disabled.
+ */
+int radix_tree_maybe_preload(gfp_t gfp_mask)
+{
+	if (gfpflags_allow_blocking(gfp_mask))
+		return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
+	/* Preloading doesn't help anything with this gfp mask, skip it */
+	preempt_disable();
+	return 0;
+}
+EXPORT_SYMBOL(radix_tree_maybe_preload);
+
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+/*
+ * Preload with enough objects to ensure that we can split a single entry
+ * of order @old_order into many entries of size @new_order
+ */
+int radix_tree_split_preload(unsigned int old_order, unsigned int new_order,
+							gfp_t gfp_mask)
+{
+	unsigned top = 1 << (old_order % RADIX_TREE_MAP_SHIFT);
+	unsigned layers = (old_order / RADIX_TREE_MAP_SHIFT) -
+				(new_order / RADIX_TREE_MAP_SHIFT);
+	unsigned nr = 0;
+
+	WARN_ON_ONCE(!gfpflags_allow_blocking(gfp_mask));
+	BUG_ON(new_order >= old_order);
+
+	while (layers--)
+		nr = nr * RADIX_TREE_MAP_SIZE + 1;
+	return __radix_tree_preload(gfp_mask, top * nr);
+}
+#endif
+
+/*
+ * The same as function above, but preload number of nodes required to insert
+ * (1 << order) continuous naturally-aligned elements.
+ */
+int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order)
+{
+	unsigned long nr_subtrees;
+	int nr_nodes, subtree_height;
+
+	/* Preloading doesn't help anything with this gfp mask, skip it */
+	if (!gfpflags_allow_blocking(gfp_mask)) {
+		preempt_disable();
+		return 0;
+	}
+
+	/*
+	 * Calculate number and height of fully populated subtrees it takes to
+	 * store (1 << order) elements.
+	 */
+	nr_subtrees = 1 << order;
+	for (subtree_height = 0; nr_subtrees > RADIX_TREE_MAP_SIZE;
+			subtree_height++)
+		nr_subtrees >>= RADIX_TREE_MAP_SHIFT;
+
+	/*
+	 * The worst case is zero height tree with a single item at index 0 and
+	 * then inserting items starting at ULONG_MAX - (1 << order).
+	 *
+	 * This requires RADIX_TREE_MAX_PATH nodes to build branch from root to
+	 * 0-index item.
+	 */
+	nr_nodes = RADIX_TREE_MAX_PATH;
+
+	/* Plus branch to fully populated subtrees. */
+	nr_nodes += RADIX_TREE_MAX_PATH - subtree_height;
+
+	/* Root node is shared. */
+	nr_nodes--;
+
+	/* Plus nodes required to build subtrees. */
+	nr_nodes += nr_subtrees * height_to_maxnodes[subtree_height];
+
+	return __radix_tree_preload(gfp_mask, nr_nodes);
+}
+
+static unsigned radix_tree_load_root(const struct radix_tree_root *root,
+		struct radix_tree_node **nodep, unsigned long *maxindex)
+{
+	struct radix_tree_node *node = rcu_dereference_raw(root->rnode);
+
+	*nodep = node;
+
+	if (likely(radix_tree_is_internal_node(node))) {
+		node = entry_to_node(node);
+		*maxindex = node_maxindex(node);
+		return node->shift + RADIX_TREE_MAP_SHIFT;
+	}
+
+	*maxindex = 0;
+	return 0;
+}
+
+/*
+ *	Extend a radix tree so it can store key @index.
+ */
+static int radix_tree_extend(struct radix_tree_root *root, gfp_t gfp,
+				unsigned long index, unsigned int shift)
+{
+	void *entry;
+	unsigned int maxshift;
+	int tag;
+
+	/* Figure out what the shift should be.  */
+	maxshift = shift;
+	while (index > shift_maxindex(maxshift))
+		maxshift += RADIX_TREE_MAP_SHIFT;
+
+	entry = rcu_dereference_raw(root->rnode);
+	if (!entry && (!is_idr(root) || root_tag_get(root, IDR_FREE)))
+		goto out;
+
+	do {
+		struct radix_tree_node *node = radix_tree_node_alloc(gfp, NULL,
+							root, shift, 0, 1, 0);
+		if (!node)
+			return -ENOMEM;
+
+		if (is_idr(root)) {
+			all_tag_set(node, IDR_FREE);
+			if (!root_tag_get(root, IDR_FREE)) {
+				tag_clear(node, IDR_FREE, 0);
+				root_tag_set(root, IDR_FREE);
+			}
+		} else {
+			/* Propagate the aggregated tag info to the new child */
+			for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
+				if (root_tag_get(root, tag))
+					tag_set(node, tag, 0);
+			}
+		}
+
+		BUG_ON(shift > BITS_PER_LONG);
+		if (radix_tree_is_internal_node(entry)) {
+			entry_to_node(entry)->parent = node;
+		} else if (radix_tree_exceptional_entry(entry)) {
+			/* Moving an exceptional root->rnode to a node */
+			node->exceptional = 1;
+		}
+		/*
+		 * entry was already in the radix tree, so we do not need
+		 * rcu_assign_pointer here
+		 */
+		node->slots[0] = (void __rcu *)entry;
+		entry = node_to_entry(node);
+		rcu_assign_pointer(root->rnode, entry);
+		shift += RADIX_TREE_MAP_SHIFT;
+	} while (shift <= maxshift);
+out:
+	return maxshift + RADIX_TREE_MAP_SHIFT;
+}
+
+/**
+ *	radix_tree_shrink    -    shrink radix tree to minimum height
+ *	@root		radix tree root
+ */
+static inline bool radix_tree_shrink(struct radix_tree_root *root,
+				     radix_tree_update_node_t update_node)
+{
+	bool shrunk = false;
+
+	for (;;) {
+		struct radix_tree_node *node = rcu_dereference_raw(root->rnode);
+		struct radix_tree_node *child;
+
+		if (!radix_tree_is_internal_node(node))
+			break;
+		node = entry_to_node(node);
+
+		/*
+		 * The candidate node has more than one child, or its child
+		 * is not at the leftmost slot, or the child is a multiorder
+		 * entry, we cannot shrink.
+		 */
+		if (node->count != 1)
+			break;
+		child = rcu_dereference_raw(node->slots[0]);
+		if (!child)
+			break;
+		if (!radix_tree_is_internal_node(child) && node->shift)
+			break;
+
+		if (radix_tree_is_internal_node(child))
+			entry_to_node(child)->parent = NULL;
+
+		/*
+		 * We don't need rcu_assign_pointer(), since we are simply
+		 * moving the node from one part of the tree to another: if it
+		 * was safe to dereference the old pointer to it
+		 * (node->slots[0]), it will be safe to dereference the new
+		 * one (root->rnode) as far as dependent read barriers go.
+		 */
+		root->rnode = (void __rcu *)child;
+		if (is_idr(root) && !tag_get(node, IDR_FREE, 0))
+			root_tag_clear(root, IDR_FREE);
+
+		/*
+		 * We have a dilemma here. The node's slot[0] must not be
+		 * NULLed in case there are concurrent lookups expecting to
+		 * find the item. However if this was a bottom-level node,
+		 * then it may be subject to the slot pointer being visible
+		 * to callers dereferencing it. If item corresponding to
+		 * slot[0] is subsequently deleted, these callers would expect
+		 * their slot to become empty sooner or later.
+		 *
+		 * For example, lockless pagecache will look up a slot, deref
+		 * the page pointer, and if the page has 0 refcount it means it
+		 * was concurrently deleted from pagecache so try the deref
+		 * again. Fortunately there is already a requirement for logic
+		 * to retry the entire slot lookup -- the indirect pointer
+		 * problem (replacing direct root node with an indirect pointer
+		 * also results in a stale slot). So tag the slot as indirect
+		 * to force callers to retry.
+		 */
+		node->count = 0;
+		if (!radix_tree_is_internal_node(child)) {
+			node->slots[0] = (void __rcu *)RADIX_TREE_RETRY;
+			if (update_node)
+				update_node(node);
+		}
+
+		WARN_ON_ONCE(!list_empty(&node->private_list));
+		radix_tree_node_free(node);
+		shrunk = true;
+	}
+
+	return shrunk;
+}
+
+static bool delete_node(struct radix_tree_root *root,
+			struct radix_tree_node *node,
+			radix_tree_update_node_t update_node)
+{
+	bool deleted = false;
+
+	do {
+		struct radix_tree_node *parent;
+
+		if (node->count) {
+			if (node_to_entry(node) ==
+					rcu_dereference_raw(root->rnode))
+				deleted |= radix_tree_shrink(root,
+								update_node);
+			return deleted;
+		}
+
+		parent = node->parent;
+		if (parent) {
+			parent->slots[node->offset] = NULL;
+			parent->count--;
+		} else {
+			/*
+			 * Shouldn't the tags already have all been cleared
+			 * by the caller?
+			 */
+			if (!is_idr(root))
+				root_tag_clear_all(root);
+			root->rnode = NULL;
+		}
+
+		WARN_ON_ONCE(!list_empty(&node->private_list));
+		radix_tree_node_free(node);
+		deleted = true;
+
+		node = parent;
+	} while (node);
+
+	return deleted;
+}
+
+/**
+ *	__radix_tree_create	-	create a slot in a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@order:		index occupies 2^order aligned slots
+ *	@nodep:		returns node
+ *	@slotp:		returns slot
+ *
+ *	Create, if necessary, and return the node and slot for an item
+ *	at position @index in the radix tree @root.
+ *
+ *	Until there is more than one item in the tree, no nodes are
+ *	allocated and @root->rnode is used as a direct slot instead of
+ *	pointing to a node, in which case *@nodep will be NULL.
+ *
+ *	Returns -ENOMEM, or 0 for success.
+ */
+int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
+			unsigned order, struct radix_tree_node **nodep,
+			void __rcu ***slotp)
+{
+	struct radix_tree_node *node = NULL, *child;
+	void __rcu **slot = (void __rcu **)&root->rnode;
+	unsigned long maxindex;
+	unsigned int shift, offset = 0;
+	unsigned long max = index | ((1UL << order) - 1);
+	gfp_t gfp = root_gfp_mask(root);
+
+	shift = radix_tree_load_root(root, &child, &maxindex);
+
+	/* Make sure the tree is high enough.  */
+	if (order > 0 && max == ((1UL << order) - 1))
+		max++;
+	if (max > maxindex) {
+		int error = radix_tree_extend(root, gfp, max, shift);
+		if (error < 0)
+			return error;
+		shift = error;
+		child = rcu_dereference_raw(root->rnode);
+	}
+
+	while (shift > order) {
+		shift -= RADIX_TREE_MAP_SHIFT;
+		if (child == NULL) {
+			/* Have to add a child node.  */
+			child = radix_tree_node_alloc(gfp, node, root, shift,
+							offset, 0, 0);
+			if (!child)
+				return -ENOMEM;
+			rcu_assign_pointer(*slot, node_to_entry(child));
+			if (node)
+				node->count++;
+		} else if (!radix_tree_is_internal_node(child))
+			break;
+
+		/* Go a level down */
+		node = entry_to_node(child);
+		offset = radix_tree_descend(node, &child, index);
+		slot = &node->slots[offset];
+	}
+
+	if (nodep)
+		*nodep = node;
+	if (slotp)
+		*slotp = slot;
+	return 0;
+}
+
+/*
+ * Free any nodes below this node.  The tree is presumed to not need
+ * shrinking, and any user data in the tree is presumed to not need a
+ * destructor called on it.  If we need to add a destructor, we can
+ * add that functionality later.  Note that we may not clear tags or
+ * slots from the tree as an RCU walker may still have a pointer into
+ * this subtree.  We could replace the entries with RADIX_TREE_RETRY,
+ * but we'll still have to clear those in rcu_free.
+ */
+static void radix_tree_free_nodes(struct radix_tree_node *node)
+{
+	unsigned offset = 0;
+	struct radix_tree_node *child = entry_to_node(node);
+
+	for (;;) {
+		void *entry = rcu_dereference_raw(child->slots[offset]);
+		if (radix_tree_is_internal_node(entry) &&
+					!is_sibling_entry(child, entry)) {
+			child = entry_to_node(entry);
+			offset = 0;
+			continue;
+		}
+		offset++;
+		while (offset == RADIX_TREE_MAP_SIZE) {
+			struct radix_tree_node *old = child;
+			offset = child->offset + 1;
+			child = child->parent;
+			WARN_ON_ONCE(!list_empty(&old->private_list));
+			radix_tree_node_free(old);
+			if (old == entry_to_node(node))
+				return;
+		}
+	}
+}
+
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+static inline int insert_entries(struct radix_tree_node *node,
+		void __rcu **slot, void *item, unsigned order, bool replace)
+{
+	struct radix_tree_node *child;
+	unsigned i, n, tag, offset, tags = 0;
+
+	if (node) {
+		if (order > node->shift)
+			n = 1 << (order - node->shift);
+		else
+			n = 1;
+		offset = get_slot_offset(node, slot);
+	} else {
+		n = 1;
+		offset = 0;
+	}
+
+	if (n > 1) {
+		offset = offset & ~(n - 1);
+		slot = &node->slots[offset];
+	}
+	child = node_to_entry(slot);
+
+	for (i = 0; i < n; i++) {
+		if (slot[i]) {
+			if (replace) {
+				node->count--;
+				for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+					if (tag_get(node, tag, offset + i))
+						tags |= 1 << tag;
+			} else
+				return -EEXIST;
+		}
+	}
+
+	for (i = 0; i < n; i++) {
+		struct radix_tree_node *old = rcu_dereference_raw(slot[i]);
+		if (i) {
+			rcu_assign_pointer(slot[i], child);
+			for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+				if (tags & (1 << tag))
+					tag_clear(node, tag, offset + i);
+		} else {
+			rcu_assign_pointer(slot[i], item);
+			for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+				if (tags & (1 << tag))
+					tag_set(node, tag, offset);
+		}
+		if (radix_tree_is_internal_node(old) &&
+					!is_sibling_entry(node, old) &&
+					(old != RADIX_TREE_RETRY))
+			radix_tree_free_nodes(old);
+		if (radix_tree_exceptional_entry(old))
+			node->exceptional--;
+	}
+	if (node) {
+		node->count += n;
+		if (radix_tree_exceptional_entry(item))
+			node->exceptional += n;
+	}
+	return n;
+}
+#else
+static inline int insert_entries(struct radix_tree_node *node,
+		void __rcu **slot, void *item, unsigned order, bool replace)
+{
+	if (*slot)
+		return -EEXIST;
+	rcu_assign_pointer(*slot, item);
+	if (node) {
+		node->count++;
+		if (radix_tree_exceptional_entry(item))
+			node->exceptional++;
+	}
+	return 1;
+}
+#endif
+
+/**
+ *	__radix_tree_insert    -    insert into a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@order:		key covers the 2^order indices around index
+ *	@item:		item to insert
+ *
+ *	Insert an item into the radix tree at position @index.
+ */
+int __radix_tree_insert(struct radix_tree_root *root, unsigned long index,
+			unsigned order, void *item)
+{
+	struct radix_tree_node *node;
+	void __rcu **slot;
+	int error;
+
+	BUG_ON(radix_tree_is_internal_node(item));
+
+	error = __radix_tree_create(root, index, order, &node, &slot);
+	if (error)
+		return error;
+
+	error = insert_entries(node, slot, item, order, false);
+	if (error < 0)
+		return error;
+
+	if (node) {
+		unsigned offset = get_slot_offset(node, slot);
+		BUG_ON(tag_get(node, 0, offset));
+		BUG_ON(tag_get(node, 1, offset));
+		BUG_ON(tag_get(node, 2, offset));
+	} else {
+		BUG_ON(root_tags_get(root));
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(__radix_tree_insert);
+
+/**
+ *	__radix_tree_lookup	-	lookup an item in a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@nodep:		returns node
+ *	@slotp:		returns slot
+ *
+ *	Lookup and return the item at position @index in the radix
+ *	tree @root.
+ *
+ *	Until there is more than one item in the tree, no nodes are
+ *	allocated and @root->rnode is used as a direct slot instead of
+ *	pointing to a node, in which case *@nodep will be NULL.
+ */
+void *__radix_tree_lookup(const struct radix_tree_root *root,
+			  unsigned long index, struct radix_tree_node **nodep,
+			  void __rcu ***slotp)
+{
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+	void __rcu **slot;
+
+ restart:
+	parent = NULL;
+	slot = (void __rcu **)&root->rnode;
+	radix_tree_load_root(root, &node, &maxindex);
+	if (index > maxindex)
+		return NULL;
+
+	while (radix_tree_is_internal_node(node)) {
+		unsigned offset;
+
+		if (node == RADIX_TREE_RETRY)
+			goto restart;
+		parent = entry_to_node(node);
+		offset = radix_tree_descend(parent, &node, index);
+		slot = parent->slots + offset;
+	}
+
+	if (nodep)
+		*nodep = parent;
+	if (slotp)
+		*slotp = slot;
+	return node;
+}
+
+/**
+ *	radix_tree_lookup_slot    -    lookup a slot in a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *
+ *	Returns:  the slot corresponding to the position @index in the
+ *	radix tree @root. This is useful for update-if-exists operations.
+ *
+ *	This function can be called under rcu_read_lock iff the slot is not
+ *	modified by radix_tree_replace_slot, otherwise it must be called
+ *	exclusive from other writers. Any dereference of the slot must be done
+ *	using radix_tree_deref_slot.
+ */
+void __rcu **radix_tree_lookup_slot(const struct radix_tree_root *root,
+				unsigned long index)
+{
+	void __rcu **slot;
+
+	if (!__radix_tree_lookup(root, index, NULL, &slot))
+		return NULL;
+	return slot;
+}
+EXPORT_SYMBOL(radix_tree_lookup_slot);
+
+/**
+ *	radix_tree_lookup    -    perform lookup operation on a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *
+ *	Lookup the item at the position @index in the radix tree @root.
+ *
+ *	This function can be called under rcu_read_lock, however the caller
+ *	must manage lifetimes of leaf nodes (eg. RCU may also be used to free
+ *	them safely). No RCU barriers are required to access or modify the
+ *	returned item, however.
+ */
+void *radix_tree_lookup(const struct radix_tree_root *root, unsigned long index)
+{
+	return __radix_tree_lookup(root, index, NULL, NULL);
+}
+EXPORT_SYMBOL(radix_tree_lookup);
+
+static inline void replace_sibling_entries(struct radix_tree_node *node,
+				void __rcu **slot, int count, int exceptional)
+{
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+	void *ptr = node_to_entry(slot);
+	unsigned offset = get_slot_offset(node, slot) + 1;
+
+	while (offset < RADIX_TREE_MAP_SIZE) {
+		if (rcu_dereference_raw(node->slots[offset]) != ptr)
+			break;
+		if (count < 0) {
+			node->slots[offset] = NULL;
+			node->count--;
+		}
+		node->exceptional += exceptional;
+		offset++;
+	}
+#endif
+}
+
+static void replace_slot(void __rcu **slot, void *item,
+		struct radix_tree_node *node, int count, int exceptional)
+{
+	if (WARN_ON_ONCE(radix_tree_is_internal_node(item)))
+		return;
+
+	if (node && (count || exceptional)) {
+		node->count += count;
+		node->exceptional += exceptional;
+		replace_sibling_entries(node, slot, count, exceptional);
+	}
+
+	rcu_assign_pointer(*slot, item);
+}
+
+static bool node_tag_get(const struct radix_tree_root *root,
+				const struct radix_tree_node *node,
+				unsigned int tag, unsigned int offset)
+{
+	if (node)
+		return tag_get(node, tag, offset);
+	return root_tag_get(root, tag);
+}
+
+/*
+ * IDR users want to be able to store NULL in the tree, so if the slot isn't
+ * free, don't adjust the count, even if it's transitioning between NULL and
+ * non-NULL.  For the IDA, we mark slots as being IDR_FREE while they still
+ * have empty bits, but it only stores NULL in slots when they're being
+ * deleted.
+ */
+static int calculate_count(struct radix_tree_root *root,
+				struct radix_tree_node *node, void __rcu **slot,
+				void *item, void *old)
+{
+	if (is_idr(root)) {
+		unsigned offset = get_slot_offset(node, slot);
+		bool free = node_tag_get(root, node, IDR_FREE, offset);
+		if (!free)
+			return 0;
+		if (!old)
+			return 1;
+	}
+	return !!item - !!old;
+}
+
+/**
+ * __radix_tree_replace		- replace item in a slot
+ * @root:		radix tree root
+ * @node:		pointer to tree node
+ * @slot:		pointer to slot in @node
+ * @item:		new item to store in the slot.
+ * @update_node:	callback for changing leaf nodes
+ *
+ * For use with __radix_tree_lookup().  Caller must hold tree write locked
+ * across slot lookup and replacement.
+ */
+void __radix_tree_replace(struct radix_tree_root *root,
+			  struct radix_tree_node *node,
+			  void __rcu **slot, void *item,
+			  radix_tree_update_node_t update_node)
+{
+	void *old = rcu_dereference_raw(*slot);
+	int exceptional = !!radix_tree_exceptional_entry(item) -
+				!!radix_tree_exceptional_entry(old);
+	int count = calculate_count(root, node, slot, item, old);
+
+	/*
+	 * This function supports replacing exceptional entries and
+	 * deleting entries, but that needs accounting against the
+	 * node unless the slot is root->rnode.
+	 */
+	WARN_ON_ONCE(!node && (slot != (void __rcu **)&root->rnode) &&
+			(count || exceptional));
+	replace_slot(slot, item, node, count, exceptional);
+
+	if (!node)
+		return;
+
+	if (update_node)
+		update_node(node);
+
+	delete_node(root, node, update_node);
+}
+
+/**
+ * radix_tree_replace_slot	- replace item in a slot
+ * @root:	radix tree root
+ * @slot:	pointer to slot
+ * @item:	new item to store in the slot.
+ *
+ * For use with radix_tree_lookup_slot(), radix_tree_gang_lookup_slot(),
+ * radix_tree_gang_lookup_tag_slot().  Caller must hold tree write locked
+ * across slot lookup and replacement.
+ *
+ * NOTE: This cannot be used to switch between non-entries (empty slots),
+ * regular entries, and exceptional entries, as that requires accounting
+ * inside the radix tree node. When switching from one type of entry or
+ * deleting, use __radix_tree_lookup() and __radix_tree_replace() or
+ * radix_tree_iter_replace().
+ */
+void radix_tree_replace_slot(struct radix_tree_root *root,
+			     void __rcu **slot, void *item)
+{
+	__radix_tree_replace(root, NULL, slot, item, NULL);
+}
+EXPORT_SYMBOL(radix_tree_replace_slot);
+
+/**
+ * radix_tree_iter_replace - replace item in a slot
+ * @root:	radix tree root
+ * @slot:	pointer to slot
+ * @item:	new item to store in the slot.
+ *
+ * For use with radix_tree_split() and radix_tree_for_each_slot().
+ * Caller must hold tree write locked across split and replacement.
+ */
+void radix_tree_iter_replace(struct radix_tree_root *root,
+				const struct radix_tree_iter *iter,
+				void __rcu **slot, void *item)
+{
+	__radix_tree_replace(root, iter->node, slot, item, NULL);
+}
+
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+/**
+ * radix_tree_join - replace multiple entries with one multiorder entry
+ * @root: radix tree root
+ * @index: an index inside the new entry
+ * @order: order of the new entry
+ * @item: new entry
+ *
+ * Call this function to replace several entries with one larger entry.
+ * The existing entries are presumed to not need freeing as a result of
+ * this call.
+ *
+ * The replacement entry will have all the tags set on it that were set
+ * on any of the entries it is replacing.
+ */
+int radix_tree_join(struct radix_tree_root *root, unsigned long index,
+			unsigned order, void *item)
+{
+	struct radix_tree_node *node;
+	void __rcu **slot;
+	int error;
+
+	BUG_ON(radix_tree_is_internal_node(item));
+
+	error = __radix_tree_create(root, index, order, &node, &slot);
+	if (!error)
+		error = insert_entries(node, slot, item, order, true);
+	if (error > 0)
+		error = 0;
+
+	return error;
+}
+
+/**
+ * radix_tree_split - Split an entry into smaller entries
+ * @root: radix tree root
+ * @index: An index within the large entry
+ * @order: Order of new entries
+ *
+ * Call this function as the first step in replacing a multiorder entry
+ * with several entries of lower order.  After this function returns,
+ * loop over the relevant portion of the tree using radix_tree_for_each_slot()
+ * and call radix_tree_iter_replace() to set up each new entry.
+ *
+ * The tags from this entry are replicated to all the new entries.
+ *
+ * The radix tree should be locked against modification during the entire
+ * replacement operation.  Lock-free lookups will see RADIX_TREE_RETRY which
+ * should prompt RCU walkers to restart the lookup from the root.
+ */
+int radix_tree_split(struct radix_tree_root *root, unsigned long index,
+				unsigned order)
+{
+	struct radix_tree_node *parent, *node, *child;
+	void __rcu **slot;
+	unsigned int offset, end;
+	unsigned n, tag, tags = 0;
+	gfp_t gfp = root_gfp_mask(root);
+
+	if (!__radix_tree_lookup(root, index, &parent, &slot))
+		return -ENOENT;
+	if (!parent)
+		return -ENOENT;
+
+	offset = get_slot_offset(parent, slot);
+
+	for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+		if (tag_get(parent, tag, offset))
+			tags |= 1 << tag;
+
+	for (end = offset + 1; end < RADIX_TREE_MAP_SIZE; end++) {
+		if (!is_sibling_entry(parent,
+				rcu_dereference_raw(parent->slots[end])))
+			break;
+		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+			if (tags & (1 << tag))
+				tag_set(parent, tag, end);
+		/* rcu_assign_pointer ensures tags are set before RETRY */
+		rcu_assign_pointer(parent->slots[end], RADIX_TREE_RETRY);
+	}
+	rcu_assign_pointer(parent->slots[offset], RADIX_TREE_RETRY);
+	parent->exceptional -= (end - offset);
+
+	if (order == parent->shift)
+		return 0;
+	if (order > parent->shift) {
+		while (offset < end)
+			offset += insert_entries(parent, &parent->slots[offset],
+					RADIX_TREE_RETRY, order, true);
+		return 0;
+	}
+
+	node = parent;
+
+	for (;;) {
+		if (node->shift > order) {
+			child = radix_tree_node_alloc(gfp, node, root,
+					node->shift - RADIX_TREE_MAP_SHIFT,
+					offset, 0, 0);
+			if (!child)
+				goto nomem;
+			if (node != parent) {
+				node->count++;
+				rcu_assign_pointer(node->slots[offset],
+							node_to_entry(child));
+				for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+					if (tags & (1 << tag))
+						tag_set(node, tag, offset);
+			}
+
+			node = child;
+			offset = 0;
+			continue;
+		}
+
+		n = insert_entries(node, &node->slots[offset],
+					RADIX_TREE_RETRY, order, false);
+		BUG_ON(n > RADIX_TREE_MAP_SIZE);
+
+		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+			if (tags & (1 << tag))
+				tag_set(node, tag, offset);
+		offset += n;
+
+		while (offset == RADIX_TREE_MAP_SIZE) {
+			if (node == parent)
+				break;
+			offset = node->offset;
+			child = node;
+			node = node->parent;
+			rcu_assign_pointer(node->slots[offset],
+						node_to_entry(child));
+			offset++;
+		}
+		if ((node == parent) && (offset == end))
+			return 0;
+	}
+
+ nomem:
+	/* Shouldn't happen; did user forget to preload? */
+	/* TODO: free all the allocated nodes */
+	WARN_ON(1);
+	return -ENOMEM;
+}
+#endif
+
+static void node_tag_set(struct radix_tree_root *root,
+				struct radix_tree_node *node,
+				unsigned int tag, unsigned int offset)
+{
+	while (node) {
+		if (tag_get(node, tag, offset))
+			return;
+		tag_set(node, tag, offset);
+		offset = node->offset;
+		node = node->parent;
+	}
+
+	if (!root_tag_get(root, tag))
+		root_tag_set(root, tag);
+}
+
+/**
+ *	radix_tree_tag_set - set a tag on a radix tree node
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@tag:		tag index
+ *
+ *	Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
+ *	corresponding to @index in the radix tree.  From
+ *	the root all the way down to the leaf node.
+ *
+ *	Returns the address of the tagged item.  Setting a tag on a not-present
+ *	item is a bug.
+ */
+void *radix_tree_tag_set(struct radix_tree_root *root,
+			unsigned long index, unsigned int tag)
+{
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+
+	radix_tree_load_root(root, &node, &maxindex);
+	BUG_ON(index > maxindex);
+
+	while (radix_tree_is_internal_node(node)) {
+		unsigned offset;
+
+		parent = entry_to_node(node);
+		offset = radix_tree_descend(parent, &node, index);
+		BUG_ON(!node);
+
+		if (!tag_get(parent, tag, offset))
+			tag_set(parent, tag, offset);
+	}
+
+	/* set the root's tag bit */
+	if (!root_tag_get(root, tag))
+		root_tag_set(root, tag);
+
+	return node;
+}
+EXPORT_SYMBOL(radix_tree_tag_set);
+
+/**
+ * radix_tree_iter_tag_set - set a tag on the current iterator entry
+ * @root:	radix tree root
+ * @iter:	iterator state
+ * @tag:	tag to set
+ */
+void radix_tree_iter_tag_set(struct radix_tree_root *root,
+			const struct radix_tree_iter *iter, unsigned int tag)
+{
+	node_tag_set(root, iter->node, tag, iter_offset(iter));
+}
+
+static void node_tag_clear(struct radix_tree_root *root,
+				struct radix_tree_node *node,
+				unsigned int tag, unsigned int offset)
+{
+	while (node) {
+		if (!tag_get(node, tag, offset))
+			return;
+		tag_clear(node, tag, offset);
+		if (any_tag_set(node, tag))
+			return;
+
+		offset = node->offset;
+		node = node->parent;
+	}
+
+	/* clear the root's tag bit */
+	if (root_tag_get(root, tag))
+		root_tag_clear(root, tag);
+}
+
+/**
+ *	radix_tree_tag_clear - clear a tag on a radix tree node
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@tag:		tag index
+ *
+ *	Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
+ *	corresponding to @index in the radix tree.  If this causes
+ *	the leaf node to have no tags set then clear the tag in the
+ *	next-to-leaf node, etc.
+ *
+ *	Returns the address of the tagged item on success, else NULL.  ie:
+ *	has the same return value and semantics as radix_tree_lookup().
+ */
+void *radix_tree_tag_clear(struct radix_tree_root *root,
+			unsigned long index, unsigned int tag)
+{
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+	int uninitialized_var(offset);
+
+	radix_tree_load_root(root, &node, &maxindex);
+	if (index > maxindex)
+		return NULL;
+
+	parent = NULL;
+
+	while (radix_tree_is_internal_node(node)) {
+		parent = entry_to_node(node);
+		offset = radix_tree_descend(parent, &node, index);
+	}
+
+	if (node)
+		node_tag_clear(root, parent, tag, offset);
+
+	return node;
+}
+EXPORT_SYMBOL(radix_tree_tag_clear);
+
+/**
+  * radix_tree_iter_tag_clear - clear a tag on the current iterator entry
+  * @root: radix tree root
+  * @iter: iterator state
+  * @tag: tag to clear
+  */
+void radix_tree_iter_tag_clear(struct radix_tree_root *root,
+			const struct radix_tree_iter *iter, unsigned int tag)
+{
+	node_tag_clear(root, iter->node, tag, iter_offset(iter));
+}
+
+/**
+ * radix_tree_tag_get - get a tag on a radix tree node
+ * @root:		radix tree root
+ * @index:		index key
+ * @tag:		tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ * Return values:
+ *
+ *  0: tag not present or not set
+ *  1: tag set
+ *
+ * Note that the return value of this function may not be relied on, even if
+ * the RCU lock is held, unless tag modification and node deletion are excluded
+ * from concurrency.
+ */
+int radix_tree_tag_get(const struct radix_tree_root *root,
+			unsigned long index, unsigned int tag)
+{
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+
+	if (!root_tag_get(root, tag))
+		return 0;
+
+	radix_tree_load_root(root, &node, &maxindex);
+	if (index > maxindex)
+		return 0;
+
+	while (radix_tree_is_internal_node(node)) {
+		unsigned offset;
+
+		parent = entry_to_node(node);
+		offset = radix_tree_descend(parent, &node, index);
+
+		if (!tag_get(parent, tag, offset))
+			return 0;
+		if (node == RADIX_TREE_RETRY)
+			break;
+	}
+
+	return 1;
+}
+EXPORT_SYMBOL(radix_tree_tag_get);
+
+static inline void __set_iter_shift(struct radix_tree_iter *iter,
+					unsigned int shift)
+{
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+	iter->shift = shift;
+#endif
+}
+
+/* Construct iter->tags bit-mask from node->tags[tag] array */
+static void set_iter_tags(struct radix_tree_iter *iter,
+				struct radix_tree_node *node, unsigned offset,
+				unsigned tag)
+{
+	unsigned tag_long = offset / BITS_PER_LONG;
+	unsigned tag_bit  = offset % BITS_PER_LONG;
+
+	if (!node) {
+		iter->tags = 1;
+		return;
+	}
+
+	iter->tags = node->tags[tag][tag_long] >> tag_bit;
+
+	/* This never happens if RADIX_TREE_TAG_LONGS == 1 */
+	if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
+		/* Pick tags from next element */
+		if (tag_bit)
+			iter->tags |= node->tags[tag][tag_long + 1] <<
+						(BITS_PER_LONG - tag_bit);
+		/* Clip chunk size, here only BITS_PER_LONG tags */
+		iter->next_index = __radix_tree_iter_add(iter, BITS_PER_LONG);
+	}
+}
+
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+static void __rcu **skip_siblings(struct radix_tree_node **nodep,
+			void __rcu **slot, struct radix_tree_iter *iter)
+{
+	while (iter->index < iter->next_index) {
+		*nodep = rcu_dereference_raw(*slot);
+		if (*nodep && !is_sibling_entry(iter->node, *nodep))
+			return slot;
+		slot++;
+		iter->index = __radix_tree_iter_add(iter, 1);
+		iter->tags >>= 1;
+	}
+
+	*nodep = NULL;
+	return NULL;
+}
+
+void __rcu **__radix_tree_next_slot(void __rcu **slot,
+				struct radix_tree_iter *iter, unsigned flags)
+{
+	unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;
+	struct radix_tree_node *node;
+
+	slot = skip_siblings(&node, slot, iter);
+
+	while (radix_tree_is_internal_node(node)) {
+		unsigned offset;
+		unsigned long next_index;
+
+		if (node == RADIX_TREE_RETRY)
+			return slot;
+		node = entry_to_node(node);
+		iter->node = node;
+		iter->shift = node->shift;
+
+		if (flags & RADIX_TREE_ITER_TAGGED) {
+			offset = radix_tree_find_next_bit(node, tag, 0);
+			if (offset == RADIX_TREE_MAP_SIZE)
+				return NULL;
+			slot = &node->slots[offset];
+			iter->index = __radix_tree_iter_add(iter, offset);
+			set_iter_tags(iter, node, offset, tag);
+			node = rcu_dereference_raw(*slot);
+		} else {
+			offset = 0;
+			slot = &node->slots[0];
+			for (;;) {
+				node = rcu_dereference_raw(*slot);
+				if (node)
+					break;
+				slot++;
+				offset++;
+				if (offset == RADIX_TREE_MAP_SIZE)
+					return NULL;
+			}
+			iter->index = __radix_tree_iter_add(iter, offset);
+		}
+		if ((flags & RADIX_TREE_ITER_CONTIG) && (offset > 0))
+			goto none;
+		next_index = (iter->index | shift_maxindex(iter->shift)) + 1;
+		if (next_index < iter->next_index)
+			iter->next_index = next_index;
+	}
+
+	return slot;
+ none:
+	iter->next_index = 0;
+	return NULL;
+}
+EXPORT_SYMBOL(__radix_tree_next_slot);
+#else
+static void __rcu **skip_siblings(struct radix_tree_node **nodep,
+			void __rcu **slot, struct radix_tree_iter *iter)
+{
+	return slot;
+}
+#endif
+
+void __rcu **radix_tree_iter_resume(void __rcu **slot,
+					struct radix_tree_iter *iter)
+{
+	struct radix_tree_node *node;
+
+	slot++;
+	iter->index = __radix_tree_iter_add(iter, 1);
+	skip_siblings(&node, slot, iter);
+	iter->next_index = iter->index;
+	iter->tags = 0;
+	return NULL;
+}
+EXPORT_SYMBOL(radix_tree_iter_resume);
+
+/**
+ * radix_tree_next_chunk - find next chunk of slots for iteration
+ *
+ * @root:	radix tree root
+ * @iter:	iterator state
+ * @flags:	RADIX_TREE_ITER_* flags and tag index
+ * Returns:	pointer to chunk first slot, or NULL if iteration is over
+ */
+void __rcu **radix_tree_next_chunk(const struct radix_tree_root *root,
+			     struct radix_tree_iter *iter, unsigned flags)
+{
+	unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;
+	struct radix_tree_node *node, *child;
+	unsigned long index, offset, maxindex;
+
+	if ((flags & RADIX_TREE_ITER_TAGGED) && !root_tag_get(root, tag))
+		return NULL;
+
+	/*
+	 * Catch next_index overflow after ~0UL. iter->index never overflows
+	 * during iterating; it can be zero only at the beginning.
+	 * And we cannot overflow iter->next_index in a single step,
+	 * because RADIX_TREE_MAP_SHIFT < BITS_PER_LONG.
+	 *
+	 * This condition also used by radix_tree_next_slot() to stop
+	 * contiguous iterating, and forbid switching to the next chunk.
+	 */
+	index = iter->next_index;
+	if (!index && iter->index)
+		return NULL;
+
+ restart:
+	radix_tree_load_root(root, &child, &maxindex);
+	if (index > maxindex)
+		return NULL;
+	if (!child)
+		return NULL;
+
+	if (!radix_tree_is_internal_node(child)) {
+		/* Single-slot tree */
+		iter->index = index;
+		iter->next_index = maxindex + 1;
+		iter->tags = 1;
+		iter->node = NULL;
+		__set_iter_shift(iter, 0);
+		return (void __rcu **)&root->rnode;
+	}
+
+	do {
+		node = entry_to_node(child);
+		offset = radix_tree_descend(node, &child, index);
+
+		if ((flags & RADIX_TREE_ITER_TAGGED) ?
+				!tag_get(node, tag, offset) : !child) {
+			/* Hole detected */
+			if (flags & RADIX_TREE_ITER_CONTIG)
+				return NULL;
+
+			if (flags & RADIX_TREE_ITER_TAGGED)
+				offset = radix_tree_find_next_bit(node, tag,
+						offset + 1);
+			else
+				while (++offset	< RADIX_TREE_MAP_SIZE) {
+					void *slot = rcu_dereference_raw(
+							node->slots[offset]);
+					if (is_sibling_entry(node, slot))
+						continue;
+					if (slot)
+						break;
+				}
+			index &= ~node_maxindex(node);
+			index += offset << node->shift;
+			/* Overflow after ~0UL */
+			if (!index)
+				return NULL;
+			if (offset == RADIX_TREE_MAP_SIZE)
+				goto restart;
+			child = rcu_dereference_raw(node->slots[offset]);
+		}
+
+		if (!child)
+			goto restart;
+		if (child == RADIX_TREE_RETRY)
+			break;
+	} while (radix_tree_is_internal_node(child));
+
+	/* Update the iterator state */
+	iter->index = (index &~ node_maxindex(node)) | (offset << node->shift);
+	iter->next_index = (index | node_maxindex(node)) + 1;
+	iter->node = node;
+	__set_iter_shift(iter, node->shift);
+
+	if (flags & RADIX_TREE_ITER_TAGGED)
+		set_iter_tags(iter, node, offset, tag);
+
+	return node->slots + offset;
+}
+EXPORT_SYMBOL(radix_tree_next_chunk);
+
+/**
+ *	radix_tree_gang_lookup - perform multiple lookup on a radix tree
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *
+ *	Performs an index-ascending scan of the tree for present items.  Places
+ *	them at *@results and returns the number of items which were placed at
+ *	*@results.
+ *
+ *	The implementation is naive.
+ *
+ *	Like radix_tree_lookup, radix_tree_gang_lookup may be called under
+ *	rcu_read_lock. In this case, rather than the returned results being
+ *	an atomic snapshot of the tree at a single point in time, the
+ *	semantics of an RCU protected gang lookup are as though multiple
+ *	radix_tree_lookups have been issued in individual locks, and results
+ *	stored in 'results'.
+ */
+unsigned int
+radix_tree_gang_lookup(const struct radix_tree_root *root, void **results,
+			unsigned long first_index, unsigned int max_items)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!max_items))
+		return 0;
+
+	radix_tree_for_each_slot(slot, root, &iter, first_index) {
+		results[ret] = rcu_dereference_raw(*slot);
+		if (!results[ret])
+			continue;
+		if (radix_tree_is_internal_node(results[ret])) {
+			slot = radix_tree_iter_retry(&iter);
+			continue;
+		}
+		if (++ret == max_items)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup);
+
+/**
+ *	radix_tree_gang_lookup_slot - perform multiple slot lookup on radix tree
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@indices:	where their indices should be placed (but usually NULL)
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *
+ *	Performs an index-ascending scan of the tree for present items.  Places
+ *	their slots at *@results and returns the number of items which were
+ *	placed at *@results.
+ *
+ *	The implementation is naive.
+ *
+ *	Like radix_tree_gang_lookup as far as RCU and locking goes. Slots must
+ *	be dereferenced with radix_tree_deref_slot, and if using only RCU
+ *	protection, radix_tree_deref_slot may fail requiring a retry.
+ */
+unsigned int
+radix_tree_gang_lookup_slot(const struct radix_tree_root *root,
+			void __rcu ***results, unsigned long *indices,
+			unsigned long first_index, unsigned int max_items)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!max_items))
+		return 0;
+
+	radix_tree_for_each_slot(slot, root, &iter, first_index) {
+		results[ret] = slot;
+		if (indices)
+			indices[ret] = iter.index;
+		if (++ret == max_items)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup_slot);
+
+/**
+ *	radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
+ *	                             based on a tag
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ *	Performs an index-ascending scan of the tree for present items which
+ *	have the tag indexed by @tag set.  Places the items at *@results and
+ *	returns the number of items which were placed at *@results.
+ */
+unsigned int
+radix_tree_gang_lookup_tag(const struct radix_tree_root *root, void **results,
+		unsigned long first_index, unsigned int max_items,
+		unsigned int tag)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!max_items))
+		return 0;
+
+	radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
+		results[ret] = rcu_dereference_raw(*slot);
+		if (!results[ret])
+			continue;
+		if (radix_tree_is_internal_node(results[ret])) {
+			slot = radix_tree_iter_retry(&iter);
+			continue;
+		}
+		if (++ret == max_items)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
+
+/**
+ *	radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
+ *					  radix tree based on a tag
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ *	Performs an index-ascending scan of the tree for present items which
+ *	have the tag indexed by @tag set.  Places the slots at *@results and
+ *	returns the number of slots which were placed at *@results.
+ */
+unsigned int
+radix_tree_gang_lookup_tag_slot(const struct radix_tree_root *root,
+		void __rcu ***results, unsigned long first_index,
+		unsigned int max_items, unsigned int tag)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!max_items))
+		return 0;
+
+	radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
+		results[ret] = slot;
+		if (++ret == max_items)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
+
+/**
+ *	__radix_tree_delete_node    -    try to free node after clearing a slot
+ *	@root:		radix tree root
+ *	@node:		node containing @index
+ *	@update_node:	callback for changing leaf nodes
+ *
+ *	After clearing the slot at @index in @node from radix tree
+ *	rooted at @root, call this function to attempt freeing the
+ *	node and shrinking the tree.
+ */
+void __radix_tree_delete_node(struct radix_tree_root *root,
+			      struct radix_tree_node *node,
+			      radix_tree_update_node_t update_node)
+{
+	delete_node(root, node, update_node);
+}
+
+static bool __radix_tree_delete(struct radix_tree_root *root,
+				struct radix_tree_node *node, void __rcu **slot)
+{
+	void *old = rcu_dereference_raw(*slot);
+	int exceptional = radix_tree_exceptional_entry(old) ? -1 : 0;
+	unsigned offset = get_slot_offset(node, slot);
+	int tag;
+
+	if (is_idr(root))
+		node_tag_set(root, node, IDR_FREE, offset);
+	else
+		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+			node_tag_clear(root, node, tag, offset);
+
+	replace_slot(slot, NULL, node, -1, exceptional);
+	return node && delete_node(root, node, NULL);
+}
+
+/**
+ * radix_tree_iter_delete - delete the entry at this iterator position
+ * @root: radix tree root
+ * @iter: iterator state
+ * @slot: pointer to slot
+ *
+ * Delete the entry at the position currently pointed to by the iterator.
+ * This may result in the current node being freed; if it is, the iterator
+ * is advanced so that it will not reference the freed memory.  This
+ * function may be called without any locking if there are no other threads
+ * which can access this tree.
+ */
+void radix_tree_iter_delete(struct radix_tree_root *root,
+				struct radix_tree_iter *iter, void __rcu **slot)
+{
+	if (__radix_tree_delete(root, iter->node, slot))
+		iter->index = iter->next_index;
+}
+EXPORT_SYMBOL(radix_tree_iter_delete);
+
+/**
+ * radix_tree_delete_item - delete an item from a radix tree
+ * @root: radix tree root
+ * @index: index key
+ * @item: expected item
+ *
+ * Remove @item at @index from the radix tree rooted at @root.
+ *
+ * Return: the deleted entry, or %NULL if it was not present
+ * or the entry at the given @index was not @item.
+ */
+void *radix_tree_delete_item(struct radix_tree_root *root,
+			     unsigned long index, void *item)
+{
+	struct radix_tree_node *node = NULL;
+	void __rcu **slot = NULL;
+	void *entry;
+
+	entry = __radix_tree_lookup(root, index, &node, &slot);
+	if (!slot)
+		return NULL;
+	if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE,
+						get_slot_offset(node, slot))))
+		return NULL;
+
+	if (item && entry != item)
+		return NULL;
+
+	__radix_tree_delete(root, node, slot);
+
+	return entry;
+}
+EXPORT_SYMBOL(radix_tree_delete_item);
+
+/**
+ * radix_tree_delete - delete an entry from a radix tree
+ * @root: radix tree root
+ * @index: index key
+ *
+ * Remove the entry at @index from the radix tree rooted at @root.
+ *
+ * Return: The deleted entry, or %NULL if it was not present.
+ */
+void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
+{
+	return radix_tree_delete_item(root, index, NULL);
+}
+EXPORT_SYMBOL(radix_tree_delete);
+
+void radix_tree_clear_tags(struct radix_tree_root *root,
+			   struct radix_tree_node *node,
+			   void __rcu **slot)
+{
+	if (node) {
+		unsigned int tag, offset = get_slot_offset(node, slot);
+		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+			node_tag_clear(root, node, tag, offset);
+	} else {
+		root_tag_clear_all(root);
+	}
+}
+
+/**
+ *	radix_tree_tagged - test whether any items in the tree are tagged
+ *	@root:		radix tree root
+ *	@tag:		tag to test
+ */
+int radix_tree_tagged(const struct radix_tree_root *root, unsigned int tag)
+{
+	return root_tag_get(root, tag);
+}
+EXPORT_SYMBOL(radix_tree_tagged);
+
+/**
+ * idr_preload - preload for idr_alloc()
+ * @gfp_mask: allocation mask to use for preloading
+ *
+ * Preallocate memory to use for the next call to idr_alloc().  This function
+ * returns with preemption disabled.  It will be enabled by idr_preload_end().
+ */
+void idr_preload(gfp_t gfp_mask)
+{
+	if (__radix_tree_preload(gfp_mask, IDR_PRELOAD_SIZE))
+		preempt_disable();
+}
+EXPORT_SYMBOL(idr_preload);
+
+int ida_pre_get(struct ida *ida, gfp_t gfp)
+{
+	/*
+	 * The IDA API has no preload_end() equivalent.  Instead,
+	 * ida_get_new() can return -EAGAIN, prompting the caller
+	 * to return to the ida_pre_get() step.
+	 */
+	if (!__radix_tree_preload(gfp, IDA_PRELOAD_SIZE))
+		preempt_enable();
+
+	if (!this_cpu_read(ida_bitmap)) {
+		struct ida_bitmap *bitmap = kzalloc(sizeof(*bitmap), gfp);
+		if (!bitmap)
+			return 0;
+		if (this_cpu_cmpxchg(ida_bitmap, NULL, bitmap))
+			kfree(bitmap);
+	}
+
+	return 1;
+}
+
+void __rcu **idr_get_free(struct radix_tree_root *root,
+			      struct radix_tree_iter *iter, gfp_t gfp,
+			      unsigned long max)
+{
+	struct radix_tree_node *node = NULL, *child;
+	void __rcu **slot = (void __rcu **)&root->rnode;
+	unsigned long maxindex, start = iter->next_index;
+	unsigned int shift, offset = 0;
+
+ grow:
+	shift = radix_tree_load_root(root, &child, &maxindex);
+	if (!radix_tree_tagged(root, IDR_FREE))
+		start = max(start, maxindex + 1);
+	if (start > max)
+		return ERR_PTR(-ENOSPC);
+
+	if (start > maxindex) {
+		int error = radix_tree_extend(root, gfp, start, shift);
+		if (error < 0)
+			return ERR_PTR(error);
+		shift = error;
+		child = rcu_dereference_raw(root->rnode);
+	}
+
+	while (shift) {
+		shift -= RADIX_TREE_MAP_SHIFT;
+		if (child == NULL) {
+			/* Have to add a child node.  */
+			child = radix_tree_node_alloc(gfp, node, root, shift,
+							offset, 0, 0);
+			if (!child)
+				return ERR_PTR(-ENOMEM);
+			all_tag_set(child, IDR_FREE);
+			rcu_assign_pointer(*slot, node_to_entry(child));
+			if (node)
+				node->count++;
+		} else if (!radix_tree_is_internal_node(child))
+			break;
+
+		node = entry_to_node(child);
+		offset = radix_tree_descend(node, &child, start);
+		if (!tag_get(node, IDR_FREE, offset)) {
+			offset = radix_tree_find_next_bit(node, IDR_FREE,
+							offset + 1);
+			start = next_index(start, node, offset);
+			if (start > max || start == 0)
+				return ERR_PTR(-ENOSPC);
+			while (offset == RADIX_TREE_MAP_SIZE) {
+				offset = node->offset + 1;
+				node = node->parent;
+				if (!node)
+					goto grow;
+				shift = node->shift;
+			}
+			child = rcu_dereference_raw(node->slots[offset]);
+		}
+		slot = &node->slots[offset];
+	}
+
+	iter->index = start;
+	if (node)
+		iter->next_index = 1 + min(max, (start | node_maxindex(node)));
+	else
+		iter->next_index = 1;
+	iter->node = node;
+	__set_iter_shift(iter, shift);
+	set_iter_tags(iter, node, offset, IDR_FREE);
+
+	return slot;
+}
+
+/**
+ * idr_destroy - release all internal memory from an IDR
+ * @idr: idr handle
+ *
+ * After this function is called, the IDR is empty, and may be reused or
+ * the data structure containing it may be freed.
+ *
+ * A typical clean-up sequence for objects stored in an idr tree will use
+ * idr_for_each() to free all objects, if necessary, then idr_destroy() to
+ * free the memory used to keep track of those objects.
+ */
+void idr_destroy(struct idr *idr)
+{
+	struct radix_tree_node *node = rcu_dereference_raw(idr->idr_rt.rnode);
+	if (radix_tree_is_internal_node(node))
+		radix_tree_free_nodes(node);
+	idr->idr_rt.rnode = NULL;
+	root_tag_set(&idr->idr_rt, IDR_FREE);
+}
+EXPORT_SYMBOL(idr_destroy);
+
+static void
+radix_tree_node_ctor(void *arg)
+{
+	struct radix_tree_node *node = arg;
+
+	memset(node, 0, sizeof(*node));
+	INIT_LIST_HEAD(&node->private_list);
+}
+
+static __init unsigned long __maxindex(unsigned int height)
+{
+	unsigned int width = height * RADIX_TREE_MAP_SHIFT;
+	int shift = RADIX_TREE_INDEX_BITS - width;
+
+	if (shift < 0)
+		return ~0UL;
+	if (shift >= BITS_PER_LONG)
+		return 0UL;
+	return ~0UL >> shift;
+}
+
+static __init void radix_tree_init_maxnodes(void)
+{
+	unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH + 1];
+	unsigned int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
+		height_to_maxindex[i] = __maxindex(i);
+	for (i = 0; i < ARRAY_SIZE(height_to_maxnodes); i++) {
+		for (j = i; j > 0; j--)
+			height_to_maxnodes[i] += height_to_maxindex[j - 1] + 1;
+	}
+}
+
+static int radix_tree_cpu_dead(unsigned int cpu)
+{
+	struct radix_tree_preload *rtp;
+	struct radix_tree_node *node;
+
+	/* Free per-cpu pool of preloaded nodes */
+	rtp = &per_cpu(radix_tree_preloads, cpu);
+	while (rtp->nr) {
+		node = rtp->nodes;
+		rtp->nodes = node->parent;
+		kmem_cache_free(radix_tree_node_cachep, node);
+		rtp->nr--;
+	}
+	kfree(per_cpu(ida_bitmap, cpu));
+	per_cpu(ida_bitmap, cpu) = NULL;
+	return 0;
+}
+
+void __init radix_tree_init(void)
+{
+	int ret;
+
+	BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32);
+	BUILD_BUG_ON(ROOT_IS_IDR & ~GFP_ZONEMASK);
+	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
+			sizeof(struct radix_tree_node), 0,
+			SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
+			radix_tree_node_ctor);
+	radix_tree_init_maxnodes();
+	ret = cpuhp_setup_state_nocalls(CPUHP_RADIX_DEAD, "lib/radix:dead",
+					NULL, radix_tree_cpu_dead);
+	WARN_ON(ret < 0);
+}