Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 1608 insertions, 0 deletions

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
new file mode 100644
index 000000000..976b9bd02
--- /dev/null
+++ b/lib/radix-tree.c
@@ -0,0 +1,1608 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2001 Momchil Velikov
+ * Portions Copyright (C) 2001 Christoph Hellwig
+ * Copyright (C) 2005 SGI, Christoph Lameter
+ * Copyright (C) 2006 Nick Piggin
+ * Copyright (C) 2012 Konstantin Khlebnikov
+ * Copyright (C) 2016 Intel, Matthew Wilcox
+ * Copyright (C) 2016 Intel, Ross Zwisler
+ */
+
+#include <linux/bitmap.h>
+#include <linux/bitops.h>
+#include <linux/bug.h>
+#include <linux/cpu.h>
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <linux/idr.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/kmemleak.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>		/* in_interrupt() */
+#include <linux/radix-tree.h>
+#include <linux/rcupdate.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/xarray.h>
+
+#include "radix-tree.h"
+
+/*
+ * Radix tree node cache.
+ */
+struct kmem_cache *radix_tree_node_cachep;
+
+/*
+ * The radix tree is variable-height, so an insert operation not only has
+ * to build the branch to its corresponding item, it also has to build the
+ * branch to existing items if the size has to be increased (by
+ * radix_tree_extend).
+ *
+ * The worst case is a zero height tree with just a single item at index 0,
+ * and then inserting an item at index ULONG_MAX. This requires 2 new branches
+ * of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
+ * Hence:
+ */
+#define RADIX_TREE_PRELOAD_SIZE (RADIX_TREE_MAX_PATH * 2 - 1)
+
+/*
+ * The IDR does not have to be as high as the radix tree since it uses
+ * signed integers, not unsigned longs.
+ */
+#define IDR_INDEX_BITS		(8 /* CHAR_BIT */ * sizeof(int) - 1)
+#define IDR_MAX_PATH		(DIV_ROUND_UP(IDR_INDEX_BITS, \
+						RADIX_TREE_MAP_SHIFT))
+#define IDR_PRELOAD_SIZE	(IDR_MAX_PATH * 2 - 1)
+
+/*
+ * Per-cpu pool of preloaded nodes
+ */
+DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = {
+	.lock = INIT_LOCAL_LOCK(lock),
+};
+EXPORT_PER_CPU_SYMBOL_GPL(radix_tree_preloads);
+
+static inline struct radix_tree_node *entry_to_node(void *ptr)
+{
+	return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
+}
+
+static inline void *node_to_entry(void *ptr)
+{
+	return (void *)((unsigned long)ptr | RADIX_TREE_INTERNAL_NODE);
+}
+
+#define RADIX_TREE_RETRY	XA_RETRY_ENTRY
+
+static inline unsigned long
+get_slot_offset(const struct radix_tree_node *parent, void __rcu **slot)
+{
+	return parent ? slot - parent->slots : 0;
+}
+
+static unsigned int radix_tree_descend(const struct radix_tree_node *parent,
+			struct radix_tree_node **nodep, unsigned long index)
+{
+	unsigned int offset = (index >> parent->shift) & RADIX_TREE_MAP_MASK;
+	void __rcu **entry = rcu_dereference_raw(parent->slots[offset]);
+
+	*nodep = (void *)entry;
+	return offset;
+}
+
+static inline gfp_t root_gfp_mask(const struct radix_tree_root *root)
+{
+	return root->xa_flags & (__GFP_BITS_MASK & ~GFP_ZONEMASK);
+}
+
+static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
+		int offset)
+{
+	__set_bit(offset, node->tags[tag]);
+}
+
+static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
+		int offset)
+{
+	__clear_bit(offset, node->tags[tag]);
+}
+
+static inline int tag_get(const struct radix_tree_node *node, unsigned int tag,
+		int offset)
+{
+	return test_bit(offset, node->tags[tag]);
+}
+
+static inline void root_tag_set(struct radix_tree_root *root, unsigned tag)
+{
+	root->xa_flags |= (__force gfp_t)(1 << (tag + ROOT_TAG_SHIFT));
+}
+
+static inline void root_tag_clear(struct radix_tree_root *root, unsigned tag)
+{
+	root->xa_flags &= (__force gfp_t)~(1 << (tag + ROOT_TAG_SHIFT));
+}
+
+static inline void root_tag_clear_all(struct radix_tree_root *root)
+{
+	root->xa_flags &= (__force gfp_t)((1 << ROOT_TAG_SHIFT) - 1);
+}
+
+static inline int root_tag_get(const struct radix_tree_root *root, unsigned tag)
+{
+	return (__force int)root->xa_flags & (1 << (tag + ROOT_TAG_SHIFT));
+}
+
+static inline unsigned root_tags_get(const struct radix_tree_root *root)
+{
+	return (__force unsigned)root->xa_flags >> ROOT_TAG_SHIFT;
+}
+
+static inline bool is_idr(const struct radix_tree_root *root)
+{
+	return !!(root->xa_flags & ROOT_IS_IDR);
+}
+
+/*
+ * Returns 1 if any slot in the node has this tag set.
+ * Otherwise returns 0.
+ */
+static inline int any_tag_set(const struct radix_tree_node *node,
+							unsigned int tag)
+{
+	unsigned idx;
+	for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
+		if (node->tags[tag][idx])
+			return 1;
+	}
+	return 0;
+}
+
+static inline void all_tag_set(struct radix_tree_node *node, unsigned int tag)
+{
+	bitmap_fill(node->tags[tag], RADIX_TREE_MAP_SIZE);
+}
+
+/**
+ * radix_tree_find_next_bit - find the next set bit in a memory region
+ *
+ * @node: where to begin the search
+ * @tag: the tag index
+ * @offset: the bitnumber to start searching at
+ *
+ * Unrollable variant of find_next_bit() for constant size arrays.
+ * Tail bits starting from size to roundup(size, BITS_PER_LONG) must be zero.
+ * Returns next bit offset, or size if nothing found.
+ */
+static __always_inline unsigned long
+radix_tree_find_next_bit(struct radix_tree_node *node, unsigned int tag,
+			 unsigned long offset)
+{
+	const unsigned long *addr = node->tags[tag];
+
+	if (offset < RADIX_TREE_MAP_SIZE) {
+		unsigned long tmp;
+
+		addr += offset / BITS_PER_LONG;
+		tmp = *addr >> (offset % BITS_PER_LONG);
+		if (tmp)
+			return __ffs(tmp) + offset;
+		offset = (offset + BITS_PER_LONG) & ~(BITS_PER_LONG - 1);
+		while (offset < RADIX_TREE_MAP_SIZE) {
+			tmp = *++addr;
+			if (tmp)
+				return __ffs(tmp) + offset;
+			offset += BITS_PER_LONG;
+		}
+	}
+	return RADIX_TREE_MAP_SIZE;
+}
+
+static unsigned int iter_offset(const struct radix_tree_iter *iter)
+{
+	return iter->index & RADIX_TREE_MAP_MASK;
+}
+
+/*
+ * The maximum index which can be stored in a radix tree
+ */
+static inline unsigned long shift_maxindex(unsigned int shift)
+{
+	return (RADIX_TREE_MAP_SIZE << shift) - 1;
+}
+
+static inline unsigned long node_maxindex(const struct radix_tree_node *node)
+{
+	return shift_maxindex(node->shift);
+}
+
+static unsigned long next_index(unsigned long index,
+				const struct radix_tree_node *node,
+				unsigned long offset)
+{
+	return (index & ~node_maxindex(node)) + (offset << node->shift);
+}
+
+/*
+ * This assumes that the caller has performed appropriate preallocation, and
+ * that the caller has pinned this thread of control to the current CPU.
+ */
+static struct radix_tree_node *
+radix_tree_node_alloc(gfp_t gfp_mask, struct radix_tree_node *parent,
+			struct radix_tree_root *root,
+			unsigned int shift, unsigned int offset,
+			unsigned int count, unsigned int nr_values)
+{
+	struct radix_tree_node *ret = NULL;
+
+	/*
+	 * Preload code isn't irq safe and it doesn't make sense to use
+	 * preloading during an interrupt anyway as all the allocations have
+	 * to be atomic. So just do normal allocation when in interrupt.
+	 */
+	if (!gfpflags_allow_blocking(gfp_mask) && !in_interrupt()) {
+		struct radix_tree_preload *rtp;
+
+		/*
+		 * Even if the caller has preloaded, try to allocate from the
+		 * cache first for the new node to get accounted to the memory
+		 * cgroup.
+		 */
+		ret = kmem_cache_alloc(radix_tree_node_cachep,
+				       gfp_mask | __GFP_NOWARN);
+		if (ret)
+			goto out;
+
+		/*
+		 * Provided the caller has preloaded here, we will always
+		 * succeed in getting a node here (and never reach
+		 * kmem_cache_alloc)
+		 */
+		rtp = this_cpu_ptr(&radix_tree_preloads);
+		if (rtp->nr) {
+			ret = rtp->nodes;
+			rtp->nodes = ret->parent;
+			rtp->nr--;
+		}
+		/*
+		 * Update the allocation stack trace as this is more useful
+		 * for debugging.
+		 */
+		kmemleak_update_trace(ret);
+		goto out;
+	}
+	ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
+out:
+	BUG_ON(radix_tree_is_internal_node(ret));
+	if (ret) {
+		ret->shift = shift;
+		ret->offset = offset;
+		ret->count = count;
+		ret->nr_values = nr_values;
+		ret->parent = parent;
+		ret->array = root;
+	}
+	return ret;
+}
+
+void radix_tree_node_rcu_free(struct rcu_head *head)
+{
+	struct radix_tree_node *node =
+			container_of(head, struct radix_tree_node, rcu_head);
+
+	/*
+	 * Must only free zeroed nodes into the slab.  We can be left with
+	 * non-NULL entries by radix_tree_free_nodes, so clear the entries
+	 * and tags here.
+	 */
+	memset(node->slots, 0, sizeof(node->slots));
+	memset(node->tags, 0, sizeof(node->tags));
+	INIT_LIST_HEAD(&node->private_list);
+
+	kmem_cache_free(radix_tree_node_cachep, node);
+}
+
+static inline void
+radix_tree_node_free(struct radix_tree_node *node)
+{
+	call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
+}
+
+/*
+ * Load up this CPU's radix_tree_node buffer with sufficient objects to
+ * ensure that the addition of a single element in the tree cannot fail.  On
+ * success, return zero, with preemption disabled.  On error, return -ENOMEM
+ * with preemption not disabled.
+ *
+ * To make use of this facility, the radix tree must be initialised without
+ * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
+ */
+static __must_check int __radix_tree_preload(gfp_t gfp_mask, unsigned nr)
+{
+	struct radix_tree_preload *rtp;
+	struct radix_tree_node *node;
+	int ret = -ENOMEM;
+
+	/*
+	 * Nodes preloaded by one cgroup can be used by another cgroup, so
+	 * they should never be accounted to any particular memory cgroup.
+	 */
+	gfp_mask &= ~__GFP_ACCOUNT;
+
+	local_lock(&radix_tree_preloads.lock);
+	rtp = this_cpu_ptr(&radix_tree_preloads);
+	while (rtp->nr < nr) {
+		local_unlock(&radix_tree_preloads.lock);
+		node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
+		if (node == NULL)
+			goto out;
+		local_lock(&radix_tree_preloads.lock);
+		rtp = this_cpu_ptr(&radix_tree_preloads);
+		if (rtp->nr < nr) {
+			node->parent = rtp->nodes;
+			rtp->nodes = node;
+			rtp->nr++;
+		} else {
+			kmem_cache_free(radix_tree_node_cachep, node);
+		}
+	}
+	ret = 0;
+out:
+	return ret;
+}
+
+/*
+ * Load up this CPU's radix_tree_node buffer with sufficient objects to
+ * ensure that the addition of a single element in the tree cannot fail.  On
+ * success, return zero, with preemption disabled.  On error, return -ENOMEM
+ * with preemption not disabled.
+ *
+ * To make use of this facility, the radix tree must be initialised without
+ * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
+ */
+int radix_tree_preload(gfp_t gfp_mask)
+{
+	/* Warn on non-sensical use... */
+	WARN_ON_ONCE(!gfpflags_allow_blocking(gfp_mask));
+	return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
+}
+EXPORT_SYMBOL(radix_tree_preload);
+
+/*
+ * The same as above function, except we don't guarantee preloading happens.
+ * We do it, if we decide it helps. On success, return zero with preemption
+ * disabled. On error, return -ENOMEM with preemption not disabled.
+ */
+int radix_tree_maybe_preload(gfp_t gfp_mask)
+{
+	if (gfpflags_allow_blocking(gfp_mask))
+		return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
+	/* Preloading doesn't help anything with this gfp mask, skip it */
+	local_lock(&radix_tree_preloads.lock);
+	return 0;
+}
+EXPORT_SYMBOL(radix_tree_maybe_preload);
+
+static unsigned radix_tree_load_root(const struct radix_tree_root *root,
+		struct radix_tree_node **nodep, unsigned long *maxindex)
+{
+	struct radix_tree_node *node = rcu_dereference_raw(root->xa_head);
+
+	*nodep = node;
+
+	if (likely(radix_tree_is_internal_node(node))) {
+		node = entry_to_node(node);
+		*maxindex = node_maxindex(node);
+		return node->shift + RADIX_TREE_MAP_SHIFT;
+	}
+
+	*maxindex = 0;
+	return 0;
+}
+
+/*
+ *	Extend a radix tree so it can store key @index.
+ */
+static int radix_tree_extend(struct radix_tree_root *root, gfp_t gfp,
+				unsigned long index, unsigned int shift)
+{
+	void *entry;
+	unsigned int maxshift;
+	int tag;
+
+	/* Figure out what the shift should be.  */
+	maxshift = shift;
+	while (index > shift_maxindex(maxshift))
+		maxshift += RADIX_TREE_MAP_SHIFT;
+
+	entry = rcu_dereference_raw(root->xa_head);
+	if (!entry && (!is_idr(root) || root_tag_get(root, IDR_FREE)))
+		goto out;
+
+	do {
+		struct radix_tree_node *node = radix_tree_node_alloc(gfp, NULL,
+							root, shift, 0, 1, 0);
+		if (!node)
+			return -ENOMEM;
+
+		if (is_idr(root)) {
+			all_tag_set(node, IDR_FREE);
+			if (!root_tag_get(root, IDR_FREE)) {
+				tag_clear(node, IDR_FREE, 0);
+				root_tag_set(root, IDR_FREE);
+			}
+		} else {
+			/* Propagate the aggregated tag info to the new child */
+			for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
+				if (root_tag_get(root, tag))
+					tag_set(node, tag, 0);
+			}
+		}
+
+		BUG_ON(shift > BITS_PER_LONG);
+		if (radix_tree_is_internal_node(entry)) {
+			entry_to_node(entry)->parent = node;
+		} else if (xa_is_value(entry)) {
+			/* Moving a value entry root->xa_head to a node */
+			node->nr_values = 1;
+		}
+		/*
+		 * entry was already in the radix tree, so we do not need
+		 * rcu_assign_pointer here
+		 */
+		node->slots[0] = (void __rcu *)entry;
+		entry = node_to_entry(node);
+		rcu_assign_pointer(root->xa_head, entry);
+		shift += RADIX_TREE_MAP_SHIFT;
+	} while (shift <= maxshift);
+out:
+	return maxshift + RADIX_TREE_MAP_SHIFT;
+}
+
+/**
+ *	radix_tree_shrink    -    shrink radix tree to minimum height
+ *	@root:		radix tree root
+ */
+static inline bool radix_tree_shrink(struct radix_tree_root *root)
+{
+	bool shrunk = false;
+
+	for (;;) {
+		struct radix_tree_node *node = rcu_dereference_raw(root->xa_head);
+		struct radix_tree_node *child;
+
+		if (!radix_tree_is_internal_node(node))
+			break;
+		node = entry_to_node(node);
+
+		/*
+		 * The candidate node has more than one child, or its child
+		 * is not at the leftmost slot, we cannot shrink.
+		 */
+		if (node->count != 1)
+			break;
+		child = rcu_dereference_raw(node->slots[0]);
+		if (!child)
+			break;
+
+		/*
+		 * For an IDR, we must not shrink entry 0 into the root in
+		 * case somebody calls idr_replace() with a pointer that
+		 * appears to be an internal entry
+		 */
+		if (!node->shift && is_idr(root))
+			break;
+
+		if (radix_tree_is_internal_node(child))
+			entry_to_node(child)->parent = NULL;
+
+		/*
+		 * We don't need rcu_assign_pointer(), since we are simply
+		 * moving the node from one part of the tree to another: if it
+		 * was safe to dereference the old pointer to it
+		 * (node->slots[0]), it will be safe to dereference the new
+		 * one (root->xa_head) as far as dependent read barriers go.
+		 */
+		root->xa_head = (void __rcu *)child;
+		if (is_idr(root) && !tag_get(node, IDR_FREE, 0))
+			root_tag_clear(root, IDR_FREE);
+
+		/*
+		 * We have a dilemma here. The node's slot[0] must not be
+		 * NULLed in case there are concurrent lookups expecting to
+		 * find the item. However if this was a bottom-level node,
+		 * then it may be subject to the slot pointer being visible
+		 * to callers dereferencing it. If item corresponding to
+		 * slot[0] is subsequently deleted, these callers would expect
+		 * their slot to become empty sooner or later.
+		 *
+		 * For example, lockless pagecache will look up a slot, deref
+		 * the page pointer, and if the page has 0 refcount it means it
+		 * was concurrently deleted from pagecache so try the deref
+		 * again. Fortunately there is already a requirement for logic
+		 * to retry the entire slot lookup -- the indirect pointer
+		 * problem (replacing direct root node with an indirect pointer
+		 * also results in a stale slot). So tag the slot as indirect
+		 * to force callers to retry.
+		 */
+		node->count = 0;
+		if (!radix_tree_is_internal_node(child)) {
+			node->slots[0] = (void __rcu *)RADIX_TREE_RETRY;
+		}
+
+		WARN_ON_ONCE(!list_empty(&node->private_list));
+		radix_tree_node_free(node);
+		shrunk = true;
+	}
+
+	return shrunk;
+}
+
+static bool delete_node(struct radix_tree_root *root,
+			struct radix_tree_node *node)
+{
+	bool deleted = false;
+
+	do {
+		struct radix_tree_node *parent;
+
+		if (node->count) {
+			if (node_to_entry(node) ==
+					rcu_dereference_raw(root->xa_head))
+				deleted |= radix_tree_shrink(root);
+			return deleted;
+		}
+
+		parent = node->parent;
+		if (parent) {
+			parent->slots[node->offset] = NULL;
+			parent->count--;
+		} else {
+			/*
+			 * Shouldn't the tags already have all been cleared
+			 * by the caller?
+			 */
+			if (!is_idr(root))
+				root_tag_clear_all(root);
+			root->xa_head = NULL;
+		}
+
+		WARN_ON_ONCE(!list_empty(&node->private_list));
+		radix_tree_node_free(node);
+		deleted = true;
+
+		node = parent;
+	} while (node);
+
+	return deleted;
+}
+
+/**
+ *	__radix_tree_create	-	create a slot in a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@nodep:		returns node
+ *	@slotp:		returns slot
+ *
+ *	Create, if necessary, and return the node and slot for an item
+ *	at position @index in the radix tree @root.
+ *
+ *	Until there is more than one item in the tree, no nodes are
+ *	allocated and @root->xa_head is used as a direct slot instead of
+ *	pointing to a node, in which case *@nodep will be NULL.
+ *
+ *	Returns -ENOMEM, or 0 for success.
+ */
+static int __radix_tree_create(struct radix_tree_root *root,
+		unsigned long index, struct radix_tree_node **nodep,
+		void __rcu ***slotp)
+{
+	struct radix_tree_node *node = NULL, *child;
+	void __rcu **slot = (void __rcu **)&root->xa_head;
+	unsigned long maxindex;
+	unsigned int shift, offset = 0;
+	unsigned long max = index;
+	gfp_t gfp = root_gfp_mask(root);
+
+	shift = radix_tree_load_root(root, &child, &maxindex);
+
+	/* Make sure the tree is high enough.  */
+	if (max > maxindex) {
+		int error = radix_tree_extend(root, gfp, max, shift);
+		if (error < 0)
+			return error;
+		shift = error;
+		child = rcu_dereference_raw(root->xa_head);
+	}
+
+	while (shift > 0) {
+		shift -= RADIX_TREE_MAP_SHIFT;
+		if (child == NULL) {
+			/* Have to add a child node.  */
+			child = radix_tree_node_alloc(gfp, node, root, shift,
+							offset, 0, 0);
+			if (!child)
+				return -ENOMEM;
+			rcu_assign_pointer(*slot, node_to_entry(child));
+			if (node)
+				node->count++;
+		} else if (!radix_tree_is_internal_node(child))
+			break;
+
+		/* Go a level down */
+		node = entry_to_node(child);
+		offset = radix_tree_descend(node, &child, index);
+		slot = &node->slots[offset];
+	}
+
+	if (nodep)
+		*nodep = node;
+	if (slotp)
+		*slotp = slot;
+	return 0;
+}
+
+/*
+ * Free any nodes below this node.  The tree is presumed to not need
+ * shrinking, and any user data in the tree is presumed to not need a
+ * destructor called on it.  If we need to add a destructor, we can
+ * add that functionality later.  Note that we may not clear tags or
+ * slots from the tree as an RCU walker may still have a pointer into
+ * this subtree.  We could replace the entries with RADIX_TREE_RETRY,
+ * but we'll still have to clear those in rcu_free.
+ */
+static void radix_tree_free_nodes(struct radix_tree_node *node)
+{
+	unsigned offset = 0;
+	struct radix_tree_node *child = entry_to_node(node);
+
+	for (;;) {
+		void *entry = rcu_dereference_raw(child->slots[offset]);
+		if (xa_is_node(entry) && child->shift) {
+			child = entry_to_node(entry);
+			offset = 0;
+			continue;
+		}
+		offset++;
+		while (offset == RADIX_TREE_MAP_SIZE) {
+			struct radix_tree_node *old = child;
+			offset = child->offset + 1;
+			child = child->parent;
+			WARN_ON_ONCE(!list_empty(&old->private_list));
+			radix_tree_node_free(old);
+			if (old == entry_to_node(node))
+				return;
+		}
+	}
+}
+
+static inline int insert_entries(struct radix_tree_node *node,
+		void __rcu **slot, void *item)
+{
+	if (*slot)
+		return -EEXIST;
+	rcu_assign_pointer(*slot, item);
+	if (node) {
+		node->count++;
+		if (xa_is_value(item))
+			node->nr_values++;
+	}
+	return 1;
+}
+
+/**
+ *	radix_tree_insert    -    insert into a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@item:		item to insert
+ *
+ *	Insert an item into the radix tree at position @index.
+ */
+int radix_tree_insert(struct radix_tree_root *root, unsigned long index,
+			void *item)
+{
+	struct radix_tree_node *node;
+	void __rcu **slot;
+	int error;
+
+	BUG_ON(radix_tree_is_internal_node(item));
+
+	error = __radix_tree_create(root, index, &node, &slot);
+	if (error)
+		return error;
+
+	error = insert_entries(node, slot, item);
+	if (error < 0)
+		return error;
+
+	if (node) {
+		unsigned offset = get_slot_offset(node, slot);
+		BUG_ON(tag_get(node, 0, offset));
+		BUG_ON(tag_get(node, 1, offset));
+		BUG_ON(tag_get(node, 2, offset));
+	} else {
+		BUG_ON(root_tags_get(root));
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(radix_tree_insert);
+
+/**
+ *	__radix_tree_lookup	-	lookup an item in a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@nodep:		returns node
+ *	@slotp:		returns slot
+ *
+ *	Lookup and return the item at position @index in the radix
+ *	tree @root.
+ *
+ *	Until there is more than one item in the tree, no nodes are
+ *	allocated and @root->xa_head is used as a direct slot instead of
+ *	pointing to a node, in which case *@nodep will be NULL.
+ */
+void *__radix_tree_lookup(const struct radix_tree_root *root,
+			  unsigned long index, struct radix_tree_node **nodep,
+			  void __rcu ***slotp)
+{
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+	void __rcu **slot;
+
+ restart:
+	parent = NULL;
+	slot = (void __rcu **)&root->xa_head;
+	radix_tree_load_root(root, &node, &maxindex);
+	if (index > maxindex)
+		return NULL;
+
+	while (radix_tree_is_internal_node(node)) {
+		unsigned offset;
+
+		parent = entry_to_node(node);
+		offset = radix_tree_descend(parent, &node, index);
+		slot = parent->slots + offset;
+		if (node == RADIX_TREE_RETRY)
+			goto restart;
+		if (parent->shift == 0)
+			break;
+	}
+
+	if (nodep)
+		*nodep = parent;
+	if (slotp)
+		*slotp = slot;
+	return node;
+}
+
+/**
+ *	radix_tree_lookup_slot    -    lookup a slot in a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *
+ *	Returns:  the slot corresponding to the position @index in the
+ *	radix tree @root. This is useful for update-if-exists operations.
+ *
+ *	This function can be called under rcu_read_lock iff the slot is not
+ *	modified by radix_tree_replace_slot, otherwise it must be called
+ *	exclusive from other writers. Any dereference of the slot must be done
+ *	using radix_tree_deref_slot.
+ */
+void __rcu **radix_tree_lookup_slot(const struct radix_tree_root *root,
+				unsigned long index)
+{
+	void __rcu **slot;
+
+	if (!__radix_tree_lookup(root, index, NULL, &slot))
+		return NULL;
+	return slot;
+}
+EXPORT_SYMBOL(radix_tree_lookup_slot);
+
+/**
+ *	radix_tree_lookup    -    perform lookup operation on a radix tree
+ *	@root:		radix tree root
+ *	@index:		index key
+ *
+ *	Lookup the item at the position @index in the radix tree @root.
+ *
+ *	This function can be called under rcu_read_lock, however the caller
+ *	must manage lifetimes of leaf nodes (eg. RCU may also be used to free
+ *	them safely). No RCU barriers are required to access or modify the
+ *	returned item, however.
+ */
+void *radix_tree_lookup(const struct radix_tree_root *root, unsigned long index)
+{
+	return __radix_tree_lookup(root, index, NULL, NULL);
+}
+EXPORT_SYMBOL(radix_tree_lookup);
+
+static void replace_slot(void __rcu **slot, void *item,
+		struct radix_tree_node *node, int count, int values)
+{
+	if (node && (count || values)) {
+		node->count += count;
+		node->nr_values += values;
+	}
+
+	rcu_assign_pointer(*slot, item);
+}
+
+static bool node_tag_get(const struct radix_tree_root *root,
+				const struct radix_tree_node *node,
+				unsigned int tag, unsigned int offset)
+{
+	if (node)
+		return tag_get(node, tag, offset);
+	return root_tag_get(root, tag);
+}
+
+/*
+ * IDR users want to be able to store NULL in the tree, so if the slot isn't
+ * free, don't adjust the count, even if it's transitioning between NULL and
+ * non-NULL.  For the IDA, we mark slots as being IDR_FREE while they still
+ * have empty bits, but it only stores NULL in slots when they're being
+ * deleted.
+ */
+static int calculate_count(struct radix_tree_root *root,
+				struct radix_tree_node *node, void __rcu **slot,
+				void *item, void *old)
+{
+	if (is_idr(root)) {
+		unsigned offset = get_slot_offset(node, slot);
+		bool free = node_tag_get(root, node, IDR_FREE, offset);
+		if (!free)
+			return 0;
+		if (!old)
+			return 1;
+	}
+	return !!item - !!old;
+}
+
+/**
+ * __radix_tree_replace		- replace item in a slot
+ * @root:		radix tree root
+ * @node:		pointer to tree node
+ * @slot:		pointer to slot in @node
+ * @item:		new item to store in the slot.
+ *
+ * For use with __radix_tree_lookup().  Caller must hold tree write locked
+ * across slot lookup and replacement.
+ */
+void __radix_tree_replace(struct radix_tree_root *root,
+			  struct radix_tree_node *node,
+			  void __rcu **slot, void *item)
+{
+	void *old = rcu_dereference_raw(*slot);
+	int values = !!xa_is_value(item) - !!xa_is_value(old);
+	int count = calculate_count(root, node, slot, item, old);
+
+	/*
+	 * This function supports replacing value entries and
+	 * deleting entries, but that needs accounting against the
+	 * node unless the slot is root->xa_head.
+	 */
+	WARN_ON_ONCE(!node && (slot != (void __rcu **)&root->xa_head) &&
+			(count || values));
+	replace_slot(slot, item, node, count, values);
+
+	if (!node)
+		return;
+
+	delete_node(root, node);
+}
+
+/**
+ * radix_tree_replace_slot	- replace item in a slot
+ * @root:	radix tree root
+ * @slot:	pointer to slot
+ * @item:	new item to store in the slot.
+ *
+ * For use with radix_tree_lookup_slot() and
+ * radix_tree_gang_lookup_tag_slot().  Caller must hold tree write locked
+ * across slot lookup and replacement.
+ *
+ * NOTE: This cannot be used to switch between non-entries (empty slots),
+ * regular entries, and value entries, as that requires accounting
+ * inside the radix tree node. When switching from one type of entry or
+ * deleting, use __radix_tree_lookup() and __radix_tree_replace() or
+ * radix_tree_iter_replace().
+ */
+void radix_tree_replace_slot(struct radix_tree_root *root,
+			     void __rcu **slot, void *item)
+{
+	__radix_tree_replace(root, NULL, slot, item);
+}
+EXPORT_SYMBOL(radix_tree_replace_slot);
+
+/**
+ * radix_tree_iter_replace - replace item in a slot
+ * @root:	radix tree root
+ * @iter:	iterator state
+ * @slot:	pointer to slot
+ * @item:	new item to store in the slot.
+ *
+ * For use with radix_tree_for_each_slot().
+ * Caller must hold tree write locked.
+ */
+void radix_tree_iter_replace(struct radix_tree_root *root,
+				const struct radix_tree_iter *iter,
+				void __rcu **slot, void *item)
+{
+	__radix_tree_replace(root, iter->node, slot, item);
+}
+
+static void node_tag_set(struct radix_tree_root *root,
+				struct radix_tree_node *node,
+				unsigned int tag, unsigned int offset)
+{
+	while (node) {
+		if (tag_get(node, tag, offset))
+			return;
+		tag_set(node, tag, offset);
+		offset = node->offset;
+		node = node->parent;
+	}
+
+	if (!root_tag_get(root, tag))
+		root_tag_set(root, tag);
+}
+
+/**
+ *	radix_tree_tag_set - set a tag on a radix tree node
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@tag:		tag index
+ *
+ *	Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
+ *	corresponding to @index in the radix tree.  From
+ *	the root all the way down to the leaf node.
+ *
+ *	Returns the address of the tagged item.  Setting a tag on a not-present
+ *	item is a bug.
+ */
+void *radix_tree_tag_set(struct radix_tree_root *root,
+			unsigned long index, unsigned int tag)
+{
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+
+	radix_tree_load_root(root, &node, &maxindex);
+	BUG_ON(index > maxindex);
+
+	while (radix_tree_is_internal_node(node)) {
+		unsigned offset;
+
+		parent = entry_to_node(node);
+		offset = radix_tree_descend(parent, &node, index);
+		BUG_ON(!node);
+
+		if (!tag_get(parent, tag, offset))
+			tag_set(parent, tag, offset);
+	}
+
+	/* set the root's tag bit */
+	if (!root_tag_get(root, tag))
+		root_tag_set(root, tag);
+
+	return node;
+}
+EXPORT_SYMBOL(radix_tree_tag_set);
+
+static void node_tag_clear(struct radix_tree_root *root,
+				struct radix_tree_node *node,
+				unsigned int tag, unsigned int offset)
+{
+	while (node) {
+		if (!tag_get(node, tag, offset))
+			return;
+		tag_clear(node, tag, offset);
+		if (any_tag_set(node, tag))
+			return;
+
+		offset = node->offset;
+		node = node->parent;
+	}
+
+	/* clear the root's tag bit */
+	if (root_tag_get(root, tag))
+		root_tag_clear(root, tag);
+}
+
+/**
+ *	radix_tree_tag_clear - clear a tag on a radix tree node
+ *	@root:		radix tree root
+ *	@index:		index key
+ *	@tag:		tag index
+ *
+ *	Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
+ *	corresponding to @index in the radix tree.  If this causes
+ *	the leaf node to have no tags set then clear the tag in the
+ *	next-to-leaf node, etc.
+ *
+ *	Returns the address of the tagged item on success, else NULL.  ie:
+ *	has the same return value and semantics as radix_tree_lookup().
+ */
+void *radix_tree_tag_clear(struct radix_tree_root *root,
+			unsigned long index, unsigned int tag)
+{
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+	int offset = 0;
+
+	radix_tree_load_root(root, &node, &maxindex);
+	if (index > maxindex)
+		return NULL;
+
+	parent = NULL;
+
+	while (radix_tree_is_internal_node(node)) {
+		parent = entry_to_node(node);
+		offset = radix_tree_descend(parent, &node, index);
+	}
+
+	if (node)
+		node_tag_clear(root, parent, tag, offset);
+
+	return node;
+}
+EXPORT_SYMBOL(radix_tree_tag_clear);
+
+/**
+  * radix_tree_iter_tag_clear - clear a tag on the current iterator entry
+  * @root: radix tree root
+  * @iter: iterator state
+  * @tag: tag to clear
+  */
+void radix_tree_iter_tag_clear(struct radix_tree_root *root,
+			const struct radix_tree_iter *iter, unsigned int tag)
+{
+	node_tag_clear(root, iter->node, tag, iter_offset(iter));
+}
+
+/**
+ * radix_tree_tag_get - get a tag on a radix tree node
+ * @root:		radix tree root
+ * @index:		index key
+ * @tag:		tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ * Return values:
+ *
+ *  0: tag not present or not set
+ *  1: tag set
+ *
+ * Note that the return value of this function may not be relied on, even if
+ * the RCU lock is held, unless tag modification and node deletion are excluded
+ * from concurrency.
+ */
+int radix_tree_tag_get(const struct radix_tree_root *root,
+			unsigned long index, unsigned int tag)
+{
+	struct radix_tree_node *node, *parent;
+	unsigned long maxindex;
+
+	if (!root_tag_get(root, tag))
+		return 0;
+
+	radix_tree_load_root(root, &node, &maxindex);
+	if (index > maxindex)
+		return 0;
+
+	while (radix_tree_is_internal_node(node)) {
+		unsigned offset;
+
+		parent = entry_to_node(node);
+		offset = radix_tree_descend(parent, &node, index);
+
+		if (!tag_get(parent, tag, offset))
+			return 0;
+		if (node == RADIX_TREE_RETRY)
+			break;
+	}
+
+	return 1;
+}
+EXPORT_SYMBOL(radix_tree_tag_get);
+
+/* Construct iter->tags bit-mask from node->tags[tag] array */
+static void set_iter_tags(struct radix_tree_iter *iter,
+				struct radix_tree_node *node, unsigned offset,
+				unsigned tag)
+{
+	unsigned tag_long = offset / BITS_PER_LONG;
+	unsigned tag_bit  = offset % BITS_PER_LONG;
+
+	if (!node) {
+		iter->tags = 1;
+		return;
+	}
+
+	iter->tags = node->tags[tag][tag_long] >> tag_bit;
+
+	/* This never happens if RADIX_TREE_TAG_LONGS == 1 */
+	if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
+		/* Pick tags from next element */
+		if (tag_bit)
+			iter->tags |= node->tags[tag][tag_long + 1] <<
+						(BITS_PER_LONG - tag_bit);
+		/* Clip chunk size, here only BITS_PER_LONG tags */
+		iter->next_index = __radix_tree_iter_add(iter, BITS_PER_LONG);
+	}
+}
+
+void __rcu **radix_tree_iter_resume(void __rcu **slot,
+					struct radix_tree_iter *iter)
+{
+	iter->index = __radix_tree_iter_add(iter, 1);
+	iter->next_index = iter->index;
+	iter->tags = 0;
+	return NULL;
+}
+EXPORT_SYMBOL(radix_tree_iter_resume);
+
+/**
+ * radix_tree_next_chunk - find next chunk of slots for iteration
+ *
+ * @root:	radix tree root
+ * @iter:	iterator state
+ * @flags:	RADIX_TREE_ITER_* flags and tag index
+ * Returns:	pointer to chunk first slot, or NULL if iteration is over
+ */
+void __rcu **radix_tree_next_chunk(const struct radix_tree_root *root,
+			     struct radix_tree_iter *iter, unsigned flags)
+{
+	unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;
+	struct radix_tree_node *node, *child;
+	unsigned long index, offset, maxindex;
+
+	if ((flags & RADIX_TREE_ITER_TAGGED) && !root_tag_get(root, tag))
+		return NULL;
+
+	/*
+	 * Catch next_index overflow after ~0UL. iter->index never overflows
+	 * during iterating; it can be zero only at the beginning.
+	 * And we cannot overflow iter->next_index in a single step,
+	 * because RADIX_TREE_MAP_SHIFT < BITS_PER_LONG.
+	 *
+	 * This condition also used by radix_tree_next_slot() to stop
+	 * contiguous iterating, and forbid switching to the next chunk.
+	 */
+	index = iter->next_index;
+	if (!index && iter->index)
+		return NULL;
+
+ restart:
+	radix_tree_load_root(root, &child, &maxindex);
+	if (index > maxindex)
+		return NULL;
+	if (!child)
+		return NULL;
+
+	if (!radix_tree_is_internal_node(child)) {
+		/* Single-slot tree */
+		iter->index = index;
+		iter->next_index = maxindex + 1;
+		iter->tags = 1;
+		iter->node = NULL;
+		return (void __rcu **)&root->xa_head;
+	}
+
+	do {
+		node = entry_to_node(child);
+		offset = radix_tree_descend(node, &child, index);
+
+		if ((flags & RADIX_TREE_ITER_TAGGED) ?
+				!tag_get(node, tag, offset) : !child) {
+			/* Hole detected */
+			if (flags & RADIX_TREE_ITER_CONTIG)
+				return NULL;
+
+			if (flags & RADIX_TREE_ITER_TAGGED)
+				offset = radix_tree_find_next_bit(node, tag,
+						offset + 1);
+			else
+				while (++offset	< RADIX_TREE_MAP_SIZE) {
+					void *slot = rcu_dereference_raw(
+							node->slots[offset]);
+					if (slot)
+						break;
+				}
+			index &= ~node_maxindex(node);
+			index += offset << node->shift;
+			/* Overflow after ~0UL */
+			if (!index)
+				return NULL;
+			if (offset == RADIX_TREE_MAP_SIZE)
+				goto restart;
+			child = rcu_dereference_raw(node->slots[offset]);
+		}
+
+		if (!child)
+			goto restart;
+		if (child == RADIX_TREE_RETRY)
+			break;
+	} while (node->shift && radix_tree_is_internal_node(child));
+
+	/* Update the iterator state */
+	iter->index = (index &~ node_maxindex(node)) | offset;
+	iter->next_index = (index | node_maxindex(node)) + 1;
+	iter->node = node;
+
+	if (flags & RADIX_TREE_ITER_TAGGED)
+		set_iter_tags(iter, node, offset, tag);
+
+	return node->slots + offset;
+}
+EXPORT_SYMBOL(radix_tree_next_chunk);
+
+/**
+ *	radix_tree_gang_lookup - perform multiple lookup on a radix tree
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *
+ *	Performs an index-ascending scan of the tree for present items.  Places
+ *	them at *@results and returns the number of items which were placed at
+ *	*@results.
+ *
+ *	The implementation is naive.
+ *
+ *	Like radix_tree_lookup, radix_tree_gang_lookup may be called under
+ *	rcu_read_lock. In this case, rather than the returned results being
+ *	an atomic snapshot of the tree at a single point in time, the
+ *	semantics of an RCU protected gang lookup are as though multiple
+ *	radix_tree_lookups have been issued in individual locks, and results
+ *	stored in 'results'.
+ */
+unsigned int
+radix_tree_gang_lookup(const struct radix_tree_root *root, void **results,
+			unsigned long first_index, unsigned int max_items)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!max_items))
+		return 0;
+
+	radix_tree_for_each_slot(slot, root, &iter, first_index) {
+		results[ret] = rcu_dereference_raw(*slot);
+		if (!results[ret])
+			continue;
+		if (radix_tree_is_internal_node(results[ret])) {
+			slot = radix_tree_iter_retry(&iter);
+			continue;
+		}
+		if (++ret == max_items)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup);
+
+/**
+ *	radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
+ *	                             based on a tag
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ *	Performs an index-ascending scan of the tree for present items which
+ *	have the tag indexed by @tag set.  Places the items at *@results and
+ *	returns the number of items which were placed at *@results.
+ */
+unsigned int
+radix_tree_gang_lookup_tag(const struct radix_tree_root *root, void **results,
+		unsigned long first_index, unsigned int max_items,
+		unsigned int tag)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!max_items))
+		return 0;
+
+	radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
+		results[ret] = rcu_dereference_raw(*slot);
+		if (!results[ret])
+			continue;
+		if (radix_tree_is_internal_node(results[ret])) {
+			slot = radix_tree_iter_retry(&iter);
+			continue;
+		}
+		if (++ret == max_items)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
+
+/**
+ *	radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
+ *					  radix tree based on a tag
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ *	Performs an index-ascending scan of the tree for present items which
+ *	have the tag indexed by @tag set.  Places the slots at *@results and
+ *	returns the number of slots which were placed at *@results.
+ */
+unsigned int
+radix_tree_gang_lookup_tag_slot(const struct radix_tree_root *root,
+		void __rcu ***results, unsigned long first_index,
+		unsigned int max_items, unsigned int tag)
+{
+	struct radix_tree_iter iter;
+	void __rcu **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!max_items))
+		return 0;
+
+	radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
+		results[ret] = slot;
+		if (++ret == max_items)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
+
+static bool __radix_tree_delete(struct radix_tree_root *root,
+				struct radix_tree_node *node, void __rcu **slot)
+{
+	void *old = rcu_dereference_raw(*slot);
+	int values = xa_is_value(old) ? -1 : 0;
+	unsigned offset = get_slot_offset(node, slot);
+	int tag;
+
+	if (is_idr(root))
+		node_tag_set(root, node, IDR_FREE, offset);
+	else
+		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+			node_tag_clear(root, node, tag, offset);
+
+	replace_slot(slot, NULL, node, -1, values);
+	return node && delete_node(root, node);
+}
+
+/**
+ * radix_tree_iter_delete - delete the entry at this iterator position
+ * @root: radix tree root
+ * @iter: iterator state
+ * @slot: pointer to slot
+ *
+ * Delete the entry at the position currently pointed to by the iterator.
+ * This may result in the current node being freed; if it is, the iterator
+ * is advanced so that it will not reference the freed memory.  This
+ * function may be called without any locking if there are no other threads
+ * which can access this tree.
+ */
+void radix_tree_iter_delete(struct radix_tree_root *root,
+				struct radix_tree_iter *iter, void __rcu **slot)
+{
+	if (__radix_tree_delete(root, iter->node, slot))
+		iter->index = iter->next_index;
+}
+EXPORT_SYMBOL(radix_tree_iter_delete);
+
+/**
+ * radix_tree_delete_item - delete an item from a radix tree
+ * @root: radix tree root
+ * @index: index key
+ * @item: expected item
+ *
+ * Remove @item at @index from the radix tree rooted at @root.
+ *
+ * Return: the deleted entry, or %NULL if it was not present
+ * or the entry at the given @index was not @item.
+ */
+void *radix_tree_delete_item(struct radix_tree_root *root,
+			     unsigned long index, void *item)
+{
+	struct radix_tree_node *node = NULL;
+	void __rcu **slot = NULL;
+	void *entry;
+
+	entry = __radix_tree_lookup(root, index, &node, &slot);
+	if (!slot)
+		return NULL;
+	if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE,
+						get_slot_offset(node, slot))))
+		return NULL;
+
+	if (item && entry != item)
+		return NULL;
+
+	__radix_tree_delete(root, node, slot);
+
+	return entry;
+}
+EXPORT_SYMBOL(radix_tree_delete_item);
+
+/**
+ * radix_tree_delete - delete an entry from a radix tree
+ * @root: radix tree root
+ * @index: index key
+ *
+ * Remove the entry at @index from the radix tree rooted at @root.
+ *
+ * Return: The deleted entry, or %NULL if it was not present.
+ */
+void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
+{
+	return radix_tree_delete_item(root, index, NULL);
+}
+EXPORT_SYMBOL(radix_tree_delete);
+
+/**
+ *	radix_tree_tagged - test whether any items in the tree are tagged
+ *	@root:		radix tree root
+ *	@tag:		tag to test
+ */
+int radix_tree_tagged(const struct radix_tree_root *root, unsigned int tag)
+{
+	return root_tag_get(root, tag);
+}
+EXPORT_SYMBOL(radix_tree_tagged);
+
+/**
+ * idr_preload - preload for idr_alloc()
+ * @gfp_mask: allocation mask to use for preloading
+ *
+ * Preallocate memory to use for the next call to idr_alloc().  This function
+ * returns with preemption disabled.  It will be enabled by idr_preload_end().
+ */
+void idr_preload(gfp_t gfp_mask)
+{
+	if (__radix_tree_preload(gfp_mask, IDR_PRELOAD_SIZE))
+		local_lock(&radix_tree_preloads.lock);
+}
+EXPORT_SYMBOL(idr_preload);
+
+void __rcu **idr_get_free(struct radix_tree_root *root,
+			      struct radix_tree_iter *iter, gfp_t gfp,
+			      unsigned long max)
+{
+	struct radix_tree_node *node = NULL, *child;
+	void __rcu **slot = (void __rcu **)&root->xa_head;
+	unsigned long maxindex, start = iter->next_index;
+	unsigned int shift, offset = 0;
+
+ grow:
+	shift = radix_tree_load_root(root, &child, &maxindex);
+	if (!radix_tree_tagged(root, IDR_FREE))
+		start = max(start, maxindex + 1);
+	if (start > max)
+		return ERR_PTR(-ENOSPC);
+
+	if (start > maxindex) {
+		int error = radix_tree_extend(root, gfp, start, shift);
+		if (error < 0)
+			return ERR_PTR(error);
+		shift = error;
+		child = rcu_dereference_raw(root->xa_head);
+	}
+	if (start == 0 && shift == 0)
+		shift = RADIX_TREE_MAP_SHIFT;
+
+	while (shift) {
+		shift -= RADIX_TREE_MAP_SHIFT;
+		if (child == NULL) {
+			/* Have to add a child node.  */
+			child = radix_tree_node_alloc(gfp, node, root, shift,
+							offset, 0, 0);
+			if (!child)
+				return ERR_PTR(-ENOMEM);
+			all_tag_set(child, IDR_FREE);
+			rcu_assign_pointer(*slot, node_to_entry(child));
+			if (node)
+				node->count++;
+		} else if (!radix_tree_is_internal_node(child))
+			break;
+
+		node = entry_to_node(child);
+		offset = radix_tree_descend(node, &child, start);
+		if (!tag_get(node, IDR_FREE, offset)) {
+			offset = radix_tree_find_next_bit(node, IDR_FREE,
+							offset + 1);
+			start = next_index(start, node, offset);
+			if (start > max || start == 0)
+				return ERR_PTR(-ENOSPC);
+			while (offset == RADIX_TREE_MAP_SIZE) {
+				offset = node->offset + 1;
+				node = node->parent;
+				if (!node)
+					goto grow;
+				shift = node->shift;
+			}
+			child = rcu_dereference_raw(node->slots[offset]);
+		}
+		slot = &node->slots[offset];
+	}
+
+	iter->index = start;
+	if (node)
+		iter->next_index = 1 + min(max, (start | node_maxindex(node)));
+	else
+		iter->next_index = 1;
+	iter->node = node;
+	set_iter_tags(iter, node, offset, IDR_FREE);
+
+	return slot;
+}
+
+/**
+ * idr_destroy - release all internal memory from an IDR
+ * @idr: idr handle
+ *
+ * After this function is called, the IDR is empty, and may be reused or
+ * the data structure containing it may be freed.
+ *
+ * A typical clean-up sequence for objects stored in an idr tree will use
+ * idr_for_each() to free all objects, if necessary, then idr_destroy() to
+ * free the memory used to keep track of those objects.
+ */
+void idr_destroy(struct idr *idr)
+{
+	struct radix_tree_node *node = rcu_dereference_raw(idr->idr_rt.xa_head);
+	if (radix_tree_is_internal_node(node))
+		radix_tree_free_nodes(node);
+	idr->idr_rt.xa_head = NULL;
+	root_tag_set(&idr->idr_rt, IDR_FREE);
+}
+EXPORT_SYMBOL(idr_destroy);
+
+static void
+radix_tree_node_ctor(void *arg)
+{
+	struct radix_tree_node *node = arg;
+
+	memset(node, 0, sizeof(*node));
+	INIT_LIST_HEAD(&node->private_list);
+}
+
+static int radix_tree_cpu_dead(unsigned int cpu)
+{
+	struct radix_tree_preload *rtp;
+	struct radix_tree_node *node;
+
+	/* Free per-cpu pool of preloaded nodes */
+	rtp = &per_cpu(radix_tree_preloads, cpu);
+	while (rtp->nr) {
+		node = rtp->nodes;
+		rtp->nodes = node->parent;
+		kmem_cache_free(radix_tree_node_cachep, node);
+		rtp->nr--;
+	}
+	return 0;
+}
+
+void __init radix_tree_init(void)
+{
+	int ret;
+
+	BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32);
+	BUILD_BUG_ON(ROOT_IS_IDR & ~GFP_ZONEMASK);
+	BUILD_BUG_ON(XA_CHUNK_SIZE > 255);
+	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
+			sizeof(struct radix_tree_node), 0,
+			SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
+			radix_tree_node_ctor);
+	ret = cpuhp_setup_state_nocalls(CPUHP_RADIX_DEAD, "lib/radix:dead",
+					NULL, radix_tree_cpu_dead);
+	WARN_ON(ret < 0);
+}