Reimplement IDR and IDA using the radix tree

The IDR is very similar to the radix tree.  It has some functionality that
the radix tree did not have (alloc next free, cyclic allocation, a
callback-based for_each, destroy tree), which is readily implementable on
top of the radix tree.  A few small changes were needed in order to use a
tag to represent nodes with free space below them.  More extensive
changes were needed to support storing NULL as a valid entry in an IDR.
Plain radix trees still interpret NULL as a not-present entry.

The IDA is reimplemented as a client of the newly enhanced radix tree.  As
in the current implementation, it uses a bitmap at the last level of the
tree.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

13 files changed, 995 insertions, 1126 deletions

diff --git a/include/linux/idr.h b/include/linux/idr.h
index 3c01b89aed67..f58c0a3addc3 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -12,47 +12,28 @@
 #ifndef __IDR_H__
 #define __IDR_H__
 
-#include <linux/types.h>
-#include <linux/bitops.h>
-#include <linux/init.h>
-#include <linux/rcupdate.h>
+#include <linux/radix-tree.h>
+#include <linux/gfp.h>
+
+struct idr {
+	struct radix_tree_root	idr_rt;
+	unsigned int		idr_next;
+};
 
 /*
- * Using 6 bits at each layer allows us to allocate 7 layers out of each page.
- * 8 bits only gave us 3 layers out of every pair of pages, which is less
- * efficient except for trees with a largest element between 192-255 inclusive.
+ * The IDR API does not expose the tagging functionality of the radix tree
+ * to users.  Use tag 0 to track whether a node has free space below it.
  */
-#define IDR_BITS 6
-#define IDR_SIZE (1 << IDR_BITS)
-#define IDR_MASK ((1 << IDR_BITS)-1)
-
-struct idr_layer {
-	int			prefix;	/* the ID prefix of this idr_layer */
-	int			layer;	/* distance from leaf */
-	struct idr_layer __rcu	*ary[1<<IDR_BITS];
-	int			count;	/* When zero, we can release it */
-	union {
-		/* A zero bit means "space here" */
-		DECLARE_BITMAP(bitmap, IDR_SIZE);
-		struct rcu_head		rcu_head;
-	};
-};
+#define IDR_FREE	0
 
-struct idr {
-	struct idr_layer __rcu	*hint;	/* the last layer allocated from */
-	struct idr_layer __rcu	*top;
-	int			layers;	/* only valid w/o concurrent changes */
-	int			cur;	/* current pos for cyclic allocation */
-	spinlock_t		lock;
-	int			id_free_cnt;
-	struct idr_layer	*id_free;
-};
+/* Set the IDR flag and the IDR_FREE tag */
+#define IDR_RT_MARKER		((__force gfp_t)(3 << __GFP_BITS_SHIFT))
 
-#define IDR_INIT(name)							\
+#define IDR_INIT							\
 {									\
-	.lock			= __SPIN_LOCK_UNLOCKED(name.lock),	\
+	.idr_rt = RADIX_TREE_INIT(IDR_RT_MARKER)			\
 }
-#define DEFINE_IDR(name)	struct idr name = IDR_INIT(name)
+#define DEFINE_IDR(name)	struct idr name = IDR_INIT
 
 /**
  * idr_get_cursor - Return the current position of the cyclic allocator
@@ -62,9 +43,9 @@ struct idr {
  * idr_alloc_cyclic() if it is free (otherwise the search will start from
  * this position).
  */
-static inline unsigned int idr_get_cursor(struct idr *idr)
+static inline unsigned int idr_get_cursor(const struct idr *idr)
 {
-	return READ_ONCE(idr->cur);
+	return READ_ONCE(idr->idr_next);
 }
 
 /**
@@ -77,7 +58,7 @@ static inline unsigned int idr_get_cursor(struct idr *idr)
  */
 static inline void idr_set_cursor(struct idr *idr, unsigned int val)
 {
-	WRITE_ONCE(idr->cur, val);
+	WRITE_ONCE(idr->idr_next, val);
 }
 
 /**
@@ -97,22 +78,31 @@ static inline void idr_set_cursor(struct idr *idr, unsigned int val)
  * period).
  */
 
-/*
- * This is what we export.
- */
-
-void *idr_find_slowpath(struct idr *idp, int id);
 void idr_preload(gfp_t gfp_mask);
-int idr_alloc(struct idr *idp, void *ptr, int start, int end, gfp_t gfp_mask);
-int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask);
-int idr_for_each(struct idr *idp,
+int idr_alloc(struct idr *, void *entry, int start, int end, gfp_t);
+int idr_alloc_cyclic(struct idr *, void *entry, int start, int end, gfp_t);
+int idr_for_each(const struct idr *,
 		 int (*fn)(int id, void *p, void *data), void *data);
-void *idr_get_next(struct idr *idp, int *nextid);
-void *idr_replace(struct idr *idp, void *ptr, int id);
-void idr_remove(struct idr *idp, int id);
-void idr_destroy(struct idr *idp);
-void idr_init(struct idr *idp);
-bool idr_is_empty(struct idr *idp);
+void *idr_get_next(struct idr *, int *nextid);
+void *idr_replace(struct idr *, void *, int id);
+void idr_destroy(struct idr *);
+
+static inline void idr_remove(struct idr *idr, int id)
+{
+	radix_tree_delete(&idr->idr_rt, id);
+}
+
+static inline void idr_init(struct idr *idr)
+{
+	INIT_RADIX_TREE(&idr->idr_rt, IDR_RT_MARKER);
+	idr->idr_next = 0;
+}
+
+static inline bool idr_is_empty(const struct idr *idr)
+{
+	return radix_tree_empty(&idr->idr_rt) &&
+		radix_tree_tagged(&idr->idr_rt, IDR_FREE);
+}
 
 /**
  * idr_preload_end - end preload section started with idr_preload()
@@ -137,19 +127,14 @@ static inline void idr_preload_end(void)
  * This function can be called under rcu_read_lock(), given that the leaf
  * pointers lifetimes are correctly managed.
  */
-static inline void *idr_find(struct idr *idr, int id)
+static inline void *idr_find(const struct idr *idr, int id)
 {
-	struct idr_layer *hint = rcu_dereference_raw(idr->hint);
-
-	if (hint && (id & ~IDR_MASK) == hint->prefix)
-		return rcu_dereference_raw(hint->ary[id & IDR_MASK]);
-
-	return idr_find_slowpath(idr, id);
+	return radix_tree_lookup(&idr->idr_rt, id);
 }
 
 /**
  * idr_for_each_entry - iterate over an idr's elements of a given type
- * @idp:     idr handle
+ * @idr:     idr handle
  * @entry:   the type * to use as cursor
  * @id:      id entry's key
  *
@@ -157,57 +142,60 @@ static inline void *idr_find(struct idr *idr, int id)
  * after normal terminatinon @entry is left with the value NULL.  This
  * is convenient for a "not found" value.
  */
-#define idr_for_each_entry(idp, entry, id)			\
-	for (id = 0; ((entry) = idr_get_next(idp, &(id))) != NULL; ++id)
+#define idr_for_each_entry(idr, entry, id)			\
+	for (id = 0; ((entry) = idr_get_next(idr, &(id))) != NULL; ++id)
 
 /**
- * idr_for_each_entry - continue iteration over an idr's elements of a given type
- * @idp:     idr handle
+ * idr_for_each_entry_continue - continue iteration over an idr's elements of a given type
+ * @idr:     idr handle
  * @entry:   the type * to use as cursor
  * @id:      id entry's key
  *
  * Continue to iterate over list of given type, continuing after
  * the current position.
  */
-#define idr_for_each_entry_continue(idp, entry, id)			\
-	for ((entry) = idr_get_next((idp), &(id));			\
+#define idr_for_each_entry_continue(idr, entry, id)			\
+	for ((entry) = idr_get_next((idr), &(id));			\
 	     entry;							\
-	     ++id, (entry) = idr_get_next((idp), &(id)))
+	     ++id, (entry) = idr_get_next((idr), &(id)))
 
 /*
  * IDA - IDR based id allocator, use when translation from id to
  * pointer isn't necessary.
- *
- * IDA_BITMAP_LONGS is calculated to be one less to accommodate
- * ida_bitmap->nr_busy so that the whole struct fits in 128 bytes.
  */
 #define IDA_CHUNK_SIZE		128	/* 128 bytes per chunk */
-#define IDA_BITMAP_LONGS	(IDA_CHUNK_SIZE / sizeof(long) - 1)
+#define IDA_BITMAP_LONGS	(IDA_CHUNK_SIZE / sizeof(long))
 #define IDA_BITMAP_BITS 	(IDA_BITMAP_LONGS * sizeof(long) * 8)
 
 struct ida_bitmap {
-	long			nr_busy;
 	unsigned long		bitmap[IDA_BITMAP_LONGS];
 };
 
 struct ida {
-	struct idr		idr;
+	struct radix_tree_root	ida_rt;
 	struct ida_bitmap	*free_bitmap;
 };
 
-#define IDA_INIT(name)		{ .idr = IDR_INIT((name).idr), .free_bitmap = NULL, }
-#define DEFINE_IDA(name)	struct ida name = IDA_INIT(name)
+#define IDA_INIT	{						\
+	.ida_rt = RADIX_TREE_INIT(IDR_RT_MARKER | GFP_NOWAIT),		\
+}
+#define DEFINE_IDA(name)	struct ida name = IDA_INIT
 
 int ida_pre_get(struct ida *ida, gfp_t gfp_mask);
 int ida_get_new_above(struct ida *ida, int starting_id, int *p_id);
 void ida_remove(struct ida *ida, int id);
 void ida_destroy(struct ida *ida);
-void ida_init(struct ida *ida);
 
 int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
 		   gfp_t gfp_mask);
 void ida_simple_remove(struct ida *ida, unsigned int id);
 
+static inline void ida_init(struct ida *ida)
+{
+	INIT_RADIX_TREE(&ida->ida_rt, IDR_RT_MARKER | GFP_NOWAIT);
+	ida->free_bitmap = NULL;
+}
+
 /**
  * ida_get_new - allocate new ID
  * @ida:	idr handle
@@ -220,11 +208,8 @@ static inline int ida_get_new(struct ida *ida, int *p_id)
 	return ida_get_new_above(ida, 0, p_id);
 }
 
-static inline bool ida_is_empty(struct ida *ida)
+static inline bool ida_is_empty(const struct ida *ida)
 {
-	return idr_is_empty(&ida->idr);
+	return radix_tree_empty(&ida->ida_rt);
 }
-
-void __init idr_init_cache(void);
-
 #endif /* __IDR_H__ */
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 05f715cb8062..2ba0c1f46c84 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -105,7 +105,10 @@ struct radix_tree_node {
 	unsigned long	tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
 };
 
-/* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
+/* The top bits of gfp_mask are used to store the root tags and the IDR flag */
+#define ROOT_IS_IDR	((__force gfp_t)(1 << __GFP_BITS_SHIFT))
+#define ROOT_TAG_SHIFT	(__GFP_BITS_SHIFT + 1)
+
 struct radix_tree_root {
 	gfp_t			gfp_mask;
 	struct radix_tree_node	__rcu *rnode;
@@ -358,10 +361,14 @@ int radix_tree_split(struct radix_tree_root *, unsigned long index,
 			unsigned new_order);
 int radix_tree_join(struct radix_tree_root *, unsigned long index,
 			unsigned new_order, void *);
+void **idr_get_free(struct radix_tree_root *, struct radix_tree_iter *,
+			gfp_t, int end);
 
-#define RADIX_TREE_ITER_TAG_MASK	0x00FF	/* tag index in lower byte */
-#define RADIX_TREE_ITER_TAGGED		0x0100	/* lookup tagged slots */
-#define RADIX_TREE_ITER_CONTIG		0x0200	/* stop at first hole */
+enum {
+	RADIX_TREE_ITER_TAG_MASK = 0x0f,	/* tag index in lower nybble */
+	RADIX_TREE_ITER_TAGGED   = 0x10,	/* lookup tagged slots */
+	RADIX_TREE_ITER_CONTIG   = 0x20,	/* stop at first hole */
+};
 
 /**
  * radix_tree_iter_init - initialize radix tree iterator
@@ -403,6 +410,40 @@ void **radix_tree_next_chunk(const struct radix_tree_root *,
 			     struct radix_tree_iter *iter, unsigned flags);
 
 /**
+ * radix_tree_iter_lookup - look up an index in the radix tree
+ * @root: radix tree root
+ * @iter: iterator state
+ * @index: key to look up
+ *
+ * If @index is present in the radix tree, this function returns the slot
+ * containing it and updates @iter to describe the entry.  If @index is not
+ * present, it returns NULL.
+ */
+static inline void **radix_tree_iter_lookup(const struct radix_tree_root *root,
+			struct radix_tree_iter *iter, unsigned long index)
+{
+	radix_tree_iter_init(iter, index);
+	return radix_tree_next_chunk(root, iter, RADIX_TREE_ITER_CONTIG);
+}
+
+/**
+ * radix_tree_iter_find - find a present entry
+ * @root: radix tree root
+ * @iter: iterator state
+ * @index: start location
+ *
+ * This function returns the slot containing the entry with the lowest index
+ * which is at least @index.  If @index is larger than any present entry, this
+ * function returns NULL.  The @iter is updated to describe the entry found.
+ */
+static inline void **radix_tree_iter_find(const struct radix_tree_root *root,
+			struct radix_tree_iter *iter, unsigned long index)
+{
+	radix_tree_iter_init(iter, index);
+	return radix_tree_next_chunk(root, iter, 0);
+}
+
+/**
  * radix_tree_iter_retry - retry this chunk of the iteration
  * @iter:	iterator state
  *
diff --git a/init/main.c b/init/main.c
index b0c9d6facef9..a65e3aad31bc 100644
--- a/init/main.c
+++ b/init/main.c
@@ -553,7 +553,7 @@ asmlinkage __visible void __init start_kernel(void)
 	if (WARN(!irqs_disabled(),
 		 "Interrupts were enabled *very* early, fixing it\n"))
 		local_irq_disable();
-	idr_init_cache();
+	radix_tree_init();
 
 	/*
 	 * Allow workqueue creation and work item queueing/cancelling
@@ -568,7 +568,6 @@ asmlinkage __visible void __init start_kernel(void)
 	trace_init();
 
 	context_tracking_init();
-	radix_tree_init();
 	/* init some links before init_ISA_irqs() */
 	early_irq_init();
 	init_IRQ();
diff --git a/lib/idr.c b/lib/idr.c
index 52d2979a05e8..b87056e2cc4c 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -1,1068 +1,369 @@
-/*
- * 2002-10-18  written by Jim Houston jim.houston@ccur.com
- *	Copyright (C) 2002 by Concurrent Computer Corporation
- *	Distributed under the GNU GPL license version 2.
- *
- * Modified by George Anzinger to reuse immediately and to use
- * find bit instructions.  Also removed _irq on spinlocks.
- *
- * Modified by Nadia Derbey to make it RCU safe.
- *
- * Small id to pointer translation service.
- *
- * It uses a radix tree like structure as a sparse array indexed
- * by the id to obtain the pointer.  The bitmap makes allocating
- * a new id quick.
- *
- * You call it to allocate an id (an int) an associate with that id a
- * pointer or what ever, we treat it as a (void *).  You can pass this
- * id to a user for him to pass back at a later time.  You then pass
- * that id to this code and it returns your pointer.
- */
-
-#ifndef TEST                        // to test in user space...
-#include <linux/slab.h>
-#include <linux/init.h>
+#include <linux/bitmap.h>
 #include <linux/export.h>
-#endif
-#include <linux/err.h>
-#include <linux/string.h>
 #include <linux/idr.h>
+#include <linux/slab.h>
 #include <linux/spinlock.h>
-#include <linux/percpu.h>
 
-#define MAX_IDR_SHIFT		(sizeof(int) * 8 - 1)
-#define MAX_IDR_BIT		(1U << MAX_IDR_SHIFT)
-
-/* Leave the possibility of an incomplete final layer */
-#define MAX_IDR_LEVEL ((MAX_IDR_SHIFT + IDR_BITS - 1) / IDR_BITS)
-
-/* Number of id_layer structs to leave in free list */
-#define MAX_IDR_FREE (MAX_IDR_LEVEL * 2)
-
-static struct kmem_cache *idr_layer_cache;
-static DEFINE_PER_CPU(struct idr_layer *, idr_preload_head);
-static DEFINE_PER_CPU(int, idr_preload_cnt);
 static DEFINE_SPINLOCK(simple_ida_lock);
 
-/* the maximum ID which can be allocated given idr->layers */
-static int idr_max(int layers)
-{
-	int bits = min_t(int, layers * IDR_BITS, MAX_IDR_SHIFT);
-
-	return (1 << bits) - 1;
-}
-
-/*
- * Prefix mask for an idr_layer at @layer.  For layer 0, the prefix mask is
- * all bits except for the lower IDR_BITS.  For layer 1, 2 * IDR_BITS, and
- * so on.
- */
-static int idr_layer_prefix_mask(int layer)
-{
-	return ~idr_max(layer + 1);
-}
-
-static struct idr_layer *get_from_free_list(struct idr *idp)
-{
-	struct idr_layer *p;
-	unsigned long flags;
-
-	spin_lock_irqsave(&idp->lock, flags);
-	if ((p = idp->id_free)) {
-		idp->id_free = p->ary[0];
-		idp->id_free_cnt--;
-		p->ary[0] = NULL;
-	}
-	spin_unlock_irqrestore(&idp->lock, flags);
-	return(p);
-}
-
-/**
- * idr_layer_alloc - allocate a new idr_layer
- * @gfp_mask: allocation mask
- * @layer_idr: optional idr to allocate from
- *
- * If @layer_idr is %NULL, directly allocate one using @gfp_mask or fetch
- * one from the per-cpu preload buffer.  If @layer_idr is not %NULL, fetch
- * an idr_layer from @idr->id_free.
- *
- * @layer_idr is to maintain backward compatibility with the old alloc
- * interface - idr_pre_get() and idr_get_new*() - and will be removed
- * together with per-pool preload buffer.
- */
-static struct idr_layer *idr_layer_alloc(gfp_t gfp_mask, struct idr *layer_idr)
-{
-	struct idr_layer *new;
-
-	/* this is the old path, bypass to get_from_free_list() */
-	if (layer_idr)
-		return get_from_free_list(layer_idr);
-
-	/*
-	 * Try to allocate directly from kmem_cache.  We want to try this
-	 * before preload buffer; otherwise, non-preloading idr_alloc()
-	 * users will end up taking advantage of preloading ones.  As the
-	 * following is allowed to fail for preloaded cases, suppress
-	 * warning this time.
-	 */
-	new = kmem_cache_zalloc(idr_layer_cache, gfp_mask | __GFP_NOWARN);
-	if (new)
-		return new;
-
-	/*
-	 * Try to fetch one from the per-cpu preload buffer if in process
-	 * context.  See idr_preload() for details.
-	 */
-	if (!in_interrupt()) {
-		preempt_disable();
-		new = __this_cpu_read(idr_preload_head);
-		if (new) {
-			__this_cpu_write(idr_preload_head, new->ary[0]);
-			__this_cpu_dec(idr_preload_cnt);
-			new->ary[0] = NULL;
-		}
-		preempt_enable();
-		if (new)
-			return new;
-	}
-
-	/*
-	 * Both failed.  Try kmem_cache again w/o adding __GFP_NOWARN so
-	 * that memory allocation failure warning is printed as intended.
-	 */
-	return kmem_cache_zalloc(idr_layer_cache, gfp_mask);
-}
-
-static void idr_layer_rcu_free(struct rcu_head *head)
-{
-	struct idr_layer *layer;
-
-	layer = container_of(head, struct idr_layer, rcu_head);
-	kmem_cache_free(idr_layer_cache, layer);
-}
-
-static inline void free_layer(struct idr *idr, struct idr_layer *p)
-{
-	if (idr->hint == p)
-		RCU_INIT_POINTER(idr->hint, NULL);
-	call_rcu(&p->rcu_head, idr_layer_rcu_free);
-}
-
-/* only called when idp->lock is held */
-static void __move_to_free_list(struct idr *idp, struct idr_layer *p)
-{
-	p->ary[0] = idp->id_free;
-	idp->id_free = p;
-	idp->id_free_cnt++;
-}
-
-static void move_to_free_list(struct idr *idp, struct idr_layer *p)
-{
-	unsigned long flags;
-
-	/*
-	 * Depends on the return element being zeroed.
-	 */
-	spin_lock_irqsave(&idp->lock, flags);
-	__move_to_free_list(idp, p);
-	spin_unlock_irqrestore(&idp->lock, flags);
-}
-
-static void idr_mark_full(struct idr_layer **pa, int id)
-{
-	struct idr_layer *p = pa[0];
-	int l = 0;
-
-	__set_bit(id & IDR_MASK, p->bitmap);
-	/*
-	 * If this layer is full mark the bit in the layer above to
-	 * show that this part of the radix tree is full.  This may
-	 * complete the layer above and require walking up the radix
-	 * tree.
-	 */
-	while (bitmap_full(p->bitmap, IDR_SIZE)) {
-		if (!(p = pa[++l]))
-			break;
-		id = id >> IDR_BITS;
-		__set_bit((id & IDR_MASK), p->bitmap);
-	}
-}
-
-static int __idr_pre_get(struct idr *idp, gfp_t gfp_mask)
-{
-	while (idp->id_free_cnt < MAX_IDR_FREE) {
-		struct idr_layer *new;
-		new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
-		if (new == NULL)
-			return (0);
-		move_to_free_list(idp, new);
-	}
-	return 1;
-}
-
-/**
- * sub_alloc - try to allocate an id without growing the tree depth
- * @idp: idr handle
- * @starting_id: id to start search at
- * @pa: idr_layer[MAX_IDR_LEVEL] used as backtrack buffer
- * @gfp_mask: allocation mask for idr_layer_alloc()
- * @layer_idr: optional idr passed to idr_layer_alloc()
- *
- * Allocate an id in range [@starting_id, INT_MAX] from @idp without
- * growing its depth.  Returns
- *
- *  the allocated id >= 0 if successful,
- *  -EAGAIN if the tree needs to grow for allocation to succeed,
- *  -ENOSPC if the id space is exhausted,
- *  -ENOMEM if more idr_layers need to be allocated.
- */
-static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa,
-		     gfp_t gfp_mask, struct idr *layer_idr)
-{
-	int n, m, sh;
-	struct idr_layer *p, *new;
-	int l, id, oid;
-
-	id = *starting_id;
- restart:
-	p = idp->top;
-	l = idp->layers;
-	pa[l--] = NULL;
-	while (1) {
-		/*
-		 * We run around this while until we reach the leaf node...
-		 */
-		n = (id >> (IDR_BITS*l)) & IDR_MASK;
-		m = find_next_zero_bit(p->bitmap, IDR_SIZE, n);
-		if (m == IDR_SIZE) {
-			/* no space available go back to previous layer. */
-			l++;
-			oid = id;
-			id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;
-
-			/* if already at the top layer, we need to grow */
-			if (id > idr_max(idp->layers)) {
-				*starting_id = id;
-				return -EAGAIN;
-			}
-			p = pa[l];
-			BUG_ON(!p);
-
-			/* If we need to go up one layer, continue the
-			 * loop; otherwise, restart from the top.
-			 */
-			sh = IDR_BITS * (l + 1);
-			if (oid >> sh == id >> sh)
-				continue;
-			else
-				goto restart;
-		}
-		if (m != n) {
-			sh = IDR_BITS*l;
-			id = ((id >> sh) ^ n ^ m) << sh;
-		}
-		if ((id >= MAX_IDR_BIT) || (id < 0))
-			return -ENOSPC;
-		if (l == 0)
-			break;
-		/*
-		 * Create the layer below if it is missing.
-		 */
-		if (!p->ary[m]) {
-			new = idr_layer_alloc(gfp_mask, layer_idr);
-			if (!new)
-				return -ENOMEM;
-			new->layer = l-1;
-			new->prefix = id & idr_layer_prefix_mask(new->layer);
-			rcu_assign_pointer(p->ary[m], new);
-			p->count++;
-		}
-		pa[l--] = p;
-		p = p->ary[m];
-	}
-
-	pa[l] = p;
-	return id;
-}
-
-static int idr_get_empty_slot(struct idr *idp, int starting_id,
-			      struct idr_layer **pa, gfp_t gfp_mask,
-			      struct idr *layer_idr)
-{
-	struct idr_layer *p, *new;
-	int layers, v, id;
-	unsigned long flags;
-
-	id = starting_id;
-build_up:
-	p = idp->top;
-	layers = idp->layers;
-	if (unlikely(!p)) {
-		if (!(p = idr_layer_alloc(gfp_mask, layer_idr)))
-			return -ENOMEM;
-		p->layer = 0;
-		layers = 1;
-	}
-	/*
-	 * Add a new layer to the top of the tree if the requested
-	 * id is larger than the currently allocated space.
-	 */
-	while (id > idr_max(layers)) {
-		layers++;
-		if (!p->count) {
-			/* special case: if the tree is currently empty,
-			 * then we grow the tree by moving the top node
-			 * upwards.
-			 */
-			p->layer++;
-			WARN_ON_ONCE(p->prefix);
-			continue;
-		}
-		if (!(new = idr_layer_alloc(gfp_mask, layer_idr))) {
-			/*
-			 * The allocation failed.  If we built part of
-			 * the structure tear it down.
-			 */
-			spin_lock_irqsave(&idp->lock, flags);
-			for (new = p; p && p != idp->top; new = p) {
-				p = p->ary[0];
-				new->ary[0] = NULL;
-				new->count = 0;
-				bitmap_clear(new->bitmap, 0, IDR_SIZE);
-				__move_to_free_list(idp, new);
-			}
-			spin_unlock_irqrestore(&idp->lock, flags);
-			return -ENOMEM;
-		}
-		new->ary[0] = p;
-		new->count = 1;
-		new->layer = layers-1;
-		new->prefix = id & idr_layer_prefix_mask(new->layer);
-		if (bitmap_full(p->bitmap, IDR_SIZE))
-			__set_bit(0, new->bitmap);
-		p = new;
-	}
-	rcu_assign_pointer(idp->top, p);
-	idp->layers = layers;
-	v = sub_alloc(idp, &id, pa, gfp_mask, layer_idr);
-	if (v == -EAGAIN)
-		goto build_up;
-	return(v);
-}
-
-/*
- * @id and @pa are from a successful allocation from idr_get_empty_slot().
- * Install the user pointer @ptr and mark the slot full.
- */
-static void idr_fill_slot(struct idr *idr, void *ptr, int id,
-			  struct idr_layer **pa)
-{
-	/* update hint used for lookup, cleared from free_layer() */
-	rcu_assign_pointer(idr->hint, pa[0]);
-
-	rcu_assign_pointer(pa[0]->ary[id & IDR_MASK], (struct idr_layer *)ptr);
-	pa[0]->count++;
-	idr_mark_full(pa, id);
-}
-
-
-/**
- * idr_preload - preload for idr_alloc()
- * @gfp_mask: allocation mask to use for preloading
- *
- * Preload per-cpu layer buffer for idr_alloc().  Can only be used from
- * process context and each idr_preload() invocation should be matched with
- * idr_preload_end().  Note that preemption is disabled while preloaded.
- *
- * The first idr_alloc() in the preloaded section can be treated as if it
- * were invoked with @gfp_mask used for preloading.  This allows using more
- * permissive allocation masks for idrs protected by spinlocks.
- *
- * For example, if idr_alloc() below fails, the failure can be treated as
- * if idr_alloc() were called with GFP_KERNEL rather than GFP_NOWAIT.
- *
- *	idr_preload(GFP_KERNEL);
- *	spin_lock(lock);
- *
- *	id = idr_alloc(idr, ptr, start, end, GFP_NOWAIT);
- *
- *	spin_unlock(lock);
- *	idr_preload_end();
- *	if (id < 0)
- *		error;
- */
-void idr_preload(gfp_t gfp_mask)
-{
-	/*
-	 * Consuming preload buffer from non-process context breaks preload
-	 * allocation guarantee.  Disallow usage from those contexts.
-	 */
-	WARN_ON_ONCE(in_interrupt());
-	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
-
-	preempt_disable();
-
-	/*
-	 * idr_alloc() is likely to succeed w/o full idr_layer buffer and
-	 * return value from idr_alloc() needs to be checked for failure
-	 * anyway.  Silently give up if allocation fails.  The caller can
-	 * treat failures from idr_alloc() as if idr_alloc() were called
-	 * with @gfp_mask which should be enough.
-	 */
-	while (__this_cpu_read(idr_preload_cnt) < MAX_IDR_FREE) {
-		struct idr_layer *new;
-
-		preempt_enable();
-		new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
-		preempt_disable();
-		if (!new)
-			break;
-
-		/* link the new one to per-cpu preload list */
-		new->ary[0] = __this_cpu_read(idr_preload_head);
-		__this_cpu_write(idr_preload_head, new);
-		__this_cpu_inc(idr_preload_cnt);
-	}
-}
-EXPORT_SYMBOL(idr_preload);
-
 /**
- * idr_alloc - allocate new idr entry
- * @idr: the (initialized) idr
+ * idr_alloc - allocate an id
+ * @idr: idr handle
  * @ptr: pointer to be associated with the new id
  * @start: the minimum id (inclusive)
- * @end: the maximum id (exclusive, <= 0 for max)
- * @gfp_mask: memory allocation flags
+ * @end: the maximum id (exclusive)
+ * @gfp: memory allocation flags
  *
- * Allocate an id in [start, end) and associate it with @ptr.  If no ID is
- * available in the specified range, returns -ENOSPC.  On memory allocation
- * failure, returns -ENOMEM.
+ * Allocates an unused ID in the range [start, end).  Returns -ENOSPC
+ * if there are no unused IDs in that range.
  *
  * Note that @end is treated as max when <= 0.  This is to always allow
  * using @start + N as @end as long as N is inside integer range.
  *
- * The user is responsible for exclusively synchronizing all operations
- * which may modify @idr.  However, read-only accesses such as idr_find()
- * or iteration can be performed under RCU read lock provided the user
- * destroys @ptr in RCU-safe way after removal from idr.
+ * Simultaneous modifications to the @idr are not allowed and should be
+ * prevented by the user, usually with a lock.  idr_alloc() may be called
+ * concurrently with read-only accesses to the @idr, such as idr_find() and
+ * idr_for_each_entry().
  */
-int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask)
+int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
 {
-	int max = end > 0 ? end - 1 : INT_MAX;	/* inclusive upper limit */
-	struct idr_layer *pa[MAX_IDR_LEVEL + 1];
-	int id;
-
-	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
+	void **slot;
+	struct radix_tree_iter iter;
 
-	/* sanity checks */
 	if (WARN_ON_ONCE(start < 0))
 		return -EINVAL;
-	if (unlikely(max < start))
-		return -ENOSPC;
+	if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
+		return -EINVAL;
 
-	/* allocate id */
-	id = idr_get_empty_slot(idr, start, pa, gfp_mask, NULL);
-	if (unlikely(id < 0))
-		return id;
-	if (unlikely(id > max))
-		return -ENOSPC;
+	radix_tree_iter_init(&iter, start);
+	slot = idr_get_free(&idr->idr_rt, &iter, gfp, end);
+	if (IS_ERR(slot))
+		return PTR_ERR(slot);
 
-	idr_fill_slot(idr, ptr, id, pa);
-	return id;
+	radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
+	radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);
+	return iter.index;
 }
 EXPORT_SYMBOL_GPL(idr_alloc);
 
 /**
  * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion
- * @idr: the (initialized) idr
+ * @idr: idr handle
  * @ptr: pointer to be associated with the new id
  * @start: the minimum id (inclusive)
- * @end: the maximum id (exclusive, <= 0 for max)
- * @gfp_mask: memory allocation flags
- *
- * Essentially the same as idr_alloc, but prefers to allocate progressively
- * higher ids if it can. If the "cur" counter wraps, then it will start again
- * at the "start" end of the range and allocate one that has already been used.
- */
-int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end,
-			gfp_t gfp_mask)
-{
-	int id;
-
-	id = idr_alloc(idr, ptr, max(start, idr->cur), end, gfp_mask);
-	if (id == -ENOSPC)
-		id = idr_alloc(idr, ptr, start, end, gfp_mask);
-
-	if (likely(id >= 0))
-		idr->cur = id + 1;
-	return id;
-}
-EXPORT_SYMBOL(idr_alloc_cyclic);
-
-static void idr_remove_warning(int id)
-{
-	WARN(1, "idr_remove called for id=%d which is not allocated.\n", id);
-}
-
-static void sub_remove(struct idr *idp, int shift, int id)
-{
-	struct idr_layer *p = idp->top;
-	struct idr_layer **pa[MAX_IDR_LEVEL + 1];
-	struct idr_layer ***paa = &pa[0];
-	struct idr_layer *to_free;
-	int n;
-
-	*paa = NULL;
-	*++paa = &idp->top;
-
-	while ((shift > 0) && p) {
-		n = (id >> shift) & IDR_MASK;
-		__clear_bit(n, p->bitmap);
-		*++paa = &p->ary[n];
-		p = p->ary[n];
-		shift -= IDR_BITS;
-	}
-	n = id & IDR_MASK;
-	if (likely(p != NULL && test_bit(n, p->bitmap))) {
-		__clear_bit(n, p->bitmap);
-		RCU_INIT_POINTER(p->ary[n], NULL);
-		to_free = NULL;
-		while(*paa && ! --((**paa)->count)){
-			if (to_free)
-				free_layer(idp, to_free);
-			to_free = **paa;
-			**paa-- = NULL;
-		}
-		if (!*paa)
-			idp->layers = 0;
-		if (to_free)
-			free_layer(idp, to_free);
-	} else
-		idr_remove_warning(id);
-}
-
-/**
- * idr_remove - remove the given id and free its slot
- * @idp: idr handle
- * @id: unique key
- */
-void idr_remove(struct idr *idp, int id)
-{
-	struct idr_layer *p;
-	struct idr_layer *to_free;
-
-	if (id < 0)
-		return;
-
-	if (id > idr_max(idp->layers)) {
-		idr_remove_warning(id);
-		return;
-	}
-
-	sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
-	if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
-	    idp->top->ary[0]) {
-		/*
-		 * Single child at leftmost slot: we can shrink the tree.
-		 * This level is not needed anymore since when layers are
-		 * inserted, they are inserted at the top of the existing
-		 * tree.
-		 */
-		to_free = idp->top;
-		p = idp->top->ary[0];
-		rcu_assign_pointer(idp->top, p);
-		--idp->layers;
-		to_free->count = 0;
-		bitmap_clear(to_free->bitmap, 0, IDR_SIZE);
-		free_layer(idp, to_free);
-	}
-}
-EXPORT_SYMBOL(idr_remove);
-
-static void __idr_remove_all(struct idr *idp)
-{
-	int n, id, max;
-	int bt_mask;
-	struct idr_layer *p;
-	struct idr_layer *pa[MAX_IDR_LEVEL + 1];
-	struct idr_layer **paa = &pa[0];
-
-	n = idp->layers * IDR_BITS;
-	*paa = idp->top;
-	RCU_INIT_POINTER(idp->top, NULL);
-	max = idr_max(idp->layers);
-
-	id = 0;
-	while (id >= 0 && id <= max) {
-		p = *paa;
-		while (n > IDR_BITS && p) {
-			n -= IDR_BITS;
-			p = p->ary[(id >> n) & IDR_MASK];
-			*++paa = p;
-		}
-
-		bt_mask = id;
-		id += 1 << n;
-		/* Get the highest bit that the above add changed from 0->1. */
-		while (n < fls(id ^ bt_mask)) {
-			if (*paa)
-				free_layer(idp, *paa);
-			n += IDR_BITS;
-			--paa;
-		}
-	}
-	idp->layers = 0;
-}
-
-/**
- * idr_destroy - release all cached layers within an idr tree
- * @idp: idr handle
- *
- * Free all id mappings and all idp_layers.  After this function, @idp is
- * completely unused and can be freed / recycled.  The caller is
- * responsible for ensuring that no one else accesses @idp during or after
- * idr_destroy().
+ * @end: the maximum id (exclusive)
+ * @gfp: memory allocation flags
  *
- * 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 up the id mappings and cached idr_layers.
+ * Allocates an ID larger than the last ID allocated if one is available.
+ * If not, it will attempt to allocate the smallest ID that is larger or
+ * equal to @start.
  */
-void idr_destroy(struct idr *idp)
-{
-	__idr_remove_all(idp);
-
-	while (idp->id_free_cnt) {
-		struct idr_layer *p = get_from_free_list(idp);
-		kmem_cache_free(idr_layer_cache, p);
-	}
-}
-EXPORT_SYMBOL(idr_destroy);
-
-void *idr_find_slowpath(struct idr *idp, int id)
+int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
 {
-	int n;
-	struct idr_layer *p;
+	int id, curr = idr->idr_next;
 
-	if (id < 0)
-		return NULL;
+	if (curr < start)
+		curr = start;
 
-	p = rcu_dereference_raw(idp->top);
-	if (!p)
-		return NULL;
-	n = (p->layer+1) * IDR_BITS;
+	id = idr_alloc(idr, ptr, curr, end, gfp);
+	if ((id == -ENOSPC) && (curr > start))
+		id = idr_alloc(idr, ptr, start, curr, gfp);
 
-	if (id > idr_max(p->layer + 1))
-		return NULL;
-	BUG_ON(n == 0);
+	if (id >= 0)
+		idr->idr_next = id + 1U;
 
-	while (n > 0 && p) {
-		n -= IDR_BITS;
-		BUG_ON(n != p->layer*IDR_BITS);
-		p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);
-	}
-	return((void *)p);
+	return id;
 }
-EXPORT_SYMBOL(idr_find_slowpath);
+EXPORT_SYMBOL(idr_alloc_cyclic);
 
 /**
  * idr_for_each - iterate through all stored pointers
- * @idp: idr handle
+ * @idr: idr handle
  * @fn: function to be called for each pointer
- * @data: data passed back to callback function
+ * @data: data passed to callback function
  *
- * Iterate over the pointers registered with the given idr.  The
- * callback function will be called for each pointer currently
- * registered, passing the id, the pointer and the data pointer passed
- * to this function.  It is not safe to modify the idr tree while in
- * the callback, so functions such as idr_get_new and idr_remove are
- * not allowed.
+ * The callback function will be called for each entry in @idr, passing
+ * the id, the pointer and the data pointer passed to this function.
  *
- * We check the return of @fn each time. If it returns anything other
- * than %0, we break out and return that value.
+ * If @fn returns anything other than %0, the iteration stops and that
+ * value is returned from this function.
  *
- * The caller must serialize idr_for_each() vs idr_get_new() and idr_remove().
+ * idr_for_each() can be called concurrently with idr_alloc() and
+ * idr_remove() if protected by RCU.  Newly added entries may not be
+ * seen and deleted entries may be seen, but adding and removing entries
+ * will not cause other entries to be skipped, nor spurious ones to be seen.
  */
-int idr_for_each(struct idr *idp,
-		 int (*fn)(int id, void *p, void *data), void *data)
+int idr_for_each(const struct idr *idr,
+		int (*fn)(int id, void *p, void *data), void *data)
 {
-	int n, id, max, error = 0;
-	struct idr_layer *p;
-	struct idr_layer *pa[MAX_IDR_LEVEL + 1];
-	struct idr_layer **paa = &pa[0];
-
-	n = idp->layers * IDR_BITS;
-	*paa = rcu_dereference_raw(idp->top);
-	max = idr_max(idp->layers);
-
-	id = 0;
-	while (id >= 0 && id <= max) {
-		p = *paa;
-		while (n > 0 && p) {
-			n -= IDR_BITS;
-			p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);
-			*++paa = p;
-		}
-
-		if (p) {
-			error = fn(id, (void *)p, data);
-			if (error)
-				break;
-		}
+	struct radix_tree_iter iter;
+	void **slot;
 
-		id += 1 << n;
-		while (n < fls(id)) {
-			n += IDR_BITS;
-			--paa;
-		}
+	radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
+		int ret = fn(iter.index, rcu_dereference_raw(*slot), data);
+		if (ret)
+			return ret;
 	}
 
-	return error;
+	return 0;
 }
 EXPORT_SYMBOL(idr_for_each);
 
 /**
- * idr_get_next - lookup next object of id to given id.
- * @idp: idr handle
- * @nextidp:  pointer to lookup key
- *
- * Returns pointer to registered object with id, which is next number to
- * given id. After being looked up, *@nextidp will be updated for the next
- * iteration.
- *
- * This function can be called under rcu_read_lock(), given that the leaf
- * pointers lifetimes are correctly managed.
+ * idr_get_next - Find next populated entry
+ * @idr: idr handle
+ * @nextid: Pointer to lowest possible ID to return
+ *
+ * Returns the next populated entry in the tree with an ID greater than
+ * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
+ * to the ID of the found value.  To use in a loop, the value pointed to by
+ * nextid must be incremented by the user.
  */
-void *idr_get_next(struct idr *idp, int *nextidp)
+void *idr_get_next(struct idr *idr, int *nextid)
 {
-	struct idr_layer *p, *pa[MAX_IDR_LEVEL + 1];
-	struct idr_layer **paa = &pa[0];
-	int id = *nextidp;
-	int n, max;
+	struct radix_tree_iter iter;
+	void **slot;
 
-	/* find first ent */
-	p = *paa = rcu_dereference_raw(idp->top);
-	if (!p)
+	slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
+	if (!slot)
 		return NULL;
-	n = (p->layer + 1) * IDR_BITS;
-	max = idr_max(p->layer + 1);
-
-	while (id >= 0 && id <= max) {
-		p = *paa;
-		while (n > 0 && p) {
-			n -= IDR_BITS;
-			p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);
-			*++paa = p;
-		}
 
-		if (p) {
-			*nextidp = id;
-			return p;
-		}
-
-		/*
-		 * Proceed to the next layer at the current level.  Unlike
-		 * idr_for_each(), @id isn't guaranteed to be aligned to
-		 * layer boundary at this point and adding 1 << n may
-		 * incorrectly skip IDs.  Make sure we jump to the
-		 * beginning of the next layer using round_up().
-		 */
-		id = round_up(id + 1, 1 << n);
-		while (n < fls(id)) {
-			n += IDR_BITS;
-			--paa;
-		}
-	}
-	return NULL;
+	*nextid = iter.index;
+	return rcu_dereference_raw(*slot);
 }
 EXPORT_SYMBOL(idr_get_next);
 
-
 /**
  * idr_replace - replace pointer for given id
- * @idp: idr handle
- * @ptr: pointer you want associated with the id
- * @id: lookup key
+ * @idr: idr handle
+ * @ptr: New pointer to associate with the ID
+ * @id: Lookup key
  *
- * Replace the pointer registered with an id and return the old value.
- * A %-ENOENT return indicates that @id was not found.
- * A %-EINVAL return indicates that @id was not within valid constraints.
+ * Replace the pointer registered with an ID and return the old value.
+ * This function can be called under the RCU read lock concurrently with
+ * idr_alloc() and idr_remove() (as long as the ID being removed is not
+ * the one being replaced!).
  *
- * The caller must serialize with writers.
+ * Returns: 0 on success.  %-ENOENT indicates that @id was not found.
+ * %-EINVAL indicates that @id or @ptr were not valid.
  */
-void *idr_replace(struct idr *idp, void *ptr, int id)
+void *idr_replace(struct idr *idr, void *ptr, int id)
 {
-	int n;
-	struct idr_layer *p, *old_p;
+	struct radix_tree_node *node;
+	void **slot = NULL;
+	void *entry;
 
-	if (id < 0)
+	if (WARN_ON_ONCE(id < 0))
+		return ERR_PTR(-EINVAL);
+	if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
 		return ERR_PTR(-EINVAL);
 
-	p = idp->top;
-	if (!p)
-		return ERR_PTR(-ENOENT);
-
-	if (id > idr_max(p->layer + 1))
-		return ERR_PTR(-ENOENT);
-
-	n = p->layer * IDR_BITS;
-	while ((n > 0) && p) {
-		p = p->ary[(id >> n) & IDR_MASK];
-		n -= IDR_BITS;
-	}
-
-	n = id & IDR_MASK;
-	if (unlikely(p == NULL || !test_bit(n, p->bitmap)))
+	entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
+	if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
 		return ERR_PTR(-ENOENT);
 
-	old_p = p->ary[n];
-	rcu_assign_pointer(p->ary[n], ptr);
+	__radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL, NULL);
 
-	return old_p;
+	return entry;
 }
 EXPORT_SYMBOL(idr_replace);
 
-void __init idr_init_cache(void)
-{
-	idr_layer_cache = kmem_cache_create("idr_layer_cache",
-				sizeof(struct idr_layer), 0, SLAB_PANIC, NULL);
-}
-
-/**
- * idr_init - initialize idr handle
- * @idp:	idr handle
- *
- * This function is use to set up the handle (@idp) that you will pass
- * to the rest of the functions.
- */
-void idr_init(struct idr *idp)
-{
-	memset(idp, 0, sizeof(struct idr));
-	spin_lock_init(&idp->lock);
-}
-EXPORT_SYMBOL(idr_init);
-
-static int idr_has_entry(int id, void *p, void *data)
-{
-	return 1;
-}
-
-bool idr_is_empty(struct idr *idp)
-{
-	return !idr_for_each(idp, idr_has_entry, NULL);
-}
-EXPORT_SYMBOL(idr_is_empty);
-
 /**
  * DOC: IDA description
- * IDA - IDR based ID allocator
- *
- * This is id allocator without id -> pointer translation.  Memory
- * usage is much lower than full blown idr because each id only
- * occupies a bit.  ida uses a custom leaf node which contains
- * IDA_BITMAP_BITS slots.
  *
- * 2007-04-25  written by Tejun Heo <htejun@gmail.com>
+ * The IDA is an ID allocator which does not provide the ability to
+ * associate an ID with a pointer.  As such, it only needs to store one
+ * bit per ID, and so is more space efficient than an IDR.  To use an IDA,
+ * define it using DEFINE_IDA() (or embed a &struct ida in a data structure,
+ * then initialise it using ida_init()).  To allocate a new ID, call
+ * ida_simple_get().  To free an ID, call ida_simple_remove().
+ *
+ * If you have more complex locking requirements, use a loop around
+ * ida_pre_get() and ida_get_new() to allocate a new ID.  Then use
+ * ida_remove() to free an ID.  You must make sure that ida_get_new() and
+ * ida_remove() cannot be called at the same time as each other for the
+ * same IDA.
+ *
+ * You can also use ida_get_new_above() if you need an ID to be allocated
+ * above a particular number.  ida_destroy() can be used to dispose of an
+ * IDA without needing to free the individual IDs in it.  You can use
+ * ida_is_empty() to find out whether the IDA has any IDs currently allocated.
+ *
+ * IDs are currently limited to the range [0-INT_MAX].  If this is an awkward
+ * limitation, it should be quite straightforward to raise the maximum.
  */
 
-static void free_bitmap(struct ida *ida, struct ida_bitmap *bitmap)
-{
-	unsigned long flags;
-
-	if (!ida->free_bitmap) {
-		spin_lock_irqsave(&ida->idr.lock, flags);
-		if (!ida->free_bitmap) {
-			ida->free_bitmap = bitmap;
-			bitmap = NULL;
-		}
-		spin_unlock_irqrestore(&ida->idr.lock, flags);
-	}
-
-	kfree(bitmap);
-}
-
 /**
  * ida_pre_get - reserve resources for ida allocation
- * @ida:	ida handle
- * @gfp_mask:	memory allocation flag
- *
- * This function should be called prior to locking and calling the
- * following function.  It preallocates enough memory to satisfy the
- * worst possible allocation.
+ * @ida: ida handle
+ * @gfp: memory allocation flags
  *
- * If the system is REALLY out of memory this function returns %0,
- * otherwise %1.
+ * This function should be called before calling ida_get_new_above().  If it
+ * is unable to allocate memory, it will return %0.  On success, it returns %1.
  */
-int ida_pre_get(struct ida *ida, gfp_t gfp_mask)
+int ida_pre_get(struct ida *ida, gfp_t gfp)
 {
-	/* allocate idr_layers */
-	if (!__idr_pre_get(&ida->idr, gfp_mask))
-		return 0;
+	struct ida_bitmap *bitmap;
 
-	/* allocate free_bitmap */
-	if (!ida->free_bitmap) {
-		struct ida_bitmap *bitmap;
+	/*
+	 * This looks weird, but 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.
+	 */
+	idr_preload(gfp);
+	idr_preload_end();
 
-		bitmap = kmalloc(sizeof(struct ida_bitmap), gfp_mask);
+	if (!ida->free_bitmap) {
+		bitmap = kmalloc(sizeof(struct ida_bitmap), gfp);
 		if (!bitmap)
 			return 0;
-
-		free_bitmap(ida, bitmap);
+		bitmap = xchg(&ida->free_bitmap, bitmap);
+		kfree(bitmap);
 	}
 
 	return 1;
 }
 EXPORT_SYMBOL(ida_pre_get);
 
+#define IDA_MAX (0x80000000U / IDA_BITMAP_BITS)
+
 /**
  * ida_get_new_above - allocate new ID above or equal to a start id
- * @ida:	ida handle
- * @starting_id: id to start search at
- * @p_id:	pointer to the allocated handle
+ * @ida: ida handle
+ * @start: id to start search at
+ * @id: pointer to the allocated handle
  *
- * Allocate new ID above or equal to @starting_id.  It should be called
- * with any required locks.
+ * Allocate new ID above or equal to @start.  It should be called
+ * with any required locks to ensure that concurrent calls to
+ * ida_get_new_above() / ida_get_new() / ida_remove() are not allowed.
+ * Consider using ida_simple_get() if you do not have complex locking
+ * requirements.
  *
  * If memory is required, it will return %-EAGAIN, you should unlock
  * and go back to the ida_pre_get() call.  If the ida is full, it will
- * return %-ENOSPC.
- *
- * Note that callers must ensure that concurrent access to @ida is not possible.
- * See ida_simple_get() for a varaint which takes care of locking.
+ * return %-ENOSPC.  On success, it will return 0.
  *
- * @p_id returns a value in the range @starting_id ... %0x7fffffff.
+ * @id returns a value in the range @start ... %0x7fffffff.
  */
-int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
+int ida_get_new_above(struct ida *ida, int start, int *id)
 {
-	struct idr_layer *pa[MAX_IDR_LEVEL + 1];
+	struct radix_tree_root *root = &ida->ida_rt;
+	void **slot;
+	struct radix_tree_iter iter;
 	struct ida_bitmap *bitmap;
-	unsigned long flags;
-	int idr_id = starting_id / IDA_BITMAP_BITS;
-	int offset = starting_id % IDA_BITMAP_BITS;
-	int t, id;
-
- restart:
-	/* get vacant slot */
-	t = idr_get_empty_slot(&ida->idr, idr_id, pa, 0, &ida->idr);
-	if (t < 0)
-		return t == -ENOMEM ? -EAGAIN : t;
-
-	if (t * IDA_BITMAP_BITS >= MAX_IDR_BIT)
-		return -ENOSPC;
-
-	if (t != idr_id)
-		offset = 0;
-	idr_id = t;
-
-	/* if bitmap isn't there, create a new one */
-	bitmap = (void *)pa[0]->ary[idr_id & IDR_MASK];
-	if (!bitmap) {
-		spin_lock_irqsave(&ida->idr.lock, flags);
-		bitmap = ida->free_bitmap;
-		ida->free_bitmap = NULL;
-		spin_unlock_irqrestore(&ida->idr.lock, flags);
-
-		if (!bitmap)
-			return -EAGAIN;
-
-		memset(bitmap, 0, sizeof(struct ida_bitmap));
-		rcu_assign_pointer(pa[0]->ary[idr_id & IDR_MASK],
-				(void *)bitmap);
-		pa[0]->count++;
-	}
-
-	/* lookup for empty slot */
-	t = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, offset);
-	if (t == IDA_BITMAP_BITS) {
-		/* no empty slot after offset, continue to the next chunk */
-		idr_id++;
-		offset = 0;
-		goto restart;
-	}
-
-	id = idr_id * IDA_BITMAP_BITS + t;
-	if (id >= MAX_IDR_BIT)
-		return -ENOSPC;
-
-	__set_bit(t, bitmap->bitmap);
-	if (++bitmap->nr_busy == IDA_BITMAP_BITS)
-		idr_mark_full(pa, idr_id);
+	unsigned long index;
+	unsigned bit;
+	int new;
+
+	index = start / IDA_BITMAP_BITS;
+	bit = start % IDA_BITMAP_BITS;
+
+	slot = radix_tree_iter_init(&iter, index);
+	for (;;) {
+		if (slot)
+			slot = radix_tree_next_slot(slot, &iter,
+						RADIX_TREE_ITER_TAGGED);
+		if (!slot) {
+			slot = idr_get_free(root, &iter, GFP_NOWAIT, IDA_MAX);
+			if (IS_ERR(slot)) {
+				if (slot == ERR_PTR(-ENOMEM))
+					return -EAGAIN;
+				return PTR_ERR(slot);
+			}
+		}
+		if (iter.index > index)
+			bit = 0;
+		new = iter.index * IDA_BITMAP_BITS;
+		bitmap = rcu_dereference_raw(*slot);
+		if (bitmap) {
+			bit = find_next_zero_bit(bitmap->bitmap,
+							IDA_BITMAP_BITS, bit);
+			new += bit;
+			if (new < 0)
+				return -ENOSPC;
+			if (bit == IDA_BITMAP_BITS)
+				continue;
 
-	*p_id = id;
+			__set_bit(bit, bitmap->bitmap);
+			if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
+				radix_tree_iter_tag_clear(root, &iter,
+								IDR_FREE);
+		} else {
+			new += bit;
+			if (new < 0)
+				return -ENOSPC;
+			bitmap = ida->free_bitmap;
+			if (!bitmap)
+				return -EAGAIN;
+			ida->free_bitmap = NULL;
+			memset(bitmap, 0, sizeof(*bitmap));
+			__set_bit(bit, bitmap->bitmap);
+			radix_tree_iter_replace(root, &iter, slot, bitmap);
+		}
 
-	/* Each leaf node can handle nearly a thousand slots and the
-	 * whole idea of ida is to have small memory foot print.
-	 * Throw away extra resources one by one after each successful
-	 * allocation.
-	 */
-	if (ida->idr.id_free_cnt || ida->free_bitmap) {
-		struct idr_layer *p = get_from_free_list(&ida->idr);
-		if (p)
-			kmem_cache_free(idr_layer_cache, p);
+		*id = new;
+		return 0;
 	}
-
-	return 0;
 }
 EXPORT_SYMBOL(ida_get_new_above);
 
 /**
- * ida_remove - remove the given ID
- * @ida:	ida handle
- * @id:		ID to free
+ * ida_remove - Free the given ID
+ * @ida: ida handle
+ * @id: ID to free
+ *
+ * This function should not be called at the same time as ida_get_new_above().
  */
 void ida_remove(struct ida *ida, int id)
 {
-	struct idr_layer *p = ida->idr.top;
-	int shift = (ida->idr.layers - 1) * IDR_BITS;
-	int idr_id = id / IDA_BITMAP_BITS;
-	int offset = id % IDA_BITMAP_BITS;
-	int n;
+	unsigned long index = id / IDA_BITMAP_BITS;
+	unsigned offset = id % IDA_BITMAP_BITS;
 	struct ida_bitmap *bitmap;
+	struct radix_tree_iter iter;
+	void **slot;
 
-	if (idr_id > idr_max(ida->idr.layers))
+	slot = radix_tree_iter_lookup(&ida->ida_rt, &iter, index);
+	if (!slot)
 		goto err;
 
-	/* clear full bits while looking up the leaf idr_layer */
-	while ((shift > 0) && p) {
-		n = (idr_id >> shift) & IDR_MASK;
-		__clear_bit(n, p->bitmap);
-		p = p->ary[n];
-		shift -= IDR_BITS;
-	}
-
-	if (p == NULL)
-		goto err;
-
-	n = idr_id & IDR_MASK;
-	__clear_bit(n, p->bitmap);
-
-	bitmap = (void *)p->ary[n];
-	if (!bitmap || !test_bit(offset, bitmap->bitmap))
+	bitmap = rcu_dereference_raw(*slot);
+	if (!test_bit(offset, bitmap->bitmap))
 		goto err;
 
-	/* update bitmap and remove it if empty */
 	__clear_bit(offset, bitmap->bitmap);
-	if (--bitmap->nr_busy == 0) {
-		__set_bit(n, p->bitmap);	/* to please idr_remove() */
-		idr_remove(&ida->idr, idr_id);
-		free_bitmap(ida, bitmap);
+	radix_tree_iter_tag_set(&ida->ida_rt, &iter, IDR_FREE);
+	if (bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) {
+		kfree(bitmap);
+		radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
 	}
-
 	return;
-
  err:
 	WARN(1, "ida_remove called for id=%d which is not allocated.\n", id);
 }
 EXPORT_SYMBOL(ida_remove);
 
 /**
- * ida_destroy - release all cached layers within an ida tree
- * @ida:		ida handle
+ * ida_destroy - Free the contents of an ida
+ * @ida: ida handle
+ *
+ * Calling this function releases all resources associated with an IDA.  When
+ * this call returns, the IDA is empty and can be reused or freed.  The caller
+ * should not allow ida_remove() or ida_get_new_above() to be called at the
+ * same time.
  */
 void ida_destroy(struct ida *ida)
 {
-	idr_destroy(&ida->idr);
+	struct radix_tree_iter iter;
+	void **slot;
+
+	radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) {
+		struct ida_bitmap *bitmap = rcu_dereference_raw(*slot);
+		kfree(bitmap);
+		radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
+	}
+
 	kfree(ida->free_bitmap);
+	ida->free_bitmap = NULL;
 }
 EXPORT_SYMBOL(ida_destroy);
 
@@ -1141,18 +442,3 @@ void ida_simple_remove(struct ida *ida, unsigned int id)
 	spin_unlock_irqrestore(&simple_ida_lock, flags);
 }
 EXPORT_SYMBOL(ida_simple_remove);
-
-/**
- * ida_init - initialize ida handle
- * @ida:	ida handle
- *
- * This function is use to set up the handle (@ida) that you will pass
- * to the rest of the functions.
- */
-void ida_init(struct ida *ida)
-{
-	memset(ida, 0, sizeof(struct ida));
-	idr_init(&ida->idr);
-
-}
-EXPORT_SYMBOL(ida_init);
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 7bf7d4e60e43..eaea14b8f2ca 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -22,20 +22,21 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include <linux/bitmap.h>
+#include <linux/bitops.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/export.h>
-#include <linux/radix-tree.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/kmemleak.h>
-#include <linux/cpu.h>
 #include <linux/string.h>
-#include <linux/bitops.h>
-#include <linux/rcupdate.h>
-#include <linux/preempt.h>		/* in_interrupt() */
 
 
 /* Number of nodes in fully populated tree of given height */
@@ -60,6 +61,15 @@ static struct kmem_cache *radix_tree_node_cachep;
 #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
  */
 struct radix_tree_preload {
@@ -149,27 +159,32 @@ static inline int tag_get(const struct radix_tree_node *node, unsigned int tag,
 
 static inline void root_tag_set(struct radix_tree_root *root, unsigned tag)
 {
-	root->gfp_mask |= (__force gfp_t)(1 << (tag + __GFP_BITS_SHIFT));
+	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 + __GFP_BITS_SHIFT));
+	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 &= __GFP_BITS_MASK;
+	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 + __GFP_BITS_SHIFT));
+	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 >> __GFP_BITS_SHIFT;
+	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);
 }
 
 /*
@@ -187,6 +202,11 @@ static inline int any_tag_set(const struct radix_tree_node *node,
 	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
  *
@@ -240,6 +260,13 @@ 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)
 {
@@ -278,11 +305,52 @@ 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 >> __GFP_BITS_SHIFT);
+			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 {
+		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 %p free %d bitmap %p\n", ida, root->rnode,
+				root->gfp_mask >> ROOT_TAG_SHIFT,
+				ida->free_bitmap);
+	dump_ida_node(root->rnode, 0);
+}
 #endif
 
 /*
@@ -290,13 +358,11 @@ static void radix_tree_dump(struct radix_tree_root *root)
  * that the caller has pinned this thread of control to the current CPU.
  */
 static struct radix_tree_node *
-radix_tree_node_alloc(struct radix_tree_root *root,
-			struct radix_tree_node *parent,
+radix_tree_node_alloc(gfp_t gfp_mask, struct radix_tree_node *parent,
 			unsigned int shift, unsigned int offset,
 			unsigned int count, unsigned int exceptional)
 {
 	struct radix_tree_node *ret = NULL;
-	gfp_t gfp_mask = root_gfp_mask(root);
 
 	/*
 	 * Preload code isn't irq safe and it doesn't make sense to use
@@ -533,7 +599,7 @@ static unsigned radix_tree_load_root(const struct radix_tree_root *root,
 /*
  *	Extend a radix tree so it can store key @index.
  */
-static int radix_tree_extend(struct radix_tree_root *root,
+static int radix_tree_extend(struct radix_tree_root *root, gfp_t gfp,
 				unsigned long index, unsigned int shift)
 {
 	struct radix_tree_node *slot;
@@ -546,19 +612,27 @@ static int radix_tree_extend(struct radix_tree_root *root,
 		maxshift += RADIX_TREE_MAP_SHIFT;
 
 	slot = root->rnode;
-	if (!slot)
+	if (!slot && (!is_idr(root) || root_tag_get(root, IDR_FREE)))
 		goto out;
 
 	do {
-		struct radix_tree_node *node = radix_tree_node_alloc(root,
-							NULL, shift, 0, 1, 0);
+		struct radix_tree_node *node = radix_tree_node_alloc(gfp, NULL,
+								shift, 0, 1, 0);
 		if (!node)
 			return -ENOMEM;
 
-		/* Propagate the aggregated tag info into the new root */
-		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
-			if (root_tag_get(root, tag))
-				tag_set(node, tag, 0);
+		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);
@@ -619,6 +693,8 @@ static inline bool radix_tree_shrink(struct radix_tree_root *root,
 		 * one (root->rnode) as far as dependent read barriers go.
 		 */
 		root->rnode = 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
@@ -674,7 +750,12 @@ static bool delete_node(struct radix_tree_root *root,
 			parent->slots[node->offset] = NULL;
 			parent->count--;
 		} else {
-			root_tag_clear_all(root);
+			/*
+			 * Shouldn't the tags already have all been cleared
+			 * by the caller?
+			 */
+			if (!is_idr(root))
+				root_tag_clear_all(root);
 			root->rnode = NULL;
 		}
 
@@ -714,6 +795,7 @@ int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 	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);
 
@@ -721,7 +803,7 @@ int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 	if (order > 0 && max == ((1UL << order) - 1))
 		max++;
 	if (max > maxindex) {
-		int error = radix_tree_extend(root, max, shift);
+		int error = radix_tree_extend(root, gfp, max, shift);
 		if (error < 0)
 			return error;
 		shift = error;
@@ -732,7 +814,7 @@ int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 		shift -= RADIX_TREE_MAP_SHIFT;
 		if (child == NULL) {
 			/* Have to add a child node.  */
-			child = radix_tree_node_alloc(root, node, shift,
+			child = radix_tree_node_alloc(gfp, node, shift,
 							offset, 0, 0);
 			if (!child)
 				return -ENOMEM;
@@ -755,7 +837,6 @@ int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 	return 0;
 }
 
-#ifdef CONFIG_RADIX_TREE_MULTIORDER
 /*
  * 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
@@ -791,6 +872,7 @@ static void radix_tree_free_nodes(struct radix_tree_node *node)
 	}
 }
 
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
 static inline int insert_entries(struct radix_tree_node *node, void **slot,
 				void *item, unsigned order, bool replace)
 {
@@ -996,69 +1078,70 @@ void *radix_tree_lookup(const struct radix_tree_root *root, unsigned long index)
 }
 EXPORT_SYMBOL(radix_tree_lookup);
 
-static inline int slot_count(struct radix_tree_node *node,
-						void **slot)
+static inline void replace_sibling_entries(struct radix_tree_node *node,
+				void **slot, int count, int exceptional)
 {
-	int n = 1;
 #ifdef CONFIG_RADIX_TREE_MULTIORDER
 	void *ptr = node_to_entry(slot);
-	unsigned offset = get_slot_offset(node, slot);
-	int i;
+	unsigned offset = get_slot_offset(node, slot) + 1;
 
-	for (i = 1; offset + i < RADIX_TREE_MAP_SIZE; i++) {
-		if (node->slots[offset + i] != ptr)
+	while (offset < RADIX_TREE_MAP_SIZE) {
+		if (node->slots[offset] != ptr)
 			break;
-		n++;
+		if (count < 0) {
+			node->slots[offset] = NULL;
+			node->count--;
+		}
+		node->exceptional += exceptional;
+		offset++;
 	}
 #endif
-	return n;
 }
 
-static void replace_slot(struct radix_tree_root *root,
-			 struct radix_tree_node *node,
-			 void **slot, void *item,
-			 bool warn_typeswitch)
+static void replace_slot(void **slot, void *item, struct radix_tree_node *node,
+				int count, int exceptional)
 {
-	void *old = rcu_dereference_raw(*slot);
-	int count, exceptional;
-
-	WARN_ON_ONCE(radix_tree_is_internal_node(item));
-
-	count = !!item - !!old;
-	exceptional = !!radix_tree_exceptional_entry(item) -
-		      !!radix_tree_exceptional_entry(old);
-
-	WARN_ON_ONCE(warn_typeswitch && (count || exceptional));
+	if (WARN_ON_ONCE(radix_tree_is_internal_node(item)))
+		return;
 
-	if (node) {
+	if (node && (count || exceptional)) {
 		node->count += count;
-		if (exceptional) {
-			exceptional *= slot_count(node, slot);
-			node->exceptional += exceptional;
-		}
+		node->exceptional += exceptional;
+		replace_sibling_entries(node, slot, count, exceptional);
 	}
 
 	rcu_assign_pointer(*slot, item);
 }
 
-static inline void delete_sibling_entries(struct radix_tree_node *node,
-						void **slot)
+static bool node_tag_get(const struct radix_tree_root *root,
+				const struct radix_tree_node *node,
+				unsigned int tag, unsigned int offset)
 {
-#ifdef CONFIG_RADIX_TREE_MULTIORDER
-	bool exceptional = radix_tree_exceptional_entry(*slot);
-	void *ptr = node_to_entry(slot);
-	unsigned offset = get_slot_offset(node, slot);
-	int i;
+	if (node)
+		return tag_get(node, tag, offset);
+	return root_tag_get(root, tag);
+}
 
-	for (i = 1; offset + i < RADIX_TREE_MAP_SIZE; i++) {
-		if (node->slots[offset + i] != ptr)
-			break;
-		node->slots[offset + i] = NULL;
-		node->count--;
-		if (exceptional)
-			node->exceptional--;
+/*
+ * 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 **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;
 	}
-#endif
+	return !!item - !!old;
 }
 
 /**
@@ -1078,15 +1161,19 @@ void __radix_tree_replace(struct radix_tree_root *root,
 			  void **slot, void *item,
 			  radix_tree_update_node_t update_node, void *private)
 {
-	if (!item)
-		delete_sibling_entries(node, slot);
+	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.
 	 */
-	replace_slot(root, node, slot, item,
-		     !node && slot != (void **)&root->rnode);
+	WARN_ON_ONCE(!node && (slot != (void **)&root->rnode) &&
+			(count || exceptional));
+	replace_slot(slot, item, node, count, exceptional);
 
 	if (!node)
 		return;
@@ -1116,7 +1203,7 @@ void __radix_tree_replace(struct radix_tree_root *root,
 void radix_tree_replace_slot(struct radix_tree_root *root,
 			     void **slot, void *item)
 {
-	replace_slot(root, NULL, slot, item, true);
+	__radix_tree_replace(root, NULL, slot, item, NULL, NULL);
 }
 
 /**
@@ -1191,6 +1278,7 @@ int radix_tree_split(struct radix_tree_root *root, unsigned long index,
 	void **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;
@@ -1228,7 +1316,7 @@ int radix_tree_split(struct radix_tree_root *root, unsigned long index,
 
 	for (;;) {
 		if (node->shift > order) {
-			child = radix_tree_node_alloc(root, node,
+			child = radix_tree_node_alloc(gfp, node,
 					node->shift - RADIX_TREE_MAP_SHIFT,
 					offset, 0, 0);
 			if (!child)
@@ -1444,8 +1532,6 @@ int radix_tree_tag_get(const struct radix_tree_root *root,
 	radix_tree_load_root(root, &node, &maxindex);
 	if (index > maxindex)
 		return 0;
-	if (node == NULL)
-		return 0;
 
 	while (radix_tree_is_internal_node(node)) {
 		unsigned offset;
@@ -1453,8 +1539,6 @@ int radix_tree_tag_get(const struct radix_tree_root *root,
 		parent = entry_to_node(node);
 		offset = radix_tree_descend(parent, &node, index);
 
-		if (!node)
-			return 0;
 		if (!tag_get(parent, tag, offset))
 			return 0;
 		if (node == RADIX_TREE_RETRY)
@@ -1481,6 +1565,11 @@ static void set_iter_tags(struct radix_tree_iter *iter,
 	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 */
@@ -1873,13 +1962,18 @@ void __radix_tree_delete_node(struct radix_tree_root *root,
 static bool __radix_tree_delete(struct radix_tree_root *root,
 				struct radix_tree_node *node, void **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;
 
-	for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
-		node_tag_clear(root, node, tag, offset);
+	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(root, node, slot, NULL, true);
+	replace_slot(slot, NULL, node, -1, exceptional);
 	return node && delete_node(root, node, NULL, NULL);
 }
 
@@ -1916,12 +2010,13 @@ void radix_tree_iter_delete(struct radix_tree_root *root,
 void *radix_tree_delete_item(struct radix_tree_root *root,
 			     unsigned long index, void *item)
 {
-	struct radix_tree_node *node;
+	struct radix_tree_node *node = NULL;
 	void **slot;
 	void *entry;
 
 	entry = __radix_tree_lookup(root, index, &node, &slot);
-	if (!entry)
+	if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE,
+						get_slot_offset(node, slot))))
 		return NULL;
 
 	if (item && entry != item)
@@ -1957,8 +2052,7 @@ void radix_tree_clear_tags(struct radix_tree_root *root,
 		for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
 			node_tag_clear(root, node, tag, offset);
 	} else {
-		/* Clear root node tags */
-		root->gfp_mask &= __GFP_BITS_MASK;
+		root_tag_clear_all(root);
 	}
 }
 
@@ -1973,6 +2067,111 @@ int radix_tree_tagged(const struct radix_tree_root *root, unsigned int 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)
+{
+	__radix_tree_preload(gfp_mask, IDR_PRELOAD_SIZE);
+}
+EXPORT_SYMBOL(idr_preload);
+
+void **idr_get_free(struct radix_tree_root *root,
+			struct radix_tree_iter *iter, gfp_t gfp, int end)
+{
+	struct radix_tree_node *node = NULL, *child;
+	void **slot = (void **)&root->rnode;
+	unsigned long maxindex, start = iter->next_index;
+	unsigned long max = end > 0 ? end - 1 : INT_MAX;
+	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, 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)
+				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)
 {
diff --git a/tools/testing/radix-tree/.gitignore b/tools/testing/radix-tree/.gitignore
index 11d888ca6a92..3b5534b643f0 100644
--- a/tools/testing/radix-tree/.gitignore
+++ b/tools/testing/radix-tree/.gitignore
@@ -1,2 +1,3 @@
 main
 radix-tree.c
+idr.c
diff --git a/tools/testing/radix-tree/Makefile b/tools/testing/radix-tree/Makefile
index 5274e88cd293..3597a3a9f269 100644
--- a/tools/testing/radix-tree/Makefile
+++ b/tools/testing/radix-tree/Makefile
@@ -2,8 +2,8 @@
 CFLAGS += -I. -I../../include -g -O2 -Wall -D_LGPL_SOURCE
 LDFLAGS += -lpthread -lurcu
 TARGETS = main
-OFILES = main.o radix-tree.o linux.o test.o tag_check.o find_bit.o \
-	 regression1.o regression2.o regression3.o multiorder.o \
+OFILES = main.o radix-tree.o idr.o linux.o test.o tag_check.o find_bit.o \
+	 regression1.o regression2.o regression3.o multiorder.o idr-test.o \
 	 iteration_check.o benchmark.o
 
 ifdef BENCHMARK
@@ -23,7 +23,11 @@ vpath %.c ../../lib
 $(OFILES): *.h */*.h \
 	../../include/linux/*.h \
 	../../include/asm/*.h \
-	../../../include/linux/radix-tree.h
+	../../../include/linux/radix-tree.h \
+	../../../include/linux/idr.h
 
 radix-tree.c: ../../../lib/radix-tree.c
 	sed -e 's/^static //' -e 's/__always_inline //' -e 's/inline //' < $< > $@
+
+idr.c: ../../../lib/idr.c
+	sed -e 's/^static //' -e 's/__always_inline //' -e 's/inline //' < $< > $@
diff --git a/tools/testing/radix-tree/idr-test.c b/tools/testing/radix-tree/idr-test.c
new file mode 100644
index 000000000000..4dffad9284e0
--- /dev/null
+++ b/tools/testing/radix-tree/idr-test.c
@@ -0,0 +1,342 @@
+/*
+ * idr-test.c: Test the IDR API
+ * Copyright (c) 2016 Matthew Wilcox <willy@infradead.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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.
+ */
+#include <linux/idr.h>
+#include <linux/slab.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+
+#include "test.h"
+
+#define DUMMY_PTR	((void *)0x12)
+
+int item_idr_free(int id, void *p, void *data)
+{
+	struct item *item = p;
+	assert(item->index == id);
+	free(p);
+
+	return 0;
+}
+
+void item_idr_remove(struct idr *idr, int id)
+{
+	struct item *item = idr_find(idr, id);
+	assert(item->index == id);
+	idr_remove(idr, id);
+	free(item);
+}
+
+void idr_alloc_test(void)
+{
+	unsigned long i;
+	DEFINE_IDR(idr);
+
+	assert(idr_alloc_cyclic(&idr, DUMMY_PTR, 0, 0x4000, GFP_KERNEL) == 0);
+	assert(idr_alloc_cyclic(&idr, DUMMY_PTR, 0x3ffd, 0x4000, GFP_KERNEL) == 0x3ffd);
+	idr_remove(&idr, 0x3ffd);
+	idr_remove(&idr, 0);
+
+	for (i = 0x3ffe; i < 0x4003; i++) {
+		int id;
+		struct item *item;
+
+		if (i < 0x4000)
+			item = item_create(i, 0);
+		else
+			item = item_create(i - 0x3fff, 0);
+
+		id = idr_alloc_cyclic(&idr, item, 1, 0x4000, GFP_KERNEL);
+		assert(id == item->index);
+	}
+
+	idr_for_each(&idr, item_idr_free, &idr);
+	idr_destroy(&idr);
+}
+
+void idr_replace_test(void)
+{
+	DEFINE_IDR(idr);
+
+	idr_alloc(&idr, (void *)-1, 10, 11, GFP_KERNEL);
+	idr_replace(&idr, &idr, 10);
+
+	idr_destroy(&idr);
+}
+
+/*
+ * Unlike the radix tree, you can put a NULL pointer -- with care -- into
+ * the IDR.  Some interfaces, like idr_find() do not distinguish between
+ * "present, value is NULL" and "not present", but that's exactly what some
+ * users want.
+ */
+void idr_null_test(void)
+{
+	int i;
+	DEFINE_IDR(idr);
+
+	assert(idr_is_empty(&idr));
+
+	assert(idr_alloc(&idr, NULL, 0, 0, GFP_KERNEL) == 0);
+	assert(!idr_is_empty(&idr));
+	idr_remove(&idr, 0);
+	assert(idr_is_empty(&idr));
+
+	assert(idr_alloc(&idr, NULL, 0, 0, GFP_KERNEL) == 0);
+	assert(!idr_is_empty(&idr));
+	idr_destroy(&idr);
+	assert(idr_is_empty(&idr));
+
+	for (i = 0; i < 10; i++) {
+		assert(idr_alloc(&idr, NULL, 0, 0, GFP_KERNEL) == i);
+	}
+
+	assert(idr_replace(&idr, DUMMY_PTR, 3) == NULL);
+	assert(idr_replace(&idr, DUMMY_PTR, 4) == NULL);
+	assert(idr_replace(&idr, NULL, 4) == DUMMY_PTR);
+	assert(idr_replace(&idr, DUMMY_PTR, 11) == ERR_PTR(-ENOENT));
+	idr_remove(&idr, 5);
+	assert(idr_alloc(&idr, NULL, 0, 0, GFP_KERNEL) == 5);
+	idr_remove(&idr, 5);
+
+	for (i = 0; i < 9; i++) {
+		idr_remove(&idr, i);
+		assert(!idr_is_empty(&idr));
+	}
+	idr_remove(&idr, 8);
+	assert(!idr_is_empty(&idr));
+	idr_remove(&idr, 9);
+	assert(idr_is_empty(&idr));
+
+	assert(idr_alloc(&idr, NULL, 0, 0, GFP_KERNEL) == 0);
+	assert(idr_replace(&idr, DUMMY_PTR, 3) == ERR_PTR(-ENOENT));
+	assert(idr_replace(&idr, DUMMY_PTR, 0) == NULL);
+	assert(idr_replace(&idr, NULL, 0) == DUMMY_PTR);
+
+	idr_destroy(&idr);
+	assert(idr_is_empty(&idr));
+
+	for (i = 1; i < 10; i++) {
+		assert(idr_alloc(&idr, NULL, 1, 0, GFP_KERNEL) == i);
+	}
+
+	idr_destroy(&idr);
+	assert(idr_is_empty(&idr));
+}
+
+void idr_nowait_test(void)
+{
+	unsigned int i;
+	DEFINE_IDR(idr);
+
+	idr_preload(GFP_KERNEL);
+
+	for (i = 0; i < 3; i++) {
+		struct item *item = item_create(i, 0);
+		assert(idr_alloc(&idr, item, i, i + 1, GFP_NOWAIT) == i);
+	}
+
+	idr_preload_end();
+
+	idr_for_each(&idr, item_idr_free, &idr);
+	idr_destroy(&idr);
+}
+
+void idr_checks(void)
+{
+	unsigned long i;
+	DEFINE_IDR(idr);
+
+	for (i = 0; i < 10000; i++) {
+		struct item *item = item_create(i, 0);
+		assert(idr_alloc(&idr, item, 0, 20000, GFP_KERNEL) == i);
+	}
+
+	assert(idr_alloc(&idr, DUMMY_PTR, 5, 30, GFP_KERNEL) < 0);
+
+	for (i = 0; i < 5000; i++)
+		item_idr_remove(&idr, i);
+
+	idr_remove(&idr, 3);
+
+	idr_for_each(&idr, item_idr_free, &idr);
+	idr_destroy(&idr);
+
+	assert(idr_is_empty(&idr));
+
+	idr_remove(&idr, 3);
+	idr_remove(&idr, 0);
+
+	for (i = INT_MAX - 3UL; i < INT_MAX + 1UL; i++) {
+		struct item *item = item_create(i, 0);
+		assert(idr_alloc(&idr, item, i, i + 10, GFP_KERNEL) == i);
+	}
+	assert(idr_alloc(&idr, DUMMY_PTR, i - 2, i, GFP_KERNEL) == -ENOSPC);
+
+	idr_for_each(&idr, item_idr_free, &idr);
+	idr_destroy(&idr);
+	idr_destroy(&idr);
+
+	assert(idr_is_empty(&idr));
+
+	for (i = 1; i < 10000; i++) {
+		struct item *item = item_create(i, 0);
+		assert(idr_alloc(&idr, item, 1, 20000, GFP_KERNEL) == i);
+	}
+
+	idr_for_each(&idr, item_idr_free, &idr);
+	idr_destroy(&idr);
+
+	idr_replace_test();
+	idr_alloc_test();
+	idr_null_test();
+	idr_nowait_test();
+}
+
+/*
+ * Check that we get the correct error when we run out of memory doing
+ * allocations.  To ensure we run out of memory, just "forget" to preload.
+ * The first test is for not having a bitmap available, and the second test
+ * is for not being able to allocate a level of the radix tree.
+ */
+void ida_check_nomem(void)
+{
+	DEFINE_IDA(ida);
+	int id, err;
+
+	err = ida_get_new(&ida, &id);
+	assert(err == -EAGAIN);
+	err = ida_get_new_above(&ida, 1UL << 30, &id);
+	assert(err == -EAGAIN);
+}
+
+/*
+ * Check what happens when we fill a leaf and then delete it.  This may
+ * discover mishandling of IDR_FREE.
+ */
+void ida_check_leaf(void)
+{
+	DEFINE_IDA(ida);
+	int id;
+	unsigned long i;
+
+	for (i = 0; i < IDA_BITMAP_BITS; i++) {
+		assert(ida_pre_get(&ida, GFP_KERNEL));
+		assert(!ida_get_new(&ida, &id));
+		assert(id == i);
+	}
+
+	ida_destroy(&ida);
+	assert(ida_is_empty(&ida));
+
+	assert(ida_pre_get(&ida, GFP_KERNEL));
+	assert(!ida_get_new(&ida, &id));
+	assert(id == 0);
+	ida_destroy(&ida);
+	assert(ida_is_empty(&ida));
+}
+
+/*
+ * Check allocations up to and slightly above the maximum allowed (2^31-1) ID.
+ * Allocating up to 2^31-1 should succeed, and then allocating the next one
+ * should fail.
+ */
+void ida_check_max(void)
+{
+	DEFINE_IDA(ida);
+	int id, err;
+	unsigned long i, j;
+
+	for (j = 1; j < 65537; j *= 2) {
+		unsigned long base = (1UL << 31) - j;
+		for (i = 0; i < j; i++) {
+			assert(ida_pre_get(&ida, GFP_KERNEL));
+			assert(!ida_get_new_above(&ida, base, &id));
+			assert(id == base + i);
+		}
+		assert(ida_pre_get(&ida, GFP_KERNEL));
+		err = ida_get_new_above(&ida, base, &id);
+		assert(err == -ENOSPC);
+		ida_destroy(&ida);
+		assert(ida_is_empty(&ida));
+		rcu_barrier();
+	}
+}
+
+void ida_checks(void)
+{
+	DEFINE_IDA(ida);
+	int id;
+	unsigned long i;
+
+	radix_tree_cpu_dead(1);
+	ida_check_nomem();
+
+	for (i = 0; i < 10000; i++) {
+		assert(ida_pre_get(&ida, GFP_KERNEL));
+		assert(!ida_get_new(&ida, &id));
+		assert(id == i);
+	}
+
+	ida_remove(&ida, 20);
+	ida_remove(&ida, 21);
+	for (i = 0; i < 3; i++) {
+		assert(ida_pre_get(&ida, GFP_KERNEL));
+		assert(!ida_get_new(&ida, &id));
+		if (i == 2)
+			assert(id == 10000);
+	}
+
+	for (i = 0; i < 5000; i++)
+		ida_remove(&ida, i);
+
+	assert(ida_pre_get(&ida, GFP_KERNEL));
+	assert(!ida_get_new_above(&ida, 5000, &id));
+	assert(id == 10001);
+
+	ida_destroy(&ida);
+
+	assert(ida_is_empty(&ida));
+
+	assert(ida_pre_get(&ida, GFP_KERNEL));
+	assert(!ida_get_new_above(&ida, 1, &id));
+	assert(id == 1);
+
+	ida_remove(&ida, id);
+	assert(ida_is_empty(&ida));
+	ida_destroy(&ida);
+	assert(ida_is_empty(&ida));
+
+	assert(ida_pre_get(&ida, GFP_KERNEL));
+	assert(!ida_get_new_above(&ida, 1, &id));
+	ida_destroy(&ida);
+	assert(ida_is_empty(&ida));
+
+	assert(ida_pre_get(&ida, GFP_KERNEL));
+	assert(!ida_get_new_above(&ida, 1, &id));
+	assert(id == 1);
+	assert(ida_pre_get(&ida, GFP_KERNEL));
+	assert(!ida_get_new_above(&ida, 1025, &id));
+	assert(id == 1025);
+	assert(ida_pre_get(&ida, GFP_KERNEL));
+	assert(!ida_get_new_above(&ida, 10000, &id));
+	assert(id == 10000);
+	ida_remove(&ida, 1025);
+	ida_destroy(&ida);
+	assert(ida_is_empty(&ida));
+
+	ida_check_leaf();
+	ida_check_max();
+
+	radix_tree_cpu_dead(1);
+}
diff --git a/tools/testing/radix-tree/linux/gfp.h b/tools/testing/radix-tree/linux/gfp.h
index 701209816a6b..39a0dcb9475a 100644
--- a/tools/testing/radix-tree/linux/gfp.h
+++ b/tools/testing/radix-tree/linux/gfp.h
@@ -15,10 +15,12 @@
 #define __GFP_DIRECT_RECLAIM	0x400000u
 #define __GFP_KSWAPD_RECLAIM	0x2000000u
 
-#define __GFP_RECLAIM		(__GFP_DIRECT_RECLAIM|__GFP_KSWAPD_RECLAIM)
+#define __GFP_RECLAIM	(__GFP_DIRECT_RECLAIM|__GFP_KSWAPD_RECLAIM)
+
+#define GFP_ATOMIC	(__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
+#define GFP_KERNEL	(__GFP_RECLAIM | __GFP_IO | __GFP_FS)
+#define GFP_NOWAIT	(__GFP_KSWAPD_RECLAIM)
 
-#define GFP_ATOMIC		(__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
-#define GFP_KERNEL		(__GFP_RECLAIM | __GFP_IO | __GFP_FS)
 
 static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags)
 {
diff --git a/tools/testing/radix-tree/linux/idr.h b/tools/testing/radix-tree/linux/idr.h
new file mode 100644
index 000000000000..4e342f2e37cf
--- /dev/null
+++ b/tools/testing/radix-tree/linux/idr.h
@@ -0,0 +1 @@
+#include "../../../../include/linux/idr.h"
diff --git a/tools/testing/radix-tree/linux/kernel.h b/tools/testing/radix-tree/linux/kernel.h
index dd1d9aefb14f..63fce553781a 100644
--- a/tools/testing/radix-tree/linux/kernel.h
+++ b/tools/testing/radix-tree/linux/kernel.h
@@ -20,6 +20,7 @@
 
 #define printk printf
 #define pr_debug printk
+#define pr_cont printk
 
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 
diff --git a/tools/testing/radix-tree/main.c b/tools/testing/radix-tree/main.c
index f7e9801a6754..ddd90a11db3f 100644
--- a/tools/testing/radix-tree/main.c
+++ b/tools/testing/radix-tree/main.c
@@ -3,6 +3,7 @@
 #include <unistd.h>
 #include <time.h>
 #include <assert.h>
+#include <limits.h>
 
 #include <linux/slab.h>
 #include <linux/radix-tree.h>
@@ -314,6 +315,11 @@ static void single_thread_tests(bool long_run)
 	rcu_barrier();
 	printf("after dynamic_height_check: %d allocated, preempt %d\n",
 		nr_allocated, preempt_count);
+	idr_checks();
+	ida_checks();
+	rcu_barrier();
+	printf("after idr_checks: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
 	big_gang_check(long_run);
 	rcu_barrier();
 	printf("after big_gang_check: %d allocated, preempt %d\n",
diff --git a/tools/testing/radix-tree/test.h b/tools/testing/radix-tree/test.h
index 056a23b56467..b30e11d9d271 100644
--- a/tools/testing/radix-tree/test.h
+++ b/tools/testing/radix-tree/test.h
@@ -34,6 +34,8 @@ void tag_check(void);
 void multiorder_checks(void);
 void iteration_test(unsigned order, unsigned duration);
 void benchmark(void);
+void idr_checks(void);
+void ida_checks(void);
 
 struct item *
 item_tag_set(struct radix_tree_root *root, unsigned long index, int tag);