Root/lib/radix-tree.c

1/*
2 * Copyright (C) 2001 Momchil Velikov
3 * Portions Copyright (C) 2001 Christoph Hellwig
4 * Copyright (C) 2005 SGI, Christoph Lameter
5 * Copyright (C) 2006 Nick Piggin
6 * Copyright (C) 2012 Konstantin Khlebnikov
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as
10 * published by the Free Software Foundation; either version 2, or (at
11 * your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful, but
14 * WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * General Public License for more details.
17 *
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21 */
22
23#include <linux/errno.h>
24#include <linux/init.h>
25#include <linux/kernel.h>
26#include <linux/export.h>
27#include <linux/radix-tree.h>
28#include <linux/percpu.h>
29#include <linux/slab.h>
30#include <linux/notifier.h>
31#include <linux/cpu.h>
32#include <linux/string.h>
33#include <linux/bitops.h>
34#include <linux/rcupdate.h>
35#include <linux/hardirq.h> /* in_interrupt() */
36
37
38#ifdef __KERNEL__
39#define RADIX_TREE_MAP_SHIFT (CONFIG_BASE_SMALL ? 4 : 6)
40#else
41#define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */
42#endif
43
44#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
45#define RADIX_TREE_MAP_MASK (RADIX_TREE_MAP_SIZE-1)
46
47#define RADIX_TREE_TAG_LONGS \
48    ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
49
50struct radix_tree_node {
51    unsigned int height; /* Height from the bottom */
52    unsigned int count;
53    union {
54        struct radix_tree_node *parent; /* Used when ascending tree */
55        struct rcu_head rcu_head; /* Used when freeing node */
56    };
57    void __rcu *slots[RADIX_TREE_MAP_SIZE];
58    unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
59};
60
61#define RADIX_TREE_INDEX_BITS (8 /* CHAR_BIT */ * sizeof(unsigned long))
62#define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
63                      RADIX_TREE_MAP_SHIFT))
64
65/*
66 * The height_to_maxindex array needs to be one deeper than the maximum
67 * path as height 0 holds only 1 entry.
68 */
69static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH + 1] __read_mostly;
70
71/*
72 * Radix tree node cache.
73 */
74static struct kmem_cache *radix_tree_node_cachep;
75
76/*
77 * The radix tree is variable-height, so an insert operation not only has
78 * to build the branch to its corresponding item, it also has to build the
79 * branch to existing items if the size has to be increased (by
80 * radix_tree_extend).
81 *
82 * The worst case is a zero height tree with just a single item at index 0,
83 * and then inserting an item at index ULONG_MAX. This requires 2 new branches
84 * of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
85 * Hence:
86 */
87#define RADIX_TREE_PRELOAD_SIZE (RADIX_TREE_MAX_PATH * 2 - 1)
88
89/*
90 * Per-cpu pool of preloaded nodes
91 */
92struct radix_tree_preload {
93    int nr;
94    struct radix_tree_node *nodes[RADIX_TREE_PRELOAD_SIZE];
95};
96static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
97
98static inline void *ptr_to_indirect(void *ptr)
99{
100    return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR);
101}
102
103static inline void *indirect_to_ptr(void *ptr)
104{
105    return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
106}
107
108static inline gfp_t root_gfp_mask(struct radix_tree_root *root)
109{
110    return root->gfp_mask & __GFP_BITS_MASK;
111}
112
113static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
114        int offset)
115{
116    __set_bit(offset, node->tags[tag]);
117}
118
119static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
120        int offset)
121{
122    __clear_bit(offset, node->tags[tag]);
123}
124
125static inline int tag_get(struct radix_tree_node *node, unsigned int tag,
126        int offset)
127{
128    return test_bit(offset, node->tags[tag]);
129}
130
131static inline void root_tag_set(struct radix_tree_root *root, unsigned int tag)
132{
133    root->gfp_mask |= (__force gfp_t)(1 << (tag + __GFP_BITS_SHIFT));
134}
135
136static inline void root_tag_clear(struct radix_tree_root *root, unsigned int tag)
137{
138    root->gfp_mask &= (__force gfp_t)~(1 << (tag + __GFP_BITS_SHIFT));
139}
140
141static inline void root_tag_clear_all(struct radix_tree_root *root)
142{
143    root->gfp_mask &= __GFP_BITS_MASK;
144}
145
146static inline int root_tag_get(struct radix_tree_root *root, unsigned int tag)
147{
148    return (__force unsigned)root->gfp_mask & (1 << (tag + __GFP_BITS_SHIFT));
149}
150
151/*
152 * Returns 1 if any slot in the node has this tag set.
153 * Otherwise returns 0.
154 */
155static inline int any_tag_set(struct radix_tree_node *node, unsigned int tag)
156{
157    int idx;
158    for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
159        if (node->tags[tag][idx])
160            return 1;
161    }
162    return 0;
163}
164
165/**
166 * radix_tree_find_next_bit - find the next set bit in a memory region
167 *
168 * @addr: The address to base the search on
169 * @size: The bitmap size in bits
170 * @offset: The bitnumber to start searching at
171 *
172 * Unrollable variant of find_next_bit() for constant size arrays.
173 * Tail bits starting from size to roundup(size, BITS_PER_LONG) must be zero.
174 * Returns next bit offset, or size if nothing found.
175 */
176static __always_inline unsigned long
177radix_tree_find_next_bit(const unsigned long *addr,
178             unsigned long size, unsigned long offset)
179{
180    if (!__builtin_constant_p(size))
181        return find_next_bit(addr, size, offset);
182
183    if (offset < size) {
184        unsigned long tmp;
185
186        addr += offset / BITS_PER_LONG;
187        tmp = *addr >> (offset % BITS_PER_LONG);
188        if (tmp)
189            return __ffs(tmp) + offset;
190        offset = (offset + BITS_PER_LONG) & ~(BITS_PER_LONG - 1);
191        while (offset < size) {
192            tmp = *++addr;
193            if (tmp)
194                return __ffs(tmp) + offset;
195            offset += BITS_PER_LONG;
196        }
197    }
198    return size;
199}
200
201/*
202 * This assumes that the caller has performed appropriate preallocation, and
203 * that the caller has pinned this thread of control to the current CPU.
204 */
205static struct radix_tree_node *
206radix_tree_node_alloc(struct radix_tree_root *root)
207{
208    struct radix_tree_node *ret = NULL;
209    gfp_t gfp_mask = root_gfp_mask(root);
210
211    /*
212     * Preload code isn't irq safe and it doesn't make sence to use
213     * preloading in the interrupt anyway as all the allocations have to
214     * be atomic. So just do normal allocation when in interrupt.
215     */
216    if (!(gfp_mask & __GFP_WAIT) && !in_interrupt()) {
217        struct radix_tree_preload *rtp;
218
219        /*
220         * Provided the caller has preloaded here, we will always
221         * succeed in getting a node here (and never reach
222         * kmem_cache_alloc)
223         */
224        rtp = &__get_cpu_var(radix_tree_preloads);
225        if (rtp->nr) {
226            ret = rtp->nodes[rtp->nr - 1];
227            rtp->nodes[rtp->nr - 1] = NULL;
228            rtp->nr--;
229        }
230    }
231    if (ret == NULL)
232        ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
233
234    BUG_ON(radix_tree_is_indirect_ptr(ret));
235    return ret;
236}
237
238static void radix_tree_node_rcu_free(struct rcu_head *head)
239{
240    struct radix_tree_node *node =
241            container_of(head, struct radix_tree_node, rcu_head);
242    int i;
243
244    /*
245     * must only free zeroed nodes into the slab. radix_tree_shrink
246     * can leave us with a non-NULL entry in the first slot, so clear
247     * that here to make sure.
248     */
249    for (i = 0; i < RADIX_TREE_MAX_TAGS; i++)
250        tag_clear(node, i, 0);
251
252    node->slots[0] = NULL;
253    node->count = 0;
254
255    kmem_cache_free(radix_tree_node_cachep, node);
256}
257
258static inline void
259radix_tree_node_free(struct radix_tree_node *node)
260{
261    call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
262}
263
264/*
265 * Load up this CPU's radix_tree_node buffer with sufficient objects to
266 * ensure that the addition of a single element in the tree cannot fail. On
267 * success, return zero, with preemption disabled. On error, return -ENOMEM
268 * with preemption not disabled.
269 *
270 * To make use of this facility, the radix tree must be initialised without
271 * __GFP_WAIT being passed to INIT_RADIX_TREE().
272 */
273static int __radix_tree_preload(gfp_t gfp_mask)
274{
275    struct radix_tree_preload *rtp;
276    struct radix_tree_node *node;
277    int ret = -ENOMEM;
278
279    preempt_disable();
280    rtp = &__get_cpu_var(radix_tree_preloads);
281    while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {
282        preempt_enable();
283        node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
284        if (node == NULL)
285            goto out;
286        preempt_disable();
287        rtp = &__get_cpu_var(radix_tree_preloads);
288        if (rtp->nr < ARRAY_SIZE(rtp->nodes))
289            rtp->nodes[rtp->nr++] = node;
290        else
291            kmem_cache_free(radix_tree_node_cachep, node);
292    }
293    ret = 0;
294out:
295    return ret;
296}
297
298/*
299 * Load up this CPU's radix_tree_node buffer with sufficient objects to
300 * ensure that the addition of a single element in the tree cannot fail. On
301 * success, return zero, with preemption disabled. On error, return -ENOMEM
302 * with preemption not disabled.
303 *
304 * To make use of this facility, the radix tree must be initialised without
305 * __GFP_WAIT being passed to INIT_RADIX_TREE().
306 */
307int radix_tree_preload(gfp_t gfp_mask)
308{
309    /* Warn on non-sensical use... */
310    WARN_ON_ONCE(!(gfp_mask & __GFP_WAIT));
311    return __radix_tree_preload(gfp_mask);
312}
313EXPORT_SYMBOL(radix_tree_preload);
314
315/*
316 * The same as above function, except we don't guarantee preloading happens.
317 * We do it, if we decide it helps. On success, return zero with preemption
318 * disabled. On error, return -ENOMEM with preemption not disabled.
319 */
320int radix_tree_maybe_preload(gfp_t gfp_mask)
321{
322    if (gfp_mask & __GFP_WAIT)
323        return __radix_tree_preload(gfp_mask);
324    /* Preloading doesn't help anything with this gfp mask, skip it */
325    preempt_disable();
326    return 0;
327}
328EXPORT_SYMBOL(radix_tree_maybe_preload);
329
330/*
331 * Return the maximum key which can be store into a
332 * radix tree with height HEIGHT.
333 */
334static inline unsigned long radix_tree_maxindex(unsigned int height)
335{
336    return height_to_maxindex[height];
337}
338
339/*
340 * Extend a radix tree so it can store key @index.
341 */
342static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
343{
344    struct radix_tree_node *node;
345    struct radix_tree_node *slot;
346    unsigned int height;
347    int tag;
348
349    /* Figure out what the height should be. */
350    height = root->height + 1;
351    while (index > radix_tree_maxindex(height))
352        height++;
353
354    if (root->rnode == NULL) {
355        root->height = height;
356        goto out;
357    }
358
359    do {
360        unsigned int newheight;
361        if (!(node = radix_tree_node_alloc(root)))
362            return -ENOMEM;
363
364        /* Propagate the aggregated tag info into the new root */
365        for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
366            if (root_tag_get(root, tag))
367                tag_set(node, tag, 0);
368        }
369
370        /* Increase the height. */
371        newheight = root->height+1;
372        node->height = newheight;
373        node->count = 1;
374        node->parent = NULL;
375        slot = root->rnode;
376        if (newheight > 1) {
377            slot = indirect_to_ptr(slot);
378            slot->parent = node;
379        }
380        node->slots[0] = slot;
381        node = ptr_to_indirect(node);
382        rcu_assign_pointer(root->rnode, node);
383        root->height = newheight;
384    } while (height > root->height);
385out:
386    return 0;
387}
388
389/**
390 * radix_tree_insert - insert into a radix tree
391 * @root: radix tree root
392 * @index: index key
393 * @item: item to insert
394 *
395 * Insert an item into the radix tree at position @index.
396 */
397int radix_tree_insert(struct radix_tree_root *root,
398            unsigned long index, void *item)
399{
400    struct radix_tree_node *node = NULL, *slot;
401    unsigned int height, shift;
402    int offset;
403    int error;
404
405    BUG_ON(radix_tree_is_indirect_ptr(item));
406
407    /* Make sure the tree is high enough. */
408    if (index > radix_tree_maxindex(root->height)) {
409        error = radix_tree_extend(root, index);
410        if (error)
411            return error;
412    }
413
414    slot = indirect_to_ptr(root->rnode);
415
416    height = root->height;
417    shift = (height-1) * RADIX_TREE_MAP_SHIFT;
418
419    offset = 0; /* uninitialised var warning */
420    while (height > 0) {
421        if (slot == NULL) {
422            /* Have to add a child node. */
423            if (!(slot = radix_tree_node_alloc(root)))
424                return -ENOMEM;
425            slot->height = height;
426            slot->parent = node;
427            if (node) {
428                rcu_assign_pointer(node->slots[offset], slot);
429                node->count++;
430            } else
431                rcu_assign_pointer(root->rnode, ptr_to_indirect(slot));
432        }
433
434        /* Go a level down */
435        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
436        node = slot;
437        slot = node->slots[offset];
438        shift -= RADIX_TREE_MAP_SHIFT;
439        height--;
440    }
441
442    if (slot != NULL)
443        return -EEXIST;
444
445    if (node) {
446        node->count++;
447        rcu_assign_pointer(node->slots[offset], item);
448        BUG_ON(tag_get(node, 0, offset));
449        BUG_ON(tag_get(node, 1, offset));
450    } else {
451        rcu_assign_pointer(root->rnode, item);
452        BUG_ON(root_tag_get(root, 0));
453        BUG_ON(root_tag_get(root, 1));
454    }
455
456    return 0;
457}
458EXPORT_SYMBOL(radix_tree_insert);
459
460/*
461 * is_slot == 1 : search for the slot.
462 * is_slot == 0 : search for the node.
463 */
464static void *radix_tree_lookup_element(struct radix_tree_root *root,
465                unsigned long index, int is_slot)
466{
467    unsigned int height, shift;
468    struct radix_tree_node *node, **slot;
469
470    node = rcu_dereference_raw(root->rnode);
471    if (node == NULL)
472        return NULL;
473
474    if (!radix_tree_is_indirect_ptr(node)) {
475        if (index > 0)
476            return NULL;
477        return is_slot ? (void *)&root->rnode : node;
478    }
479    node = indirect_to_ptr(node);
480
481    height = node->height;
482    if (index > radix_tree_maxindex(height))
483        return NULL;
484
485    shift = (height-1) * RADIX_TREE_MAP_SHIFT;
486
487    do {
488        slot = (struct radix_tree_node **)
489            (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
490        node = rcu_dereference_raw(*slot);
491        if (node == NULL)
492            return NULL;
493
494        shift -= RADIX_TREE_MAP_SHIFT;
495        height--;
496    } while (height > 0);
497
498    return is_slot ? (void *)slot : indirect_to_ptr(node);
499}
500
501/**
502 * radix_tree_lookup_slot - lookup a slot in a radix tree
503 * @root: radix tree root
504 * @index: index key
505 *
506 * Returns: the slot corresponding to the position @index in the
507 * radix tree @root. This is useful for update-if-exists operations.
508 *
509 * This function can be called under rcu_read_lock iff the slot is not
510 * modified by radix_tree_replace_slot, otherwise it must be called
511 * exclusive from other writers. Any dereference of the slot must be done
512 * using radix_tree_deref_slot.
513 */
514void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
515{
516    return (void **)radix_tree_lookup_element(root, index, 1);
517}
518EXPORT_SYMBOL(radix_tree_lookup_slot);
519
520/**
521 * radix_tree_lookup - perform lookup operation on a radix tree
522 * @root: radix tree root
523 * @index: index key
524 *
525 * Lookup the item at the position @index in the radix tree @root.
526 *
527 * This function can be called under rcu_read_lock, however the caller
528 * must manage lifetimes of leaf nodes (eg. RCU may also be used to free
529 * them safely). No RCU barriers are required to access or modify the
530 * returned item, however.
531 */
532void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
533{
534    return radix_tree_lookup_element(root, index, 0);
535}
536EXPORT_SYMBOL(radix_tree_lookup);
537
538/**
539 * radix_tree_tag_set - set a tag on a radix tree node
540 * @root: radix tree root
541 * @index: index key
542 * @tag: tag index
543 *
544 * Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
545 * corresponding to @index in the radix tree. From
546 * the root all the way down to the leaf node.
547 *
548 * Returns the address of the tagged item. Setting a tag on a not-present
549 * item is a bug.
550 */
551void *radix_tree_tag_set(struct radix_tree_root *root,
552            unsigned long index, unsigned int tag)
553{
554    unsigned int height, shift;
555    struct radix_tree_node *slot;
556
557    height = root->height;
558    BUG_ON(index > radix_tree_maxindex(height));
559
560    slot = indirect_to_ptr(root->rnode);
561    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
562
563    while (height > 0) {
564        int offset;
565
566        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
567        if (!tag_get(slot, tag, offset))
568            tag_set(slot, tag, offset);
569        slot = slot->slots[offset];
570        BUG_ON(slot == NULL);
571        shift -= RADIX_TREE_MAP_SHIFT;
572        height--;
573    }
574
575    /* set the root's tag bit */
576    if (slot && !root_tag_get(root, tag))
577        root_tag_set(root, tag);
578
579    return slot;
580}
581EXPORT_SYMBOL(radix_tree_tag_set);
582
583/**
584 * radix_tree_tag_clear - clear a tag on a radix tree node
585 * @root: radix tree root
586 * @index: index key
587 * @tag: tag index
588 *
589 * Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
590 * corresponding to @index in the radix tree. If
591 * this causes the leaf node to have no tags set then clear the tag in the
592 * next-to-leaf node, etc.
593 *
594 * Returns the address of the tagged item on success, else NULL. ie:
595 * has the same return value and semantics as radix_tree_lookup().
596 */
597void *radix_tree_tag_clear(struct radix_tree_root *root,
598            unsigned long index, unsigned int tag)
599{
600    struct radix_tree_node *node = NULL;
601    struct radix_tree_node *slot = NULL;
602    unsigned int height, shift;
603    int uninitialized_var(offset);
604
605    height = root->height;
606    if (index > radix_tree_maxindex(height))
607        goto out;
608
609    shift = height * RADIX_TREE_MAP_SHIFT;
610    slot = indirect_to_ptr(root->rnode);
611
612    while (shift) {
613        if (slot == NULL)
614            goto out;
615
616        shift -= RADIX_TREE_MAP_SHIFT;
617        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
618        node = slot;
619        slot = slot->slots[offset];
620    }
621
622    if (slot == NULL)
623        goto out;
624
625    while (node) {
626        if (!tag_get(node, tag, offset))
627            goto out;
628        tag_clear(node, tag, offset);
629        if (any_tag_set(node, tag))
630            goto out;
631
632        index >>= RADIX_TREE_MAP_SHIFT;
633        offset = index & RADIX_TREE_MAP_MASK;
634        node = node->parent;
635    }
636
637    /* clear the root's tag bit */
638    if (root_tag_get(root, tag))
639        root_tag_clear(root, tag);
640
641out:
642    return slot;
643}
644EXPORT_SYMBOL(radix_tree_tag_clear);
645
646/**
647 * radix_tree_tag_get - get a tag on a radix tree node
648 * @root: radix tree root
649 * @index: index key
650 * @tag: tag index (< RADIX_TREE_MAX_TAGS)
651 *
652 * Return values:
653 *
654 * 0: tag not present or not set
655 * 1: tag set
656 *
657 * Note that the return value of this function may not be relied on, even if
658 * the RCU lock is held, unless tag modification and node deletion are excluded
659 * from concurrency.
660 */
661int radix_tree_tag_get(struct radix_tree_root *root,
662            unsigned long index, unsigned int tag)
663{
664    unsigned int height, shift;
665    struct radix_tree_node *node;
666
667    /* check the root's tag bit */
668    if (!root_tag_get(root, tag))
669        return 0;
670
671    node = rcu_dereference_raw(root->rnode);
672    if (node == NULL)
673        return 0;
674
675    if (!radix_tree_is_indirect_ptr(node))
676        return (index == 0);
677    node = indirect_to_ptr(node);
678
679    height = node->height;
680    if (index > radix_tree_maxindex(height))
681        return 0;
682
683    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
684
685    for ( ; ; ) {
686        int offset;
687
688        if (node == NULL)
689            return 0;
690
691        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
692        if (!tag_get(node, tag, offset))
693            return 0;
694        if (height == 1)
695            return 1;
696        node = rcu_dereference_raw(node->slots[offset]);
697        shift -= RADIX_TREE_MAP_SHIFT;
698        height--;
699    }
700}
701EXPORT_SYMBOL(radix_tree_tag_get);
702
703/**
704 * radix_tree_next_chunk - find next chunk of slots for iteration
705 *
706 * @root: radix tree root
707 * @iter: iterator state
708 * @flags: RADIX_TREE_ITER_* flags and tag index
709 * Returns: pointer to chunk first slot, or NULL if iteration is over
710 */
711void **radix_tree_next_chunk(struct radix_tree_root *root,
712                 struct radix_tree_iter *iter, unsigned flags)
713{
714    unsigned shift, tag = flags & RADIX_TREE_ITER_TAG_MASK;
715    struct radix_tree_node *rnode, *node;
716    unsigned long index, offset;
717
718    if ((flags & RADIX_TREE_ITER_TAGGED) && !root_tag_get(root, tag))
719        return NULL;
720
721    /*
722     * Catch next_index overflow after ~0UL. iter->index never overflows
723     * during iterating; it can be zero only at the beginning.
724     * And we cannot overflow iter->next_index in a single step,
725     * because RADIX_TREE_MAP_SHIFT < BITS_PER_LONG.
726     *
727     * This condition also used by radix_tree_next_slot() to stop
728     * contiguous iterating, and forbid swithing to the next chunk.
729     */
730    index = iter->next_index;
731    if (!index && iter->index)
732        return NULL;
733
734    rnode = rcu_dereference_raw(root->rnode);
735    if (radix_tree_is_indirect_ptr(rnode)) {
736        rnode = indirect_to_ptr(rnode);
737    } else if (rnode && !index) {
738        /* Single-slot tree */
739        iter->index = 0;
740        iter->next_index = 1;
741        iter->tags = 1;
742        return (void **)&root->rnode;
743    } else
744        return NULL;
745
746restart:
747    shift = (rnode->height - 1) * RADIX_TREE_MAP_SHIFT;
748    offset = index >> shift;
749
750    /* Index outside of the tree */
751    if (offset >= RADIX_TREE_MAP_SIZE)
752        return NULL;
753
754    node = rnode;
755    while (1) {
756        if ((flags & RADIX_TREE_ITER_TAGGED) ?
757                !test_bit(offset, node->tags[tag]) :
758                !node->slots[offset]) {
759            /* Hole detected */
760            if (flags & RADIX_TREE_ITER_CONTIG)
761                return NULL;
762
763            if (flags & RADIX_TREE_ITER_TAGGED)
764                offset = radix_tree_find_next_bit(
765                        node->tags[tag],
766                        RADIX_TREE_MAP_SIZE,
767                        offset + 1);
768            else
769                while (++offset < RADIX_TREE_MAP_SIZE) {
770                    if (node->slots[offset])
771                        break;
772                }
773            index &= ~((RADIX_TREE_MAP_SIZE << shift) - 1);
774            index += offset << shift;
775            /* Overflow after ~0UL */
776            if (!index)
777                return NULL;
778            if (offset == RADIX_TREE_MAP_SIZE)
779                goto restart;
780        }
781
782        /* This is leaf-node */
783        if (!shift)
784            break;
785
786        node = rcu_dereference_raw(node->slots[offset]);
787        if (node == NULL)
788            goto restart;
789        shift -= RADIX_TREE_MAP_SHIFT;
790        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
791    }
792
793    /* Update the iterator state */
794    iter->index = index;
795    iter->next_index = (index | RADIX_TREE_MAP_MASK) + 1;
796
797    /* Construct iter->tags bit-mask from node->tags[tag] array */
798    if (flags & RADIX_TREE_ITER_TAGGED) {
799        unsigned tag_long, tag_bit;
800
801        tag_long = offset / BITS_PER_LONG;
802        tag_bit = offset % BITS_PER_LONG;
803        iter->tags = node->tags[tag][tag_long] >> tag_bit;
804        /* This never happens if RADIX_TREE_TAG_LONGS == 1 */
805        if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
806            /* Pick tags from next element */
807            if (tag_bit)
808                iter->tags |= node->tags[tag][tag_long + 1] <<
809                        (BITS_PER_LONG - tag_bit);
810            /* Clip chunk size, here only BITS_PER_LONG tags */
811            iter->next_index = index + BITS_PER_LONG;
812        }
813    }
814
815    return node->slots + offset;
816}
817EXPORT_SYMBOL(radix_tree_next_chunk);
818
819/**
820 * radix_tree_range_tag_if_tagged - for each item in given range set given
821 * tag if item has another tag set
822 * @root: radix tree root
823 * @first_indexp: pointer to a starting index of a range to scan
824 * @last_index: last index of a range to scan
825 * @nr_to_tag: maximum number items to tag
826 * @iftag: tag index to test
827 * @settag: tag index to set if tested tag is set
828 *
829 * This function scans range of radix tree from first_index to last_index
830 * (inclusive). For each item in the range if iftag is set, the function sets
831 * also settag. The function stops either after tagging nr_to_tag items or
832 * after reaching last_index.
833 *
834 * The tags must be set from the leaf level only and propagated back up the
835 * path to the root. We must do this so that we resolve the full path before
836 * setting any tags on intermediate nodes. If we set tags as we descend, then
837 * we can get to the leaf node and find that the index that has the iftag
838 * set is outside the range we are scanning. This reults in dangling tags and
839 * can lead to problems with later tag operations (e.g. livelocks on lookups).
840 *
841 * The function returns number of leaves where the tag was set and sets
842 * *first_indexp to the first unscanned index.
843 * WARNING! *first_indexp can wrap if last_index is ULONG_MAX. Caller must
844 * be prepared to handle that.
845 */
846unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
847        unsigned long *first_indexp, unsigned long last_index,
848        unsigned long nr_to_tag,
849        unsigned int iftag, unsigned int settag)
850{
851    unsigned int height = root->height;
852    struct radix_tree_node *node = NULL;
853    struct radix_tree_node *slot;
854    unsigned int shift;
855    unsigned long tagged = 0;
856    unsigned long index = *first_indexp;
857
858    last_index = min(last_index, radix_tree_maxindex(height));
859    if (index > last_index)
860        return 0;
861    if (!nr_to_tag)
862        return 0;
863    if (!root_tag_get(root, iftag)) {
864        *first_indexp = last_index + 1;
865        return 0;
866    }
867    if (height == 0) {
868        *first_indexp = last_index + 1;
869        root_tag_set(root, settag);
870        return 1;
871    }
872
873    shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
874    slot = indirect_to_ptr(root->rnode);
875
876    for (;;) {
877        unsigned long upindex;
878        int offset;
879
880        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
881        if (!slot->slots[offset])
882            goto next;
883        if (!tag_get(slot, iftag, offset))
884            goto next;
885        if (shift) {
886            /* Go down one level */
887            shift -= RADIX_TREE_MAP_SHIFT;
888            node = slot;
889            slot = slot->slots[offset];
890            continue;
891        }
892
893        /* tag the leaf */
894        tagged++;
895        tag_set(slot, settag, offset);
896
897        /* walk back up the path tagging interior nodes */
898        upindex = index;
899        while (node) {
900            upindex >>= RADIX_TREE_MAP_SHIFT;
901            offset = upindex & RADIX_TREE_MAP_MASK;
902
903            /* stop if we find a node with the tag already set */
904            if (tag_get(node, settag, offset))
905                break;
906            tag_set(node, settag, offset);
907            node = node->parent;
908        }
909
910        /*
911         * Small optimization: now clear that node pointer.
912         * Since all of this slot's ancestors now have the tag set
913         * from setting it above, we have no further need to walk
914         * back up the tree setting tags, until we update slot to
915         * point to another radix_tree_node.
916         */
917        node = NULL;
918
919next:
920        /* Go to next item at level determined by 'shift' */
921        index = ((index >> shift) + 1) << shift;
922        /* Overflow can happen when last_index is ~0UL... */
923        if (index > last_index || !index)
924            break;
925        if (tagged >= nr_to_tag)
926            break;
927        while (((index >> shift) & RADIX_TREE_MAP_MASK) == 0) {
928            /*
929             * We've fully scanned this node. Go up. Because
930             * last_index is guaranteed to be in the tree, what
931             * we do below cannot wander astray.
932             */
933            slot = slot->parent;
934            shift += RADIX_TREE_MAP_SHIFT;
935        }
936    }
937    /*
938     * We need not to tag the root tag if there is no tag which is set with
939     * settag within the range from *first_indexp to last_index.
940     */
941    if (tagged > 0)
942        root_tag_set(root, settag);
943    *first_indexp = index;
944
945    return tagged;
946}
947EXPORT_SYMBOL(radix_tree_range_tag_if_tagged);
948
949
950/**
951 * radix_tree_next_hole - find the next hole (not-present entry)
952 * @root: tree root
953 * @index: index key
954 * @max_scan: maximum range to search
955 *
956 * Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the lowest
957 * indexed hole.
958 *
959 * Returns: the index of the hole if found, otherwise returns an index
960 * outside of the set specified (in which case 'return - index >= max_scan'
961 * will be true). In rare cases of index wrap-around, 0 will be returned.
962 *
963 * radix_tree_next_hole may be called under rcu_read_lock. However, like
964 * radix_tree_gang_lookup, this will not atomically search a snapshot of
965 * the tree at a single point in time. For example, if a hole is created
966 * at index 5, then subsequently a hole is created at index 10,
967 * radix_tree_next_hole covering both indexes may return 10 if called
968 * under rcu_read_lock.
969 */
970unsigned long radix_tree_next_hole(struct radix_tree_root *root,
971                unsigned long index, unsigned long max_scan)
972{
973    unsigned long i;
974
975    for (i = 0; i < max_scan; i++) {
976        if (!radix_tree_lookup(root, index))
977            break;
978        index++;
979        if (index == 0)
980            break;
981    }
982
983    return index;
984}
985EXPORT_SYMBOL(radix_tree_next_hole);
986
987/**
988 * radix_tree_prev_hole - find the prev hole (not-present entry)
989 * @root: tree root
990 * @index: index key
991 * @max_scan: maximum range to search
992 *
993 * Search backwards in the range [max(index-max_scan+1, 0), index]
994 * for the first hole.
995 *
996 * Returns: the index of the hole if found, otherwise returns an index
997 * outside of the set specified (in which case 'index - return >= max_scan'
998 * will be true). In rare cases of wrap-around, ULONG_MAX will be returned.
999 *
1000 * radix_tree_next_hole may be called under rcu_read_lock. However, like
1001 * radix_tree_gang_lookup, this will not atomically search a snapshot of
1002 * the tree at a single point in time. For example, if a hole is created
1003 * at index 10, then subsequently a hole is created at index 5,
1004 * radix_tree_prev_hole covering both indexes may return 5 if called under
1005 * rcu_read_lock.
1006 */
1007unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
1008                   unsigned long index, unsigned long max_scan)
1009{
1010    unsigned long i;
1011
1012    for (i = 0; i < max_scan; i++) {
1013        if (!radix_tree_lookup(root, index))
1014            break;
1015        index--;
1016        if (index == ULONG_MAX)
1017            break;
1018    }
1019
1020    return index;
1021}
1022EXPORT_SYMBOL(radix_tree_prev_hole);
1023
1024/**
1025 * radix_tree_gang_lookup - perform multiple lookup on a radix tree
1026 * @root: radix tree root
1027 * @results: where the results of the lookup are placed
1028 * @first_index: start the lookup from this key
1029 * @max_items: place up to this many items at *results
1030 *
1031 * Performs an index-ascending scan of the tree for present items. Places
1032 * them at *@results and returns the number of items which were placed at
1033 * *@results.
1034 *
1035 * The implementation is naive.
1036 *
1037 * Like radix_tree_lookup, radix_tree_gang_lookup may be called under
1038 * rcu_read_lock. In this case, rather than the returned results being
1039 * an atomic snapshot of the tree at a single point in time, the semantics
1040 * of an RCU protected gang lookup are as though multiple radix_tree_lookups
1041 * have been issued in individual locks, and results stored in 'results'.
1042 */
1043unsigned int
1044radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
1045            unsigned long first_index, unsigned int max_items)
1046{
1047    struct radix_tree_iter iter;
1048    void **slot;
1049    unsigned int ret = 0;
1050
1051    if (unlikely(!max_items))
1052        return 0;
1053
1054    radix_tree_for_each_slot(slot, root, &iter, first_index) {
1055        results[ret] = indirect_to_ptr(rcu_dereference_raw(*slot));
1056        if (!results[ret])
1057            continue;
1058        if (++ret == max_items)
1059            break;
1060    }
1061
1062    return ret;
1063}
1064EXPORT_SYMBOL(radix_tree_gang_lookup);
1065
1066/**
1067 * radix_tree_gang_lookup_slot - perform multiple slot lookup on radix tree
1068 * @root: radix tree root
1069 * @results: where the results of the lookup are placed
1070 * @indices: where their indices should be placed (but usually NULL)
1071 * @first_index: start the lookup from this key
1072 * @max_items: place up to this many items at *results
1073 *
1074 * Performs an index-ascending scan of the tree for present items. Places
1075 * their slots at *@results and returns the number of items which were
1076 * placed at *@results.
1077 *
1078 * The implementation is naive.
1079 *
1080 * Like radix_tree_gang_lookup as far as RCU and locking goes. Slots must
1081 * be dereferenced with radix_tree_deref_slot, and if using only RCU
1082 * protection, radix_tree_deref_slot may fail requiring a retry.
1083 */
1084unsigned int
1085radix_tree_gang_lookup_slot(struct radix_tree_root *root,
1086            void ***results, unsigned long *indices,
1087            unsigned long first_index, unsigned int max_items)
1088{
1089    struct radix_tree_iter iter;
1090    void **slot;
1091    unsigned int ret = 0;
1092
1093    if (unlikely(!max_items))
1094        return 0;
1095
1096    radix_tree_for_each_slot(slot, root, &iter, first_index) {
1097        results[ret] = slot;
1098        if (indices)
1099            indices[ret] = iter.index;
1100        if (++ret == max_items)
1101            break;
1102    }
1103
1104    return ret;
1105}
1106EXPORT_SYMBOL(radix_tree_gang_lookup_slot);
1107
1108/**
1109 * radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
1110 * based on a tag
1111 * @root: radix tree root
1112 * @results: where the results of the lookup are placed
1113 * @first_index: start the lookup from this key
1114 * @max_items: place up to this many items at *results
1115 * @tag: the tag index (< RADIX_TREE_MAX_TAGS)
1116 *
1117 * Performs an index-ascending scan of the tree for present items which
1118 * have the tag indexed by @tag set. Places the items at *@results and
1119 * returns the number of items which were placed at *@results.
1120 */
1121unsigned int
1122radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
1123        unsigned long first_index, unsigned int max_items,
1124        unsigned int tag)
1125{
1126    struct radix_tree_iter iter;
1127    void **slot;
1128    unsigned int ret = 0;
1129
1130    if (unlikely(!max_items))
1131        return 0;
1132
1133    radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
1134        results[ret] = indirect_to_ptr(rcu_dereference_raw(*slot));
1135        if (!results[ret])
1136            continue;
1137        if (++ret == max_items)
1138            break;
1139    }
1140
1141    return ret;
1142}
1143EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
1144
1145/**
1146 * radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
1147 * radix tree based on a tag
1148 * @root: radix tree root
1149 * @results: where the results of the lookup are placed
1150 * @first_index: start the lookup from this key
1151 * @max_items: place up to this many items at *results
1152 * @tag: the tag index (< RADIX_TREE_MAX_TAGS)
1153 *
1154 * Performs an index-ascending scan of the tree for present items which
1155 * have the tag indexed by @tag set. Places the slots at *@results and
1156 * returns the number of slots which were placed at *@results.
1157 */
1158unsigned int
1159radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
1160        unsigned long first_index, unsigned int max_items,
1161        unsigned int tag)
1162{
1163    struct radix_tree_iter iter;
1164    void **slot;
1165    unsigned int ret = 0;
1166
1167    if (unlikely(!max_items))
1168        return 0;
1169
1170    radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
1171        results[ret] = slot;
1172        if (++ret == max_items)
1173            break;
1174    }
1175
1176    return ret;
1177}
1178EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
1179
1180#if defined(CONFIG_SHMEM) && defined(CONFIG_SWAP)
1181#include <linux/sched.h> /* for cond_resched() */
1182
1183/*
1184 * This linear search is at present only useful to shmem_unuse_inode().
1185 */
1186static unsigned long __locate(struct radix_tree_node *slot, void *item,
1187                  unsigned long index, unsigned long *found_index)
1188{
1189    unsigned int shift, height;
1190    unsigned long i;
1191
1192    height = slot->height;
1193    shift = (height-1) * RADIX_TREE_MAP_SHIFT;
1194
1195    for ( ; height > 1; height--) {
1196        i = (index >> shift) & RADIX_TREE_MAP_MASK;
1197        for (;;) {
1198            if (slot->slots[i] != NULL)
1199                break;
1200            index &= ~((1UL << shift) - 1);
1201            index += 1UL << shift;
1202            if (index == 0)
1203                goto out; /* 32-bit wraparound */
1204            i++;
1205            if (i == RADIX_TREE_MAP_SIZE)
1206                goto out;
1207        }
1208
1209        shift -= RADIX_TREE_MAP_SHIFT;
1210        slot = rcu_dereference_raw(slot->slots[i]);
1211        if (slot == NULL)
1212            goto out;
1213    }
1214
1215    /* Bottom level: check items */
1216    for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
1217        if (slot->slots[i] == item) {
1218            *found_index = index + i;
1219            index = 0;
1220            goto out;
1221        }
1222    }
1223    index += RADIX_TREE_MAP_SIZE;
1224out:
1225    return index;
1226}
1227
1228/**
1229 * radix_tree_locate_item - search through radix tree for item
1230 * @root: radix tree root
1231 * @item: item to be found
1232 *
1233 * Returns index where item was found, or -1 if not found.
1234 * Caller must hold no lock (since this time-consuming function needs
1235 * to be preemptible), and must check afterwards if item is still there.
1236 */
1237unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
1238{
1239    struct radix_tree_node *node;
1240    unsigned long max_index;
1241    unsigned long cur_index = 0;
1242    unsigned long found_index = -1;
1243
1244    do {
1245        rcu_read_lock();
1246        node = rcu_dereference_raw(root->rnode);
1247        if (!radix_tree_is_indirect_ptr(node)) {
1248            rcu_read_unlock();
1249            if (node == item)
1250                found_index = 0;
1251            break;
1252        }
1253
1254        node = indirect_to_ptr(node);
1255        max_index = radix_tree_maxindex(node->height);
1256        if (cur_index > max_index)
1257            break;
1258
1259        cur_index = __locate(node, item, cur_index, &found_index);
1260        rcu_read_unlock();
1261        cond_resched();
1262    } while (cur_index != 0 && cur_index <= max_index);
1263
1264    return found_index;
1265}
1266#else
1267unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
1268{
1269    return -1;
1270}
1271#endif /* CONFIG_SHMEM && CONFIG_SWAP */
1272
1273/**
1274 * radix_tree_shrink - shrink height of a radix tree to minimal
1275 * @root radix tree root
1276 */
1277static inline void radix_tree_shrink(struct radix_tree_root *root)
1278{
1279    /* try to shrink tree height */
1280    while (root->height > 0) {
1281        struct radix_tree_node *to_free = root->rnode;
1282        struct radix_tree_node *slot;
1283
1284        BUG_ON(!radix_tree_is_indirect_ptr(to_free));
1285        to_free = indirect_to_ptr(to_free);
1286
1287        /*
1288         * The candidate node has more than one child, or its child
1289         * is not at the leftmost slot, we cannot shrink.
1290         */
1291        if (to_free->count != 1)
1292            break;
1293        if (!to_free->slots[0])
1294            break;
1295
1296        /*
1297         * We don't need rcu_assign_pointer(), since we are simply
1298         * moving the node from one part of the tree to another: if it
1299         * was safe to dereference the old pointer to it
1300         * (to_free->slots[0]), it will be safe to dereference the new
1301         * one (root->rnode) as far as dependent read barriers go.
1302         */
1303        slot = to_free->slots[0];
1304        if (root->height > 1) {
1305            slot->parent = NULL;
1306            slot = ptr_to_indirect(slot);
1307        }
1308        root->rnode = slot;
1309        root->height--;
1310
1311        /*
1312         * We have a dilemma here. The node's slot[0] must not be
1313         * NULLed in case there are concurrent lookups expecting to
1314         * find the item. However if this was a bottom-level node,
1315         * then it may be subject to the slot pointer being visible
1316         * to callers dereferencing it. If item corresponding to
1317         * slot[0] is subsequently deleted, these callers would expect
1318         * their slot to become empty sooner or later.
1319         *
1320         * For example, lockless pagecache will look up a slot, deref
1321         * the page pointer, and if the page is 0 refcount it means it
1322         * was concurrently deleted from pagecache so try the deref
1323         * again. Fortunately there is already a requirement for logic
1324         * to retry the entire slot lookup -- the indirect pointer
1325         * problem (replacing direct root node with an indirect pointer
1326         * also results in a stale slot). So tag the slot as indirect
1327         * to force callers to retry.
1328         */
1329        if (root->height == 0)
1330            *((unsigned long *)&to_free->slots[0]) |=
1331                        RADIX_TREE_INDIRECT_PTR;
1332
1333        radix_tree_node_free(to_free);
1334    }
1335}
1336
1337/**
1338 * radix_tree_delete - delete an item from a radix tree
1339 * @root: radix tree root
1340 * @index: index key
1341 *
1342 * Remove the item at @index from the radix tree rooted at @root.
1343 *
1344 * Returns the address of the deleted item, or NULL if it was not present.
1345 */
1346void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
1347{
1348    struct radix_tree_node *node = NULL;
1349    struct radix_tree_node *slot = NULL;
1350    struct radix_tree_node *to_free;
1351    unsigned int height, shift;
1352    int tag;
1353    int uninitialized_var(offset);
1354
1355    height = root->height;
1356    if (index > radix_tree_maxindex(height))
1357        goto out;
1358
1359    slot = root->rnode;
1360    if (height == 0) {
1361        root_tag_clear_all(root);
1362        root->rnode = NULL;
1363        goto out;
1364    }
1365    slot = indirect_to_ptr(slot);
1366    shift = height * RADIX_TREE_MAP_SHIFT;
1367
1368    do {
1369        if (slot == NULL)
1370            goto out;
1371
1372        shift -= RADIX_TREE_MAP_SHIFT;
1373        offset = (index >> shift) & RADIX_TREE_MAP_MASK;
1374        node = slot;
1375        slot = slot->slots[offset];
1376    } while (shift);
1377
1378    if (slot == NULL)
1379        goto out;
1380
1381    /*
1382     * Clear all tags associated with the item to be deleted.
1383     * This way of doing it would be inefficient, but seldom is any set.
1384     */
1385    for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
1386        if (tag_get(node, tag, offset))
1387            radix_tree_tag_clear(root, index, tag);
1388    }
1389
1390    to_free = NULL;
1391    /* Now free the nodes we do not need anymore */
1392    while (node) {
1393        node->slots[offset] = NULL;
1394        node->count--;
1395        /*
1396         * Queue the node for deferred freeing after the
1397         * last reference to it disappears (set NULL, above).
1398         */
1399        if (to_free)
1400            radix_tree_node_free(to_free);
1401
1402        if (node->count) {
1403            if (node == indirect_to_ptr(root->rnode))
1404                radix_tree_shrink(root);
1405            goto out;
1406        }
1407
1408        /* Node with zero slots in use so free it */
1409        to_free = node;
1410
1411        index >>= RADIX_TREE_MAP_SHIFT;
1412        offset = index & RADIX_TREE_MAP_MASK;
1413        node = node->parent;
1414    }
1415
1416    root_tag_clear_all(root);
1417    root->height = 0;
1418    root->rnode = NULL;
1419    if (to_free)
1420        radix_tree_node_free(to_free);
1421
1422out:
1423    return slot;
1424}
1425EXPORT_SYMBOL(radix_tree_delete);
1426
1427/**
1428 * radix_tree_tagged - test whether any items in the tree are tagged
1429 * @root: radix tree root
1430 * @tag: tag to test
1431 */
1432int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)
1433{
1434    return root_tag_get(root, tag);
1435}
1436EXPORT_SYMBOL(radix_tree_tagged);
1437
1438static void
1439radix_tree_node_ctor(void *node)
1440{
1441    memset(node, 0, sizeof(struct radix_tree_node));
1442}
1443
1444static __init unsigned long __maxindex(unsigned int height)
1445{
1446    unsigned int width = height * RADIX_TREE_MAP_SHIFT;
1447    int shift = RADIX_TREE_INDEX_BITS - width;
1448
1449    if (shift < 0)
1450        return ~0UL;
1451    if (shift >= BITS_PER_LONG)
1452        return 0UL;
1453    return ~0UL >> shift;
1454}
1455
1456static __init void radix_tree_init_maxindex(void)
1457{
1458    unsigned int i;
1459
1460    for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
1461        height_to_maxindex[i] = __maxindex(i);
1462}
1463
1464static int radix_tree_callback(struct notifier_block *nfb,
1465                            unsigned long action,
1466                            void *hcpu)
1467{
1468       int cpu = (long)hcpu;
1469       struct radix_tree_preload *rtp;
1470
1471       /* Free per-cpu pool of perloaded nodes */
1472       if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
1473               rtp = &per_cpu(radix_tree_preloads, cpu);
1474               while (rtp->nr) {
1475                       kmem_cache_free(radix_tree_node_cachep,
1476                                       rtp->nodes[rtp->nr-1]);
1477                       rtp->nodes[rtp->nr-1] = NULL;
1478                       rtp->nr--;
1479               }
1480       }
1481       return NOTIFY_OK;
1482}
1483
1484void __init radix_tree_init(void)
1485{
1486    radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
1487            sizeof(struct radix_tree_node), 0,
1488            SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
1489            radix_tree_node_ctor);
1490    radix_tree_init_maxindex();
1491    hotcpu_notifier(radix_tree_callback, 0);
1492}
1493

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