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

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