9927cca14cb70fd0d65a9ca63c297258dfebdc87
[linux-2.6.git] / 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 <clameter@sgi.com>
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/gfp.h>
32 #include <linux/string.h>
33 #include <linux/bitops.h>
34 #include <linux/rcupdate.h>
35
36
37 #ifdef __KERNEL__
38 #define RADIX_TREE_MAP_SHIFT    (CONFIG_BASE_SMALL ? 4 : 6)
39 #else
40 #define RADIX_TREE_MAP_SHIFT    3       /* For more stressful testing */
41 #endif
42
43 #define RADIX_TREE_MAP_SIZE     (1UL << RADIX_TREE_MAP_SHIFT)
44 #define RADIX_TREE_MAP_MASK     (RADIX_TREE_MAP_SIZE-1)
45
46 #define RADIX_TREE_TAG_LONGS    \
47         ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
48
49 struct radix_tree_node {
50         unsigned int    height;         /* Height from the bottom */
51         unsigned int    count;
52         struct rcu_head rcu_head;
53         void            *slots[RADIX_TREE_MAP_SIZE];
54         unsigned long   tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
55 };
56
57 struct radix_tree_path {
58         struct radix_tree_node *node;
59         int offset;
60 };
61
62 #define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
63 #define RADIX_TREE_MAX_PATH (RADIX_TREE_INDEX_BITS/RADIX_TREE_MAP_SHIFT + 2)
64
65 static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH] __read_mostly;
66
67 /*
68  * Radix tree node cache.
69  */
70 static struct kmem_cache *radix_tree_node_cachep;
71
72 /*
73  * Per-cpu pool of preloaded nodes
74  */
75 struct radix_tree_preload {
76         int nr;
77         struct radix_tree_node *nodes[RADIX_TREE_MAX_PATH];
78 };
79 DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
80
81 static inline gfp_t root_gfp_mask(struct radix_tree_root *root)
82 {
83         return root->gfp_mask & __GFP_BITS_MASK;
84 }
85
86 /*
87  * This assumes that the caller has performed appropriate preallocation, and
88  * that the caller has pinned this thread of control to the current CPU.
89  */
90 static struct radix_tree_node *
91 radix_tree_node_alloc(struct radix_tree_root *root)
92 {
93         struct radix_tree_node *ret;
94         gfp_t gfp_mask = root_gfp_mask(root);
95
96         ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
97         if (ret == NULL && !(gfp_mask & __GFP_WAIT)) {
98                 struct radix_tree_preload *rtp;
99
100                 rtp = &__get_cpu_var(radix_tree_preloads);
101                 if (rtp->nr) {
102                         ret = rtp->nodes[rtp->nr - 1];
103                         rtp->nodes[rtp->nr - 1] = NULL;
104                         rtp->nr--;
105                 }
106         }
107         BUG_ON(radix_tree_is_direct_ptr(ret));
108         return ret;
109 }
110
111 static void radix_tree_node_rcu_free(struct rcu_head *head)
112 {
113         struct radix_tree_node *node =
114                         container_of(head, struct radix_tree_node, rcu_head);
115         kmem_cache_free(radix_tree_node_cachep, node);
116 }
117
118 static inline void
119 radix_tree_node_free(struct radix_tree_node *node)
120 {
121         call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
122 }
123
124 /*
125  * Load up this CPU's radix_tree_node buffer with sufficient objects to
126  * ensure that the addition of a single element in the tree cannot fail.  On
127  * success, return zero, with preemption disabled.  On error, return -ENOMEM
128  * with preemption not disabled.
129  */
130 int radix_tree_preload(gfp_t gfp_mask)
131 {
132         struct radix_tree_preload *rtp;
133         struct radix_tree_node *node;
134         int ret = -ENOMEM;
135
136         preempt_disable();
137         rtp = &__get_cpu_var(radix_tree_preloads);
138         while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {
139                 preempt_enable();
140                 node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
141                 if (node == NULL)
142                         goto out;
143                 preempt_disable();
144                 rtp = &__get_cpu_var(radix_tree_preloads);
145                 if (rtp->nr < ARRAY_SIZE(rtp->nodes))
146                         rtp->nodes[rtp->nr++] = node;
147                 else
148                         kmem_cache_free(radix_tree_node_cachep, node);
149         }
150         ret = 0;
151 out:
152         return ret;
153 }
154 EXPORT_SYMBOL(radix_tree_preload);
155
156 static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
157                 int offset)
158 {
159         __set_bit(offset, node->tags[tag]);
160 }
161
162 static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
163                 int offset)
164 {
165         __clear_bit(offset, node->tags[tag]);
166 }
167
168 static inline int tag_get(struct radix_tree_node *node, unsigned int tag,
169                 int offset)
170 {
171         return test_bit(offset, node->tags[tag]);
172 }
173
174 static inline void root_tag_set(struct radix_tree_root *root, unsigned int tag)
175 {
176         root->gfp_mask |= (__force gfp_t)(1 << (tag + __GFP_BITS_SHIFT));
177 }
178
179
180 static inline void root_tag_clear(struct radix_tree_root *root, unsigned int tag)
181 {
182         root->gfp_mask &= (__force gfp_t)~(1 << (tag + __GFP_BITS_SHIFT));
183 }
184
185 static inline void root_tag_clear_all(struct radix_tree_root *root)
186 {
187         root->gfp_mask &= __GFP_BITS_MASK;
188 }
189
190 static inline int root_tag_get(struct radix_tree_root *root, unsigned int tag)
191 {
192         return (__force unsigned)root->gfp_mask & (1 << (tag + __GFP_BITS_SHIFT));
193 }
194
195 /*
196  * Returns 1 if any slot in the node has this tag set.
197  * Otherwise returns 0.
198  */
199 static inline int any_tag_set(struct radix_tree_node *node, unsigned int tag)
200 {
201         int idx;
202         for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
203                 if (node->tags[tag][idx])
204                         return 1;
205         }
206         return 0;
207 }
208
209 /*
210  *      Return the maximum key which can be store into a
211  *      radix tree with height HEIGHT.
212  */
213 static inline unsigned long radix_tree_maxindex(unsigned int height)
214 {
215         return height_to_maxindex[height];
216 }
217
218 /*
219  *      Extend a radix tree so it can store key @index.
220  */
221 static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
222 {
223         struct radix_tree_node *node;
224         unsigned int height;
225         int tag;
226
227         /* Figure out what the height should be.  */
228         height = root->height + 1;
229         while (index > radix_tree_maxindex(height))
230                 height++;
231
232         if (root->rnode == NULL) {
233                 root->height = height;
234                 goto out;
235         }
236
237         do {
238                 unsigned int newheight;
239                 if (!(node = radix_tree_node_alloc(root)))
240                         return -ENOMEM;
241
242                 /* Increase the height.  */
243                 node->slots[0] = radix_tree_direct_to_ptr(root->rnode);
244
245                 /* Propagate the aggregated tag info into the new root */
246                 for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
247                         if (root_tag_get(root, tag))
248                                 tag_set(node, tag, 0);
249                 }
250
251                 newheight = root->height+1;
252                 node->height = newheight;
253                 node->count = 1;
254                 rcu_assign_pointer(root->rnode, node);
255                 root->height = newheight;
256         } while (height > root->height);
257 out:
258         return 0;
259 }
260
261 /**
262  *      radix_tree_insert    -    insert into a radix tree
263  *      @root:          radix tree root
264  *      @index:         index key
265  *      @item:          item to insert
266  *
267  *      Insert an item into the radix tree at position @index.
268  */
269 int radix_tree_insert(struct radix_tree_root *root,
270                         unsigned long index, void *item)
271 {
272         struct radix_tree_node *node = NULL, *slot;
273         unsigned int height, shift;
274         int offset;
275         int error;
276
277         BUG_ON(radix_tree_is_direct_ptr(item));
278
279         /* Make sure the tree is high enough.  */
280         if (index > radix_tree_maxindex(root->height)) {
281                 error = radix_tree_extend(root, index);
282                 if (error)
283                         return error;
284         }
285
286         slot = root->rnode;
287         height = root->height;
288         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
289
290         offset = 0;                     /* uninitialised var warning */
291         while (height > 0) {
292                 if (slot == NULL) {
293                         /* Have to add a child node.  */
294                         if (!(slot = radix_tree_node_alloc(root)))
295                                 return -ENOMEM;
296                         slot->height = height;
297                         if (node) {
298                                 rcu_assign_pointer(node->slots[offset], slot);
299                                 node->count++;
300                         } else
301                                 rcu_assign_pointer(root->rnode, slot);
302                 }
303
304                 /* Go a level down */
305                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
306                 node = slot;
307                 slot = node->slots[offset];
308                 shift -= RADIX_TREE_MAP_SHIFT;
309                 height--;
310         }
311
312         if (slot != NULL)
313                 return -EEXIST;
314
315         if (node) {
316                 node->count++;
317                 rcu_assign_pointer(node->slots[offset], item);
318                 BUG_ON(tag_get(node, 0, offset));
319                 BUG_ON(tag_get(node, 1, offset));
320         } else {
321                 rcu_assign_pointer(root->rnode, radix_tree_ptr_to_direct(item));
322                 BUG_ON(root_tag_get(root, 0));
323                 BUG_ON(root_tag_get(root, 1));
324         }
325
326         return 0;
327 }
328 EXPORT_SYMBOL(radix_tree_insert);
329
330 /**
331  *      radix_tree_lookup_slot    -    lookup a slot in a radix tree
332  *      @root:          radix tree root
333  *      @index:         index key
334  *
335  *      Returns:  the slot corresponding to the position @index in the
336  *      radix tree @root. This is useful for update-if-exists operations.
337  *
338  *      This function cannot be called under rcu_read_lock, it must be
339  *      excluded from writers, as must the returned slot for subsequent
340  *      use by radix_tree_deref_slot() and radix_tree_replace slot.
341  *      Caller must hold tree write locked across slot lookup and
342  *      replace.
343  */
344 void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
345 {
346         unsigned int height, shift;
347         struct radix_tree_node *node, **slot;
348
349         node = root->rnode;
350         if (node == NULL)
351                 return NULL;
352
353         if (radix_tree_is_direct_ptr(node)) {
354                 if (index > 0)
355                         return NULL;
356                 return (void **)&root->rnode;
357         }
358
359         height = node->height;
360         if (index > radix_tree_maxindex(height))
361                 return NULL;
362
363         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
364
365         do {
366                 slot = (struct radix_tree_node **)
367                         (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
368                 node = *slot;
369                 if (node == NULL)
370                         return NULL;
371
372                 shift -= RADIX_TREE_MAP_SHIFT;
373                 height--;
374         } while (height > 0);
375
376         return (void **)slot;
377 }
378 EXPORT_SYMBOL(radix_tree_lookup_slot);
379
380 /**
381  *      radix_tree_lookup    -    perform lookup operation on a radix tree
382  *      @root:          radix tree root
383  *      @index:         index key
384  *
385  *      Lookup the item at the position @index in the radix tree @root.
386  *
387  *      This function can be called under rcu_read_lock, however the caller
388  *      must manage lifetimes of leaf nodes (eg. RCU may also be used to free
389  *      them safely). No RCU barriers are required to access or modify the
390  *      returned item, however.
391  */
392 void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
393 {
394         unsigned int height, shift;
395         struct radix_tree_node *node, **slot;
396
397         node = rcu_dereference(root->rnode);
398         if (node == NULL)
399                 return NULL;
400
401         if (radix_tree_is_direct_ptr(node)) {
402                 if (index > 0)
403                         return NULL;
404                 return radix_tree_direct_to_ptr(node);
405         }
406
407         height = node->height;
408         if (index > radix_tree_maxindex(height))
409                 return NULL;
410
411         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
412
413         do {
414                 slot = (struct radix_tree_node **)
415                         (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
416                 node = rcu_dereference(*slot);
417                 if (node == NULL)
418                         return NULL;
419
420                 shift -= RADIX_TREE_MAP_SHIFT;
421                 height--;
422         } while (height > 0);
423
424         return node;
425 }
426 EXPORT_SYMBOL(radix_tree_lookup);
427
428 /**
429  *      radix_tree_tag_set - set a tag on a radix tree node
430  *      @root:          radix tree root
431  *      @index:         index key
432  *      @tag:           tag index
433  *
434  *      Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
435  *      corresponding to @index in the radix tree.  From
436  *      the root all the way down to the leaf node.
437  *
438  *      Returns the address of the tagged item.   Setting a tag on a not-present
439  *      item is a bug.
440  */
441 void *radix_tree_tag_set(struct radix_tree_root *root,
442                         unsigned long index, unsigned int tag)
443 {
444         unsigned int height, shift;
445         struct radix_tree_node *slot;
446
447         height = root->height;
448         BUG_ON(index > radix_tree_maxindex(height));
449
450         slot = root->rnode;
451         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
452
453         while (height > 0) {
454                 int offset;
455
456                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
457                 if (!tag_get(slot, tag, offset))
458                         tag_set(slot, tag, offset);
459                 slot = slot->slots[offset];
460                 BUG_ON(slot == NULL);
461                 shift -= RADIX_TREE_MAP_SHIFT;
462                 height--;
463         }
464
465         /* set the root's tag bit */
466         if (slot && !root_tag_get(root, tag))
467                 root_tag_set(root, tag);
468
469         return slot;
470 }
471 EXPORT_SYMBOL(radix_tree_tag_set);
472
473 /**
474  *      radix_tree_tag_clear - clear a tag on a radix tree node
475  *      @root:          radix tree root
476  *      @index:         index key
477  *      @tag:           tag index
478  *
479  *      Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
480  *      corresponding to @index in the radix tree.  If
481  *      this causes the leaf node to have no tags set then clear the tag in the
482  *      next-to-leaf node, etc.
483  *
484  *      Returns the address of the tagged item on success, else NULL.  ie:
485  *      has the same return value and semantics as radix_tree_lookup().
486  */
487 void *radix_tree_tag_clear(struct radix_tree_root *root,
488                         unsigned long index, unsigned int tag)
489 {
490         struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
491         struct radix_tree_node *slot = NULL;
492         unsigned int height, shift;
493
494         height = root->height;
495         if (index > radix_tree_maxindex(height))
496                 goto out;
497
498         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
499         pathp->node = NULL;
500         slot = root->rnode;
501
502         while (height > 0) {
503                 int offset;
504
505                 if (slot == NULL)
506                         goto out;
507
508                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
509                 pathp[1].offset = offset;
510                 pathp[1].node = slot;
511                 slot = slot->slots[offset];
512                 pathp++;
513                 shift -= RADIX_TREE_MAP_SHIFT;
514                 height--;
515         }
516
517         if (slot == NULL)
518                 goto out;
519
520         while (pathp->node) {
521                 if (!tag_get(pathp->node, tag, pathp->offset))
522                         goto out;
523                 tag_clear(pathp->node, tag, pathp->offset);
524                 if (any_tag_set(pathp->node, tag))
525                         goto out;
526                 pathp--;
527         }
528
529         /* clear the root's tag bit */
530         if (root_tag_get(root, tag))
531                 root_tag_clear(root, tag);
532
533 out:
534         return slot;
535 }
536 EXPORT_SYMBOL(radix_tree_tag_clear);
537
538 #ifndef __KERNEL__      /* Only the test harness uses this at present */
539 /**
540  * radix_tree_tag_get - get a tag on a radix tree node
541  * @root:               radix tree root
542  * @index:              index key
543  * @tag:                tag index (< RADIX_TREE_MAX_TAGS)
544  *
545  * Return values:
546  *
547  *  0: tag not present or not set
548  *  1: tag set
549  */
550 int radix_tree_tag_get(struct radix_tree_root *root,
551                         unsigned long index, unsigned int tag)
552 {
553         unsigned int height, shift;
554         struct radix_tree_node *node;
555         int saw_unset_tag = 0;
556
557         /* check the root's tag bit */
558         if (!root_tag_get(root, tag))
559                 return 0;
560
561         node = rcu_dereference(root->rnode);
562         if (node == NULL)
563                 return 0;
564
565         if (radix_tree_is_direct_ptr(node))
566                 return (index == 0);
567
568         height = node->height;
569         if (index > radix_tree_maxindex(height))
570                 return 0;
571
572         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
573
574         for ( ; ; ) {
575                 int offset;
576
577                 if (node == NULL)
578                         return 0;
579
580                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
581
582                 /*
583                  * This is just a debug check.  Later, we can bale as soon as
584                  * we see an unset tag.
585                  */
586                 if (!tag_get(node, tag, offset))
587                         saw_unset_tag = 1;
588                 if (height == 1) {
589                         int ret = tag_get(node, tag, offset);
590
591                         BUG_ON(ret && saw_unset_tag);
592                         return !!ret;
593                 }
594                 node = rcu_dereference(node->slots[offset]);
595                 shift -= RADIX_TREE_MAP_SHIFT;
596                 height--;
597         }
598 }
599 EXPORT_SYMBOL(radix_tree_tag_get);
600 #endif
601
602 static unsigned int
603 __lookup(struct radix_tree_node *slot, void **results, unsigned long index,
604         unsigned int max_items, unsigned long *next_index)
605 {
606         unsigned int nr_found = 0;
607         unsigned int shift, height;
608         unsigned long i;
609
610         height = slot->height;
611         if (height == 0)
612                 goto out;
613         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
614
615         for ( ; height > 1; height--) {
616                 i = (index >> shift) & RADIX_TREE_MAP_MASK;
617                 for (;;) {
618                         if (slot->slots[i] != NULL)
619                                 break;
620                         index &= ~((1UL << shift) - 1);
621                         index += 1UL << shift;
622                         if (index == 0)
623                                 goto out;       /* 32-bit wraparound */
624                         i++;
625                         if (i == RADIX_TREE_MAP_SIZE)
626                                 goto out;
627                 }
628
629                 shift -= RADIX_TREE_MAP_SHIFT;
630                 slot = rcu_dereference(slot->slots[i]);
631                 if (slot == NULL)
632                         goto out;
633         }
634
635         /* Bottom level: grab some items */
636         for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) {
637                 struct radix_tree_node *node;
638                 index++;
639                 node = slot->slots[i];
640                 if (node) {
641                         results[nr_found++] = rcu_dereference(node);
642                         if (nr_found == max_items)
643                                 goto out;
644                 }
645         }
646 out:
647         *next_index = index;
648         return nr_found;
649 }
650
651 /**
652  *      radix_tree_gang_lookup - perform multiple lookup on a radix tree
653  *      @root:          radix tree root
654  *      @results:       where the results of the lookup are placed
655  *      @first_index:   start the lookup from this key
656  *      @max_items:     place up to this many items at *results
657  *
658  *      Performs an index-ascending scan of the tree for present items.  Places
659  *      them at *@results and returns the number of items which were placed at
660  *      *@results.
661  *
662  *      The implementation is naive.
663  *
664  *      Like radix_tree_lookup, radix_tree_gang_lookup may be called under
665  *      rcu_read_lock. In this case, rather than the returned results being
666  *      an atomic snapshot of the tree at a single point in time, the semantics
667  *      of an RCU protected gang lookup are as though multiple radix_tree_lookups
668  *      have been issued in individual locks, and results stored in 'results'.
669  */
670 unsigned int
671 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
672                         unsigned long first_index, unsigned int max_items)
673 {
674         unsigned long max_index;
675         struct radix_tree_node *node;
676         unsigned long cur_index = first_index;
677         unsigned int ret;
678
679         node = rcu_dereference(root->rnode);
680         if (!node)
681                 return 0;
682
683         if (radix_tree_is_direct_ptr(node)) {
684                 if (first_index > 0)
685                         return 0;
686                 node = radix_tree_direct_to_ptr(node);
687                 results[0] = rcu_dereference(node);
688                 return 1;
689         }
690
691         max_index = radix_tree_maxindex(node->height);
692
693         ret = 0;
694         while (ret < max_items) {
695                 unsigned int nr_found;
696                 unsigned long next_index;       /* Index of next search */
697
698                 if (cur_index > max_index)
699                         break;
700                 nr_found = __lookup(node, results + ret, cur_index,
701                                         max_items - ret, &next_index);
702                 ret += nr_found;
703                 if (next_index == 0)
704                         break;
705                 cur_index = next_index;
706         }
707
708         return ret;
709 }
710 EXPORT_SYMBOL(radix_tree_gang_lookup);
711
712 /*
713  * FIXME: the two tag_get()s here should use find_next_bit() instead of
714  * open-coding the search.
715  */
716 static unsigned int
717 __lookup_tag(struct radix_tree_node *slot, void **results, unsigned long index,
718         unsigned int max_items, unsigned long *next_index, unsigned int tag)
719 {
720         unsigned int nr_found = 0;
721         unsigned int shift, height;
722
723         height = slot->height;
724         if (height == 0)
725                 goto out;
726         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
727
728         while (height > 0) {
729                 unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK ;
730
731                 for (;;) {
732                         if (tag_get(slot, tag, i))
733                                 break;
734                         index &= ~((1UL << shift) - 1);
735                         index += 1UL << shift;
736                         if (index == 0)
737                                 goto out;       /* 32-bit wraparound */
738                         i++;
739                         if (i == RADIX_TREE_MAP_SIZE)
740                                 goto out;
741                 }
742                 height--;
743                 if (height == 0) {      /* Bottom level: grab some items */
744                         unsigned long j = index & RADIX_TREE_MAP_MASK;
745
746                         for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
747                                 struct radix_tree_node *node;
748                                 index++;
749                                 if (!tag_get(slot, tag, j))
750                                         continue;
751                                 node = slot->slots[j];
752                                 /*
753                                  * Even though the tag was found set, we need to
754                                  * recheck that we have a non-NULL node, because
755                                  * if this lookup is lockless, it may have been
756                                  * subsequently deleted.
757                                  *
758                                  * Similar care must be taken in any place that
759                                  * lookup ->slots[x] without a lock (ie. can't
760                                  * rely on its value remaining the same).
761                                  */
762                                 if (node) {
763                                         node = rcu_dereference(node);
764                                         results[nr_found++] = node;
765                                         if (nr_found == max_items)
766                                                 goto out;
767                                 }
768                         }
769                 }
770                 shift -= RADIX_TREE_MAP_SHIFT;
771                 slot = rcu_dereference(slot->slots[i]);
772                 if (slot == NULL)
773                         break;
774         }
775 out:
776         *next_index = index;
777         return nr_found;
778 }
779
780 /**
781  *      radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
782  *                                   based on a tag
783  *      @root:          radix tree root
784  *      @results:       where the results of the lookup are placed
785  *      @first_index:   start the lookup from this key
786  *      @max_items:     place up to this many items at *results
787  *      @tag:           the tag index (< RADIX_TREE_MAX_TAGS)
788  *
789  *      Performs an index-ascending scan of the tree for present items which
790  *      have the tag indexed by @tag set.  Places the items at *@results and
791  *      returns the number of items which were placed at *@results.
792  */
793 unsigned int
794 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
795                 unsigned long first_index, unsigned int max_items,
796                 unsigned int tag)
797 {
798         struct radix_tree_node *node;
799         unsigned long max_index;
800         unsigned long cur_index = first_index;
801         unsigned int ret;
802
803         /* check the root's tag bit */
804         if (!root_tag_get(root, tag))
805                 return 0;
806
807         node = rcu_dereference(root->rnode);
808         if (!node)
809                 return 0;
810
811         if (radix_tree_is_direct_ptr(node)) {
812                 if (first_index > 0)
813                         return 0;
814                 node = radix_tree_direct_to_ptr(node);
815                 results[0] = rcu_dereference(node);
816                 return 1;
817         }
818
819         max_index = radix_tree_maxindex(node->height);
820
821         ret = 0;
822         while (ret < max_items) {
823                 unsigned int nr_found;
824                 unsigned long next_index;       /* Index of next search */
825
826                 if (cur_index > max_index)
827                         break;
828                 nr_found = __lookup_tag(node, results + ret, cur_index,
829                                         max_items - ret, &next_index, tag);
830                 ret += nr_found;
831                 if (next_index == 0)
832                         break;
833                 cur_index = next_index;
834         }
835
836         return ret;
837 }
838 EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
839
840 /**
841  *      radix_tree_shrink    -    shrink height of a radix tree to minimal
842  *      @root           radix tree root
843  */
844 static inline void radix_tree_shrink(struct radix_tree_root *root)
845 {
846         /* try to shrink tree height */
847         while (root->height > 0 &&
848                         root->rnode->count == 1 &&
849                         root->rnode->slots[0]) {
850                 struct radix_tree_node *to_free = root->rnode;
851                 void *newptr;
852
853                 /*
854                  * We don't need rcu_assign_pointer(), since we are simply
855                  * moving the node from one part of the tree to another. If
856                  * it was safe to dereference the old pointer to it
857                  * (to_free->slots[0]), it will be safe to dereference the new
858                  * one (root->rnode).
859                  */
860                 newptr = to_free->slots[0];
861                 if (root->height == 1)
862                         newptr = radix_tree_ptr_to_direct(newptr);
863                 root->rnode = newptr;
864                 root->height--;
865                 /* must only free zeroed nodes into the slab */
866                 tag_clear(to_free, 0, 0);
867                 tag_clear(to_free, 1, 0);
868                 to_free->slots[0] = NULL;
869                 to_free->count = 0;
870                 radix_tree_node_free(to_free);
871         }
872 }
873
874 /**
875  *      radix_tree_delete    -    delete an item from a radix tree
876  *      @root:          radix tree root
877  *      @index:         index key
878  *
879  *      Remove the item at @index from the radix tree rooted at @root.
880  *
881  *      Returns the address of the deleted item, or NULL if it was not present.
882  */
883 void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
884 {
885         struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
886         struct radix_tree_node *slot = NULL;
887         struct radix_tree_node *to_free;
888         unsigned int height, shift;
889         int tag;
890         int offset;
891
892         height = root->height;
893         if (index > radix_tree_maxindex(height))
894                 goto out;
895
896         slot = root->rnode;
897         if (height == 0 && root->rnode) {
898                 slot = radix_tree_direct_to_ptr(slot);
899                 root_tag_clear_all(root);
900                 root->rnode = NULL;
901                 goto out;
902         }
903
904         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
905         pathp->node = NULL;
906
907         do {
908                 if (slot == NULL)
909                         goto out;
910
911                 pathp++;
912                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
913                 pathp->offset = offset;
914                 pathp->node = slot;
915                 slot = slot->slots[offset];
916                 shift -= RADIX_TREE_MAP_SHIFT;
917                 height--;
918         } while (height > 0);
919
920         if (slot == NULL)
921                 goto out;
922
923         /*
924          * Clear all tags associated with the just-deleted item
925          */
926         for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
927                 if (tag_get(pathp->node, tag, pathp->offset))
928                         radix_tree_tag_clear(root, index, tag);
929         }
930
931         to_free = NULL;
932         /* Now free the nodes we do not need anymore */
933         while (pathp->node) {
934                 pathp->node->slots[pathp->offset] = NULL;
935                 pathp->node->count--;
936                 /*
937                  * Queue the node for deferred freeing after the
938                  * last reference to it disappears (set NULL, above).
939                  */
940                 if (to_free)
941                         radix_tree_node_free(to_free);
942
943                 if (pathp->node->count) {
944                         if (pathp->node == root->rnode)
945                                 radix_tree_shrink(root);
946                         goto out;
947                 }
948
949                 /* Node with zero slots in use so free it */
950                 to_free = pathp->node;
951                 pathp--;
952
953         }
954         root_tag_clear_all(root);
955         root->height = 0;
956         root->rnode = NULL;
957         if (to_free)
958                 radix_tree_node_free(to_free);
959
960 out:
961         return slot;
962 }
963 EXPORT_SYMBOL(radix_tree_delete);
964
965 /**
966  *      radix_tree_tagged - test whether any items in the tree are tagged
967  *      @root:          radix tree root
968  *      @tag:           tag to test
969  */
970 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)
971 {
972         return root_tag_get(root, tag);
973 }
974 EXPORT_SYMBOL(radix_tree_tagged);
975
976 static void
977 radix_tree_node_ctor(void *node, struct kmem_cache *cachep, unsigned long flags)
978 {
979         memset(node, 0, sizeof(struct radix_tree_node));
980 }
981
982 static __init unsigned long __maxindex(unsigned int height)
983 {
984         unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
985         unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
986
987         if (tmp >= RADIX_TREE_INDEX_BITS)
988                 index = ~0UL;
989         return index;
990 }
991
992 static __init void radix_tree_init_maxindex(void)
993 {
994         unsigned int i;
995
996         for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
997                 height_to_maxindex[i] = __maxindex(i);
998 }
999
1000 static int radix_tree_callback(struct notifier_block *nfb,
1001                             unsigned long action,
1002                             void *hcpu)
1003 {
1004        int cpu = (long)hcpu;
1005        struct radix_tree_preload *rtp;
1006
1007        /* Free per-cpu pool of perloaded nodes */
1008        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
1009                rtp = &per_cpu(radix_tree_preloads, cpu);
1010                while (rtp->nr) {
1011                        kmem_cache_free(radix_tree_node_cachep,
1012                                        rtp->nodes[rtp->nr-1]);
1013                        rtp->nodes[rtp->nr-1] = NULL;
1014                        rtp->nr--;
1015                }
1016        }
1017        return NOTIFY_OK;
1018 }
1019
1020 void __init radix_tree_init(void)
1021 {
1022         radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
1023                         sizeof(struct radix_tree_node), 0,
1024                         SLAB_PANIC, radix_tree_node_ctor, NULL);
1025         radix_tree_init_maxindex();
1026         hotcpu_notifier(radix_tree_callback, 0);
1027 }