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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 (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
64                                           RADIX_TREE_MAP_SHIFT))
65
66 /*
67  * The height_to_maxindex array needs to be one deeper than the maximum
68  * path as height 0 holds only 1 entry.
69  */
70 static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH + 1] __read_mostly;
71
72 /*
73  * Radix tree node cache.
74  */
75 static struct kmem_cache *radix_tree_node_cachep;
76
77 /*
78  * Per-cpu pool of preloaded nodes
79  */
80 struct radix_tree_preload {
81         int nr;
82         struct radix_tree_node *nodes[RADIX_TREE_MAX_PATH];
83 };
84 DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
85
86 static inline gfp_t root_gfp_mask(struct radix_tree_root *root)
87 {
88         return root->gfp_mask & __GFP_BITS_MASK;
89 }
90
91 static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
92                 int offset)
93 {
94         __set_bit(offset, node->tags[tag]);
95 }
96
97 static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
98                 int offset)
99 {
100         __clear_bit(offset, node->tags[tag]);
101 }
102
103 static inline int tag_get(struct radix_tree_node *node, unsigned int tag,
104                 int offset)
105 {
106         return test_bit(offset, node->tags[tag]);
107 }
108
109 static inline void root_tag_set(struct radix_tree_root *root, unsigned int tag)
110 {
111         root->gfp_mask |= (__force gfp_t)(1 << (tag + __GFP_BITS_SHIFT));
112 }
113
114 static inline void root_tag_clear(struct radix_tree_root *root, unsigned int tag)
115 {
116         root->gfp_mask &= (__force gfp_t)~(1 << (tag + __GFP_BITS_SHIFT));
117 }
118
119 static inline void root_tag_clear_all(struct radix_tree_root *root)
120 {
121         root->gfp_mask &= __GFP_BITS_MASK;
122 }
123
124 static inline int root_tag_get(struct radix_tree_root *root, unsigned int tag)
125 {
126         return (__force unsigned)root->gfp_mask & (1 << (tag + __GFP_BITS_SHIFT));
127 }
128
129 /*
130  * Returns 1 if any slot in the node has this tag set.
131  * Otherwise returns 0.
132  */
133 static inline int any_tag_set(struct radix_tree_node *node, unsigned int tag)
134 {
135         int idx;
136         for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
137                 if (node->tags[tag][idx])
138                         return 1;
139         }
140         return 0;
141 }
142 /*
143  * This assumes that the caller has performed appropriate preallocation, and
144  * that the caller has pinned this thread of control to the current CPU.
145  */
146 static struct radix_tree_node *
147 radix_tree_node_alloc(struct radix_tree_root *root)
148 {
149         struct radix_tree_node *ret = NULL;
150         gfp_t gfp_mask = root_gfp_mask(root);
151
152         if (!(gfp_mask & __GFP_WAIT)) {
153                 struct radix_tree_preload *rtp;
154
155                 /*
156                  * Provided the caller has preloaded here, we will always
157                  * succeed in getting a node here (and never reach
158                  * kmem_cache_alloc)
159                  */
160                 rtp = &__get_cpu_var(radix_tree_preloads);
161                 if (rtp->nr) {
162                         ret = rtp->nodes[rtp->nr - 1];
163                         rtp->nodes[rtp->nr - 1] = NULL;
164                         rtp->nr--;
165                 }
166         }
167         if (ret == NULL)
168                 ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
169
170         BUG_ON(radix_tree_is_indirect_ptr(ret));
171         return ret;
172 }
173
174 static void radix_tree_node_rcu_free(struct rcu_head *head)
175 {
176         struct radix_tree_node *node =
177                         container_of(head, struct radix_tree_node, rcu_head);
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         tag_clear(node, 0, 0);
185         tag_clear(node, 1, 0);
186         node->slots[0] = NULL;
187         node->count = 0;
188
189         kmem_cache_free(radix_tree_node_cachep, node);
190 }
191
192 static inline void
193 radix_tree_node_free(struct radix_tree_node *node)
194 {
195         call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
196 }
197
198 /*
199  * Load up this CPU's radix_tree_node buffer with sufficient objects to
200  * ensure that the addition of a single element in the tree cannot fail.  On
201  * success, return zero, with preemption disabled.  On error, return -ENOMEM
202  * with preemption not disabled.
203  */
204 int radix_tree_preload(gfp_t gfp_mask)
205 {
206         struct radix_tree_preload *rtp;
207         struct radix_tree_node *node;
208         int ret = -ENOMEM;
209
210         preempt_disable();
211         rtp = &__get_cpu_var(radix_tree_preloads);
212         while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {
213                 preempt_enable();
214                 node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
215                 if (node == NULL)
216                         goto out;
217                 preempt_disable();
218                 rtp = &__get_cpu_var(radix_tree_preloads);
219                 if (rtp->nr < ARRAY_SIZE(rtp->nodes))
220                         rtp->nodes[rtp->nr++] = node;
221                 else
222                         kmem_cache_free(radix_tree_node_cachep, node);
223         }
224         ret = 0;
225 out:
226         return ret;
227 }
228 EXPORT_SYMBOL(radix_tree_preload);
229
230 /*
231  *      Return the maximum key which can be store into a
232  *      radix tree with height HEIGHT.
233  */
234 static inline unsigned long radix_tree_maxindex(unsigned int height)
235 {
236         return height_to_maxindex[height];
237 }
238
239 /*
240  *      Extend a radix tree so it can store key @index.
241  */
242 static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
243 {
244         struct radix_tree_node *node;
245         unsigned int height;
246         int tag;
247
248         /* Figure out what the height should be.  */
249         height = root->height + 1;
250         while (index > radix_tree_maxindex(height))
251                 height++;
252
253         if (root->rnode == NULL) {
254                 root->height = height;
255                 goto out;
256         }
257
258         do {
259                 unsigned int newheight;
260                 if (!(node = radix_tree_node_alloc(root)))
261                         return -ENOMEM;
262
263                 /* Increase the height.  */
264                 node->slots[0] = radix_tree_indirect_to_ptr(root->rnode);
265
266                 /* Propagate the aggregated tag info into the new root */
267                 for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
268                         if (root_tag_get(root, tag))
269                                 tag_set(node, tag, 0);
270                 }
271
272                 newheight = root->height+1;
273                 node->height = newheight;
274                 node->count = 1;
275                 node = radix_tree_ptr_to_indirect(node);
276                 rcu_assign_pointer(root->rnode, node);
277                 root->height = newheight;
278         } while (height > root->height);
279 out:
280         return 0;
281 }
282
283 /**
284  *      radix_tree_insert    -    insert into a radix tree
285  *      @root:          radix tree root
286  *      @index:         index key
287  *      @item:          item to insert
288  *
289  *      Insert an item into the radix tree at position @index.
290  */
291 int radix_tree_insert(struct radix_tree_root *root,
292                         unsigned long index, void *item)
293 {
294         struct radix_tree_node *node = NULL, *slot;
295         unsigned int height, shift;
296         int offset;
297         int error;
298
299         BUG_ON(radix_tree_is_indirect_ptr(item));
300
301         /* Make sure the tree is high enough.  */
302         if (index > radix_tree_maxindex(root->height)) {
303                 error = radix_tree_extend(root, index);
304                 if (error)
305                         return error;
306         }
307
308         slot = radix_tree_indirect_to_ptr(root->rnode);
309
310         height = root->height;
311         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
312
313         offset = 0;                     /* uninitialised var warning */
314         while (height > 0) {
315                 if (slot == NULL) {
316                         /* Have to add a child node.  */
317                         if (!(slot = radix_tree_node_alloc(root)))
318                                 return -ENOMEM;
319                         slot->height = height;
320                         if (node) {
321                                 rcu_assign_pointer(node->slots[offset], slot);
322                                 node->count++;
323                         } else
324                                 rcu_assign_pointer(root->rnode,
325                                         radix_tree_ptr_to_indirect(slot));
326                 }
327
328                 /* Go a level down */
329                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
330                 node = slot;
331                 slot = node->slots[offset];
332                 shift -= RADIX_TREE_MAP_SHIFT;
333                 height--;
334         }
335
336         if (slot != NULL)
337                 return -EEXIST;
338
339         if (node) {
340                 node->count++;
341                 rcu_assign_pointer(node->slots[offset], item);
342                 BUG_ON(tag_get(node, 0, offset));
343                 BUG_ON(tag_get(node, 1, offset));
344         } else {
345                 rcu_assign_pointer(root->rnode, item);
346                 BUG_ON(root_tag_get(root, 0));
347                 BUG_ON(root_tag_get(root, 1));
348         }
349
350         return 0;
351 }
352 EXPORT_SYMBOL(radix_tree_insert);
353
354 /**
355  *      radix_tree_lookup_slot    -    lookup a slot in a radix tree
356  *      @root:          radix tree root
357  *      @index:         index key
358  *
359  *      Returns:  the slot corresponding to the position @index in the
360  *      radix tree @root. This is useful for update-if-exists operations.
361  *
362  *      This function cannot be called under rcu_read_lock, it must be
363  *      excluded from writers, as must the returned slot for subsequent
364  *      use by radix_tree_deref_slot() and radix_tree_replace slot.
365  *      Caller must hold tree write locked across slot lookup and
366  *      replace.
367  */
368 void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
369 {
370         unsigned int height, shift;
371         struct radix_tree_node *node, **slot;
372
373         node = root->rnode;
374         if (node == NULL)
375                 return NULL;
376
377         if (!radix_tree_is_indirect_ptr(node)) {
378                 if (index > 0)
379                         return NULL;
380                 return (void **)&root->rnode;
381         }
382         node = radix_tree_indirect_to_ptr(node);
383
384         height = node->height;
385         if (index > radix_tree_maxindex(height))
386                 return NULL;
387
388         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
389
390         do {
391                 slot = (struct radix_tree_node **)
392                         (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
393                 node = *slot;
394                 if (node == NULL)
395                         return NULL;
396
397                 shift -= RADIX_TREE_MAP_SHIFT;
398                 height--;
399         } while (height > 0);
400
401         return (void **)slot;
402 }
403 EXPORT_SYMBOL(radix_tree_lookup_slot);
404
405 /**
406  *      radix_tree_lookup    -    perform lookup operation on a radix tree
407  *      @root:          radix tree root
408  *      @index:         index key
409  *
410  *      Lookup the item at the position @index in the radix tree @root.
411  *
412  *      This function can be called under rcu_read_lock, however the caller
413  *      must manage lifetimes of leaf nodes (eg. RCU may also be used to free
414  *      them safely). No RCU barriers are required to access or modify the
415  *      returned item, however.
416  */
417 void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
418 {
419         unsigned int height, shift;
420         struct radix_tree_node *node, **slot;
421
422         node = rcu_dereference(root->rnode);
423         if (node == NULL)
424                 return NULL;
425
426         if (!radix_tree_is_indirect_ptr(node)) {
427                 if (index > 0)
428                         return NULL;
429                 return node;
430         }
431         node = radix_tree_indirect_to_ptr(node);
432
433         height = node->height;
434         if (index > radix_tree_maxindex(height))
435                 return NULL;
436
437         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
438
439         do {
440                 slot = (struct radix_tree_node **)
441                         (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
442                 node = rcu_dereference(*slot);
443                 if (node == NULL)
444                         return NULL;
445
446                 shift -= RADIX_TREE_MAP_SHIFT;
447                 height--;
448         } while (height > 0);
449
450         return node;
451 }
452 EXPORT_SYMBOL(radix_tree_lookup);
453
454 /**
455  *      radix_tree_tag_set - set a tag on a radix tree node
456  *      @root:          radix tree root
457  *      @index:         index key
458  *      @tag:           tag index
459  *
460  *      Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
461  *      corresponding to @index in the radix tree.  From
462  *      the root all the way down to the leaf node.
463  *
464  *      Returns the address of the tagged item.   Setting a tag on a not-present
465  *      item is a bug.
466  */
467 void *radix_tree_tag_set(struct radix_tree_root *root,
468                         unsigned long index, unsigned int tag)
469 {
470         unsigned int height, shift;
471         struct radix_tree_node *slot;
472
473         height = root->height;
474         BUG_ON(index > radix_tree_maxindex(height));
475
476         slot = radix_tree_indirect_to_ptr(root->rnode);
477         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
478
479         while (height > 0) {
480                 int offset;
481
482                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
483                 if (!tag_get(slot, tag, offset))
484                         tag_set(slot, tag, offset);
485                 slot = slot->slots[offset];
486                 BUG_ON(slot == NULL);
487                 shift -= RADIX_TREE_MAP_SHIFT;
488                 height--;
489         }
490
491         /* set the root's tag bit */
492         if (slot && !root_tag_get(root, tag))
493                 root_tag_set(root, tag);
494
495         return slot;
496 }
497 EXPORT_SYMBOL(radix_tree_tag_set);
498
499 /**
500  *      radix_tree_tag_clear - clear a tag on a radix tree node
501  *      @root:          radix tree root
502  *      @index:         index key
503  *      @tag:           tag index
504  *
505  *      Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
506  *      corresponding to @index in the radix tree.  If
507  *      this causes the leaf node to have no tags set then clear the tag in the
508  *      next-to-leaf node, etc.
509  *
510  *      Returns the address of the tagged item on success, else NULL.  ie:
511  *      has the same return value and semantics as radix_tree_lookup().
512  */
513 void *radix_tree_tag_clear(struct radix_tree_root *root,
514                         unsigned long index, unsigned int tag)
515 {
516         /*
517          * The radix tree path needs to be one longer than the maximum path
518          * since the "list" is null terminated.
519          */
520         struct radix_tree_path path[RADIX_TREE_MAX_PATH + 1], *pathp = path;
521         struct radix_tree_node *slot = NULL;
522         unsigned int height, shift;
523
524         height = root->height;
525         if (index > radix_tree_maxindex(height))
526                 goto out;
527
528         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
529         pathp->node = NULL;
530         slot = radix_tree_indirect_to_ptr(root->rnode);
531
532         while (height > 0) {
533                 int offset;
534
535                 if (slot == NULL)
536                         goto out;
537
538                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
539                 pathp[1].offset = offset;
540                 pathp[1].node = slot;
541                 slot = slot->slots[offset];
542                 pathp++;
543                 shift -= RADIX_TREE_MAP_SHIFT;
544                 height--;
545         }
546
547         if (slot == NULL)
548                 goto out;
549
550         while (pathp->node) {
551                 if (!tag_get(pathp->node, tag, pathp->offset))
552                         goto out;
553                 tag_clear(pathp->node, tag, pathp->offset);
554                 if (any_tag_set(pathp->node, tag))
555                         goto out;
556                 pathp--;
557         }
558
559         /* clear the root's tag bit */
560         if (root_tag_get(root, tag))
561                 root_tag_clear(root, tag);
562
563 out:
564         return slot;
565 }
566 EXPORT_SYMBOL(radix_tree_tag_clear);
567
568 #ifndef __KERNEL__      /* Only the test harness uses this at present */
569 /**
570  * radix_tree_tag_get - get a tag on a radix tree node
571  * @root:               radix tree root
572  * @index:              index key
573  * @tag:                tag index (< RADIX_TREE_MAX_TAGS)
574  *
575  * Return values:
576  *
577  *  0: tag not present or not set
578  *  1: tag set
579  */
580 int radix_tree_tag_get(struct radix_tree_root *root,
581                         unsigned long index, unsigned int tag)
582 {
583         unsigned int height, shift;
584         struct radix_tree_node *node;
585         int saw_unset_tag = 0;
586
587         /* check the root's tag bit */
588         if (!root_tag_get(root, tag))
589                 return 0;
590
591         node = rcu_dereference(root->rnode);
592         if (node == NULL)
593                 return 0;
594
595         if (!radix_tree_is_indirect_ptr(node))
596                 return (index == 0);
597         node = radix_tree_indirect_to_ptr(node);
598
599         height = node->height;
600         if (index > radix_tree_maxindex(height))
601                 return 0;
602
603         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
604
605         for ( ; ; ) {
606                 int offset;
607
608                 if (node == NULL)
609                         return 0;
610
611                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
612
613                 /*
614                  * This is just a debug check.  Later, we can bale as soon as
615                  * we see an unset tag.
616                  */
617                 if (!tag_get(node, tag, offset))
618                         saw_unset_tag = 1;
619                 if (height == 1) {
620                         int ret = tag_get(node, tag, offset);
621
622                         BUG_ON(ret && saw_unset_tag);
623                         return !!ret;
624                 }
625                 node = rcu_dereference(node->slots[offset]);
626                 shift -= RADIX_TREE_MAP_SHIFT;
627                 height--;
628         }
629 }
630 EXPORT_SYMBOL(radix_tree_tag_get);
631 #endif
632
633 /**
634  *      radix_tree_next_hole    -    find the next hole (not-present entry)
635  *      @root:          tree root
636  *      @index:         index key
637  *      @max_scan:      maximum range to search
638  *
639  *      Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the lowest
640  *      indexed hole.
641  *
642  *      Returns: the index of the hole if found, otherwise returns an index
643  *      outside of the set specified (in which case 'return - index >= max_scan'
644  *      will be true).
645  *
646  *      radix_tree_next_hole may be called under rcu_read_lock. However, like
647  *      radix_tree_gang_lookup, this will not atomically search a snapshot of the
648  *      tree at a single point in time. For example, if a hole is created at index
649  *      5, then subsequently a hole is created at index 10, radix_tree_next_hole
650  *      covering both indexes may return 10 if called under rcu_read_lock.
651  */
652 unsigned long radix_tree_next_hole(struct radix_tree_root *root,
653                                 unsigned long index, unsigned long max_scan)
654 {
655         unsigned long i;
656
657         for (i = 0; i < max_scan; i++) {
658                 if (!radix_tree_lookup(root, index))
659                         break;
660                 index++;
661                 if (index == 0)
662                         break;
663         }
664
665         return index;
666 }
667 EXPORT_SYMBOL(radix_tree_next_hole);
668
669 static unsigned int
670 __lookup(struct radix_tree_node *slot, void **results, unsigned long index,
671         unsigned int max_items, unsigned long *next_index)
672 {
673         unsigned int nr_found = 0;
674         unsigned int shift, height;
675         unsigned long i;
676
677         height = slot->height;
678         if (height == 0)
679                 goto out;
680         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
681
682         for ( ; height > 1; height--) {
683                 i = (index >> shift) & RADIX_TREE_MAP_MASK;
684                 for (;;) {
685                         if (slot->slots[i] != NULL)
686                                 break;
687                         index &= ~((1UL << shift) - 1);
688                         index += 1UL << shift;
689                         if (index == 0)
690                                 goto out;       /* 32-bit wraparound */
691                         i++;
692                         if (i == RADIX_TREE_MAP_SIZE)
693                                 goto out;
694                 }
695
696                 shift -= RADIX_TREE_MAP_SHIFT;
697                 slot = rcu_dereference(slot->slots[i]);
698                 if (slot == NULL)
699                         goto out;
700         }
701
702         /* Bottom level: grab some items */
703         for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) {
704                 struct radix_tree_node *node;
705                 index++;
706                 node = slot->slots[i];
707                 if (node) {
708                         results[nr_found++] = rcu_dereference(node);
709                         if (nr_found == max_items)
710                                 goto out;
711                 }
712         }
713 out:
714         *next_index = index;
715         return nr_found;
716 }
717
718 /**
719  *      radix_tree_gang_lookup - perform multiple lookup on a radix tree
720  *      @root:          radix tree root
721  *      @results:       where the results of the lookup are placed
722  *      @first_index:   start the lookup from this key
723  *      @max_items:     place up to this many items at *results
724  *
725  *      Performs an index-ascending scan of the tree for present items.  Places
726  *      them at *@results and returns the number of items which were placed at
727  *      *@results.
728  *
729  *      The implementation is naive.
730  *
731  *      Like radix_tree_lookup, radix_tree_gang_lookup may be called under
732  *      rcu_read_lock. In this case, rather than the returned results being
733  *      an atomic snapshot of the tree at a single point in time, the semantics
734  *      of an RCU protected gang lookup are as though multiple radix_tree_lookups
735  *      have been issued in individual locks, and results stored in 'results'.
736  */
737 unsigned int
738 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
739                         unsigned long first_index, unsigned int max_items)
740 {
741         unsigned long max_index;
742         struct radix_tree_node *node;
743         unsigned long cur_index = first_index;
744         unsigned int ret;
745
746         node = rcu_dereference(root->rnode);
747         if (!node)
748                 return 0;
749
750         if (!radix_tree_is_indirect_ptr(node)) {
751                 if (first_index > 0)
752                         return 0;
753                 results[0] = node;
754                 return 1;
755         }
756         node = radix_tree_indirect_to_ptr(node);
757
758         max_index = radix_tree_maxindex(node->height);
759
760         ret = 0;
761         while (ret < max_items) {
762                 unsigned int nr_found;
763                 unsigned long next_index;       /* Index of next search */
764
765                 if (cur_index > max_index)
766                         break;
767                 nr_found = __lookup(node, results + ret, cur_index,
768                                         max_items - ret, &next_index);
769                 ret += nr_found;
770                 if (next_index == 0)
771                         break;
772                 cur_index = next_index;
773         }
774
775         return ret;
776 }
777 EXPORT_SYMBOL(radix_tree_gang_lookup);
778
779 /*
780  * FIXME: the two tag_get()s here should use find_next_bit() instead of
781  * open-coding the search.
782  */
783 static unsigned int
784 __lookup_tag(struct radix_tree_node *slot, void **results, unsigned long index,
785         unsigned int max_items, unsigned long *next_index, unsigned int tag)
786 {
787         unsigned int nr_found = 0;
788         unsigned int shift, height;
789
790         height = slot->height;
791         if (height == 0)
792                 goto out;
793         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
794
795         while (height > 0) {
796                 unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK ;
797
798                 for (;;) {
799                         if (tag_get(slot, tag, i))
800                                 break;
801                         index &= ~((1UL << shift) - 1);
802                         index += 1UL << shift;
803                         if (index == 0)
804                                 goto out;       /* 32-bit wraparound */
805                         i++;
806                         if (i == RADIX_TREE_MAP_SIZE)
807                                 goto out;
808                 }
809                 height--;
810                 if (height == 0) {      /* Bottom level: grab some items */
811                         unsigned long j = index & RADIX_TREE_MAP_MASK;
812
813                         for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
814                                 struct radix_tree_node *node;
815                                 index++;
816                                 if (!tag_get(slot, tag, j))
817                                         continue;
818                                 node = slot->slots[j];
819                                 /*
820                                  * Even though the tag was found set, we need to
821                                  * recheck that we have a non-NULL node, because
822                                  * if this lookup is lockless, it may have been
823                                  * subsequently deleted.
824                                  *
825                                  * Similar care must be taken in any place that
826                                  * lookup ->slots[x] without a lock (ie. can't
827                                  * rely on its value remaining the same).
828                                  */
829                                 if (node) {
830                                         node = rcu_dereference(node);
831                                         results[nr_found++] = node;
832                                         if (nr_found == max_items)
833                                                 goto out;
834                                 }
835                         }
836                 }
837                 shift -= RADIX_TREE_MAP_SHIFT;
838                 slot = rcu_dereference(slot->slots[i]);
839                 if (slot == NULL)
840                         break;
841         }
842 out:
843         *next_index = index;
844         return nr_found;
845 }
846
847 /**
848  *      radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
849  *                                   based on a tag
850  *      @root:          radix tree root
851  *      @results:       where the results of the lookup are placed
852  *      @first_index:   start the lookup from this key
853  *      @max_items:     place up to this many items at *results
854  *      @tag:           the tag index (< RADIX_TREE_MAX_TAGS)
855  *
856  *      Performs an index-ascending scan of the tree for present items which
857  *      have the tag indexed by @tag set.  Places the items at *@results and
858  *      returns the number of items which were placed at *@results.
859  */
860 unsigned int
861 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
862                 unsigned long first_index, unsigned int max_items,
863                 unsigned int tag)
864 {
865         struct radix_tree_node *node;
866         unsigned long max_index;
867         unsigned long cur_index = first_index;
868         unsigned int ret;
869
870         /* check the root's tag bit */
871         if (!root_tag_get(root, tag))
872                 return 0;
873
874         node = rcu_dereference(root->rnode);
875         if (!node)
876                 return 0;
877
878         if (!radix_tree_is_indirect_ptr(node)) {
879                 if (first_index > 0)
880                         return 0;
881                 results[0] = node;
882                 return 1;
883         }
884         node = radix_tree_indirect_to_ptr(node);
885
886         max_index = radix_tree_maxindex(node->height);
887
888         ret = 0;
889         while (ret < max_items) {
890                 unsigned int nr_found;
891                 unsigned long next_index;       /* Index of next search */
892
893                 if (cur_index > max_index)
894                         break;
895                 nr_found = __lookup_tag(node, results + ret, cur_index,
896                                         max_items - ret, &next_index, tag);
897                 ret += nr_found;
898                 if (next_index == 0)
899                         break;
900                 cur_index = next_index;
901         }
902
903         return ret;
904 }
905 EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
906
907 /**
908  *      radix_tree_shrink    -    shrink height of a radix tree to minimal
909  *      @root           radix tree root
910  */
911 static inline void radix_tree_shrink(struct radix_tree_root *root)
912 {
913         /* try to shrink tree height */
914         while (root->height > 0) {
915                 struct radix_tree_node *to_free = root->rnode;
916                 void *newptr;
917
918                 BUG_ON(!radix_tree_is_indirect_ptr(to_free));
919                 to_free = radix_tree_indirect_to_ptr(to_free);
920
921                 /*
922                  * The candidate node has more than one child, or its child
923                  * is not at the leftmost slot, we cannot shrink.
924                  */
925                 if (to_free->count != 1)
926                         break;
927                 if (!to_free->slots[0])
928                         break;
929
930                 /*
931                  * We don't need rcu_assign_pointer(), since we are simply
932                  * moving the node from one part of the tree to another. If
933                  * it was safe to dereference the old pointer to it
934                  * (to_free->slots[0]), it will be safe to dereference the new
935                  * one (root->rnode).
936                  */
937                 newptr = to_free->slots[0];
938                 if (root->height > 1)
939                         newptr = radix_tree_ptr_to_indirect(newptr);
940                 root->rnode = newptr;
941                 root->height--;
942                 radix_tree_node_free(to_free);
943         }
944 }
945
946 /**
947  *      radix_tree_delete    -    delete an item from a radix tree
948  *      @root:          radix tree root
949  *      @index:         index key
950  *
951  *      Remove the item at @index from the radix tree rooted at @root.
952  *
953  *      Returns the address of the deleted item, or NULL if it was not present.
954  */
955 void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
956 {
957         /*
958          * The radix tree path needs to be one longer than the maximum path
959          * since the "list" is null terminated.
960          */
961         struct radix_tree_path path[RADIX_TREE_MAX_PATH + 1], *pathp = path;
962         struct radix_tree_node *slot = NULL;
963         struct radix_tree_node *to_free;
964         unsigned int height, shift;
965         int tag;
966         int offset;
967
968         height = root->height;
969         if (index > radix_tree_maxindex(height))
970                 goto out;
971
972         slot = root->rnode;
973         if (height == 0) {
974                 root_tag_clear_all(root);
975                 root->rnode = NULL;
976                 goto out;
977         }
978         slot = radix_tree_indirect_to_ptr(slot);
979
980         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
981         pathp->node = NULL;
982
983         do {
984                 if (slot == NULL)
985                         goto out;
986
987                 pathp++;
988                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
989                 pathp->offset = offset;
990                 pathp->node = slot;
991                 slot = slot->slots[offset];
992                 shift -= RADIX_TREE_MAP_SHIFT;
993                 height--;
994         } while (height > 0);
995
996         if (slot == NULL)
997                 goto out;
998
999         /*
1000          * Clear all tags associated with the just-deleted item
1001          */
1002         for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
1003                 if (tag_get(pathp->node, tag, pathp->offset))
1004                         radix_tree_tag_clear(root, index, tag);
1005         }
1006
1007         to_free = NULL;
1008         /* Now free the nodes we do not need anymore */
1009         while (pathp->node) {
1010                 pathp->node->slots[pathp->offset] = NULL;
1011                 pathp->node->count--;
1012                 /*
1013                  * Queue the node for deferred freeing after the
1014                  * last reference to it disappears (set NULL, above).
1015                  */
1016                 if (to_free)
1017                         radix_tree_node_free(to_free);
1018
1019                 if (pathp->node->count) {
1020                         if (pathp->node ==
1021                                         radix_tree_indirect_to_ptr(root->rnode))
1022                                 radix_tree_shrink(root);
1023                         goto out;
1024                 }
1025
1026                 /* Node with zero slots in use so free it */
1027                 to_free = pathp->node;
1028                 pathp--;
1029
1030         }
1031         root_tag_clear_all(root);
1032         root->height = 0;
1033         root->rnode = NULL;
1034         if (to_free)
1035                 radix_tree_node_free(to_free);
1036
1037 out:
1038         return slot;
1039 }
1040 EXPORT_SYMBOL(radix_tree_delete);
1041
1042 /**
1043  *      radix_tree_tagged - test whether any items in the tree are tagged
1044  *      @root:          radix tree root
1045  *      @tag:           tag to test
1046  */
1047 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)
1048 {
1049         return root_tag_get(root, tag);
1050 }
1051 EXPORT_SYMBOL(radix_tree_tagged);
1052
1053 static void
1054 radix_tree_node_ctor(struct kmem_cache *cachep, void *node)
1055 {
1056         memset(node, 0, sizeof(struct radix_tree_node));
1057 }
1058
1059 static __init unsigned long __maxindex(unsigned int height)
1060 {
1061         unsigned int width = height * RADIX_TREE_MAP_SHIFT;
1062         int shift = RADIX_TREE_INDEX_BITS - width;
1063
1064         if (shift < 0)
1065                 return ~0UL;
1066         if (shift >= BITS_PER_LONG)
1067                 return 0UL;
1068         return ~0UL >> shift;
1069 }
1070
1071 static __init void radix_tree_init_maxindex(void)
1072 {
1073         unsigned int i;
1074
1075         for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
1076                 height_to_maxindex[i] = __maxindex(i);
1077 }
1078
1079 static int radix_tree_callback(struct notifier_block *nfb,
1080                             unsigned long action,
1081                             void *hcpu)
1082 {
1083        int cpu = (long)hcpu;
1084        struct radix_tree_preload *rtp;
1085
1086        /* Free per-cpu pool of perloaded nodes */
1087        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
1088                rtp = &per_cpu(radix_tree_preloads, cpu);
1089                while (rtp->nr) {
1090                        kmem_cache_free(radix_tree_node_cachep,
1091                                        rtp->nodes[rtp->nr-1]);
1092                        rtp->nodes[rtp->nr-1] = NULL;
1093                        rtp->nr--;
1094                }
1095        }
1096        return NOTIFY_OK;
1097 }
1098
1099 void __init radix_tree_init(void)
1100 {
1101         radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
1102                         sizeof(struct radix_tree_node), 0,
1103                         SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
1104                         radix_tree_node_ctor);
1105         radix_tree_init_maxindex();
1106         hotcpu_notifier(radix_tree_callback, 0);
1107 }