xref: /openbmc/linux/lib/radix-tree.c (revision fd589a8f)
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/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 static 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  * is_slot == 1 : search for the slot.
356  * is_slot == 0 : search for the node.
357  */
358 static void *radix_tree_lookup_element(struct radix_tree_root *root,
359 				unsigned long index, int is_slot)
360 {
361 	unsigned int height, shift;
362 	struct radix_tree_node *node, **slot;
363 
364 	node = rcu_dereference(root->rnode);
365 	if (node == NULL)
366 		return NULL;
367 
368 	if (!radix_tree_is_indirect_ptr(node)) {
369 		if (index > 0)
370 			return NULL;
371 		return is_slot ? (void *)&root->rnode : node;
372 	}
373 	node = radix_tree_indirect_to_ptr(node);
374 
375 	height = node->height;
376 	if (index > radix_tree_maxindex(height))
377 		return NULL;
378 
379 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
380 
381 	do {
382 		slot = (struct radix_tree_node **)
383 			(node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
384 		node = rcu_dereference(*slot);
385 		if (node == NULL)
386 			return NULL;
387 
388 		shift -= RADIX_TREE_MAP_SHIFT;
389 		height--;
390 	} while (height > 0);
391 
392 	return is_slot ? (void *)slot:node;
393 }
394 
395 /**
396  *	radix_tree_lookup_slot    -    lookup a slot in a radix tree
397  *	@root:		radix tree root
398  *	@index:		index key
399  *
400  *	Returns:  the slot corresponding to the position @index in the
401  *	radix tree @root. This is useful for update-if-exists operations.
402  *
403  *	This function can be called under rcu_read_lock iff the slot is not
404  *	modified by radix_tree_replace_slot, otherwise it must be called
405  *	exclusive from other writers. Any dereference of the slot must be done
406  *	using radix_tree_deref_slot.
407  */
408 void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
409 {
410 	return (void **)radix_tree_lookup_element(root, index, 1);
411 }
412 EXPORT_SYMBOL(radix_tree_lookup_slot);
413 
414 /**
415  *	radix_tree_lookup    -    perform lookup operation on a radix tree
416  *	@root:		radix tree root
417  *	@index:		index key
418  *
419  *	Lookup the item at the position @index in the radix tree @root.
420  *
421  *	This function can be called under rcu_read_lock, however the caller
422  *	must manage lifetimes of leaf nodes (eg. RCU may also be used to free
423  *	them safely). No RCU barriers are required to access or modify the
424  *	returned item, however.
425  */
426 void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
427 {
428 	return radix_tree_lookup_element(root, index, 0);
429 }
430 EXPORT_SYMBOL(radix_tree_lookup);
431 
432 /**
433  *	radix_tree_tag_set - set a tag on a radix tree node
434  *	@root:		radix tree root
435  *	@index:		index key
436  *	@tag: 		tag index
437  *
438  *	Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
439  *	corresponding to @index in the radix tree.  From
440  *	the root all the way down to the leaf node.
441  *
442  *	Returns the address of the tagged item.   Setting a tag on a not-present
443  *	item is a bug.
444  */
445 void *radix_tree_tag_set(struct radix_tree_root *root,
446 			unsigned long index, unsigned int tag)
447 {
448 	unsigned int height, shift;
449 	struct radix_tree_node *slot;
450 
451 	height = root->height;
452 	BUG_ON(index > radix_tree_maxindex(height));
453 
454 	slot = radix_tree_indirect_to_ptr(root->rnode);
455 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
456 
457 	while (height > 0) {
458 		int offset;
459 
460 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
461 		if (!tag_get(slot, tag, offset))
462 			tag_set(slot, tag, offset);
463 		slot = slot->slots[offset];
464 		BUG_ON(slot == NULL);
465 		shift -= RADIX_TREE_MAP_SHIFT;
466 		height--;
467 	}
468 
469 	/* set the root's tag bit */
470 	if (slot && !root_tag_get(root, tag))
471 		root_tag_set(root, tag);
472 
473 	return slot;
474 }
475 EXPORT_SYMBOL(radix_tree_tag_set);
476 
477 /**
478  *	radix_tree_tag_clear - clear a tag on a radix tree node
479  *	@root:		radix tree root
480  *	@index:		index key
481  *	@tag: 		tag index
482  *
483  *	Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
484  *	corresponding to @index in the radix tree.  If
485  *	this causes the leaf node to have no tags set then clear the tag in the
486  *	next-to-leaf node, etc.
487  *
488  *	Returns the address of the tagged item on success, else NULL.  ie:
489  *	has the same return value and semantics as radix_tree_lookup().
490  */
491 void *radix_tree_tag_clear(struct radix_tree_root *root,
492 			unsigned long index, unsigned int tag)
493 {
494 	/*
495 	 * The radix tree path needs to be one longer than the maximum path
496 	 * since the "list" is null terminated.
497 	 */
498 	struct radix_tree_path path[RADIX_TREE_MAX_PATH + 1], *pathp = path;
499 	struct radix_tree_node *slot = NULL;
500 	unsigned int height, shift;
501 
502 	height = root->height;
503 	if (index > radix_tree_maxindex(height))
504 		goto out;
505 
506 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
507 	pathp->node = NULL;
508 	slot = radix_tree_indirect_to_ptr(root->rnode);
509 
510 	while (height > 0) {
511 		int offset;
512 
513 		if (slot == NULL)
514 			goto out;
515 
516 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
517 		pathp[1].offset = offset;
518 		pathp[1].node = slot;
519 		slot = slot->slots[offset];
520 		pathp++;
521 		shift -= RADIX_TREE_MAP_SHIFT;
522 		height--;
523 	}
524 
525 	if (slot == NULL)
526 		goto out;
527 
528 	while (pathp->node) {
529 		if (!tag_get(pathp->node, tag, pathp->offset))
530 			goto out;
531 		tag_clear(pathp->node, tag, pathp->offset);
532 		if (any_tag_set(pathp->node, tag))
533 			goto out;
534 		pathp--;
535 	}
536 
537 	/* clear the root's tag bit */
538 	if (root_tag_get(root, tag))
539 		root_tag_clear(root, tag);
540 
541 out:
542 	return slot;
543 }
544 EXPORT_SYMBOL(radix_tree_tag_clear);
545 
546 #ifndef __KERNEL__	/* Only the test harness uses this at present */
547 /**
548  * radix_tree_tag_get - get a tag on a radix tree node
549  * @root:		radix tree root
550  * @index:		index key
551  * @tag: 		tag index (< RADIX_TREE_MAX_TAGS)
552  *
553  * Return values:
554  *
555  *  0: tag not present or not set
556  *  1: tag set
557  */
558 int radix_tree_tag_get(struct radix_tree_root *root,
559 			unsigned long index, unsigned int tag)
560 {
561 	unsigned int height, shift;
562 	struct radix_tree_node *node;
563 	int saw_unset_tag = 0;
564 
565 	/* check the root's tag bit */
566 	if (!root_tag_get(root, tag))
567 		return 0;
568 
569 	node = rcu_dereference(root->rnode);
570 	if (node == NULL)
571 		return 0;
572 
573 	if (!radix_tree_is_indirect_ptr(node))
574 		return (index == 0);
575 	node = radix_tree_indirect_to_ptr(node);
576 
577 	height = node->height;
578 	if (index > radix_tree_maxindex(height))
579 		return 0;
580 
581 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
582 
583 	for ( ; ; ) {
584 		int offset;
585 
586 		if (node == NULL)
587 			return 0;
588 
589 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
590 
591 		/*
592 		 * This is just a debug check.  Later, we can bale as soon as
593 		 * we see an unset tag.
594 		 */
595 		if (!tag_get(node, tag, offset))
596 			saw_unset_tag = 1;
597 		if (height == 1) {
598 			int ret = tag_get(node, tag, offset);
599 
600 			BUG_ON(ret && saw_unset_tag);
601 			return !!ret;
602 		}
603 		node = rcu_dereference(node->slots[offset]);
604 		shift -= RADIX_TREE_MAP_SHIFT;
605 		height--;
606 	}
607 }
608 EXPORT_SYMBOL(radix_tree_tag_get);
609 #endif
610 
611 /**
612  *	radix_tree_next_hole    -    find the next hole (not-present entry)
613  *	@root:		tree root
614  *	@index:		index key
615  *	@max_scan:	maximum range to search
616  *
617  *	Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the lowest
618  *	indexed hole.
619  *
620  *	Returns: the index of the hole if found, otherwise returns an index
621  *	outside of the set specified (in which case 'return - index >= max_scan'
622  *	will be true). In rare cases of index wrap-around, 0 will be returned.
623  *
624  *	radix_tree_next_hole may be called under rcu_read_lock. However, like
625  *	radix_tree_gang_lookup, this will not atomically search a snapshot of
626  *	the tree at a single point in time. For example, if a hole is created
627  *	at index 5, then subsequently a hole is created at index 10,
628  *	radix_tree_next_hole covering both indexes may return 10 if called
629  *	under rcu_read_lock.
630  */
631 unsigned long radix_tree_next_hole(struct radix_tree_root *root,
632 				unsigned long index, unsigned long max_scan)
633 {
634 	unsigned long i;
635 
636 	for (i = 0; i < max_scan; i++) {
637 		if (!radix_tree_lookup(root, index))
638 			break;
639 		index++;
640 		if (index == 0)
641 			break;
642 	}
643 
644 	return index;
645 }
646 EXPORT_SYMBOL(radix_tree_next_hole);
647 
648 /**
649  *	radix_tree_prev_hole    -    find the prev hole (not-present entry)
650  *	@root:		tree root
651  *	@index:		index key
652  *	@max_scan:	maximum range to search
653  *
654  *	Search backwards in the range [max(index-max_scan+1, 0), index]
655  *	for the first hole.
656  *
657  *	Returns: the index of the hole if found, otherwise returns an index
658  *	outside of the set specified (in which case 'index - return >= max_scan'
659  *	will be true). In rare cases of wrap-around, LONG_MAX will be returned.
660  *
661  *	radix_tree_next_hole may be called under rcu_read_lock. However, like
662  *	radix_tree_gang_lookup, this will not atomically search a snapshot of
663  *	the tree at a single point in time. For example, if a hole is created
664  *	at index 10, then subsequently a hole is created at index 5,
665  *	radix_tree_prev_hole covering both indexes may return 5 if called under
666  *	rcu_read_lock.
667  */
668 unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
669 				   unsigned long index, unsigned long max_scan)
670 {
671 	unsigned long i;
672 
673 	for (i = 0; i < max_scan; i++) {
674 		if (!radix_tree_lookup(root, index))
675 			break;
676 		index--;
677 		if (index == LONG_MAX)
678 			break;
679 	}
680 
681 	return index;
682 }
683 EXPORT_SYMBOL(radix_tree_prev_hole);
684 
685 static unsigned int
686 __lookup(struct radix_tree_node *slot, void ***results, unsigned long index,
687 	unsigned int max_items, unsigned long *next_index)
688 {
689 	unsigned int nr_found = 0;
690 	unsigned int shift, height;
691 	unsigned long i;
692 
693 	height = slot->height;
694 	if (height == 0)
695 		goto out;
696 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
697 
698 	for ( ; height > 1; height--) {
699 		i = (index >> shift) & RADIX_TREE_MAP_MASK;
700 		for (;;) {
701 			if (slot->slots[i] != NULL)
702 				break;
703 			index &= ~((1UL << shift) - 1);
704 			index += 1UL << shift;
705 			if (index == 0)
706 				goto out;	/* 32-bit wraparound */
707 			i++;
708 			if (i == RADIX_TREE_MAP_SIZE)
709 				goto out;
710 		}
711 
712 		shift -= RADIX_TREE_MAP_SHIFT;
713 		slot = rcu_dereference(slot->slots[i]);
714 		if (slot == NULL)
715 			goto out;
716 	}
717 
718 	/* Bottom level: grab some items */
719 	for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) {
720 		index++;
721 		if (slot->slots[i]) {
722 			results[nr_found++] = &(slot->slots[i]);
723 			if (nr_found == max_items)
724 				goto out;
725 		}
726 	}
727 out:
728 	*next_index = index;
729 	return nr_found;
730 }
731 
732 /**
733  *	radix_tree_gang_lookup - perform multiple lookup on a radix tree
734  *	@root:		radix tree root
735  *	@results:	where the results of the lookup are placed
736  *	@first_index:	start the lookup from this key
737  *	@max_items:	place up to this many items at *results
738  *
739  *	Performs an index-ascending scan of the tree for present items.  Places
740  *	them at *@results and returns the number of items which were placed at
741  *	*@results.
742  *
743  *	The implementation is naive.
744  *
745  *	Like radix_tree_lookup, radix_tree_gang_lookup may be called under
746  *	rcu_read_lock. In this case, rather than the returned results being
747  *	an atomic snapshot of the tree at a single point in time, the semantics
748  *	of an RCU protected gang lookup are as though multiple radix_tree_lookups
749  *	have been issued in individual locks, and results stored in 'results'.
750  */
751 unsigned int
752 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
753 			unsigned long first_index, unsigned int max_items)
754 {
755 	unsigned long max_index;
756 	struct radix_tree_node *node;
757 	unsigned long cur_index = first_index;
758 	unsigned int ret;
759 
760 	node = rcu_dereference(root->rnode);
761 	if (!node)
762 		return 0;
763 
764 	if (!radix_tree_is_indirect_ptr(node)) {
765 		if (first_index > 0)
766 			return 0;
767 		results[0] = node;
768 		return 1;
769 	}
770 	node = radix_tree_indirect_to_ptr(node);
771 
772 	max_index = radix_tree_maxindex(node->height);
773 
774 	ret = 0;
775 	while (ret < max_items) {
776 		unsigned int nr_found, slots_found, i;
777 		unsigned long next_index;	/* Index of next search */
778 
779 		if (cur_index > max_index)
780 			break;
781 		slots_found = __lookup(node, (void ***)results + ret, cur_index,
782 					max_items - ret, &next_index);
783 		nr_found = 0;
784 		for (i = 0; i < slots_found; i++) {
785 			struct radix_tree_node *slot;
786 			slot = *(((void ***)results)[ret + i]);
787 			if (!slot)
788 				continue;
789 			results[ret + nr_found] = rcu_dereference(slot);
790 			nr_found++;
791 		}
792 		ret += nr_found;
793 		if (next_index == 0)
794 			break;
795 		cur_index = next_index;
796 	}
797 
798 	return ret;
799 }
800 EXPORT_SYMBOL(radix_tree_gang_lookup);
801 
802 /**
803  *	radix_tree_gang_lookup_slot - perform multiple slot lookup on radix tree
804  *	@root:		radix tree root
805  *	@results:	where the results of the lookup are placed
806  *	@first_index:	start the lookup from this key
807  *	@max_items:	place up to this many items at *results
808  *
809  *	Performs an index-ascending scan of the tree for present items.  Places
810  *	their slots at *@results and returns the number of items which were
811  *	placed at *@results.
812  *
813  *	The implementation is naive.
814  *
815  *	Like radix_tree_gang_lookup as far as RCU and locking goes. Slots must
816  *	be dereferenced with radix_tree_deref_slot, and if using only RCU
817  *	protection, radix_tree_deref_slot may fail requiring a retry.
818  */
819 unsigned int
820 radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
821 			unsigned long first_index, unsigned int max_items)
822 {
823 	unsigned long max_index;
824 	struct radix_tree_node *node;
825 	unsigned long cur_index = first_index;
826 	unsigned int ret;
827 
828 	node = rcu_dereference(root->rnode);
829 	if (!node)
830 		return 0;
831 
832 	if (!radix_tree_is_indirect_ptr(node)) {
833 		if (first_index > 0)
834 			return 0;
835 		results[0] = (void **)&root->rnode;
836 		return 1;
837 	}
838 	node = radix_tree_indirect_to_ptr(node);
839 
840 	max_index = radix_tree_maxindex(node->height);
841 
842 	ret = 0;
843 	while (ret < max_items) {
844 		unsigned int slots_found;
845 		unsigned long next_index;	/* Index of next search */
846 
847 		if (cur_index > max_index)
848 			break;
849 		slots_found = __lookup(node, results + ret, cur_index,
850 					max_items - ret, &next_index);
851 		ret += slots_found;
852 		if (next_index == 0)
853 			break;
854 		cur_index = next_index;
855 	}
856 
857 	return ret;
858 }
859 EXPORT_SYMBOL(radix_tree_gang_lookup_slot);
860 
861 /*
862  * FIXME: the two tag_get()s here should use find_next_bit() instead of
863  * open-coding the search.
864  */
865 static unsigned int
866 __lookup_tag(struct radix_tree_node *slot, void ***results, unsigned long index,
867 	unsigned int max_items, unsigned long *next_index, unsigned int tag)
868 {
869 	unsigned int nr_found = 0;
870 	unsigned int shift, height;
871 
872 	height = slot->height;
873 	if (height == 0)
874 		goto out;
875 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
876 
877 	while (height > 0) {
878 		unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK ;
879 
880 		for (;;) {
881 			if (tag_get(slot, tag, i))
882 				break;
883 			index &= ~((1UL << shift) - 1);
884 			index += 1UL << shift;
885 			if (index == 0)
886 				goto out;	/* 32-bit wraparound */
887 			i++;
888 			if (i == RADIX_TREE_MAP_SIZE)
889 				goto out;
890 		}
891 		height--;
892 		if (height == 0) {	/* Bottom level: grab some items */
893 			unsigned long j = index & RADIX_TREE_MAP_MASK;
894 
895 			for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
896 				index++;
897 				if (!tag_get(slot, tag, j))
898 					continue;
899 				/*
900 				 * Even though the tag was found set, we need to
901 				 * recheck that we have a non-NULL node, because
902 				 * if this lookup is lockless, it may have been
903 				 * subsequently deleted.
904 				 *
905 				 * Similar care must be taken in any place that
906 				 * lookup ->slots[x] without a lock (ie. can't
907 				 * rely on its value remaining the same).
908 				 */
909 				if (slot->slots[j]) {
910 					results[nr_found++] = &(slot->slots[j]);
911 					if (nr_found == max_items)
912 						goto out;
913 				}
914 			}
915 		}
916 		shift -= RADIX_TREE_MAP_SHIFT;
917 		slot = rcu_dereference(slot->slots[i]);
918 		if (slot == NULL)
919 			break;
920 	}
921 out:
922 	*next_index = index;
923 	return nr_found;
924 }
925 
926 /**
927  *	radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
928  *	                             based on a tag
929  *	@root:		radix tree root
930  *	@results:	where the results of the lookup are placed
931  *	@first_index:	start the lookup from this key
932  *	@max_items:	place up to this many items at *results
933  *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
934  *
935  *	Performs an index-ascending scan of the tree for present items which
936  *	have the tag indexed by @tag set.  Places the items at *@results and
937  *	returns the number of items which were placed at *@results.
938  */
939 unsigned int
940 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
941 		unsigned long first_index, unsigned int max_items,
942 		unsigned int tag)
943 {
944 	struct radix_tree_node *node;
945 	unsigned long max_index;
946 	unsigned long cur_index = first_index;
947 	unsigned int ret;
948 
949 	/* check the root's tag bit */
950 	if (!root_tag_get(root, tag))
951 		return 0;
952 
953 	node = rcu_dereference(root->rnode);
954 	if (!node)
955 		return 0;
956 
957 	if (!radix_tree_is_indirect_ptr(node)) {
958 		if (first_index > 0)
959 			return 0;
960 		results[0] = node;
961 		return 1;
962 	}
963 	node = radix_tree_indirect_to_ptr(node);
964 
965 	max_index = radix_tree_maxindex(node->height);
966 
967 	ret = 0;
968 	while (ret < max_items) {
969 		unsigned int nr_found, slots_found, i;
970 		unsigned long next_index;	/* Index of next search */
971 
972 		if (cur_index > max_index)
973 			break;
974 		slots_found = __lookup_tag(node, (void ***)results + ret,
975 				cur_index, max_items - ret, &next_index, tag);
976 		nr_found = 0;
977 		for (i = 0; i < slots_found; i++) {
978 			struct radix_tree_node *slot;
979 			slot = *(((void ***)results)[ret + i]);
980 			if (!slot)
981 				continue;
982 			results[ret + nr_found] = rcu_dereference(slot);
983 			nr_found++;
984 		}
985 		ret += nr_found;
986 		if (next_index == 0)
987 			break;
988 		cur_index = next_index;
989 	}
990 
991 	return ret;
992 }
993 EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
994 
995 /**
996  *	radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
997  *					  radix tree based on a tag
998  *	@root:		radix tree root
999  *	@results:	where the results of the lookup are placed
1000  *	@first_index:	start the lookup from this key
1001  *	@max_items:	place up to this many items at *results
1002  *	@tag:		the tag index (< RADIX_TREE_MAX_TAGS)
1003  *
1004  *	Performs an index-ascending scan of the tree for present items which
1005  *	have the tag indexed by @tag set.  Places the slots at *@results and
1006  *	returns the number of slots which were placed at *@results.
1007  */
1008 unsigned int
1009 radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
1010 		unsigned long first_index, unsigned int max_items,
1011 		unsigned int tag)
1012 {
1013 	struct radix_tree_node *node;
1014 	unsigned long max_index;
1015 	unsigned long cur_index = first_index;
1016 	unsigned int ret;
1017 
1018 	/* check the root's tag bit */
1019 	if (!root_tag_get(root, tag))
1020 		return 0;
1021 
1022 	node = rcu_dereference(root->rnode);
1023 	if (!node)
1024 		return 0;
1025 
1026 	if (!radix_tree_is_indirect_ptr(node)) {
1027 		if (first_index > 0)
1028 			return 0;
1029 		results[0] = (void **)&root->rnode;
1030 		return 1;
1031 	}
1032 	node = radix_tree_indirect_to_ptr(node);
1033 
1034 	max_index = radix_tree_maxindex(node->height);
1035 
1036 	ret = 0;
1037 	while (ret < max_items) {
1038 		unsigned int slots_found;
1039 		unsigned long next_index;	/* Index of next search */
1040 
1041 		if (cur_index > max_index)
1042 			break;
1043 		slots_found = __lookup_tag(node, results + ret,
1044 				cur_index, max_items - ret, &next_index, tag);
1045 		ret += slots_found;
1046 		if (next_index == 0)
1047 			break;
1048 		cur_index = next_index;
1049 	}
1050 
1051 	return ret;
1052 }
1053 EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
1054 
1055 
1056 /**
1057  *	radix_tree_shrink    -    shrink height of a radix tree to minimal
1058  *	@root		radix tree root
1059  */
1060 static inline void radix_tree_shrink(struct radix_tree_root *root)
1061 {
1062 	/* try to shrink tree height */
1063 	while (root->height > 0) {
1064 		struct radix_tree_node *to_free = root->rnode;
1065 		void *newptr;
1066 
1067 		BUG_ON(!radix_tree_is_indirect_ptr(to_free));
1068 		to_free = radix_tree_indirect_to_ptr(to_free);
1069 
1070 		/*
1071 		 * The candidate node has more than one child, or its child
1072 		 * is not at the leftmost slot, we cannot shrink.
1073 		 */
1074 		if (to_free->count != 1)
1075 			break;
1076 		if (!to_free->slots[0])
1077 			break;
1078 
1079 		/*
1080 		 * We don't need rcu_assign_pointer(), since we are simply
1081 		 * moving the node from one part of the tree to another. If
1082 		 * it was safe to dereference the old pointer to it
1083 		 * (to_free->slots[0]), it will be safe to dereference the new
1084 		 * one (root->rnode).
1085 		 */
1086 		newptr = to_free->slots[0];
1087 		if (root->height > 1)
1088 			newptr = radix_tree_ptr_to_indirect(newptr);
1089 		root->rnode = newptr;
1090 		root->height--;
1091 		radix_tree_node_free(to_free);
1092 	}
1093 }
1094 
1095 /**
1096  *	radix_tree_delete    -    delete an item from a radix tree
1097  *	@root:		radix tree root
1098  *	@index:		index key
1099  *
1100  *	Remove the item at @index from the radix tree rooted at @root.
1101  *
1102  *	Returns the address of the deleted item, or NULL if it was not present.
1103  */
1104 void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
1105 {
1106 	/*
1107 	 * The radix tree path needs to be one longer than the maximum path
1108 	 * since the "list" is null terminated.
1109 	 */
1110 	struct radix_tree_path path[RADIX_TREE_MAX_PATH + 1], *pathp = path;
1111 	struct radix_tree_node *slot = NULL;
1112 	struct radix_tree_node *to_free;
1113 	unsigned int height, shift;
1114 	int tag;
1115 	int offset;
1116 
1117 	height = root->height;
1118 	if (index > radix_tree_maxindex(height))
1119 		goto out;
1120 
1121 	slot = root->rnode;
1122 	if (height == 0) {
1123 		root_tag_clear_all(root);
1124 		root->rnode = NULL;
1125 		goto out;
1126 	}
1127 	slot = radix_tree_indirect_to_ptr(slot);
1128 
1129 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
1130 	pathp->node = NULL;
1131 
1132 	do {
1133 		if (slot == NULL)
1134 			goto out;
1135 
1136 		pathp++;
1137 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
1138 		pathp->offset = offset;
1139 		pathp->node = slot;
1140 		slot = slot->slots[offset];
1141 		shift -= RADIX_TREE_MAP_SHIFT;
1142 		height--;
1143 	} while (height > 0);
1144 
1145 	if (slot == NULL)
1146 		goto out;
1147 
1148 	/*
1149 	 * Clear all tags associated with the just-deleted item
1150 	 */
1151 	for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
1152 		if (tag_get(pathp->node, tag, pathp->offset))
1153 			radix_tree_tag_clear(root, index, tag);
1154 	}
1155 
1156 	to_free = NULL;
1157 	/* Now free the nodes we do not need anymore */
1158 	while (pathp->node) {
1159 		pathp->node->slots[pathp->offset] = NULL;
1160 		pathp->node->count--;
1161 		/*
1162 		 * Queue the node for deferred freeing after the
1163 		 * last reference to it disappears (set NULL, above).
1164 		 */
1165 		if (to_free)
1166 			radix_tree_node_free(to_free);
1167 
1168 		if (pathp->node->count) {
1169 			if (pathp->node ==
1170 					radix_tree_indirect_to_ptr(root->rnode))
1171 				radix_tree_shrink(root);
1172 			goto out;
1173 		}
1174 
1175 		/* Node with zero slots in use so free it */
1176 		to_free = pathp->node;
1177 		pathp--;
1178 
1179 	}
1180 	root_tag_clear_all(root);
1181 	root->height = 0;
1182 	root->rnode = NULL;
1183 	if (to_free)
1184 		radix_tree_node_free(to_free);
1185 
1186 out:
1187 	return slot;
1188 }
1189 EXPORT_SYMBOL(radix_tree_delete);
1190 
1191 /**
1192  *	radix_tree_tagged - test whether any items in the tree are tagged
1193  *	@root:		radix tree root
1194  *	@tag:		tag to test
1195  */
1196 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)
1197 {
1198 	return root_tag_get(root, tag);
1199 }
1200 EXPORT_SYMBOL(radix_tree_tagged);
1201 
1202 static void
1203 radix_tree_node_ctor(void *node)
1204 {
1205 	memset(node, 0, sizeof(struct radix_tree_node));
1206 }
1207 
1208 static __init unsigned long __maxindex(unsigned int height)
1209 {
1210 	unsigned int width = height * RADIX_TREE_MAP_SHIFT;
1211 	int shift = RADIX_TREE_INDEX_BITS - width;
1212 
1213 	if (shift < 0)
1214 		return ~0UL;
1215 	if (shift >= BITS_PER_LONG)
1216 		return 0UL;
1217 	return ~0UL >> shift;
1218 }
1219 
1220 static __init void radix_tree_init_maxindex(void)
1221 {
1222 	unsigned int i;
1223 
1224 	for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
1225 		height_to_maxindex[i] = __maxindex(i);
1226 }
1227 
1228 static int radix_tree_callback(struct notifier_block *nfb,
1229                             unsigned long action,
1230                             void *hcpu)
1231 {
1232        int cpu = (long)hcpu;
1233        struct radix_tree_preload *rtp;
1234 
1235        /* Free per-cpu pool of perloaded nodes */
1236        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
1237                rtp = &per_cpu(radix_tree_preloads, cpu);
1238                while (rtp->nr) {
1239                        kmem_cache_free(radix_tree_node_cachep,
1240                                        rtp->nodes[rtp->nr-1]);
1241                        rtp->nodes[rtp->nr-1] = NULL;
1242                        rtp->nr--;
1243                }
1244        }
1245        return NOTIFY_OK;
1246 }
1247 
1248 void __init radix_tree_init(void)
1249 {
1250 	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
1251 			sizeof(struct radix_tree_node), 0,
1252 			SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
1253 			radix_tree_node_ctor);
1254 	radix_tree_init_maxindex();
1255 	hotcpu_notifier(radix_tree_callback, 0);
1256 }
1257