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Linux/lib/radix-tree.c

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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
  5  * Copyright (C) 2006 Nick Piggin
  6  * Copyright (C) 2012 Konstantin Khlebnikov
  7  * Copyright (C) 2016 Intel, Matthew Wilcox
  8  * Copyright (C) 2016 Intel, Ross Zwisler
  9  *
 10  * This program is free software; you can redistribute it and/or
 11  * modify it under the terms of the GNU General Public License as
 12  * published by the Free Software Foundation; either version 2, or (at
 13  * your option) any later version.
 14  *
 15  * This program is distributed in the hope that it will be useful, but
 16  * WITHOUT ANY WARRANTY; without even the implied warranty of
 17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 18  * General Public License for more details.
 19  *
 20  * You should have received a copy of the GNU General Public License
 21  * along with this program; if not, write to the Free Software
 22  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 23  */
 24 
 25 #include <linux/errno.h>
 26 #include <linux/init.h>
 27 #include <linux/kernel.h>
 28 #include <linux/export.h>
 29 #include <linux/radix-tree.h>
 30 #include <linux/percpu.h>
 31 #include <linux/slab.h>
 32 #include <linux/kmemleak.h>
 33 #include <linux/notifier.h>
 34 #include <linux/cpu.h>
 35 #include <linux/string.h>
 36 #include <linux/bitops.h>
 37 #include <linux/rcupdate.h>
 38 #include <linux/preempt.h>              /* in_interrupt() */
 39 
 40 
 41 /* Number of nodes in fully populated tree of given height */
 42 static unsigned long height_to_maxnodes[RADIX_TREE_MAX_PATH + 1] __read_mostly;
 43 
 44 /*
 45  * Radix tree node cache.
 46  */
 47 static struct kmem_cache *radix_tree_node_cachep;
 48 
 49 /*
 50  * The radix tree is variable-height, so an insert operation not only has
 51  * to build the branch to its corresponding item, it also has to build the
 52  * branch to existing items if the size has to be increased (by
 53  * radix_tree_extend).
 54  *
 55  * The worst case is a zero height tree with just a single item at index 0,
 56  * and then inserting an item at index ULONG_MAX. This requires 2 new branches
 57  * of RADIX_TREE_MAX_PATH size to be created, with only the root node shared.
 58  * Hence:
 59  */
 60 #define RADIX_TREE_PRELOAD_SIZE (RADIX_TREE_MAX_PATH * 2 - 1)
 61 
 62 /*
 63  * Per-cpu pool of preloaded nodes
 64  */
 65 struct radix_tree_preload {
 66         unsigned nr;
 67         /* nodes->private_data points to next preallocated node */
 68         struct radix_tree_node *nodes;
 69 };
 70 static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
 71 
 72 static inline void *node_to_entry(void *ptr)
 73 {
 74         return (void *)((unsigned long)ptr | RADIX_TREE_INTERNAL_NODE);
 75 }
 76 
 77 #define RADIX_TREE_RETRY        node_to_entry(NULL)
 78 
 79 #ifdef CONFIG_RADIX_TREE_MULTIORDER
 80 /* Sibling slots point directly to another slot in the same node */
 81 static inline bool is_sibling_entry(struct radix_tree_node *parent, void *node)
 82 {
 83         void **ptr = node;
 84         return (parent->slots <= ptr) &&
 85                         (ptr < parent->slots + RADIX_TREE_MAP_SIZE);
 86 }
 87 #else
 88 static inline bool is_sibling_entry(struct radix_tree_node *parent, void *node)
 89 {
 90         return false;
 91 }
 92 #endif
 93 
 94 static inline unsigned long get_slot_offset(struct radix_tree_node *parent,
 95                                                  void **slot)
 96 {
 97         return slot - parent->slots;
 98 }
 99 
100 static unsigned int radix_tree_descend(struct radix_tree_node *parent,
101                         struct radix_tree_node **nodep, unsigned long index)
102 {
103         unsigned int offset = (index >> parent->shift) & RADIX_TREE_MAP_MASK;
104         void **entry = rcu_dereference_raw(parent->slots[offset]);
105 
106 #ifdef CONFIG_RADIX_TREE_MULTIORDER
107         if (radix_tree_is_internal_node(entry)) {
108                 if (is_sibling_entry(parent, entry)) {
109                         void **sibentry = (void **) entry_to_node(entry);
110                         offset = get_slot_offset(parent, sibentry);
111                         entry = rcu_dereference_raw(*sibentry);
112                 }
113         }
114 #endif
115 
116         *nodep = (void *)entry;
117         return offset;
118 }
119 
120 static inline gfp_t root_gfp_mask(struct radix_tree_root *root)
121 {
122         return root->gfp_mask & __GFP_BITS_MASK;
123 }
124 
125 static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
126                 int offset)
127 {
128         __set_bit(offset, node->tags[tag]);
129 }
130 
131 static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
132                 int offset)
133 {
134         __clear_bit(offset, node->tags[tag]);
135 }
136 
137 static inline int tag_get(struct radix_tree_node *node, unsigned int tag,
138                 int offset)
139 {
140         return test_bit(offset, node->tags[tag]);
141 }
142 
143 static inline void root_tag_set(struct radix_tree_root *root, unsigned int tag)
144 {
145         root->gfp_mask |= (__force gfp_t)(1 << (tag + __GFP_BITS_SHIFT));
146 }
147 
148 static inline void root_tag_clear(struct radix_tree_root *root, unsigned tag)
149 {
150         root->gfp_mask &= (__force gfp_t)~(1 << (tag + __GFP_BITS_SHIFT));
151 }
152 
153 static inline void root_tag_clear_all(struct radix_tree_root *root)
154 {
155         root->gfp_mask &= __GFP_BITS_MASK;
156 }
157 
158 static inline int root_tag_get(struct radix_tree_root *root, unsigned int tag)
159 {
160         return (__force int)root->gfp_mask & (1 << (tag + __GFP_BITS_SHIFT));
161 }
162 
163 static inline unsigned root_tags_get(struct radix_tree_root *root)
164 {
165         return (__force unsigned)root->gfp_mask >> __GFP_BITS_SHIFT;
166 }
167 
168 /*
169  * Returns 1 if any slot in the node has this tag set.
170  * Otherwise returns 0.
171  */
172 static inline int any_tag_set(struct radix_tree_node *node, unsigned int tag)
173 {
174         unsigned idx;
175         for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
176                 if (node->tags[tag][idx])
177                         return 1;
178         }
179         return 0;
180 }
181 
182 /**
183  * radix_tree_find_next_bit - find the next set bit in a memory region
184  *
185  * @addr: The address to base the search on
186  * @size: The bitmap size in bits
187  * @offset: The bitnumber to start searching at
188  *
189  * Unrollable variant of find_next_bit() for constant size arrays.
190  * Tail bits starting from size to roundup(size, BITS_PER_LONG) must be zero.
191  * Returns next bit offset, or size if nothing found.
192  */
193 static __always_inline unsigned long
194 radix_tree_find_next_bit(const unsigned long *addr,
195                          unsigned long size, unsigned long offset)
196 {
197         if (!__builtin_constant_p(size))
198                 return find_next_bit(addr, size, offset);
199 
200         if (offset < size) {
201                 unsigned long tmp;
202 
203                 addr += offset / BITS_PER_LONG;
204                 tmp = *addr >> (offset % BITS_PER_LONG);
205                 if (tmp)
206                         return __ffs(tmp) + offset;
207                 offset = (offset + BITS_PER_LONG) & ~(BITS_PER_LONG - 1);
208                 while (offset < size) {
209                         tmp = *++addr;
210                         if (tmp)
211                                 return __ffs(tmp) + offset;
212                         offset += BITS_PER_LONG;
213                 }
214         }
215         return size;
216 }
217 
218 #ifndef __KERNEL__
219 static void dump_node(struct radix_tree_node *node, unsigned long index)
220 {
221         unsigned long i;
222 
223         pr_debug("radix node: %p offset %d tags %lx %lx %lx shift %d count %d parent %p\n",
224                 node, node->offset,
225                 node->tags[0][0], node->tags[1][0], node->tags[2][0],
226                 node->shift, node->count, node->parent);
227 
228         for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
229                 unsigned long first = index | (i << node->shift);
230                 unsigned long last = first | ((1UL << node->shift) - 1);
231                 void *entry = node->slots[i];
232                 if (!entry)
233                         continue;
234                 if (is_sibling_entry(node, entry)) {
235                         pr_debug("radix sblng %p offset %ld val %p indices %ld-%ld\n",
236                                         entry, i,
237                                         *(void **)entry_to_node(entry),
238                                         first, last);
239                 } else if (!radix_tree_is_internal_node(entry)) {
240                         pr_debug("radix entry %p offset %ld indices %ld-%ld\n",
241                                         entry, i, first, last);
242                 } else {
243                         dump_node(entry_to_node(entry), first);
244                 }
245         }
246 }
247 
248 /* For debug */
249 static void radix_tree_dump(struct radix_tree_root *root)
250 {
251         pr_debug("radix root: %p rnode %p tags %x\n",
252                         root, root->rnode,
253                         root->gfp_mask >> __GFP_BITS_SHIFT);
254         if (!radix_tree_is_internal_node(root->rnode))
255                 return;
256         dump_node(entry_to_node(root->rnode), 0);
257 }
258 #endif
259 
260 /*
261  * This assumes that the caller has performed appropriate preallocation, and
262  * that the caller has pinned this thread of control to the current CPU.
263  */
264 static struct radix_tree_node *
265 radix_tree_node_alloc(struct radix_tree_root *root)
266 {
267         struct radix_tree_node *ret = NULL;
268         gfp_t gfp_mask = root_gfp_mask(root);
269 
270         /*
271          * Preload code isn't irq safe and it doesn't make sense to use
272          * preloading during an interrupt anyway as all the allocations have
273          * to be atomic. So just do normal allocation when in interrupt.
274          */
275         if (!gfpflags_allow_blocking(gfp_mask) && !in_interrupt()) {
276                 struct radix_tree_preload *rtp;
277 
278                 /*
279                  * Even if the caller has preloaded, try to allocate from the
280                  * cache first for the new node to get accounted to the memory
281                  * cgroup.
282                  */
283                 ret = kmem_cache_alloc(radix_tree_node_cachep,
284                                        gfp_mask | __GFP_NOWARN);
285                 if (ret)
286                         goto out;
287 
288                 /*
289                  * Provided the caller has preloaded here, we will always
290                  * succeed in getting a node here (and never reach
291                  * kmem_cache_alloc)
292                  */
293                 rtp = this_cpu_ptr(&radix_tree_preloads);
294                 if (rtp->nr) {
295                         ret = rtp->nodes;
296                         rtp->nodes = ret->private_data;
297                         ret->private_data = NULL;
298                         rtp->nr--;
299                 }
300                 /*
301                  * Update the allocation stack trace as this is more useful
302                  * for debugging.
303                  */
304                 kmemleak_update_trace(ret);
305                 goto out;
306         }
307         ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
308 out:
309         BUG_ON(radix_tree_is_internal_node(ret));
310         return ret;
311 }
312 
313 static void radix_tree_node_rcu_free(struct rcu_head *head)
314 {
315         struct radix_tree_node *node =
316                         container_of(head, struct radix_tree_node, rcu_head);
317         int i;
318 
319         /*
320          * must only free zeroed nodes into the slab. radix_tree_shrink
321          * can leave us with a non-NULL entry in the first slot, so clear
322          * that here to make sure.
323          */
324         for (i = 0; i < RADIX_TREE_MAX_TAGS; i++)
325                 tag_clear(node, i, 0);
326 
327         node->slots[0] = NULL;
328         node->count = 0;
329 
330         kmem_cache_free(radix_tree_node_cachep, node);
331 }
332 
333 static inline void
334 radix_tree_node_free(struct radix_tree_node *node)
335 {
336         call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
337 }
338 
339 /*
340  * Load up this CPU's radix_tree_node buffer with sufficient objects to
341  * ensure that the addition of a single element in the tree cannot fail.  On
342  * success, return zero, with preemption disabled.  On error, return -ENOMEM
343  * with preemption not disabled.
344  *
345  * To make use of this facility, the radix tree must be initialised without
346  * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
347  */
348 static int __radix_tree_preload(gfp_t gfp_mask, int nr)
349 {
350         struct radix_tree_preload *rtp;
351         struct radix_tree_node *node;
352         int ret = -ENOMEM;
353 
354         /*
355          * Nodes preloaded by one cgroup can be be used by another cgroup, so
356          * they should never be accounted to any particular memory cgroup.
357          */
358         gfp_mask &= ~__GFP_ACCOUNT;
359 
360         preempt_disable();
361         rtp = this_cpu_ptr(&radix_tree_preloads);
362         while (rtp->nr < nr) {
363                 preempt_enable();
364                 node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
365                 if (node == NULL)
366                         goto out;
367                 preempt_disable();
368                 rtp = this_cpu_ptr(&radix_tree_preloads);
369                 if (rtp->nr < nr) {
370                         node->private_data = rtp->nodes;
371                         rtp->nodes = node;
372                         rtp->nr++;
373                 } else {
374                         kmem_cache_free(radix_tree_node_cachep, node);
375                 }
376         }
377         ret = 0;
378 out:
379         return ret;
380 }
381 
382 /*
383  * Load up this CPU's radix_tree_node buffer with sufficient objects to
384  * ensure that the addition of a single element in the tree cannot fail.  On
385  * success, return zero, with preemption disabled.  On error, return -ENOMEM
386  * with preemption not disabled.
387  *
388  * To make use of this facility, the radix tree must be initialised without
389  * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
390  */
391 int radix_tree_preload(gfp_t gfp_mask)
392 {
393         /* Warn on non-sensical use... */
394         WARN_ON_ONCE(!gfpflags_allow_blocking(gfp_mask));
395         return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
396 }
397 EXPORT_SYMBOL(radix_tree_preload);
398 
399 /*
400  * The same as above function, except we don't guarantee preloading happens.
401  * We do it, if we decide it helps. On success, return zero with preemption
402  * disabled. On error, return -ENOMEM with preemption not disabled.
403  */
404 int radix_tree_maybe_preload(gfp_t gfp_mask)
405 {
406         if (gfpflags_allow_blocking(gfp_mask))
407                 return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
408         /* Preloading doesn't help anything with this gfp mask, skip it */
409         preempt_disable();
410         return 0;
411 }
412 EXPORT_SYMBOL(radix_tree_maybe_preload);
413 
414 /*
415  * The same as function above, but preload number of nodes required to insert
416  * (1 << order) continuous naturally-aligned elements.
417  */
418 int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order)
419 {
420         unsigned long nr_subtrees;
421         int nr_nodes, subtree_height;
422 
423         /* Preloading doesn't help anything with this gfp mask, skip it */
424         if (!gfpflags_allow_blocking(gfp_mask)) {
425                 preempt_disable();
426                 return 0;
427         }
428 
429         /*
430          * Calculate number and height of fully populated subtrees it takes to
431          * store (1 << order) elements.
432          */
433         nr_subtrees = 1 << order;
434         for (subtree_height = 0; nr_subtrees > RADIX_TREE_MAP_SIZE;
435                         subtree_height++)
436                 nr_subtrees >>= RADIX_TREE_MAP_SHIFT;
437 
438         /*
439          * The worst case is zero height tree with a single item at index 0 and
440          * then inserting items starting at ULONG_MAX - (1 << order).
441          *
442          * This requires RADIX_TREE_MAX_PATH nodes to build branch from root to
443          * 0-index item.
444          */
445         nr_nodes = RADIX_TREE_MAX_PATH;
446 
447         /* Plus branch to fully populated subtrees. */
448         nr_nodes += RADIX_TREE_MAX_PATH - subtree_height;
449 
450         /* Root node is shared. */
451         nr_nodes--;
452 
453         /* Plus nodes required to build subtrees. */
454         nr_nodes += nr_subtrees * height_to_maxnodes[subtree_height];
455 
456         return __radix_tree_preload(gfp_mask, nr_nodes);
457 }
458 
459 /*
460  * The maximum index which can be stored in a radix tree
461  */
462 static inline unsigned long shift_maxindex(unsigned int shift)
463 {
464         return (RADIX_TREE_MAP_SIZE << shift) - 1;
465 }
466 
467 static inline unsigned long node_maxindex(struct radix_tree_node *node)
468 {
469         return shift_maxindex(node->shift);
470 }
471 
472 static unsigned radix_tree_load_root(struct radix_tree_root *root,
473                 struct radix_tree_node **nodep, unsigned long *maxindex)
474 {
475         struct radix_tree_node *node = rcu_dereference_raw(root->rnode);
476 
477         *nodep = node;
478 
479         if (likely(radix_tree_is_internal_node(node))) {
480                 node = entry_to_node(node);
481                 *maxindex = node_maxindex(node);
482                 return node->shift + RADIX_TREE_MAP_SHIFT;
483         }
484 
485         *maxindex = 0;
486         return 0;
487 }
488 
489 /*
490  *      Extend a radix tree so it can store key @index.
491  */
492 static int radix_tree_extend(struct radix_tree_root *root,
493                                 unsigned long index, unsigned int shift)
494 {
495         struct radix_tree_node *slot;
496         unsigned int maxshift;
497         int tag;
498 
499         /* Figure out what the shift should be.  */
500         maxshift = shift;
501         while (index > shift_maxindex(maxshift))
502                 maxshift += RADIX_TREE_MAP_SHIFT;
503 
504         slot = root->rnode;
505         if (!slot)
506                 goto out;
507 
508         do {
509                 struct radix_tree_node *node = radix_tree_node_alloc(root);
510 
511                 if (!node)
512                         return -ENOMEM;
513 
514                 /* Propagate the aggregated tag info into the new root */
515                 for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
516                         if (root_tag_get(root, tag))
517                                 tag_set(node, tag, 0);
518                 }
519 
520                 BUG_ON(shift > BITS_PER_LONG);
521                 node->shift = shift;
522                 node->offset = 0;
523                 node->count = 1;
524                 node->parent = NULL;
525                 if (radix_tree_is_internal_node(slot))
526                         entry_to_node(slot)->parent = node;
527                 node->slots[0] = slot;
528                 slot = node_to_entry(node);
529                 rcu_assign_pointer(root->rnode, slot);
530                 shift += RADIX_TREE_MAP_SHIFT;
531         } while (shift <= maxshift);
532 out:
533         return maxshift + RADIX_TREE_MAP_SHIFT;
534 }
535 
536 /**
537  *      __radix_tree_create     -       create a slot in a radix tree
538  *      @root:          radix tree root
539  *      @index:         index key
540  *      @order:         index occupies 2^order aligned slots
541  *      @nodep:         returns node
542  *      @slotp:         returns slot
543  *
544  *      Create, if necessary, and return the node and slot for an item
545  *      at position @index in the radix tree @root.
546  *
547  *      Until there is more than one item in the tree, no nodes are
548  *      allocated and @root->rnode is used as a direct slot instead of
549  *      pointing to a node, in which case *@nodep will be NULL.
550  *
551  *      Returns -ENOMEM, or 0 for success.
552  */
553 int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
554                         unsigned order, struct radix_tree_node **nodep,
555                         void ***slotp)
556 {
557         struct radix_tree_node *node = NULL, *child;
558         void **slot = (void **)&root->rnode;
559         unsigned long maxindex;
560         unsigned int shift, offset = 0;
561         unsigned long max = index | ((1UL << order) - 1);
562 
563         shift = radix_tree_load_root(root, &child, &maxindex);
564 
565         /* Make sure the tree is high enough.  */
566         if (max > maxindex) {
567                 int error = radix_tree_extend(root, max, shift);
568                 if (error < 0)
569                         return error;
570                 shift = error;
571                 child = root->rnode;
572                 if (order == shift)
573                         shift += RADIX_TREE_MAP_SHIFT;
574         }
575 
576         while (shift > order) {
577                 shift -= RADIX_TREE_MAP_SHIFT;
578                 if (child == NULL) {
579                         /* Have to add a child node.  */
580                         child = radix_tree_node_alloc(root);
581                         if (!child)
582                                 return -ENOMEM;
583                         child->shift = shift;
584                         child->offset = offset;
585                         child->parent = node;
586                         rcu_assign_pointer(*slot, node_to_entry(child));
587                         if (node)
588                                 node->count++;
589                 } else if (!radix_tree_is_internal_node(child))
590                         break;
591 
592                 /* Go a level down */
593                 node = entry_to_node(child);
594                 offset = radix_tree_descend(node, &child, index);
595                 slot = &node->slots[offset];
596         }
597 
598 #ifdef CONFIG_RADIX_TREE_MULTIORDER
599         /* Insert pointers to the canonical entry */
600         if (order > shift) {
601                 unsigned i, n = 1 << (order - shift);
602                 offset = offset & ~(n - 1);
603                 slot = &node->slots[offset];
604                 child = node_to_entry(slot);
605                 for (i = 0; i < n; i++) {
606                         if (slot[i])
607                                 return -EEXIST;
608                 }
609 
610                 for (i = 1; i < n; i++) {
611                         rcu_assign_pointer(slot[i], child);
612                         node->count++;
613                 }
614         }
615 #endif
616 
617         if (nodep)
618                 *nodep = node;
619         if (slotp)
620                 *slotp = slot;
621         return 0;
622 }
623 
624 /**
625  *      __radix_tree_insert    -    insert into a radix tree
626  *      @root:          radix tree root
627  *      @index:         index key
628  *      @order:         key covers the 2^order indices around index
629  *      @item:          item to insert
630  *
631  *      Insert an item into the radix tree at position @index.
632  */
633 int __radix_tree_insert(struct radix_tree_root *root, unsigned long index,
634                         unsigned order, void *item)
635 {
636         struct radix_tree_node *node;
637         void **slot;
638         int error;
639 
640         BUG_ON(radix_tree_is_internal_node(item));
641 
642         error = __radix_tree_create(root, index, order, &node, &slot);
643         if (error)
644                 return error;
645         if (*slot != NULL)
646                 return -EEXIST;
647         rcu_assign_pointer(*slot, item);
648 
649         if (node) {
650                 unsigned offset = get_slot_offset(node, slot);
651                 node->count++;
652                 BUG_ON(tag_get(node, 0, offset));
653                 BUG_ON(tag_get(node, 1, offset));
654                 BUG_ON(tag_get(node, 2, offset));
655         } else {
656                 BUG_ON(root_tags_get(root));
657         }
658 
659         return 0;
660 }
661 EXPORT_SYMBOL(__radix_tree_insert);
662 
663 /**
664  *      __radix_tree_lookup     -       lookup an item in a radix tree
665  *      @root:          radix tree root
666  *      @index:         index key
667  *      @nodep:         returns node
668  *      @slotp:         returns slot
669  *
670  *      Lookup and return the item at position @index in the radix
671  *      tree @root.
672  *
673  *      Until there is more than one item in the tree, no nodes are
674  *      allocated and @root->rnode is used as a direct slot instead of
675  *      pointing to a node, in which case *@nodep will be NULL.
676  */
677 void *__radix_tree_lookup(struct radix_tree_root *root, unsigned long index,
678                           struct radix_tree_node **nodep, void ***slotp)
679 {
680         struct radix_tree_node *node, *parent;
681         unsigned long maxindex;
682         void **slot;
683 
684  restart:
685         parent = NULL;
686         slot = (void **)&root->rnode;
687         radix_tree_load_root(root, &node, &maxindex);
688         if (index > maxindex)
689                 return NULL;
690 
691         while (radix_tree_is_internal_node(node)) {
692                 unsigned offset;
693 
694                 if (node == RADIX_TREE_RETRY)
695                         goto restart;
696                 parent = entry_to_node(node);
697                 offset = radix_tree_descend(parent, &node, index);
698                 slot = parent->slots + offset;
699         }
700 
701         if (nodep)
702                 *nodep = parent;
703         if (slotp)
704                 *slotp = slot;
705         return node;
706 }
707 
708 /**
709  *      radix_tree_lookup_slot    -    lookup a slot in a radix tree
710  *      @root:          radix tree root
711  *      @index:         index key
712  *
713  *      Returns:  the slot corresponding to the position @index in the
714  *      radix tree @root. This is useful for update-if-exists operations.
715  *
716  *      This function can be called under rcu_read_lock iff the slot is not
717  *      modified by radix_tree_replace_slot, otherwise it must be called
718  *      exclusive from other writers. Any dereference of the slot must be done
719  *      using radix_tree_deref_slot.
720  */
721 void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
722 {
723         void **slot;
724 
725         if (!__radix_tree_lookup(root, index, NULL, &slot))
726                 return NULL;
727         return slot;
728 }
729 EXPORT_SYMBOL(radix_tree_lookup_slot);
730 
731 /**
732  *      radix_tree_lookup    -    perform lookup operation on a radix tree
733  *      @root:          radix tree root
734  *      @index:         index key
735  *
736  *      Lookup the item at the position @index in the radix tree @root.
737  *
738  *      This function can be called under rcu_read_lock, however the caller
739  *      must manage lifetimes of leaf nodes (eg. RCU may also be used to free
740  *      them safely). No RCU barriers are required to access or modify the
741  *      returned item, however.
742  */
743 void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
744 {
745         return __radix_tree_lookup(root, index, NULL, NULL);
746 }
747 EXPORT_SYMBOL(radix_tree_lookup);
748 
749 /**
750  *      radix_tree_tag_set - set a tag on a radix tree node
751  *      @root:          radix tree root
752  *      @index:         index key
753  *      @tag:           tag index
754  *
755  *      Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
756  *      corresponding to @index in the radix tree.  From
757  *      the root all the way down to the leaf node.
758  *
759  *      Returns the address of the tagged item.  Setting a tag on a not-present
760  *      item is a bug.
761  */
762 void *radix_tree_tag_set(struct radix_tree_root *root,
763                         unsigned long index, unsigned int tag)
764 {
765         struct radix_tree_node *node, *parent;
766         unsigned long maxindex;
767 
768         radix_tree_load_root(root, &node, &maxindex);
769         BUG_ON(index > maxindex);
770 
771         while (radix_tree_is_internal_node(node)) {
772                 unsigned offset;
773 
774                 parent = entry_to_node(node);
775                 offset = radix_tree_descend(parent, &node, index);
776                 BUG_ON(!node);
777 
778                 if (!tag_get(parent, tag, offset))
779                         tag_set(parent, tag, offset);
780         }
781 
782         /* set the root's tag bit */
783         if (!root_tag_get(root, tag))
784                 root_tag_set(root, tag);
785 
786         return node;
787 }
788 EXPORT_SYMBOL(radix_tree_tag_set);
789 
790 static void node_tag_clear(struct radix_tree_root *root,
791                                 struct radix_tree_node *node,
792                                 unsigned int tag, unsigned int offset)
793 {
794         while (node) {
795                 if (!tag_get(node, tag, offset))
796                         return;
797                 tag_clear(node, tag, offset);
798                 if (any_tag_set(node, tag))
799                         return;
800 
801                 offset = node->offset;
802                 node = node->parent;
803         }
804 
805         /* clear the root's tag bit */
806         if (root_tag_get(root, tag))
807                 root_tag_clear(root, tag);
808 }
809 
810 /**
811  *      radix_tree_tag_clear - clear a tag on a radix tree node
812  *      @root:          radix tree root
813  *      @index:         index key
814  *      @tag:           tag index
815  *
816  *      Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
817  *      corresponding to @index in the radix tree.  If this causes
818  *      the leaf node to have no tags set then clear the tag in the
819  *      next-to-leaf node, etc.
820  *
821  *      Returns the address of the tagged item on success, else NULL.  ie:
822  *      has the same return value and semantics as radix_tree_lookup().
823  */
824 void *radix_tree_tag_clear(struct radix_tree_root *root,
825                         unsigned long index, unsigned int tag)
826 {
827         struct radix_tree_node *node, *parent;
828         unsigned long maxindex;
829         int uninitialized_var(offset);
830 
831         radix_tree_load_root(root, &node, &maxindex);
832         if (index > maxindex)
833                 return NULL;
834 
835         parent = NULL;
836 
837         while (radix_tree_is_internal_node(node)) {
838                 parent = entry_to_node(node);
839                 offset = radix_tree_descend(parent, &node, index);
840         }
841 
842         if (node)
843                 node_tag_clear(root, parent, tag, offset);
844 
845         return node;
846 }
847 EXPORT_SYMBOL(radix_tree_tag_clear);
848 
849 /**
850  * radix_tree_tag_get - get a tag on a radix tree node
851  * @root:               radix tree root
852  * @index:              index key
853  * @tag:                tag index (< RADIX_TREE_MAX_TAGS)
854  *
855  * Return values:
856  *
857  *  0: tag not present or not set
858  *  1: tag set
859  *
860  * Note that the return value of this function may not be relied on, even if
861  * the RCU lock is held, unless tag modification and node deletion are excluded
862  * from concurrency.
863  */
864 int radix_tree_tag_get(struct radix_tree_root *root,
865                         unsigned long index, unsigned int tag)
866 {
867         struct radix_tree_node *node, *parent;
868         unsigned long maxindex;
869 
870         if (!root_tag_get(root, tag))
871                 return 0;
872 
873         radix_tree_load_root(root, &node, &maxindex);
874         if (index > maxindex)
875                 return 0;
876         if (node == NULL)
877                 return 0;
878 
879         while (radix_tree_is_internal_node(node)) {
880                 unsigned offset;
881 
882                 parent = entry_to_node(node);
883                 offset = radix_tree_descend(parent, &node, index);
884 
885                 if (!node)
886                         return 0;
887                 if (!tag_get(parent, tag, offset))
888                         return 0;
889                 if (node == RADIX_TREE_RETRY)
890                         break;
891         }
892 
893         return 1;
894 }
895 EXPORT_SYMBOL(radix_tree_tag_get);
896 
897 static inline void __set_iter_shift(struct radix_tree_iter *iter,
898                                         unsigned int shift)
899 {
900 #ifdef CONFIG_RADIX_TREE_MULTIORDER
901         iter->shift = shift;
902 #endif
903 }
904 
905 /**
906  * radix_tree_next_chunk - find next chunk of slots for iteration
907  *
908  * @root:       radix tree root
909  * @iter:       iterator state
910  * @flags:      RADIX_TREE_ITER_* flags and tag index
911  * Returns:     pointer to chunk first slot, or NULL if iteration is over
912  */
913 void **radix_tree_next_chunk(struct radix_tree_root *root,
914                              struct radix_tree_iter *iter, unsigned flags)
915 {
916         unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;
917         struct radix_tree_node *node, *child;
918         unsigned long index, offset, maxindex;
919 
920         if ((flags & RADIX_TREE_ITER_TAGGED) && !root_tag_get(root, tag))
921                 return NULL;
922 
923         /*
924          * Catch next_index overflow after ~0UL. iter->index never overflows
925          * during iterating; it can be zero only at the beginning.
926          * And we cannot overflow iter->next_index in a single step,
927          * because RADIX_TREE_MAP_SHIFT < BITS_PER_LONG.
928          *
929          * This condition also used by radix_tree_next_slot() to stop
930          * contiguous iterating, and forbid swithing to the next chunk.
931          */
932         index = iter->next_index;
933         if (!index && iter->index)
934                 return NULL;
935 
936  restart:
937         radix_tree_load_root(root, &child, &maxindex);
938         if (index > maxindex)
939                 return NULL;
940         if (!child)
941                 return NULL;
942 
943         if (!radix_tree_is_internal_node(child)) {
944                 /* Single-slot tree */
945                 iter->index = index;
946                 iter->next_index = maxindex + 1;
947                 iter->tags = 1;
948                 __set_iter_shift(iter, 0);
949                 return (void **)&root->rnode;
950         }
951 
952         do {
953                 node = entry_to_node(child);
954                 offset = radix_tree_descend(node, &child, index);
955 
956                 if ((flags & RADIX_TREE_ITER_TAGGED) ?
957                                 !tag_get(node, tag, offset) : !child) {
958                         /* Hole detected */
959                         if (flags & RADIX_TREE_ITER_CONTIG)
960                                 return NULL;
961 
962                         if (flags & RADIX_TREE_ITER_TAGGED)
963                                 offset = radix_tree_find_next_bit(
964                                                 node->tags[tag],
965                                                 RADIX_TREE_MAP_SIZE,
966                                                 offset + 1);
967                         else
968                                 while (++offset < RADIX_TREE_MAP_SIZE) {
969                                         void *slot = node->slots[offset];
970                                         if (is_sibling_entry(node, slot))
971                                                 continue;
972                                         if (slot)
973                                                 break;
974                                 }
975                         index &= ~node_maxindex(node);
976                         index += offset << node->shift;
977                         /* Overflow after ~0UL */
978                         if (!index)
979                                 return NULL;
980                         if (offset == RADIX_TREE_MAP_SIZE)
981                                 goto restart;
982                         child = rcu_dereference_raw(node->slots[offset]);
983                 }
984 
985                 if ((child == NULL) || (child == RADIX_TREE_RETRY))
986                         goto restart;
987         } while (radix_tree_is_internal_node(child));
988 
989         /* Update the iterator state */
990         iter->index = (index &~ node_maxindex(node)) | (offset << node->shift);
991         iter->next_index = (index | node_maxindex(node)) + 1;
992         __set_iter_shift(iter, node->shift);
993 
994         /* Construct iter->tags bit-mask from node->tags[tag] array */
995         if (flags & RADIX_TREE_ITER_TAGGED) {
996                 unsigned tag_long, tag_bit;
997 
998                 tag_long = offset / BITS_PER_LONG;
999                 tag_bit  = offset % BITS_PER_LONG;
1000                 iter->tags = node->tags[tag][tag_long] >> tag_bit;
1001                 /* This never happens if RADIX_TREE_TAG_LONGS == 1 */
1002                 if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
1003                         /* Pick tags from next element */
1004                         if (tag_bit)
1005                                 iter->tags |= node->tags[tag][tag_long + 1] <<
1006                                                 (BITS_PER_LONG - tag_bit);
1007                         /* Clip chunk size, here only BITS_PER_LONG tags */
1008                         iter->next_index = index + BITS_PER_LONG;
1009                 }
1010         }
1011 
1012         return node->slots + offset;
1013 }
1014 EXPORT_SYMBOL(radix_tree_next_chunk);
1015 
1016 /**
1017  * radix_tree_range_tag_if_tagged - for each item in given range set given
1018  *                                 tag if item has another tag set
1019  * @root:               radix tree root
1020  * @first_indexp:       pointer to a starting index of a range to scan
1021  * @last_index:         last index of a range to scan
1022  * @nr_to_tag:          maximum number items to tag
1023  * @iftag:              tag index to test
1024  * @settag:             tag index to set if tested tag is set
1025  *
1026  * This function scans range of radix tree from first_index to last_index
1027  * (inclusive).  For each item in the range if iftag is set, the function sets
1028  * also settag. The function stops either after tagging nr_to_tag items or
1029  * after reaching last_index.
1030  *
1031  * The tags must be set from the leaf level only and propagated back up the
1032  * path to the root. We must do this so that we resolve the full path before
1033  * setting any tags on intermediate nodes. If we set tags as we descend, then
1034  * we can get to the leaf node and find that the index that has the iftag
1035  * set is outside the range we are scanning. This reults in dangling tags and
1036  * can lead to problems with later tag operations (e.g. livelocks on lookups).
1037  *
1038  * The function returns the number of leaves where the tag was set and sets
1039  * *first_indexp to the first unscanned index.
1040  * WARNING! *first_indexp can wrap if last_index is ULONG_MAX. Caller must
1041  * be prepared to handle that.
1042  */
1043 unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
1044                 unsigned long *first_indexp, unsigned long last_index,
1045                 unsigned long nr_to_tag,
1046                 unsigned int iftag, unsigned int settag)
1047 {
1048         struct radix_tree_node *parent, *node, *child;
1049         unsigned long maxindex;
1050         unsigned long tagged = 0;
1051         unsigned long index = *first_indexp;
1052 
1053         radix_tree_load_root(root, &child, &maxindex);
1054         last_index = min(last_index, maxindex);
1055         if (index > last_index)
1056                 return 0;
1057         if (!nr_to_tag)
1058                 return 0;
1059         if (!root_tag_get(root, iftag)) {
1060                 *first_indexp = last_index + 1;
1061                 return 0;
1062         }
1063         if (!radix_tree_is_internal_node(child)) {
1064                 *first_indexp = last_index + 1;
1065                 root_tag_set(root, settag);
1066                 return 1;
1067         }
1068 
1069         node = entry_to_node(child);
1070 
1071         for (;;) {
1072                 unsigned offset = radix_tree_descend(node, &child, index);
1073                 if (!child)
1074                         goto next;
1075                 if (!tag_get(node, iftag, offset))
1076                         goto next;
1077                 /* Sibling slots never have tags set on them */
1078                 if (radix_tree_is_internal_node(child)) {
1079                         node = entry_to_node(child);
1080                         continue;
1081                 }
1082 
1083                 /* tag the leaf */
1084                 tagged++;
1085                 tag_set(node, settag, offset);
1086 
1087                 /* walk back up the path tagging interior nodes */
1088                 parent = node;
1089                 for (;;) {
1090                         offset = parent->offset;
1091                         parent = parent->parent;
1092                         if (!parent)
1093                                 break;
1094                         /* stop if we find a node with the tag already set */
1095                         if (tag_get(parent, settag, offset))
1096                                 break;
1097                         tag_set(parent, settag, offset);
1098                 }
1099  next:
1100                 /* Go to next entry in node */
1101                 index = ((index >> node->shift) + 1) << node->shift;
1102                 /* Overflow can happen when last_index is ~0UL... */
1103                 if (index > last_index || !index)
1104                         break;
1105                 offset = (index >> node->shift) & RADIX_TREE_MAP_MASK;
1106                 while (offset == 0) {
1107                         /*
1108                          * We've fully scanned this node. Go up. Because
1109                          * last_index is guaranteed to be in the tree, what
1110                          * we do below cannot wander astray.
1111                          */
1112                         node = node->parent;
1113                         offset = (index >> node->shift) & RADIX_TREE_MAP_MASK;
1114                 }
1115                 if (is_sibling_entry(node, node->slots[offset]))
1116                         goto next;
1117                 if (tagged >= nr_to_tag)
1118                         break;
1119         }
1120         /*
1121          * We need not to tag the root tag if there is no tag which is set with
1122          * settag within the range from *first_indexp to last_index.
1123          */
1124         if (tagged > 0)
1125                 root_tag_set(root, settag);
1126         *first_indexp = index;
1127 
1128         return tagged;
1129 }
1130 EXPORT_SYMBOL(radix_tree_range_tag_if_tagged);
1131 
1132 /**
1133  *      radix_tree_gang_lookup - perform multiple lookup on a radix tree
1134  *      @root:          radix tree root
1135  *      @results:       where the results of the lookup are placed
1136  *      @first_index:   start the lookup from this key
1137  *      @max_items:     place up to this many items at *results
1138  *
1139  *      Performs an index-ascending scan of the tree for present items.  Places
1140  *      them at *@results and returns the number of items which were placed at
1141  *      *@results.
1142  *
1143  *      The implementation is naive.
1144  *
1145  *      Like radix_tree_lookup, radix_tree_gang_lookup may be called under
1146  *      rcu_read_lock. In this case, rather than the returned results being
1147  *      an atomic snapshot of the tree at a single point in time, the
1148  *      semantics of an RCU protected gang lookup are as though multiple
1149  *      radix_tree_lookups have been issued in individual locks, and results
1150  *      stored in 'results'.
1151  */
1152 unsigned int
1153 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
1154                         unsigned long first_index, unsigned int max_items)
1155 {
1156         struct radix_tree_iter iter;
1157         void **slot;
1158         unsigned int ret = 0;
1159 
1160         if (unlikely(!max_items))
1161                 return 0;
1162 
1163         radix_tree_for_each_slot(slot, root, &iter, first_index) {
1164                 results[ret] = rcu_dereference_raw(*slot);
1165                 if (!results[ret])
1166                         continue;
1167                 if (radix_tree_is_internal_node(results[ret])) {
1168                         slot = radix_tree_iter_retry(&iter);
1169                         continue;
1170                 }
1171                 if (++ret == max_items)
1172                         break;
1173         }
1174 
1175         return ret;
1176 }
1177 EXPORT_SYMBOL(radix_tree_gang_lookup);
1178 
1179 /**
1180  *      radix_tree_gang_lookup_slot - perform multiple slot lookup on radix tree
1181  *      @root:          radix tree root
1182  *      @results:       where the results of the lookup are placed
1183  *      @indices:       where their indices should be placed (but usually NULL)
1184  *      @first_index:   start the lookup from this key
1185  *      @max_items:     place up to this many items at *results
1186  *
1187  *      Performs an index-ascending scan of the tree for present items.  Places
1188  *      their slots at *@results and returns the number of items which were
1189  *      placed at *@results.
1190  *
1191  *      The implementation is naive.
1192  *
1193  *      Like radix_tree_gang_lookup as far as RCU and locking goes. Slots must
1194  *      be dereferenced with radix_tree_deref_slot, and if using only RCU
1195  *      protection, radix_tree_deref_slot may fail requiring a retry.
1196  */
1197 unsigned int
1198 radix_tree_gang_lookup_slot(struct radix_tree_root *root,
1199                         void ***results, unsigned long *indices,
1200                         unsigned long first_index, unsigned int max_items)
1201 {
1202         struct radix_tree_iter iter;
1203         void **slot;
1204         unsigned int ret = 0;
1205 
1206         if (unlikely(!max_items))
1207                 return 0;
1208 
1209         radix_tree_for_each_slot(slot, root, &iter, first_index) {
1210                 results[ret] = slot;
1211                 if (indices)
1212                         indices[ret] = iter.index;
1213                 if (++ret == max_items)
1214                         break;
1215         }
1216 
1217         return ret;
1218 }
1219 EXPORT_SYMBOL(radix_tree_gang_lookup_slot);
1220 
1221 /**
1222  *      radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
1223  *                                   based on a tag
1224  *      @root:          radix tree root
1225  *      @results:       where the results of the lookup are placed
1226  *      @first_index:   start the lookup from this key
1227  *      @max_items:     place up to this many items at *results
1228  *      @tag:           the tag index (< RADIX_TREE_MAX_TAGS)
1229  *
1230  *      Performs an index-ascending scan of the tree for present items which
1231  *      have the tag indexed by @tag set.  Places the items at *@results and
1232  *      returns the number of items which were placed at *@results.
1233  */
1234 unsigned int
1235 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
1236                 unsigned long first_index, unsigned int max_items,
1237                 unsigned int tag)
1238 {
1239         struct radix_tree_iter iter;
1240         void **slot;
1241         unsigned int ret = 0;
1242 
1243         if (unlikely(!max_items))
1244                 return 0;
1245 
1246         radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
1247                 results[ret] = rcu_dereference_raw(*slot);
1248                 if (!results[ret])
1249                         continue;
1250                 if (radix_tree_is_internal_node(results[ret])) {
1251                         slot = radix_tree_iter_retry(&iter);
1252                         continue;
1253                 }
1254                 if (++ret == max_items)
1255                         break;
1256         }
1257 
1258         return ret;
1259 }
1260 EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
1261 
1262 /**
1263  *      radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
1264  *                                        radix tree based on a tag
1265  *      @root:          radix tree root
1266  *      @results:       where the results of the lookup are placed
1267  *      @first_index:   start the lookup from this key
1268  *      @max_items:     place up to this many items at *results
1269  *      @tag:           the tag index (< RADIX_TREE_MAX_TAGS)
1270  *
1271  *      Performs an index-ascending scan of the tree for present items which
1272  *      have the tag indexed by @tag set.  Places the slots at *@results and
1273  *      returns the number of slots which were placed at *@results.
1274  */
1275 unsigned int
1276 radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
1277                 unsigned long first_index, unsigned int max_items,
1278                 unsigned int tag)
1279 {
1280         struct radix_tree_iter iter;
1281         void **slot;
1282         unsigned int ret = 0;
1283 
1284         if (unlikely(!max_items))
1285                 return 0;
1286 
1287         radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
1288                 results[ret] = slot;
1289                 if (++ret == max_items)
1290                         break;
1291         }
1292 
1293         return ret;
1294 }
1295 EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
1296 
1297 #if defined(CONFIG_SHMEM) && defined(CONFIG_SWAP)
1298 #include <linux/sched.h> /* for cond_resched() */
1299 
1300 struct locate_info {
1301         unsigned long found_index;
1302         bool stop;
1303 };
1304 
1305 /*
1306  * This linear search is at present only useful to shmem_unuse_inode().
1307  */
1308 static unsigned long __locate(struct radix_tree_node *slot, void *item,
1309                               unsigned long index, struct locate_info *info)
1310 {
1311         unsigned long i;
1312 
1313         do {
1314                 unsigned int shift = slot->shift;
1315 
1316                 for (i = (index >> shift) & RADIX_TREE_MAP_MASK;
1317                      i < RADIX_TREE_MAP_SIZE;
1318                      i++, index += (1UL << shift)) {
1319                         struct radix_tree_node *node =
1320                                         rcu_dereference_raw(slot->slots[i]);
1321                         if (node == RADIX_TREE_RETRY)
1322                                 goto out;
1323                         if (!radix_tree_is_internal_node(node)) {
1324                                 if (node == item) {
1325                                         info->found_index = index;
1326                                         info->stop = true;
1327                                         goto out;
1328                                 }
1329                                 continue;
1330                         }
1331                         node = entry_to_node(node);
1332                         if (is_sibling_entry(slot, node))
1333                                 continue;
1334                         slot = node;
1335                         break;
1336                 }
1337         } while (i < RADIX_TREE_MAP_SIZE);
1338 
1339 out:
1340         if ((index == 0) && (i == RADIX_TREE_MAP_SIZE))
1341                 info->stop = true;
1342         return index;
1343 }
1344 
1345 /**
1346  *      radix_tree_locate_item - search through radix tree for item
1347  *      @root:          radix tree root
1348  *      @item:          item to be found
1349  *
1350  *      Returns index where item was found, or -1 if not found.
1351  *      Caller must hold no lock (since this time-consuming function needs
1352  *      to be preemptible), and must check afterwards if item is still there.
1353  */
1354 unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
1355 {
1356         struct radix_tree_node *node;
1357         unsigned long max_index;
1358         unsigned long cur_index = 0;
1359         struct locate_info info = {
1360                 .found_index = -1,
1361                 .stop = false,
1362         };
1363 
1364         do {
1365                 rcu_read_lock();
1366                 node = rcu_dereference_raw(root->rnode);
1367                 if (!radix_tree_is_internal_node(node)) {
1368                         rcu_read_unlock();
1369                         if (node == item)
1370                                 info.found_index = 0;
1371                         break;
1372                 }
1373 
1374                 node = entry_to_node(node);
1375 
1376                 max_index = node_maxindex(node);
1377                 if (cur_index > max_index) {
1378                         rcu_read_unlock();
1379                         break;
1380                 }
1381 
1382                 cur_index = __locate(node, item, cur_index, &info);
1383                 rcu_read_unlock();
1384                 cond_resched();
1385         } while (!info.stop && cur_index <= max_index);
1386 
1387         return info.found_index;
1388 }
1389 #else
1390 unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
1391 {
1392         return -1;
1393 }
1394 #endif /* CONFIG_SHMEM && CONFIG_SWAP */
1395 
1396 /**
1397  *      radix_tree_shrink    -    shrink radix tree to minimum height
1398  *      @root           radix tree root
1399  */
1400 static inline bool radix_tree_shrink(struct radix_tree_root *root)
1401 {
1402         bool shrunk = false;
1403 
1404         for (;;) {
1405                 struct radix_tree_node *node = root->rnode;
1406                 struct radix_tree_node *child;
1407 
1408                 if (!radix_tree_is_internal_node(node))
1409                         break;
1410                 node = entry_to_node(node);
1411 
1412                 /*
1413                  * The candidate node has more than one child, or its child
1414                  * is not at the leftmost slot, or the child is a multiorder
1415                  * entry, we cannot shrink.
1416                  */
1417                 if (node->count != 1)
1418                         break;
1419                 child = node->slots[0];
1420                 if (!child)
1421                         break;
1422                 if (!radix_tree_is_internal_node(child) && node->shift)
1423                         break;
1424 
1425                 if (radix_tree_is_internal_node(child))
1426                         entry_to_node(child)->parent = NULL;
1427 
1428                 /*
1429                  * We don't need rcu_assign_pointer(), since we are simply
1430                  * moving the node from one part of the tree to another: if it
1431                  * was safe to dereference the old pointer to it
1432                  * (node->slots[0]), it will be safe to dereference the new
1433                  * one (root->rnode) as far as dependent read barriers go.
1434                  */
1435                 root->rnode = child;
1436 
1437                 /*
1438                  * We have a dilemma here. The node's slot[0] must not be
1439                  * NULLed in case there are concurrent lookups expecting to
1440                  * find the item. However if this was a bottom-level node,
1441                  * then it may be subject to the slot pointer being visible
1442                  * to callers dereferencing it. If item corresponding to
1443                  * slot[0] is subsequently deleted, these callers would expect
1444                  * their slot to become empty sooner or later.
1445                  *
1446                  * For example, lockless pagecache will look up a slot, deref
1447                  * the page pointer, and if the page has 0 refcount it means it
1448                  * was concurrently deleted from pagecache so try the deref
1449                  * again. Fortunately there is already a requirement for logic
1450                  * to retry the entire slot lookup -- the indirect pointer
1451                  * problem (replacing direct root node with an indirect pointer
1452                  * also results in a stale slot). So tag the slot as indirect
1453                  * to force callers to retry.
1454                  */
1455                 if (!radix_tree_is_internal_node(child))
1456                         node->slots[0] = RADIX_TREE_RETRY;
1457 
1458                 radix_tree_node_free(node);
1459                 shrunk = true;
1460         }
1461 
1462         return shrunk;
1463 }
1464 
1465 /**
1466  *      __radix_tree_delete_node    -    try to free node after clearing a slot
1467  *      @root:          radix tree root
1468  *      @node:          node containing @index
1469  *
1470  *      After clearing the slot at @index in @node from radix tree
1471  *      rooted at @root, call this function to attempt freeing the
1472  *      node and shrinking the tree.
1473  *
1474  *      Returns %true if @node was freed, %false otherwise.
1475  */
1476 bool __radix_tree_delete_node(struct radix_tree_root *root,
1477                               struct radix_tree_node *node)
1478 {
1479         bool deleted = false;
1480 
1481         do {
1482                 struct radix_tree_node *parent;
1483 
1484                 if (node->count) {
1485                         if (node == entry_to_node(root->rnode))
1486                                 deleted |= radix_tree_shrink(root);
1487                         return deleted;
1488                 }
1489 
1490                 parent = node->parent;
1491                 if (parent) {
1492                         parent->slots[node->offset] = NULL;
1493                         parent->count--;
1494                 } else {
1495                         root_tag_clear_all(root);
1496                         root->rnode = NULL;
1497                 }
1498 
1499                 radix_tree_node_free(node);
1500                 deleted = true;
1501 
1502                 node = parent;
1503         } while (node);
1504 
1505         return deleted;
1506 }
1507 
1508 static inline void delete_sibling_entries(struct radix_tree_node *node,
1509                                         void *ptr, unsigned offset)
1510 {
1511 #ifdef CONFIG_RADIX_TREE_MULTIORDER
1512         int i;
1513         for (i = 1; offset + i < RADIX_TREE_MAP_SIZE; i++) {
1514                 if (node->slots[offset + i] != ptr)
1515                         break;
1516                 node->slots[offset + i] = NULL;
1517                 node->count--;
1518         }
1519 #endif
1520 }
1521 
1522 /**
1523  *      radix_tree_delete_item    -    delete an item from a radix tree
1524  *      @root:          radix tree root
1525  *      @index:         index key
1526  *      @item:          expected item
1527  *
1528  *      Remove @item at @index from the radix tree rooted at @root.
1529  *
1530  *      Returns the address of the deleted item, or NULL if it was not present
1531  *      or the entry at the given @index was not @item.
1532  */
1533 void *radix_tree_delete_item(struct radix_tree_root *root,
1534                              unsigned long index, void *item)
1535 {
1536         struct radix_tree_node *node;
1537         unsigned int offset;
1538         void **slot;
1539         void *entry;
1540         int tag;
1541 
1542         entry = __radix_tree_lookup(root, index, &node, &slot);
1543         if (!entry)
1544                 return NULL;
1545 
1546         if (item && entry != item)
1547                 return NULL;
1548 
1549         if (!node) {
1550                 root_tag_clear_all(root);
1551                 root->rnode = NULL;
1552                 return entry;
1553         }
1554 
1555         offset = get_slot_offset(node, slot);
1556 
1557         /* Clear all tags associated with the item to be deleted.  */
1558         for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
1559                 node_tag_clear(root, node, tag, offset);
1560 
1561         delete_sibling_entries(node, node_to_entry(slot), offset);
1562         node->slots[offset] = NULL;
1563         node->count--;
1564 
1565         __radix_tree_delete_node(root, node);
1566 
1567         return entry;
1568 }
1569 EXPORT_SYMBOL(radix_tree_delete_item);
1570 
1571 /**
1572  *      radix_tree_delete    -    delete an item from a radix tree
1573  *      @root:          radix tree root
1574  *      @index:         index key
1575  *
1576  *      Remove the item at @index from the radix tree rooted at @root.
1577  *
1578  *      Returns the address of the deleted item, or NULL if it was not present.
1579  */
1580 void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
1581 {
1582         return radix_tree_delete_item(root, index, NULL);
1583 }
1584 EXPORT_SYMBOL(radix_tree_delete);
1585 
1586 void radix_tree_clear_tags(struct radix_tree_root *root,
1587                            struct radix_tree_node *node,
1588                            void **slot)
1589 {
1590         if (node) {
1591                 unsigned int tag, offset = get_slot_offset(node, slot);
1592                 for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
1593                         node_tag_clear(root, node, tag, offset);
1594         } else {
1595                 /* Clear root node tags */
1596                 root->gfp_mask &= __GFP_BITS_MASK;
1597         }
1598 }
1599 
1600 /**
1601  *      radix_tree_tagged - test whether any items in the tree are tagged
1602  *      @root:          radix tree root
1603  *      @tag:           tag to test
1604  */
1605 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)
1606 {
1607         return root_tag_get(root, tag);
1608 }
1609 EXPORT_SYMBOL(radix_tree_tagged);
1610 
1611 static void
1612 radix_tree_node_ctor(void *arg)
1613 {
1614         struct radix_tree_node *node = arg;
1615 
1616         memset(node, 0, sizeof(*node));
1617         INIT_LIST_HEAD(&node->private_list);
1618 }
1619 
1620 static __init unsigned long __maxindex(unsigned int height)
1621 {
1622         unsigned int width = height * RADIX_TREE_MAP_SHIFT;
1623         int shift = RADIX_TREE_INDEX_BITS - width;
1624 
1625         if (shift < 0)
1626                 return ~0UL;
1627         if (shift >= BITS_PER_LONG)
1628                 return 0UL;
1629         return ~0UL >> shift;
1630 }
1631 
1632 static __init void radix_tree_init_maxnodes(void)
1633 {
1634         unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH + 1];
1635         unsigned int i, j;
1636 
1637         for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
1638                 height_to_maxindex[i] = __maxindex(i);
1639         for (i = 0; i < ARRAY_SIZE(height_to_maxnodes); i++) {
1640                 for (j = i; j > 0; j--)
1641                         height_to_maxnodes[i] += height_to_maxindex[j - 1] + 1;
1642         }
1643 }
1644 
1645 static int radix_tree_callback(struct notifier_block *nfb,
1646                                 unsigned long action, void *hcpu)
1647 {
1648         int cpu = (long)hcpu;
1649         struct radix_tree_preload *rtp;
1650         struct radix_tree_node *node;
1651 
1652         /* Free per-cpu pool of preloaded nodes */
1653         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
1654                 rtp = &per_cpu(radix_tree_preloads, cpu);
1655                 while (rtp->nr) {
1656                         node = rtp->nodes;
1657                         rtp->nodes = node->private_data;
1658                         kmem_cache_free(radix_tree_node_cachep, node);
1659                         rtp->nr--;
1660                 }
1661         }
1662         return NOTIFY_OK;
1663 }
1664 
1665 void __init radix_tree_init(void)
1666 {
1667         radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
1668                         sizeof(struct radix_tree_node), 0,
1669                         SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
1670                         radix_tree_node_ctor);
1671         radix_tree_init_maxnodes();
1672         hotcpu_notifier(radix_tree_callback, 0);
1673 }
1674 

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