xref: /openbmc/linux/lib/assoc_array.c (revision b868a02e)
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Generic associative array implementation.
3  *
4  * See Documentation/core-api/assoc_array.rst for information.
5  *
6  * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
7  * Written by David Howells (dhowells@redhat.com)
8  */
9 //#define DEBUG
10 #include <linux/rcupdate.h>
11 #include <linux/slab.h>
12 #include <linux/err.h>
13 #include <linux/assoc_array_priv.h>
14 
15 /*
16  * Iterate over an associative array.  The caller must hold the RCU read lock
17  * or better.
18  */
19 static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root,
20 				       const struct assoc_array_ptr *stop,
21 				       int (*iterator)(const void *leaf,
22 						       void *iterator_data),
23 				       void *iterator_data)
24 {
25 	const struct assoc_array_shortcut *shortcut;
26 	const struct assoc_array_node *node;
27 	const struct assoc_array_ptr *cursor, *ptr, *parent;
28 	unsigned long has_meta;
29 	int slot, ret;
30 
31 	cursor = root;
32 
33 begin_node:
34 	if (assoc_array_ptr_is_shortcut(cursor)) {
35 		/* Descend through a shortcut */
36 		shortcut = assoc_array_ptr_to_shortcut(cursor);
37 		cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */
38 	}
39 
40 	node = assoc_array_ptr_to_node(cursor);
41 	slot = 0;
42 
43 	/* We perform two passes of each node.
44 	 *
45 	 * The first pass does all the leaves in this node.  This means we
46 	 * don't miss any leaves if the node is split up by insertion whilst
47 	 * we're iterating over the branches rooted here (we may, however, see
48 	 * some leaves twice).
49 	 */
50 	has_meta = 0;
51 	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
52 		ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
53 		has_meta |= (unsigned long)ptr;
54 		if (ptr && assoc_array_ptr_is_leaf(ptr)) {
55 			/* We need a barrier between the read of the pointer,
56 			 * which is supplied by the above READ_ONCE().
57 			 */
58 			/* Invoke the callback */
59 			ret = iterator(assoc_array_ptr_to_leaf(ptr),
60 				       iterator_data);
61 			if (ret)
62 				return ret;
63 		}
64 	}
65 
66 	/* The second pass attends to all the metadata pointers.  If we follow
67 	 * one of these we may find that we don't come back here, but rather go
68 	 * back to a replacement node with the leaves in a different layout.
69 	 *
70 	 * We are guaranteed to make progress, however, as the slot number for
71 	 * a particular portion of the key space cannot change - and we
72 	 * continue at the back pointer + 1.
73 	 */
74 	if (!(has_meta & ASSOC_ARRAY_PTR_META_TYPE))
75 		goto finished_node;
76 	slot = 0;
77 
78 continue_node:
79 	node = assoc_array_ptr_to_node(cursor);
80 	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
81 		ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
82 		if (assoc_array_ptr_is_meta(ptr)) {
83 			cursor = ptr;
84 			goto begin_node;
85 		}
86 	}
87 
88 finished_node:
89 	/* Move up to the parent (may need to skip back over a shortcut) */
90 	parent = READ_ONCE(node->back_pointer); /* Address dependency. */
91 	slot = node->parent_slot;
92 	if (parent == stop)
93 		return 0;
94 
95 	if (assoc_array_ptr_is_shortcut(parent)) {
96 		shortcut = assoc_array_ptr_to_shortcut(parent);
97 		cursor = parent;
98 		parent = READ_ONCE(shortcut->back_pointer); /* Address dependency. */
99 		slot = shortcut->parent_slot;
100 		if (parent == stop)
101 			return 0;
102 	}
103 
104 	/* Ascend to next slot in parent node */
105 	cursor = parent;
106 	slot++;
107 	goto continue_node;
108 }
109 
110 /**
111  * assoc_array_iterate - Pass all objects in the array to a callback
112  * @array: The array to iterate over.
113  * @iterator: The callback function.
114  * @iterator_data: Private data for the callback function.
115  *
116  * Iterate over all the objects in an associative array.  Each one will be
117  * presented to the iterator function.
118  *
119  * If the array is being modified concurrently with the iteration then it is
120  * possible that some objects in the array will be passed to the iterator
121  * callback more than once - though every object should be passed at least
122  * once.  If this is undesirable then the caller must lock against modification
123  * for the duration of this function.
124  *
125  * The function will return 0 if no objects were in the array or else it will
126  * return the result of the last iterator function called.  Iteration stops
127  * immediately if any call to the iteration function results in a non-zero
128  * return.
129  *
130  * The caller should hold the RCU read lock or better if concurrent
131  * modification is possible.
132  */
133 int assoc_array_iterate(const struct assoc_array *array,
134 			int (*iterator)(const void *object,
135 					void *iterator_data),
136 			void *iterator_data)
137 {
138 	struct assoc_array_ptr *root = READ_ONCE(array->root); /* Address dependency. */
139 
140 	if (!root)
141 		return 0;
142 	return assoc_array_subtree_iterate(root, NULL, iterator, iterator_data);
143 }
144 
145 enum assoc_array_walk_status {
146 	assoc_array_walk_tree_empty,
147 	assoc_array_walk_found_terminal_node,
148 	assoc_array_walk_found_wrong_shortcut,
149 };
150 
151 struct assoc_array_walk_result {
152 	struct {
153 		struct assoc_array_node	*node;	/* Node in which leaf might be found */
154 		int		level;
155 		int		slot;
156 	} terminal_node;
157 	struct {
158 		struct assoc_array_shortcut *shortcut;
159 		int		level;
160 		int		sc_level;
161 		unsigned long	sc_segments;
162 		unsigned long	dissimilarity;
163 	} wrong_shortcut;
164 };
165 
166 /*
167  * Navigate through the internal tree looking for the closest node to the key.
168  */
169 static enum assoc_array_walk_status
170 assoc_array_walk(const struct assoc_array *array,
171 		 const struct assoc_array_ops *ops,
172 		 const void *index_key,
173 		 struct assoc_array_walk_result *result)
174 {
175 	struct assoc_array_shortcut *shortcut;
176 	struct assoc_array_node *node;
177 	struct assoc_array_ptr *cursor, *ptr;
178 	unsigned long sc_segments, dissimilarity;
179 	unsigned long segments;
180 	int level, sc_level, next_sc_level;
181 	int slot;
182 
183 	pr_devel("-->%s()\n", __func__);
184 
185 	cursor = READ_ONCE(array->root);  /* Address dependency. */
186 	if (!cursor)
187 		return assoc_array_walk_tree_empty;
188 
189 	level = 0;
190 
191 	/* Use segments from the key for the new leaf to navigate through the
192 	 * internal tree, skipping through nodes and shortcuts that are on
193 	 * route to the destination.  Eventually we'll come to a slot that is
194 	 * either empty or contains a leaf at which point we've found a node in
195 	 * which the leaf we're looking for might be found or into which it
196 	 * should be inserted.
197 	 */
198 jumped:
199 	segments = ops->get_key_chunk(index_key, level);
200 	pr_devel("segments[%d]: %lx\n", level, segments);
201 
202 	if (assoc_array_ptr_is_shortcut(cursor))
203 		goto follow_shortcut;
204 
205 consider_node:
206 	node = assoc_array_ptr_to_node(cursor);
207 	slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
208 	slot &= ASSOC_ARRAY_FAN_MASK;
209 	ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
210 
211 	pr_devel("consider slot %x [ix=%d type=%lu]\n",
212 		 slot, level, (unsigned long)ptr & 3);
213 
214 	if (!assoc_array_ptr_is_meta(ptr)) {
215 		/* The node doesn't have a node/shortcut pointer in the slot
216 		 * corresponding to the index key that we have to follow.
217 		 */
218 		result->terminal_node.node = node;
219 		result->terminal_node.level = level;
220 		result->terminal_node.slot = slot;
221 		pr_devel("<--%s() = terminal_node\n", __func__);
222 		return assoc_array_walk_found_terminal_node;
223 	}
224 
225 	if (assoc_array_ptr_is_node(ptr)) {
226 		/* There is a pointer to a node in the slot corresponding to
227 		 * this index key segment, so we need to follow it.
228 		 */
229 		cursor = ptr;
230 		level += ASSOC_ARRAY_LEVEL_STEP;
231 		if ((level & ASSOC_ARRAY_KEY_CHUNK_MASK) != 0)
232 			goto consider_node;
233 		goto jumped;
234 	}
235 
236 	/* There is a shortcut in the slot corresponding to the index key
237 	 * segment.  We follow the shortcut if its partial index key matches
238 	 * this leaf's.  Otherwise we need to split the shortcut.
239 	 */
240 	cursor = ptr;
241 follow_shortcut:
242 	shortcut = assoc_array_ptr_to_shortcut(cursor);
243 	pr_devel("shortcut to %d\n", shortcut->skip_to_level);
244 	sc_level = level + ASSOC_ARRAY_LEVEL_STEP;
245 	BUG_ON(sc_level > shortcut->skip_to_level);
246 
247 	do {
248 		/* Check the leaf against the shortcut's index key a word at a
249 		 * time, trimming the final word (the shortcut stores the index
250 		 * key completely from the root to the shortcut's target).
251 		 */
252 		if ((sc_level & ASSOC_ARRAY_KEY_CHUNK_MASK) == 0)
253 			segments = ops->get_key_chunk(index_key, sc_level);
254 
255 		sc_segments = shortcut->index_key[sc_level >> ASSOC_ARRAY_KEY_CHUNK_SHIFT];
256 		dissimilarity = segments ^ sc_segments;
257 
258 		if (round_up(sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE) > shortcut->skip_to_level) {
259 			/* Trim segments that are beyond the shortcut */
260 			int shift = shortcut->skip_to_level & ASSOC_ARRAY_KEY_CHUNK_MASK;
261 			dissimilarity &= ~(ULONG_MAX << shift);
262 			next_sc_level = shortcut->skip_to_level;
263 		} else {
264 			next_sc_level = sc_level + ASSOC_ARRAY_KEY_CHUNK_SIZE;
265 			next_sc_level = round_down(next_sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
266 		}
267 
268 		if (dissimilarity != 0) {
269 			/* This shortcut points elsewhere */
270 			result->wrong_shortcut.shortcut = shortcut;
271 			result->wrong_shortcut.level = level;
272 			result->wrong_shortcut.sc_level = sc_level;
273 			result->wrong_shortcut.sc_segments = sc_segments;
274 			result->wrong_shortcut.dissimilarity = dissimilarity;
275 			return assoc_array_walk_found_wrong_shortcut;
276 		}
277 
278 		sc_level = next_sc_level;
279 	} while (sc_level < shortcut->skip_to_level);
280 
281 	/* The shortcut matches the leaf's index to this point. */
282 	cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */
283 	if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) {
284 		level = sc_level;
285 		goto jumped;
286 	} else {
287 		level = sc_level;
288 		goto consider_node;
289 	}
290 }
291 
292 /**
293  * assoc_array_find - Find an object by index key
294  * @array: The associative array to search.
295  * @ops: The operations to use.
296  * @index_key: The key to the object.
297  *
298  * Find an object in an associative array by walking through the internal tree
299  * to the node that should contain the object and then searching the leaves
300  * there.  NULL is returned if the requested object was not found in the array.
301  *
302  * The caller must hold the RCU read lock or better.
303  */
304 void *assoc_array_find(const struct assoc_array *array,
305 		       const struct assoc_array_ops *ops,
306 		       const void *index_key)
307 {
308 	struct assoc_array_walk_result result;
309 	const struct assoc_array_node *node;
310 	const struct assoc_array_ptr *ptr;
311 	const void *leaf;
312 	int slot;
313 
314 	if (assoc_array_walk(array, ops, index_key, &result) !=
315 	    assoc_array_walk_found_terminal_node)
316 		return NULL;
317 
318 	node = result.terminal_node.node;
319 
320 	/* If the target key is available to us, it's has to be pointed to by
321 	 * the terminal node.
322 	 */
323 	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
324 		ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
325 		if (ptr && assoc_array_ptr_is_leaf(ptr)) {
326 			/* We need a barrier between the read of the pointer
327 			 * and dereferencing the pointer - but only if we are
328 			 * actually going to dereference it.
329 			 */
330 			leaf = assoc_array_ptr_to_leaf(ptr);
331 			if (ops->compare_object(leaf, index_key))
332 				return (void *)leaf;
333 		}
334 	}
335 
336 	return NULL;
337 }
338 
339 /*
340  * Destructively iterate over an associative array.  The caller must prevent
341  * other simultaneous accesses.
342  */
343 static void assoc_array_destroy_subtree(struct assoc_array_ptr *root,
344 					const struct assoc_array_ops *ops)
345 {
346 	struct assoc_array_shortcut *shortcut;
347 	struct assoc_array_node *node;
348 	struct assoc_array_ptr *cursor, *parent = NULL;
349 	int slot = -1;
350 
351 	pr_devel("-->%s()\n", __func__);
352 
353 	cursor = root;
354 	if (!cursor) {
355 		pr_devel("empty\n");
356 		return;
357 	}
358 
359 move_to_meta:
360 	if (assoc_array_ptr_is_shortcut(cursor)) {
361 		/* Descend through a shortcut */
362 		pr_devel("[%d] shortcut\n", slot);
363 		BUG_ON(!assoc_array_ptr_is_shortcut(cursor));
364 		shortcut = assoc_array_ptr_to_shortcut(cursor);
365 		BUG_ON(shortcut->back_pointer != parent);
366 		BUG_ON(slot != -1 && shortcut->parent_slot != slot);
367 		parent = cursor;
368 		cursor = shortcut->next_node;
369 		slot = -1;
370 		BUG_ON(!assoc_array_ptr_is_node(cursor));
371 	}
372 
373 	pr_devel("[%d] node\n", slot);
374 	node = assoc_array_ptr_to_node(cursor);
375 	BUG_ON(node->back_pointer != parent);
376 	BUG_ON(slot != -1 && node->parent_slot != slot);
377 	slot = 0;
378 
379 continue_node:
380 	pr_devel("Node %p [back=%p]\n", node, node->back_pointer);
381 	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
382 		struct assoc_array_ptr *ptr = node->slots[slot];
383 		if (!ptr)
384 			continue;
385 		if (assoc_array_ptr_is_meta(ptr)) {
386 			parent = cursor;
387 			cursor = ptr;
388 			goto move_to_meta;
389 		}
390 
391 		if (ops) {
392 			pr_devel("[%d] free leaf\n", slot);
393 			ops->free_object(assoc_array_ptr_to_leaf(ptr));
394 		}
395 	}
396 
397 	parent = node->back_pointer;
398 	slot = node->parent_slot;
399 	pr_devel("free node\n");
400 	kfree(node);
401 	if (!parent)
402 		return; /* Done */
403 
404 	/* Move back up to the parent (may need to free a shortcut on
405 	 * the way up) */
406 	if (assoc_array_ptr_is_shortcut(parent)) {
407 		shortcut = assoc_array_ptr_to_shortcut(parent);
408 		BUG_ON(shortcut->next_node != cursor);
409 		cursor = parent;
410 		parent = shortcut->back_pointer;
411 		slot = shortcut->parent_slot;
412 		pr_devel("free shortcut\n");
413 		kfree(shortcut);
414 		if (!parent)
415 			return;
416 
417 		BUG_ON(!assoc_array_ptr_is_node(parent));
418 	}
419 
420 	/* Ascend to next slot in parent node */
421 	pr_devel("ascend to %p[%d]\n", parent, slot);
422 	cursor = parent;
423 	node = assoc_array_ptr_to_node(cursor);
424 	slot++;
425 	goto continue_node;
426 }
427 
428 /**
429  * assoc_array_destroy - Destroy an associative array
430  * @array: The array to destroy.
431  * @ops: The operations to use.
432  *
433  * Discard all metadata and free all objects in an associative array.  The
434  * array will be empty and ready to use again upon completion.  This function
435  * cannot fail.
436  *
437  * The caller must prevent all other accesses whilst this takes place as no
438  * attempt is made to adjust pointers gracefully to permit RCU readlock-holding
439  * accesses to continue.  On the other hand, no memory allocation is required.
440  */
441 void assoc_array_destroy(struct assoc_array *array,
442 			 const struct assoc_array_ops *ops)
443 {
444 	assoc_array_destroy_subtree(array->root, ops);
445 	array->root = NULL;
446 }
447 
448 /*
449  * Handle insertion into an empty tree.
450  */
451 static bool assoc_array_insert_in_empty_tree(struct assoc_array_edit *edit)
452 {
453 	struct assoc_array_node *new_n0;
454 
455 	pr_devel("-->%s()\n", __func__);
456 
457 	new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
458 	if (!new_n0)
459 		return false;
460 
461 	edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
462 	edit->leaf_p = &new_n0->slots[0];
463 	edit->adjust_count_on = new_n0;
464 	edit->set[0].ptr = &edit->array->root;
465 	edit->set[0].to = assoc_array_node_to_ptr(new_n0);
466 
467 	pr_devel("<--%s() = ok [no root]\n", __func__);
468 	return true;
469 }
470 
471 /*
472  * Handle insertion into a terminal node.
473  */
474 static bool assoc_array_insert_into_terminal_node(struct assoc_array_edit *edit,
475 						  const struct assoc_array_ops *ops,
476 						  const void *index_key,
477 						  struct assoc_array_walk_result *result)
478 {
479 	struct assoc_array_shortcut *shortcut, *new_s0;
480 	struct assoc_array_node *node, *new_n0, *new_n1, *side;
481 	struct assoc_array_ptr *ptr;
482 	unsigned long dissimilarity, base_seg, blank;
483 	size_t keylen;
484 	bool have_meta;
485 	int level, diff;
486 	int slot, next_slot, free_slot, i, j;
487 
488 	node	= result->terminal_node.node;
489 	level	= result->terminal_node.level;
490 	edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = result->terminal_node.slot;
491 
492 	pr_devel("-->%s()\n", __func__);
493 
494 	/* We arrived at a node which doesn't have an onward node or shortcut
495 	 * pointer that we have to follow.  This means that (a) the leaf we
496 	 * want must go here (either by insertion or replacement) or (b) we
497 	 * need to split this node and insert in one of the fragments.
498 	 */
499 	free_slot = -1;
500 
501 	/* Firstly, we have to check the leaves in this node to see if there's
502 	 * a matching one we should replace in place.
503 	 */
504 	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
505 		ptr = node->slots[i];
506 		if (!ptr) {
507 			free_slot = i;
508 			continue;
509 		}
510 		if (assoc_array_ptr_is_leaf(ptr) &&
511 		    ops->compare_object(assoc_array_ptr_to_leaf(ptr),
512 					index_key)) {
513 			pr_devel("replace in slot %d\n", i);
514 			edit->leaf_p = &node->slots[i];
515 			edit->dead_leaf = node->slots[i];
516 			pr_devel("<--%s() = ok [replace]\n", __func__);
517 			return true;
518 		}
519 	}
520 
521 	/* If there is a free slot in this node then we can just insert the
522 	 * leaf here.
523 	 */
524 	if (free_slot >= 0) {
525 		pr_devel("insert in free slot %d\n", free_slot);
526 		edit->leaf_p = &node->slots[free_slot];
527 		edit->adjust_count_on = node;
528 		pr_devel("<--%s() = ok [insert]\n", __func__);
529 		return true;
530 	}
531 
532 	/* The node has no spare slots - so we're either going to have to split
533 	 * it or insert another node before it.
534 	 *
535 	 * Whatever, we're going to need at least two new nodes - so allocate
536 	 * those now.  We may also need a new shortcut, but we deal with that
537 	 * when we need it.
538 	 */
539 	new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
540 	if (!new_n0)
541 		return false;
542 	edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
543 	new_n1 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
544 	if (!new_n1)
545 		return false;
546 	edit->new_meta[1] = assoc_array_node_to_ptr(new_n1);
547 
548 	/* We need to find out how similar the leaves are. */
549 	pr_devel("no spare slots\n");
550 	have_meta = false;
551 	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
552 		ptr = node->slots[i];
553 		if (assoc_array_ptr_is_meta(ptr)) {
554 			edit->segment_cache[i] = 0xff;
555 			have_meta = true;
556 			continue;
557 		}
558 		base_seg = ops->get_object_key_chunk(
559 			assoc_array_ptr_to_leaf(ptr), level);
560 		base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
561 		edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
562 	}
563 
564 	if (have_meta) {
565 		pr_devel("have meta\n");
566 		goto split_node;
567 	}
568 
569 	/* The node contains only leaves */
570 	dissimilarity = 0;
571 	base_seg = edit->segment_cache[0];
572 	for (i = 1; i < ASSOC_ARRAY_FAN_OUT; i++)
573 		dissimilarity |= edit->segment_cache[i] ^ base_seg;
574 
575 	pr_devel("only leaves; dissimilarity=%lx\n", dissimilarity);
576 
577 	if ((dissimilarity & ASSOC_ARRAY_FAN_MASK) == 0) {
578 		/* The old leaves all cluster in the same slot.  We will need
579 		 * to insert a shortcut if the new node wants to cluster with them.
580 		 */
581 		if ((edit->segment_cache[ASSOC_ARRAY_FAN_OUT] ^ base_seg) == 0)
582 			goto all_leaves_cluster_together;
583 
584 		/* Otherwise all the old leaves cluster in the same slot, but
585 		 * the new leaf wants to go into a different slot - so we
586 		 * create a new node (n0) to hold the new leaf and a pointer to
587 		 * a new node (n1) holding all the old leaves.
588 		 *
589 		 * This can be done by falling through to the node splitting
590 		 * path.
591 		 */
592 		pr_devel("present leaves cluster but not new leaf\n");
593 	}
594 
595 split_node:
596 	pr_devel("split node\n");
597 
598 	/* We need to split the current node.  The node must contain anything
599 	 * from a single leaf (in the one leaf case, this leaf will cluster
600 	 * with the new leaf) and the rest meta-pointers, to all leaves, some
601 	 * of which may cluster.
602 	 *
603 	 * It won't contain the case in which all the current leaves plus the
604 	 * new leaves want to cluster in the same slot.
605 	 *
606 	 * We need to expel at least two leaves out of a set consisting of the
607 	 * leaves in the node and the new leaf.  The current meta pointers can
608 	 * just be copied as they shouldn't cluster with any of the leaves.
609 	 *
610 	 * We need a new node (n0) to replace the current one and a new node to
611 	 * take the expelled nodes (n1).
612 	 */
613 	edit->set[0].to = assoc_array_node_to_ptr(new_n0);
614 	new_n0->back_pointer = node->back_pointer;
615 	new_n0->parent_slot = node->parent_slot;
616 	new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
617 	new_n1->parent_slot = -1; /* Need to calculate this */
618 
619 do_split_node:
620 	pr_devel("do_split_node\n");
621 
622 	new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
623 	new_n1->nr_leaves_on_branch = 0;
624 
625 	/* Begin by finding two matching leaves.  There have to be at least two
626 	 * that match - even if there are meta pointers - because any leaf that
627 	 * would match a slot with a meta pointer in it must be somewhere
628 	 * behind that meta pointer and cannot be here.  Further, given N
629 	 * remaining leaf slots, we now have N+1 leaves to go in them.
630 	 */
631 	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
632 		slot = edit->segment_cache[i];
633 		if (slot != 0xff)
634 			for (j = i + 1; j < ASSOC_ARRAY_FAN_OUT + 1; j++)
635 				if (edit->segment_cache[j] == slot)
636 					goto found_slot_for_multiple_occupancy;
637 	}
638 found_slot_for_multiple_occupancy:
639 	pr_devel("same slot: %x %x [%02x]\n", i, j, slot);
640 	BUG_ON(i >= ASSOC_ARRAY_FAN_OUT);
641 	BUG_ON(j >= ASSOC_ARRAY_FAN_OUT + 1);
642 	BUG_ON(slot >= ASSOC_ARRAY_FAN_OUT);
643 
644 	new_n1->parent_slot = slot;
645 
646 	/* Metadata pointers cannot change slot */
647 	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
648 		if (assoc_array_ptr_is_meta(node->slots[i]))
649 			new_n0->slots[i] = node->slots[i];
650 		else
651 			new_n0->slots[i] = NULL;
652 	BUG_ON(new_n0->slots[slot] != NULL);
653 	new_n0->slots[slot] = assoc_array_node_to_ptr(new_n1);
654 
655 	/* Filter the leaf pointers between the new nodes */
656 	free_slot = -1;
657 	next_slot = 0;
658 	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
659 		if (assoc_array_ptr_is_meta(node->slots[i]))
660 			continue;
661 		if (edit->segment_cache[i] == slot) {
662 			new_n1->slots[next_slot++] = node->slots[i];
663 			new_n1->nr_leaves_on_branch++;
664 		} else {
665 			do {
666 				free_slot++;
667 			} while (new_n0->slots[free_slot] != NULL);
668 			new_n0->slots[free_slot] = node->slots[i];
669 		}
670 	}
671 
672 	pr_devel("filtered: f=%x n=%x\n", free_slot, next_slot);
673 
674 	if (edit->segment_cache[ASSOC_ARRAY_FAN_OUT] != slot) {
675 		do {
676 			free_slot++;
677 		} while (new_n0->slots[free_slot] != NULL);
678 		edit->leaf_p = &new_n0->slots[free_slot];
679 		edit->adjust_count_on = new_n0;
680 	} else {
681 		edit->leaf_p = &new_n1->slots[next_slot++];
682 		edit->adjust_count_on = new_n1;
683 	}
684 
685 	BUG_ON(next_slot <= 1);
686 
687 	edit->set_backpointers_to = assoc_array_node_to_ptr(new_n0);
688 	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
689 		if (edit->segment_cache[i] == 0xff) {
690 			ptr = node->slots[i];
691 			BUG_ON(assoc_array_ptr_is_leaf(ptr));
692 			if (assoc_array_ptr_is_node(ptr)) {
693 				side = assoc_array_ptr_to_node(ptr);
694 				edit->set_backpointers[i] = &side->back_pointer;
695 			} else {
696 				shortcut = assoc_array_ptr_to_shortcut(ptr);
697 				edit->set_backpointers[i] = &shortcut->back_pointer;
698 			}
699 		}
700 	}
701 
702 	ptr = node->back_pointer;
703 	if (!ptr)
704 		edit->set[0].ptr = &edit->array->root;
705 	else if (assoc_array_ptr_is_node(ptr))
706 		edit->set[0].ptr = &assoc_array_ptr_to_node(ptr)->slots[node->parent_slot];
707 	else
708 		edit->set[0].ptr = &assoc_array_ptr_to_shortcut(ptr)->next_node;
709 	edit->excised_meta[0] = assoc_array_node_to_ptr(node);
710 	pr_devel("<--%s() = ok [split node]\n", __func__);
711 	return true;
712 
713 all_leaves_cluster_together:
714 	/* All the leaves, new and old, want to cluster together in this node
715 	 * in the same slot, so we have to replace this node with a shortcut to
716 	 * skip over the identical parts of the key and then place a pair of
717 	 * nodes, one inside the other, at the end of the shortcut and
718 	 * distribute the keys between them.
719 	 *
720 	 * Firstly we need to work out where the leaves start diverging as a
721 	 * bit position into their keys so that we know how big the shortcut
722 	 * needs to be.
723 	 *
724 	 * We only need to make a single pass of N of the N+1 leaves because if
725 	 * any keys differ between themselves at bit X then at least one of
726 	 * them must also differ with the base key at bit X or before.
727 	 */
728 	pr_devel("all leaves cluster together\n");
729 	diff = INT_MAX;
730 	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
731 		int x = ops->diff_objects(assoc_array_ptr_to_leaf(node->slots[i]),
732 					  index_key);
733 		if (x < diff) {
734 			BUG_ON(x < 0);
735 			diff = x;
736 		}
737 	}
738 	BUG_ON(diff == INT_MAX);
739 	BUG_ON(diff < level + ASSOC_ARRAY_LEVEL_STEP);
740 
741 	keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
742 	keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
743 
744 	new_s0 = kzalloc(struct_size(new_s0, index_key, keylen), GFP_KERNEL);
745 	if (!new_s0)
746 		return false;
747 	edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s0);
748 
749 	edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
750 	new_s0->back_pointer = node->back_pointer;
751 	new_s0->parent_slot = node->parent_slot;
752 	new_s0->next_node = assoc_array_node_to_ptr(new_n0);
753 	new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
754 	new_n0->parent_slot = 0;
755 	new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
756 	new_n1->parent_slot = -1; /* Need to calculate this */
757 
758 	new_s0->skip_to_level = level = diff & ~ASSOC_ARRAY_LEVEL_STEP_MASK;
759 	pr_devel("skip_to_level = %d [diff %d]\n", level, diff);
760 	BUG_ON(level <= 0);
761 
762 	for (i = 0; i < keylen; i++)
763 		new_s0->index_key[i] =
764 			ops->get_key_chunk(index_key, i * ASSOC_ARRAY_KEY_CHUNK_SIZE);
765 
766 	if (level & ASSOC_ARRAY_KEY_CHUNK_MASK) {
767 		blank = ULONG_MAX << (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
768 		pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, level, blank);
769 		new_s0->index_key[keylen - 1] &= ~blank;
770 	}
771 
772 	/* This now reduces to a node splitting exercise for which we'll need
773 	 * to regenerate the disparity table.
774 	 */
775 	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
776 		ptr = node->slots[i];
777 		base_seg = ops->get_object_key_chunk(assoc_array_ptr_to_leaf(ptr),
778 						     level);
779 		base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
780 		edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
781 	}
782 
783 	base_seg = ops->get_key_chunk(index_key, level);
784 	base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
785 	edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = base_seg & ASSOC_ARRAY_FAN_MASK;
786 	goto do_split_node;
787 }
788 
789 /*
790  * Handle insertion into the middle of a shortcut.
791  */
792 static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
793 					    const struct assoc_array_ops *ops,
794 					    struct assoc_array_walk_result *result)
795 {
796 	struct assoc_array_shortcut *shortcut, *new_s0, *new_s1;
797 	struct assoc_array_node *node, *new_n0, *side;
798 	unsigned long sc_segments, dissimilarity, blank;
799 	size_t keylen;
800 	int level, sc_level, diff;
801 	int sc_slot;
802 
803 	shortcut	= result->wrong_shortcut.shortcut;
804 	level		= result->wrong_shortcut.level;
805 	sc_level	= result->wrong_shortcut.sc_level;
806 	sc_segments	= result->wrong_shortcut.sc_segments;
807 	dissimilarity	= result->wrong_shortcut.dissimilarity;
808 
809 	pr_devel("-->%s(ix=%d dis=%lx scix=%d)\n",
810 		 __func__, level, dissimilarity, sc_level);
811 
812 	/* We need to split a shortcut and insert a node between the two
813 	 * pieces.  Zero-length pieces will be dispensed with entirely.
814 	 *
815 	 * First of all, we need to find out in which level the first
816 	 * difference was.
817 	 */
818 	diff = __ffs(dissimilarity);
819 	diff &= ~ASSOC_ARRAY_LEVEL_STEP_MASK;
820 	diff += sc_level & ~ASSOC_ARRAY_KEY_CHUNK_MASK;
821 	pr_devel("diff=%d\n", diff);
822 
823 	if (!shortcut->back_pointer) {
824 		edit->set[0].ptr = &edit->array->root;
825 	} else if (assoc_array_ptr_is_node(shortcut->back_pointer)) {
826 		node = assoc_array_ptr_to_node(shortcut->back_pointer);
827 		edit->set[0].ptr = &node->slots[shortcut->parent_slot];
828 	} else {
829 		BUG();
830 	}
831 
832 	edit->excised_meta[0] = assoc_array_shortcut_to_ptr(shortcut);
833 
834 	/* Create a new node now since we're going to need it anyway */
835 	new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
836 	if (!new_n0)
837 		return false;
838 	edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
839 	edit->adjust_count_on = new_n0;
840 
841 	/* Insert a new shortcut before the new node if this segment isn't of
842 	 * zero length - otherwise we just connect the new node directly to the
843 	 * parent.
844 	 */
845 	level += ASSOC_ARRAY_LEVEL_STEP;
846 	if (diff > level) {
847 		pr_devel("pre-shortcut %d...%d\n", level, diff);
848 		keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
849 		keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
850 
851 		new_s0 = kzalloc(struct_size(new_s0, index_key, keylen),
852 				 GFP_KERNEL);
853 		if (!new_s0)
854 			return false;
855 		edit->new_meta[1] = assoc_array_shortcut_to_ptr(new_s0);
856 		edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
857 		new_s0->back_pointer = shortcut->back_pointer;
858 		new_s0->parent_slot = shortcut->parent_slot;
859 		new_s0->next_node = assoc_array_node_to_ptr(new_n0);
860 		new_s0->skip_to_level = diff;
861 
862 		new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
863 		new_n0->parent_slot = 0;
864 
865 		memcpy(new_s0->index_key, shortcut->index_key,
866 		       flex_array_size(new_s0, index_key, keylen));
867 
868 		blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
869 		pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank);
870 		new_s0->index_key[keylen - 1] &= ~blank;
871 	} else {
872 		pr_devel("no pre-shortcut\n");
873 		edit->set[0].to = assoc_array_node_to_ptr(new_n0);
874 		new_n0->back_pointer = shortcut->back_pointer;
875 		new_n0->parent_slot = shortcut->parent_slot;
876 	}
877 
878 	side = assoc_array_ptr_to_node(shortcut->next_node);
879 	new_n0->nr_leaves_on_branch = side->nr_leaves_on_branch;
880 
881 	/* We need to know which slot in the new node is going to take a
882 	 * metadata pointer.
883 	 */
884 	sc_slot = sc_segments >> (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
885 	sc_slot &= ASSOC_ARRAY_FAN_MASK;
886 
887 	pr_devel("new slot %lx >> %d -> %d\n",
888 		 sc_segments, diff & ASSOC_ARRAY_KEY_CHUNK_MASK, sc_slot);
889 
890 	/* Determine whether we need to follow the new node with a replacement
891 	 * for the current shortcut.  We could in theory reuse the current
892 	 * shortcut if its parent slot number doesn't change - but that's a
893 	 * 1-in-16 chance so not worth expending the code upon.
894 	 */
895 	level = diff + ASSOC_ARRAY_LEVEL_STEP;
896 	if (level < shortcut->skip_to_level) {
897 		pr_devel("post-shortcut %d...%d\n", level, shortcut->skip_to_level);
898 		keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
899 		keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
900 
901 		new_s1 = kzalloc(struct_size(new_s1, index_key, keylen),
902 				 GFP_KERNEL);
903 		if (!new_s1)
904 			return false;
905 		edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s1);
906 
907 		new_s1->back_pointer = assoc_array_node_to_ptr(new_n0);
908 		new_s1->parent_slot = sc_slot;
909 		new_s1->next_node = shortcut->next_node;
910 		new_s1->skip_to_level = shortcut->skip_to_level;
911 
912 		new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(new_s1);
913 
914 		memcpy(new_s1->index_key, shortcut->index_key,
915 		       flex_array_size(new_s1, index_key, keylen));
916 
917 		edit->set[1].ptr = &side->back_pointer;
918 		edit->set[1].to = assoc_array_shortcut_to_ptr(new_s1);
919 	} else {
920 		pr_devel("no post-shortcut\n");
921 
922 		/* We don't have to replace the pointed-to node as long as we
923 		 * use memory barriers to make sure the parent slot number is
924 		 * changed before the back pointer (the parent slot number is
925 		 * irrelevant to the old parent shortcut).
926 		 */
927 		new_n0->slots[sc_slot] = shortcut->next_node;
928 		edit->set_parent_slot[0].p = &side->parent_slot;
929 		edit->set_parent_slot[0].to = sc_slot;
930 		edit->set[1].ptr = &side->back_pointer;
931 		edit->set[1].to = assoc_array_node_to_ptr(new_n0);
932 	}
933 
934 	/* Install the new leaf in a spare slot in the new node. */
935 	if (sc_slot == 0)
936 		edit->leaf_p = &new_n0->slots[1];
937 	else
938 		edit->leaf_p = &new_n0->slots[0];
939 
940 	pr_devel("<--%s() = ok [split shortcut]\n", __func__);
941 	return edit;
942 }
943 
944 /**
945  * assoc_array_insert - Script insertion of an object into an associative array
946  * @array: The array to insert into.
947  * @ops: The operations to use.
948  * @index_key: The key to insert at.
949  * @object: The object to insert.
950  *
951  * Precalculate and preallocate a script for the insertion or replacement of an
952  * object in an associative array.  This results in an edit script that can
953  * either be applied or cancelled.
954  *
955  * The function returns a pointer to an edit script or -ENOMEM.
956  *
957  * The caller should lock against other modifications and must continue to hold
958  * the lock until assoc_array_apply_edit() has been called.
959  *
960  * Accesses to the tree may take place concurrently with this function,
961  * provided they hold the RCU read lock.
962  */
963 struct assoc_array_edit *assoc_array_insert(struct assoc_array *array,
964 					    const struct assoc_array_ops *ops,
965 					    const void *index_key,
966 					    void *object)
967 {
968 	struct assoc_array_walk_result result;
969 	struct assoc_array_edit *edit;
970 
971 	pr_devel("-->%s()\n", __func__);
972 
973 	/* The leaf pointer we're given must not have the bottom bit set as we
974 	 * use those for type-marking the pointer.  NULL pointers are also not
975 	 * allowed as they indicate an empty slot but we have to allow them
976 	 * here as they can be updated later.
977 	 */
978 	BUG_ON(assoc_array_ptr_is_meta(object));
979 
980 	edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
981 	if (!edit)
982 		return ERR_PTR(-ENOMEM);
983 	edit->array = array;
984 	edit->ops = ops;
985 	edit->leaf = assoc_array_leaf_to_ptr(object);
986 	edit->adjust_count_by = 1;
987 
988 	switch (assoc_array_walk(array, ops, index_key, &result)) {
989 	case assoc_array_walk_tree_empty:
990 		/* Allocate a root node if there isn't one yet */
991 		if (!assoc_array_insert_in_empty_tree(edit))
992 			goto enomem;
993 		return edit;
994 
995 	case assoc_array_walk_found_terminal_node:
996 		/* We found a node that doesn't have a node/shortcut pointer in
997 		 * the slot corresponding to the index key that we have to
998 		 * follow.
999 		 */
1000 		if (!assoc_array_insert_into_terminal_node(edit, ops, index_key,
1001 							   &result))
1002 			goto enomem;
1003 		return edit;
1004 
1005 	case assoc_array_walk_found_wrong_shortcut:
1006 		/* We found a shortcut that didn't match our key in a slot we
1007 		 * needed to follow.
1008 		 */
1009 		if (!assoc_array_insert_mid_shortcut(edit, ops, &result))
1010 			goto enomem;
1011 		return edit;
1012 	}
1013 
1014 enomem:
1015 	/* Clean up after an out of memory error */
1016 	pr_devel("enomem\n");
1017 	assoc_array_cancel_edit(edit);
1018 	return ERR_PTR(-ENOMEM);
1019 }
1020 
1021 /**
1022  * assoc_array_insert_set_object - Set the new object pointer in an edit script
1023  * @edit: The edit script to modify.
1024  * @object: The object pointer to set.
1025  *
1026  * Change the object to be inserted in an edit script.  The object pointed to
1027  * by the old object is not freed.  This must be done prior to applying the
1028  * script.
1029  */
1030 void assoc_array_insert_set_object(struct assoc_array_edit *edit, void *object)
1031 {
1032 	BUG_ON(!object);
1033 	edit->leaf = assoc_array_leaf_to_ptr(object);
1034 }
1035 
1036 struct assoc_array_delete_collapse_context {
1037 	struct assoc_array_node	*node;
1038 	const void		*skip_leaf;
1039 	int			slot;
1040 };
1041 
1042 /*
1043  * Subtree collapse to node iterator.
1044  */
1045 static int assoc_array_delete_collapse_iterator(const void *leaf,
1046 						void *iterator_data)
1047 {
1048 	struct assoc_array_delete_collapse_context *collapse = iterator_data;
1049 
1050 	if (leaf == collapse->skip_leaf)
1051 		return 0;
1052 
1053 	BUG_ON(collapse->slot >= ASSOC_ARRAY_FAN_OUT);
1054 
1055 	collapse->node->slots[collapse->slot++] = assoc_array_leaf_to_ptr(leaf);
1056 	return 0;
1057 }
1058 
1059 /**
1060  * assoc_array_delete - Script deletion of an object from an associative array
1061  * @array: The array to search.
1062  * @ops: The operations to use.
1063  * @index_key: The key to the object.
1064  *
1065  * Precalculate and preallocate a script for the deletion of an object from an
1066  * associative array.  This results in an edit script that can either be
1067  * applied or cancelled.
1068  *
1069  * The function returns a pointer to an edit script if the object was found,
1070  * NULL if the object was not found or -ENOMEM.
1071  *
1072  * The caller should lock against other modifications and must continue to hold
1073  * the lock until assoc_array_apply_edit() has been called.
1074  *
1075  * Accesses to the tree may take place concurrently with this function,
1076  * provided they hold the RCU read lock.
1077  */
1078 struct assoc_array_edit *assoc_array_delete(struct assoc_array *array,
1079 					    const struct assoc_array_ops *ops,
1080 					    const void *index_key)
1081 {
1082 	struct assoc_array_delete_collapse_context collapse;
1083 	struct assoc_array_walk_result result;
1084 	struct assoc_array_node *node, *new_n0;
1085 	struct assoc_array_edit *edit;
1086 	struct assoc_array_ptr *ptr;
1087 	bool has_meta;
1088 	int slot, i;
1089 
1090 	pr_devel("-->%s()\n", __func__);
1091 
1092 	edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1093 	if (!edit)
1094 		return ERR_PTR(-ENOMEM);
1095 	edit->array = array;
1096 	edit->ops = ops;
1097 	edit->adjust_count_by = -1;
1098 
1099 	switch (assoc_array_walk(array, ops, index_key, &result)) {
1100 	case assoc_array_walk_found_terminal_node:
1101 		/* We found a node that should contain the leaf we've been
1102 		 * asked to remove - *if* it's in the tree.
1103 		 */
1104 		pr_devel("terminal_node\n");
1105 		node = result.terminal_node.node;
1106 
1107 		for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1108 			ptr = node->slots[slot];
1109 			if (ptr &&
1110 			    assoc_array_ptr_is_leaf(ptr) &&
1111 			    ops->compare_object(assoc_array_ptr_to_leaf(ptr),
1112 						index_key))
1113 				goto found_leaf;
1114 		}
1115 		fallthrough;
1116 	case assoc_array_walk_tree_empty:
1117 	case assoc_array_walk_found_wrong_shortcut:
1118 	default:
1119 		assoc_array_cancel_edit(edit);
1120 		pr_devel("not found\n");
1121 		return NULL;
1122 	}
1123 
1124 found_leaf:
1125 	BUG_ON(array->nr_leaves_on_tree <= 0);
1126 
1127 	/* In the simplest form of deletion we just clear the slot and release
1128 	 * the leaf after a suitable interval.
1129 	 */
1130 	edit->dead_leaf = node->slots[slot];
1131 	edit->set[0].ptr = &node->slots[slot];
1132 	edit->set[0].to = NULL;
1133 	edit->adjust_count_on = node;
1134 
1135 	/* If that concludes erasure of the last leaf, then delete the entire
1136 	 * internal array.
1137 	 */
1138 	if (array->nr_leaves_on_tree == 1) {
1139 		edit->set[1].ptr = &array->root;
1140 		edit->set[1].to = NULL;
1141 		edit->adjust_count_on = NULL;
1142 		edit->excised_subtree = array->root;
1143 		pr_devel("all gone\n");
1144 		return edit;
1145 	}
1146 
1147 	/* However, we'd also like to clear up some metadata blocks if we
1148 	 * possibly can.
1149 	 *
1150 	 * We go for a simple algorithm of: if this node has FAN_OUT or fewer
1151 	 * leaves in it, then attempt to collapse it - and attempt to
1152 	 * recursively collapse up the tree.
1153 	 *
1154 	 * We could also try and collapse in partially filled subtrees to take
1155 	 * up space in this node.
1156 	 */
1157 	if (node->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1158 		struct assoc_array_node *parent, *grandparent;
1159 		struct assoc_array_ptr *ptr;
1160 
1161 		/* First of all, we need to know if this node has metadata so
1162 		 * that we don't try collapsing if all the leaves are already
1163 		 * here.
1164 		 */
1165 		has_meta = false;
1166 		for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1167 			ptr = node->slots[i];
1168 			if (assoc_array_ptr_is_meta(ptr)) {
1169 				has_meta = true;
1170 				break;
1171 			}
1172 		}
1173 
1174 		pr_devel("leaves: %ld [m=%d]\n",
1175 			 node->nr_leaves_on_branch - 1, has_meta);
1176 
1177 		/* Look further up the tree to see if we can collapse this node
1178 		 * into a more proximal node too.
1179 		 */
1180 		parent = node;
1181 	collapse_up:
1182 		pr_devel("collapse subtree: %ld\n", parent->nr_leaves_on_branch);
1183 
1184 		ptr = parent->back_pointer;
1185 		if (!ptr)
1186 			goto do_collapse;
1187 		if (assoc_array_ptr_is_shortcut(ptr)) {
1188 			struct assoc_array_shortcut *s = assoc_array_ptr_to_shortcut(ptr);
1189 			ptr = s->back_pointer;
1190 			if (!ptr)
1191 				goto do_collapse;
1192 		}
1193 
1194 		grandparent = assoc_array_ptr_to_node(ptr);
1195 		if (grandparent->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1196 			parent = grandparent;
1197 			goto collapse_up;
1198 		}
1199 
1200 	do_collapse:
1201 		/* There's no point collapsing if the original node has no meta
1202 		 * pointers to discard and if we didn't merge into one of that
1203 		 * node's ancestry.
1204 		 */
1205 		if (has_meta || parent != node) {
1206 			node = parent;
1207 
1208 			/* Create a new node to collapse into */
1209 			new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1210 			if (!new_n0)
1211 				goto enomem;
1212 			edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
1213 
1214 			new_n0->back_pointer = node->back_pointer;
1215 			new_n0->parent_slot = node->parent_slot;
1216 			new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
1217 			edit->adjust_count_on = new_n0;
1218 
1219 			collapse.node = new_n0;
1220 			collapse.skip_leaf = assoc_array_ptr_to_leaf(edit->dead_leaf);
1221 			collapse.slot = 0;
1222 			assoc_array_subtree_iterate(assoc_array_node_to_ptr(node),
1223 						    node->back_pointer,
1224 						    assoc_array_delete_collapse_iterator,
1225 						    &collapse);
1226 			pr_devel("collapsed %d,%lu\n", collapse.slot, new_n0->nr_leaves_on_branch);
1227 			BUG_ON(collapse.slot != new_n0->nr_leaves_on_branch - 1);
1228 
1229 			if (!node->back_pointer) {
1230 				edit->set[1].ptr = &array->root;
1231 			} else if (assoc_array_ptr_is_leaf(node->back_pointer)) {
1232 				BUG();
1233 			} else if (assoc_array_ptr_is_node(node->back_pointer)) {
1234 				struct assoc_array_node *p =
1235 					assoc_array_ptr_to_node(node->back_pointer);
1236 				edit->set[1].ptr = &p->slots[node->parent_slot];
1237 			} else if (assoc_array_ptr_is_shortcut(node->back_pointer)) {
1238 				struct assoc_array_shortcut *s =
1239 					assoc_array_ptr_to_shortcut(node->back_pointer);
1240 				edit->set[1].ptr = &s->next_node;
1241 			}
1242 			edit->set[1].to = assoc_array_node_to_ptr(new_n0);
1243 			edit->excised_subtree = assoc_array_node_to_ptr(node);
1244 		}
1245 	}
1246 
1247 	return edit;
1248 
1249 enomem:
1250 	/* Clean up after an out of memory error */
1251 	pr_devel("enomem\n");
1252 	assoc_array_cancel_edit(edit);
1253 	return ERR_PTR(-ENOMEM);
1254 }
1255 
1256 /**
1257  * assoc_array_clear - Script deletion of all objects from an associative array
1258  * @array: The array to clear.
1259  * @ops: The operations to use.
1260  *
1261  * Precalculate and preallocate a script for the deletion of all the objects
1262  * from an associative array.  This results in an edit script that can either
1263  * be applied or cancelled.
1264  *
1265  * The function returns a pointer to an edit script if there are objects to be
1266  * deleted, NULL if there are no objects in the array or -ENOMEM.
1267  *
1268  * The caller should lock against other modifications and must continue to hold
1269  * the lock until assoc_array_apply_edit() has been called.
1270  *
1271  * Accesses to the tree may take place concurrently with this function,
1272  * provided they hold the RCU read lock.
1273  */
1274 struct assoc_array_edit *assoc_array_clear(struct assoc_array *array,
1275 					   const struct assoc_array_ops *ops)
1276 {
1277 	struct assoc_array_edit *edit;
1278 
1279 	pr_devel("-->%s()\n", __func__);
1280 
1281 	if (!array->root)
1282 		return NULL;
1283 
1284 	edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1285 	if (!edit)
1286 		return ERR_PTR(-ENOMEM);
1287 	edit->array = array;
1288 	edit->ops = ops;
1289 	edit->set[1].ptr = &array->root;
1290 	edit->set[1].to = NULL;
1291 	edit->excised_subtree = array->root;
1292 	edit->ops_for_excised_subtree = ops;
1293 	pr_devel("all gone\n");
1294 	return edit;
1295 }
1296 
1297 /*
1298  * Handle the deferred destruction after an applied edit.
1299  */
1300 static void assoc_array_rcu_cleanup(struct rcu_head *head)
1301 {
1302 	struct assoc_array_edit *edit =
1303 		container_of(head, struct assoc_array_edit, rcu);
1304 	int i;
1305 
1306 	pr_devel("-->%s()\n", __func__);
1307 
1308 	if (edit->dead_leaf)
1309 		edit->ops->free_object(assoc_array_ptr_to_leaf(edit->dead_leaf));
1310 	for (i = 0; i < ARRAY_SIZE(edit->excised_meta); i++)
1311 		if (edit->excised_meta[i])
1312 			kfree(assoc_array_ptr_to_node(edit->excised_meta[i]));
1313 
1314 	if (edit->excised_subtree) {
1315 		BUG_ON(assoc_array_ptr_is_leaf(edit->excised_subtree));
1316 		if (assoc_array_ptr_is_node(edit->excised_subtree)) {
1317 			struct assoc_array_node *n =
1318 				assoc_array_ptr_to_node(edit->excised_subtree);
1319 			n->back_pointer = NULL;
1320 		} else {
1321 			struct assoc_array_shortcut *s =
1322 				assoc_array_ptr_to_shortcut(edit->excised_subtree);
1323 			s->back_pointer = NULL;
1324 		}
1325 		assoc_array_destroy_subtree(edit->excised_subtree,
1326 					    edit->ops_for_excised_subtree);
1327 	}
1328 
1329 	kfree(edit);
1330 }
1331 
1332 /**
1333  * assoc_array_apply_edit - Apply an edit script to an associative array
1334  * @edit: The script to apply.
1335  *
1336  * Apply an edit script to an associative array to effect an insertion,
1337  * deletion or clearance.  As the edit script includes preallocated memory,
1338  * this is guaranteed not to fail.
1339  *
1340  * The edit script, dead objects and dead metadata will be scheduled for
1341  * destruction after an RCU grace period to permit those doing read-only
1342  * accesses on the array to continue to do so under the RCU read lock whilst
1343  * the edit is taking place.
1344  */
1345 void assoc_array_apply_edit(struct assoc_array_edit *edit)
1346 {
1347 	struct assoc_array_shortcut *shortcut;
1348 	struct assoc_array_node *node;
1349 	struct assoc_array_ptr *ptr;
1350 	int i;
1351 
1352 	pr_devel("-->%s()\n", __func__);
1353 
1354 	smp_wmb();
1355 	if (edit->leaf_p)
1356 		*edit->leaf_p = edit->leaf;
1357 
1358 	smp_wmb();
1359 	for (i = 0; i < ARRAY_SIZE(edit->set_parent_slot); i++)
1360 		if (edit->set_parent_slot[i].p)
1361 			*edit->set_parent_slot[i].p = edit->set_parent_slot[i].to;
1362 
1363 	smp_wmb();
1364 	for (i = 0; i < ARRAY_SIZE(edit->set_backpointers); i++)
1365 		if (edit->set_backpointers[i])
1366 			*edit->set_backpointers[i] = edit->set_backpointers_to;
1367 
1368 	smp_wmb();
1369 	for (i = 0; i < ARRAY_SIZE(edit->set); i++)
1370 		if (edit->set[i].ptr)
1371 			*edit->set[i].ptr = edit->set[i].to;
1372 
1373 	if (edit->array->root == NULL) {
1374 		edit->array->nr_leaves_on_tree = 0;
1375 	} else if (edit->adjust_count_on) {
1376 		node = edit->adjust_count_on;
1377 		for (;;) {
1378 			node->nr_leaves_on_branch += edit->adjust_count_by;
1379 
1380 			ptr = node->back_pointer;
1381 			if (!ptr)
1382 				break;
1383 			if (assoc_array_ptr_is_shortcut(ptr)) {
1384 				shortcut = assoc_array_ptr_to_shortcut(ptr);
1385 				ptr = shortcut->back_pointer;
1386 				if (!ptr)
1387 					break;
1388 			}
1389 			BUG_ON(!assoc_array_ptr_is_node(ptr));
1390 			node = assoc_array_ptr_to_node(ptr);
1391 		}
1392 
1393 		edit->array->nr_leaves_on_tree += edit->adjust_count_by;
1394 	}
1395 
1396 	call_rcu(&edit->rcu, assoc_array_rcu_cleanup);
1397 }
1398 
1399 /**
1400  * assoc_array_cancel_edit - Discard an edit script.
1401  * @edit: The script to discard.
1402  *
1403  * Free an edit script and all the preallocated data it holds without making
1404  * any changes to the associative array it was intended for.
1405  *
1406  * NOTE!  In the case of an insertion script, this does _not_ release the leaf
1407  * that was to be inserted.  That is left to the caller.
1408  */
1409 void assoc_array_cancel_edit(struct assoc_array_edit *edit)
1410 {
1411 	struct assoc_array_ptr *ptr;
1412 	int i;
1413 
1414 	pr_devel("-->%s()\n", __func__);
1415 
1416 	/* Clean up after an out of memory error */
1417 	for (i = 0; i < ARRAY_SIZE(edit->new_meta); i++) {
1418 		ptr = edit->new_meta[i];
1419 		if (ptr) {
1420 			if (assoc_array_ptr_is_node(ptr))
1421 				kfree(assoc_array_ptr_to_node(ptr));
1422 			else
1423 				kfree(assoc_array_ptr_to_shortcut(ptr));
1424 		}
1425 	}
1426 	kfree(edit);
1427 }
1428 
1429 /**
1430  * assoc_array_gc - Garbage collect an associative array.
1431  * @array: The array to clean.
1432  * @ops: The operations to use.
1433  * @iterator: A callback function to pass judgement on each object.
1434  * @iterator_data: Private data for the callback function.
1435  *
1436  * Collect garbage from an associative array and pack down the internal tree to
1437  * save memory.
1438  *
1439  * The iterator function is asked to pass judgement upon each object in the
1440  * array.  If it returns false, the object is discard and if it returns true,
1441  * the object is kept.  If it returns true, it must increment the object's
1442  * usage count (or whatever it needs to do to retain it) before returning.
1443  *
1444  * This function returns 0 if successful or -ENOMEM if out of memory.  In the
1445  * latter case, the array is not changed.
1446  *
1447  * The caller should lock against other modifications and must continue to hold
1448  * the lock until assoc_array_apply_edit() has been called.
1449  *
1450  * Accesses to the tree may take place concurrently with this function,
1451  * provided they hold the RCU read lock.
1452  */
1453 int assoc_array_gc(struct assoc_array *array,
1454 		   const struct assoc_array_ops *ops,
1455 		   bool (*iterator)(void *object, void *iterator_data),
1456 		   void *iterator_data)
1457 {
1458 	struct assoc_array_shortcut *shortcut, *new_s;
1459 	struct assoc_array_node *node, *new_n;
1460 	struct assoc_array_edit *edit;
1461 	struct assoc_array_ptr *cursor, *ptr;
1462 	struct assoc_array_ptr *new_root, *new_parent, **new_ptr_pp;
1463 	unsigned long nr_leaves_on_tree;
1464 	bool retained;
1465 	int keylen, slot, nr_free, next_slot, i;
1466 
1467 	pr_devel("-->%s()\n", __func__);
1468 
1469 	if (!array->root)
1470 		return 0;
1471 
1472 	edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1473 	if (!edit)
1474 		return -ENOMEM;
1475 	edit->array = array;
1476 	edit->ops = ops;
1477 	edit->ops_for_excised_subtree = ops;
1478 	edit->set[0].ptr = &array->root;
1479 	edit->excised_subtree = array->root;
1480 
1481 	new_root = new_parent = NULL;
1482 	new_ptr_pp = &new_root;
1483 	cursor = array->root;
1484 
1485 descend:
1486 	/* If this point is a shortcut, then we need to duplicate it and
1487 	 * advance the target cursor.
1488 	 */
1489 	if (assoc_array_ptr_is_shortcut(cursor)) {
1490 		shortcut = assoc_array_ptr_to_shortcut(cursor);
1491 		keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
1492 		keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
1493 		new_s = kmalloc(struct_size(new_s, index_key, keylen),
1494 				GFP_KERNEL);
1495 		if (!new_s)
1496 			goto enomem;
1497 		pr_devel("dup shortcut %p -> %p\n", shortcut, new_s);
1498 		memcpy(new_s, shortcut, struct_size(new_s, index_key, keylen));
1499 		new_s->back_pointer = new_parent;
1500 		new_s->parent_slot = shortcut->parent_slot;
1501 		*new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(new_s);
1502 		new_ptr_pp = &new_s->next_node;
1503 		cursor = shortcut->next_node;
1504 	}
1505 
1506 	/* Duplicate the node at this position */
1507 	node = assoc_array_ptr_to_node(cursor);
1508 	new_n = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1509 	if (!new_n)
1510 		goto enomem;
1511 	pr_devel("dup node %p -> %p\n", node, new_n);
1512 	new_n->back_pointer = new_parent;
1513 	new_n->parent_slot = node->parent_slot;
1514 	*new_ptr_pp = new_parent = assoc_array_node_to_ptr(new_n);
1515 	new_ptr_pp = NULL;
1516 	slot = 0;
1517 
1518 continue_node:
1519 	/* Filter across any leaves and gc any subtrees */
1520 	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1521 		ptr = node->slots[slot];
1522 		if (!ptr)
1523 			continue;
1524 
1525 		if (assoc_array_ptr_is_leaf(ptr)) {
1526 			if (iterator(assoc_array_ptr_to_leaf(ptr),
1527 				     iterator_data))
1528 				/* The iterator will have done any reference
1529 				 * counting on the object for us.
1530 				 */
1531 				new_n->slots[slot] = ptr;
1532 			continue;
1533 		}
1534 
1535 		new_ptr_pp = &new_n->slots[slot];
1536 		cursor = ptr;
1537 		goto descend;
1538 	}
1539 
1540 retry_compress:
1541 	pr_devel("-- compress node %p --\n", new_n);
1542 
1543 	/* Count up the number of empty slots in this node and work out the
1544 	 * subtree leaf count.
1545 	 */
1546 	new_n->nr_leaves_on_branch = 0;
1547 	nr_free = 0;
1548 	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1549 		ptr = new_n->slots[slot];
1550 		if (!ptr)
1551 			nr_free++;
1552 		else if (assoc_array_ptr_is_leaf(ptr))
1553 			new_n->nr_leaves_on_branch++;
1554 	}
1555 	pr_devel("free=%d, leaves=%lu\n", nr_free, new_n->nr_leaves_on_branch);
1556 
1557 	/* See what we can fold in */
1558 	retained = false;
1559 	next_slot = 0;
1560 	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1561 		struct assoc_array_shortcut *s;
1562 		struct assoc_array_node *child;
1563 
1564 		ptr = new_n->slots[slot];
1565 		if (!ptr || assoc_array_ptr_is_leaf(ptr))
1566 			continue;
1567 
1568 		s = NULL;
1569 		if (assoc_array_ptr_is_shortcut(ptr)) {
1570 			s = assoc_array_ptr_to_shortcut(ptr);
1571 			ptr = s->next_node;
1572 		}
1573 
1574 		child = assoc_array_ptr_to_node(ptr);
1575 		new_n->nr_leaves_on_branch += child->nr_leaves_on_branch;
1576 
1577 		if (child->nr_leaves_on_branch <= nr_free + 1) {
1578 			/* Fold the child node into this one */
1579 			pr_devel("[%d] fold node %lu/%d [nx %d]\n",
1580 				 slot, child->nr_leaves_on_branch, nr_free + 1,
1581 				 next_slot);
1582 
1583 			/* We would already have reaped an intervening shortcut
1584 			 * on the way back up the tree.
1585 			 */
1586 			BUG_ON(s);
1587 
1588 			new_n->slots[slot] = NULL;
1589 			nr_free++;
1590 			if (slot < next_slot)
1591 				next_slot = slot;
1592 			for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1593 				struct assoc_array_ptr *p = child->slots[i];
1594 				if (!p)
1595 					continue;
1596 				BUG_ON(assoc_array_ptr_is_meta(p));
1597 				while (new_n->slots[next_slot])
1598 					next_slot++;
1599 				BUG_ON(next_slot >= ASSOC_ARRAY_FAN_OUT);
1600 				new_n->slots[next_slot++] = p;
1601 				nr_free--;
1602 			}
1603 			kfree(child);
1604 		} else {
1605 			pr_devel("[%d] retain node %lu/%d [nx %d]\n",
1606 				 slot, child->nr_leaves_on_branch, nr_free + 1,
1607 				 next_slot);
1608 			retained = true;
1609 		}
1610 	}
1611 
1612 	if (retained && new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1613 		pr_devel("internal nodes remain despite enough space, retrying\n");
1614 		goto retry_compress;
1615 	}
1616 	pr_devel("after: %lu\n", new_n->nr_leaves_on_branch);
1617 
1618 	nr_leaves_on_tree = new_n->nr_leaves_on_branch;
1619 
1620 	/* Excise this node if it is singly occupied by a shortcut */
1621 	if (nr_free == ASSOC_ARRAY_FAN_OUT - 1) {
1622 		for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++)
1623 			if ((ptr = new_n->slots[slot]))
1624 				break;
1625 
1626 		if (assoc_array_ptr_is_meta(ptr) &&
1627 		    assoc_array_ptr_is_shortcut(ptr)) {
1628 			pr_devel("excise node %p with 1 shortcut\n", new_n);
1629 			new_s = assoc_array_ptr_to_shortcut(ptr);
1630 			new_parent = new_n->back_pointer;
1631 			slot = new_n->parent_slot;
1632 			kfree(new_n);
1633 			if (!new_parent) {
1634 				new_s->back_pointer = NULL;
1635 				new_s->parent_slot = 0;
1636 				new_root = ptr;
1637 				goto gc_complete;
1638 			}
1639 
1640 			if (assoc_array_ptr_is_shortcut(new_parent)) {
1641 				/* We can discard any preceding shortcut also */
1642 				struct assoc_array_shortcut *s =
1643 					assoc_array_ptr_to_shortcut(new_parent);
1644 
1645 				pr_devel("excise preceding shortcut\n");
1646 
1647 				new_parent = new_s->back_pointer = s->back_pointer;
1648 				slot = new_s->parent_slot = s->parent_slot;
1649 				kfree(s);
1650 				if (!new_parent) {
1651 					new_s->back_pointer = NULL;
1652 					new_s->parent_slot = 0;
1653 					new_root = ptr;
1654 					goto gc_complete;
1655 				}
1656 			}
1657 
1658 			new_s->back_pointer = new_parent;
1659 			new_s->parent_slot = slot;
1660 			new_n = assoc_array_ptr_to_node(new_parent);
1661 			new_n->slots[slot] = ptr;
1662 			goto ascend_old_tree;
1663 		}
1664 	}
1665 
1666 	/* Excise any shortcuts we might encounter that point to nodes that
1667 	 * only contain leaves.
1668 	 */
1669 	ptr = new_n->back_pointer;
1670 	if (!ptr)
1671 		goto gc_complete;
1672 
1673 	if (assoc_array_ptr_is_shortcut(ptr)) {
1674 		new_s = assoc_array_ptr_to_shortcut(ptr);
1675 		new_parent = new_s->back_pointer;
1676 		slot = new_s->parent_slot;
1677 
1678 		if (new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1679 			struct assoc_array_node *n;
1680 
1681 			pr_devel("excise shortcut\n");
1682 			new_n->back_pointer = new_parent;
1683 			new_n->parent_slot = slot;
1684 			kfree(new_s);
1685 			if (!new_parent) {
1686 				new_root = assoc_array_node_to_ptr(new_n);
1687 				goto gc_complete;
1688 			}
1689 
1690 			n = assoc_array_ptr_to_node(new_parent);
1691 			n->slots[slot] = assoc_array_node_to_ptr(new_n);
1692 		}
1693 	} else {
1694 		new_parent = ptr;
1695 	}
1696 	new_n = assoc_array_ptr_to_node(new_parent);
1697 
1698 ascend_old_tree:
1699 	ptr = node->back_pointer;
1700 	if (assoc_array_ptr_is_shortcut(ptr)) {
1701 		shortcut = assoc_array_ptr_to_shortcut(ptr);
1702 		slot = shortcut->parent_slot;
1703 		cursor = shortcut->back_pointer;
1704 		if (!cursor)
1705 			goto gc_complete;
1706 	} else {
1707 		slot = node->parent_slot;
1708 		cursor = ptr;
1709 	}
1710 	BUG_ON(!cursor);
1711 	node = assoc_array_ptr_to_node(cursor);
1712 	slot++;
1713 	goto continue_node;
1714 
1715 gc_complete:
1716 	edit->set[0].to = new_root;
1717 	assoc_array_apply_edit(edit);
1718 	array->nr_leaves_on_tree = nr_leaves_on_tree;
1719 	return 0;
1720 
1721 enomem:
1722 	pr_devel("enomem\n");
1723 	assoc_array_destroy_subtree(new_root, edit->ops);
1724 	kfree(edit);
1725 	return -ENOMEM;
1726 }
1727