1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_RCULIST_H
3#define _LINUX_RCULIST_H
4
5#ifdef __KERNEL__
6
7/*
8 * RCU-protected list version
9 */
10#include <linux/list.h>
11#include <linux/rcupdate.h>
12
13/*
14 * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers
15 * @list: list to be initialized
16 *
17 * You should instead use INIT_LIST_HEAD() for normal initialization and
18 * cleanup tasks, when readers have no access to the list being initialized.
19 * However, if the list being initialized is visible to readers, you
20 * need to keep the compiler from being too mischievous.
21 */
22static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
23{
24 WRITE_ONCE(list->next, list);
25 WRITE_ONCE(list->prev, list);
26}
27
28/*
29 * return the ->next pointer of a list_head in an rcu safe
30 * way, we must not access it directly
31 */
32#define list_next_rcu(list) (*((struct list_head __rcu **)(&(list)->next)))
33/*
34 * Return the ->prev pointer of a list_head in an rcu safe way. Don't
35 * access it directly.
36 *
37 * Any list traversed with list_bidir_prev_rcu() must never use
38 * list_del_rcu(). Doing so will poison the ->prev pointer that
39 * list_bidir_prev_rcu() relies on, which will result in segfaults.
40 * To prevent these segfaults, use list_bidir_del_rcu() instead
41 * of list_del_rcu().
42 */
43#define list_bidir_prev_rcu(list) (*((struct list_head __rcu **)(&(list)->prev)))
44
45/**
46 * list_for_each_rcu - Iterate over a list in an RCU-safe fashion
47 * @pos: the &struct list_head to use as a loop cursor.
48 * @head: the head for your list.
49 */
50#define list_for_each_rcu(pos, head) \
51 for (pos = rcu_dereference((head)->next); \
52 !list_is_head(pos, (head)); \
53 pos = rcu_dereference(pos->next))
54
55/**
56 * list_tail_rcu - returns the prev pointer of the head of the list
57 * @head: the head of the list
58 *
59 * Note: This should only be used with the list header, and even then
60 * only if list_del() and similar primitives are not also used on the
61 * list header.
62 */
63#define list_tail_rcu(head) (*((struct list_head __rcu **)(&(head)->prev)))
64
65/*
66 * Check during list traversal that we are within an RCU reader
67 */
68
69#define check_arg_count_one(dummy)
70
71#ifdef CONFIG_PROVE_RCU_LIST
72#define __list_check_rcu(dummy, cond, extra...) \
73 ({ \
74 check_arg_count_one(extra); \
75 RCU_LOCKDEP_WARN(!(cond) && !rcu_read_lock_any_held(), \
76 "RCU-list traversed in non-reader section!"); \
77 })
78
79#define __list_check_srcu(cond) \
80 ({ \
81 RCU_LOCKDEP_WARN(!(cond), \
82 "RCU-list traversed without holding the required lock!");\
83 })
84#else
85#define __list_check_rcu(dummy, cond, extra...) \
86 ({ check_arg_count_one(extra); })
87
88#define __list_check_srcu(cond) ({ })
89#endif
90
91/*
92 * Insert a new entry between two known consecutive entries.
93 *
94 * This is only for internal list manipulation where we know
95 * the prev/next entries already!
96 */
97static inline void __list_add_rcu(struct list_head *new,
98 struct list_head *prev, struct list_head *next)
99{
100 if (!__list_add_valid(new, prev, next))
101 return;
102
103 new->next = next;
104 new->prev = prev;
105 rcu_assign_pointer(list_next_rcu(prev), new);
106 next->prev = new;
107}
108
109/**
110 * list_add_rcu - add a new entry to rcu-protected list
111 * @new: new entry to be added
112 * @head: list head to add it after
113 *
114 * Insert a new entry after the specified head.
115 * This is good for implementing stacks.
116 *
117 * The caller must take whatever precautions are necessary
118 * (such as holding appropriate locks) to avoid racing
119 * with another list-mutation primitive, such as list_add_rcu()
120 * or list_del_rcu(), running on this same list.
121 * However, it is perfectly legal to run concurrently with
122 * the _rcu list-traversal primitives, such as
123 * list_for_each_entry_rcu().
124 */
125static inline void list_add_rcu(struct list_head *new, struct list_head *head)
126{
127 __list_add_rcu(new, prev: head, next: head->next);
128}
129
130/**
131 * list_add_tail_rcu - add a new entry to rcu-protected list
132 * @new: new entry to be added
133 * @head: list head to add it before
134 *
135 * Insert a new entry before the specified head.
136 * This is useful for implementing queues.
137 *
138 * The caller must take whatever precautions are necessary
139 * (such as holding appropriate locks) to avoid racing
140 * with another list-mutation primitive, such as list_add_tail_rcu()
141 * or list_del_rcu(), running on this same list.
142 * However, it is perfectly legal to run concurrently with
143 * the _rcu list-traversal primitives, such as
144 * list_for_each_entry_rcu().
145 */
146static inline void list_add_tail_rcu(struct list_head *new,
147 struct list_head *head)
148{
149 __list_add_rcu(new, prev: head->prev, next: head);
150}
151
152/**
153 * list_del_rcu - deletes entry from list without re-initialization
154 * @entry: the element to delete from the list.
155 *
156 * Note: list_empty() on entry does not return true after this,
157 * the entry is in an undefined state. It is useful for RCU based
158 * lockfree traversal.
159 *
160 * In particular, it means that we can not poison the forward
161 * pointers that may still be used for walking the list.
162 *
163 * The caller must take whatever precautions are necessary
164 * (such as holding appropriate locks) to avoid racing
165 * with another list-mutation primitive, such as list_del_rcu()
166 * or list_add_rcu(), running on this same list.
167 * However, it is perfectly legal to run concurrently with
168 * the _rcu list-traversal primitives, such as
169 * list_for_each_entry_rcu().
170 *
171 * Note that the caller is not permitted to immediately free
172 * the newly deleted entry. Instead, either synchronize_rcu()
173 * or call_rcu() must be used to defer freeing until an RCU
174 * grace period has elapsed.
175 */
176static inline void list_del_rcu(struct list_head *entry)
177{
178 __list_del_entry(entry);
179 entry->prev = LIST_POISON2;
180}
181
182/**
183 * list_bidir_del_rcu - deletes entry from list without re-initialization
184 * @entry: the element to delete from the list.
185 *
186 * In contrast to list_del_rcu() doesn't poison the prev pointer thus
187 * allowing backwards traversal via list_bidir_prev_rcu().
188 *
189 * Note: list_empty() on entry does not return true after this because
190 * the entry is in a special undefined state that permits RCU-based
191 * lockfree reverse traversal. In particular this means that we can not
192 * poison the forward and backwards pointers that may still be used for
193 * walking the list.
194 *
195 * The caller must take whatever precautions are necessary (such as
196 * holding appropriate locks) to avoid racing with another list-mutation
197 * primitive, such as list_bidir_del_rcu() or list_add_rcu(), running on
198 * this same list. However, it is perfectly legal to run concurrently
199 * with the _rcu list-traversal primitives, such as
200 * list_for_each_entry_rcu().
201 *
202 * Note that list_del_rcu() and list_bidir_del_rcu() must not be used on
203 * the same list.
204 *
205 * Note that the caller is not permitted to immediately free
206 * the newly deleted entry. Instead, either synchronize_rcu()
207 * or call_rcu() must be used to defer freeing until an RCU
208 * grace period has elapsed.
209 */
210static inline void list_bidir_del_rcu(struct list_head *entry)
211{
212 __list_del_entry(entry);
213}
214
215/**
216 * hlist_del_init_rcu - deletes entry from hash list with re-initialization
217 * @n: the element to delete from the hash list.
218 *
219 * Note: list_unhashed() on the node return true after this. It is
220 * useful for RCU based read lockfree traversal if the writer side
221 * must know if the list entry is still hashed or already unhashed.
222 *
223 * In particular, it means that we can not poison the forward pointers
224 * that may still be used for walking the hash list and we can only
225 * zero the pprev pointer so list_unhashed() will return true after
226 * this.
227 *
228 * The caller must take whatever precautions are necessary (such as
229 * holding appropriate locks) to avoid racing with another
230 * list-mutation primitive, such as hlist_add_head_rcu() or
231 * hlist_del_rcu(), running on this same list. However, it is
232 * perfectly legal to run concurrently with the _rcu list-traversal
233 * primitives, such as hlist_for_each_entry_rcu().
234 */
235static inline void hlist_del_init_rcu(struct hlist_node *n)
236{
237 if (!hlist_unhashed(h: n)) {
238 __hlist_del(n);
239 WRITE_ONCE(n->pprev, NULL);
240 }
241}
242
243/**
244 * list_replace_rcu - replace old entry by new one
245 * @old : the element to be replaced
246 * @new : the new element to insert
247 *
248 * The @old entry will be replaced with the @new entry atomically from
249 * the perspective of concurrent readers. It is the caller's responsibility
250 * to synchronize with concurrent updaters, if any.
251 *
252 * Note: @old should not be empty.
253 */
254static inline void list_replace_rcu(struct list_head *old,
255 struct list_head *new)
256{
257 new->next = old->next;
258 new->prev = old->prev;
259 rcu_assign_pointer(list_next_rcu(new->prev), new);
260 new->next->prev = new;
261 old->prev = LIST_POISON2;
262}
263
264/**
265 * __list_splice_init_rcu - join an RCU-protected list into an existing list.
266 * @list: the RCU-protected list to splice
267 * @prev: points to the last element of the existing list
268 * @next: points to the first element of the existing list
269 * @sync: synchronize_rcu, synchronize_rcu_expedited, ...
270 *
271 * The list pointed to by @prev and @next can be RCU-read traversed
272 * concurrently with this function.
273 *
274 * Note that this function blocks.
275 *
276 * Important note: the caller must take whatever action is necessary to prevent
277 * any other updates to the existing list. In principle, it is possible to
278 * modify the list as soon as sync() begins execution. If this sort of thing
279 * becomes necessary, an alternative version based on call_rcu() could be
280 * created. But only if -really- needed -- there is no shortage of RCU API
281 * members.
282 */
283static inline void __list_splice_init_rcu(struct list_head *list,
284 struct list_head *prev,
285 struct list_head *next,
286 void (*sync)(void))
287{
288 struct list_head *first = list->next;
289 struct list_head *last = list->prev;
290
291 /*
292 * "first" and "last" tracking list, so initialize it. RCU readers
293 * have access to this list, so we must use INIT_LIST_HEAD_RCU()
294 * instead of INIT_LIST_HEAD().
295 */
296
297 INIT_LIST_HEAD_RCU(list);
298
299 /*
300 * At this point, the list body still points to the source list.
301 * Wait for any readers to finish using the list before splicing
302 * the list body into the new list. Any new readers will see
303 * an empty list.
304 */
305
306 sync();
307 ASSERT_EXCLUSIVE_ACCESS(*first);
308 ASSERT_EXCLUSIVE_ACCESS(*last);
309
310 /*
311 * Readers are finished with the source list, so perform splice.
312 * The order is important if the new list is global and accessible
313 * to concurrent RCU readers. Note that RCU readers are not
314 * permitted to traverse the prev pointers without excluding
315 * this function.
316 */
317
318 last->next = next;
319 rcu_assign_pointer(list_next_rcu(prev), first);
320 first->prev = prev;
321 next->prev = last;
322}
323
324/**
325 * list_splice_init_rcu - splice an RCU-protected list into an existing list,
326 * designed for stacks.
327 * @list: the RCU-protected list to splice
328 * @head: the place in the existing list to splice the first list into
329 * @sync: synchronize_rcu, synchronize_rcu_expedited, ...
330 */
331static inline void list_splice_init_rcu(struct list_head *list,
332 struct list_head *head,
333 void (*sync)(void))
334{
335 if (!list_empty(head: list))
336 __list_splice_init_rcu(list, prev: head, next: head->next, sync);
337}
338
339/**
340 * list_splice_tail_init_rcu - splice an RCU-protected list into an existing
341 * list, designed for queues.
342 * @list: the RCU-protected list to splice
343 * @head: the place in the existing list to splice the first list into
344 * @sync: synchronize_rcu, synchronize_rcu_expedited, ...
345 */
346static inline void list_splice_tail_init_rcu(struct list_head *list,
347 struct list_head *head,
348 void (*sync)(void))
349{
350 if (!list_empty(head: list))
351 __list_splice_init_rcu(list, prev: head->prev, next: head, sync);
352}
353
354/**
355 * list_entry_rcu - get the struct for this entry
356 * @ptr: the &struct list_head pointer.
357 * @type: the type of the struct this is embedded in.
358 * @member: the name of the list_head within the struct.
359 *
360 * This primitive may safely run concurrently with the _rcu list-mutation
361 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
362 */
363#define list_entry_rcu(ptr, type, member) \
364 container_of(READ_ONCE(ptr), type, member)
365
366/*
367 * Where are list_empty_rcu() and list_first_entry_rcu()?
368 *
369 * They do not exist because they would lead to subtle race conditions:
370 *
371 * if (!list_empty_rcu(mylist)) {
372 * struct foo *bar = list_first_entry_rcu(mylist, struct foo, list_member);
373 * do_something(bar);
374 * }
375 *
376 * The list might be non-empty when list_empty_rcu() checks it, but it
377 * might have become empty by the time that list_first_entry_rcu() rereads
378 * the ->next pointer, which would result in a SEGV.
379 *
380 * When not using RCU, it is OK for list_first_entry() to re-read that
381 * pointer because both functions should be protected by some lock that
382 * blocks writers.
383 *
384 * When using RCU, list_empty() uses READ_ONCE() to fetch the
385 * RCU-protected ->next pointer and then compares it to the address of the
386 * list head. However, it neither dereferences this pointer nor provides
387 * this pointer to its caller. Thus, READ_ONCE() suffices (that is,
388 * rcu_dereference() is not needed), which means that list_empty() can be
389 * used anywhere you would want to use list_empty_rcu(). Just don't
390 * expect anything useful to happen if you do a subsequent lockless
391 * call to list_first_entry_rcu()!!!
392 *
393 * See list_first_or_null_rcu for an alternative.
394 */
395
396/**
397 * list_first_or_null_rcu - get the first element from a list
398 * @ptr: the list head to take the element from.
399 * @type: the type of the struct this is embedded in.
400 * @member: the name of the list_head within the struct.
401 *
402 * Note that if the list is empty, it returns NULL.
403 *
404 * This primitive may safely run concurrently with the _rcu list-mutation
405 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
406 */
407#define list_first_or_null_rcu(ptr, type, member) \
408({ \
409 struct list_head *__ptr = (ptr); \
410 struct list_head *__next = READ_ONCE(__ptr->next); \
411 likely(__ptr != __next) ? list_entry_rcu(__next, type, member) : NULL; \
412})
413
414/**
415 * list_next_or_null_rcu - get the next element from a list
416 * @head: the head for the list.
417 * @ptr: the list head to take the next element from.
418 * @type: the type of the struct this is embedded in.
419 * @member: the name of the list_head within the struct.
420 *
421 * Note that if the ptr is at the end of the list, NULL is returned.
422 *
423 * This primitive may safely run concurrently with the _rcu list-mutation
424 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
425 */
426#define list_next_or_null_rcu(head, ptr, type, member) \
427({ \
428 struct list_head *__head = (head); \
429 struct list_head *__ptr = (ptr); \
430 struct list_head *__next = READ_ONCE(__ptr->next); \
431 likely(__next != __head) ? list_entry_rcu(__next, type, \
432 member) : NULL; \
433})
434
435/**
436 * list_for_each_entry_rcu - iterate over rcu list of given type
437 * @pos: the type * to use as a loop cursor.
438 * @head: the head for your list.
439 * @member: the name of the list_head within the struct.
440 * @cond: optional lockdep expression if called from non-RCU protection.
441 *
442 * This list-traversal primitive may safely run concurrently with
443 * the _rcu list-mutation primitives such as list_add_rcu()
444 * as long as the traversal is guarded by rcu_read_lock().
445 */
446#define list_for_each_entry_rcu(pos, head, member, cond...) \
447 for (__list_check_rcu(dummy, ## cond, 0), \
448 pos = list_entry_rcu((head)->next, typeof(*pos), member); \
449 &pos->member != (head); \
450 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
451
452/**
453 * list_for_each_entry_srcu - iterate over rcu list of given type
454 * @pos: the type * to use as a loop cursor.
455 * @head: the head for your list.
456 * @member: the name of the list_head within the struct.
457 * @cond: lockdep expression for the lock required to traverse the list.
458 *
459 * This list-traversal primitive may safely run concurrently with
460 * the _rcu list-mutation primitives such as list_add_rcu()
461 * as long as the traversal is guarded by srcu_read_lock().
462 * The lockdep expression srcu_read_lock_held() can be passed as the
463 * cond argument from read side.
464 */
465#define list_for_each_entry_srcu(pos, head, member, cond) \
466 for (__list_check_srcu(cond), \
467 pos = list_entry_rcu((head)->next, typeof(*pos), member); \
468 &pos->member != (head); \
469 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
470
471/**
472 * list_entry_lockless - get the struct for this entry
473 * @ptr: the &struct list_head pointer.
474 * @type: the type of the struct this is embedded in.
475 * @member: the name of the list_head within the struct.
476 *
477 * This primitive may safely run concurrently with the _rcu
478 * list-mutation primitives such as list_add_rcu(), but requires some
479 * implicit RCU read-side guarding. One example is running within a special
480 * exception-time environment where preemption is disabled and where lockdep
481 * cannot be invoked. Another example is when items are added to the list,
482 * but never deleted.
483 */
484#define list_entry_lockless(ptr, type, member) \
485 container_of((typeof(ptr))READ_ONCE(ptr), type, member)
486
487/**
488 * list_for_each_entry_lockless - iterate over rcu list of given type
489 * @pos: the type * to use as a loop cursor.
490 * @head: the head for your list.
491 * @member: the name of the list_struct within the struct.
492 *
493 * This primitive may safely run concurrently with the _rcu
494 * list-mutation primitives such as list_add_rcu(), but requires some
495 * implicit RCU read-side guarding. One example is running within a special
496 * exception-time environment where preemption is disabled and where lockdep
497 * cannot be invoked. Another example is when items are added to the list,
498 * but never deleted.
499 */
500#define list_for_each_entry_lockless(pos, head, member) \
501 for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \
502 &pos->member != (head); \
503 pos = list_entry_lockless(pos->member.next, typeof(*pos), member))
504
505/**
506 * list_for_each_entry_continue_rcu - continue iteration over list of given type
507 * @pos: the type * to use as a loop cursor.
508 * @head: the head for your list.
509 * @member: the name of the list_head within the struct.
510 *
511 * Continue to iterate over list of given type, continuing after
512 * the current position which must have been in the list when the RCU read
513 * lock was taken.
514 * This would typically require either that you obtained the node from a
515 * previous walk of the list in the same RCU read-side critical section, or
516 * that you held some sort of non-RCU reference (such as a reference count)
517 * to keep the node alive *and* in the list.
518 *
519 * This iterator is similar to list_for_each_entry_from_rcu() except
520 * this starts after the given position and that one starts at the given
521 * position.
522 */
523#define list_for_each_entry_continue_rcu(pos, head, member) \
524 for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
525 &pos->member != (head); \
526 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
527
528/**
529 * list_for_each_entry_from_rcu - iterate over a list from current point
530 * @pos: the type * to use as a loop cursor.
531 * @head: the head for your list.
532 * @member: the name of the list_node within the struct.
533 *
534 * Iterate over the tail of a list starting from a given position,
535 * which must have been in the list when the RCU read lock was taken.
536 * This would typically require either that you obtained the node from a
537 * previous walk of the list in the same RCU read-side critical section, or
538 * that you held some sort of non-RCU reference (such as a reference count)
539 * to keep the node alive *and* in the list.
540 *
541 * This iterator is similar to list_for_each_entry_continue_rcu() except
542 * this starts from the given position and that one starts from the position
543 * after the given position.
544 */
545#define list_for_each_entry_from_rcu(pos, head, member) \
546 for (; &(pos)->member != (head); \
547 pos = list_entry_rcu(pos->member.next, typeof(*(pos)), member))
548
549/**
550 * hlist_del_rcu - deletes entry from hash list without re-initialization
551 * @n: the element to delete from the hash list.
552 *
553 * Note: list_unhashed() on entry does not return true after this,
554 * the entry is in an undefined state. It is useful for RCU based
555 * lockfree traversal.
556 *
557 * In particular, it means that we can not poison the forward
558 * pointers that may still be used for walking the hash list.
559 *
560 * The caller must take whatever precautions are necessary
561 * (such as holding appropriate locks) to avoid racing
562 * with another list-mutation primitive, such as hlist_add_head_rcu()
563 * or hlist_del_rcu(), running on this same list.
564 * However, it is perfectly legal to run concurrently with
565 * the _rcu list-traversal primitives, such as
566 * hlist_for_each_entry().
567 */
568static inline void hlist_del_rcu(struct hlist_node *n)
569{
570 __hlist_del(n);
571 WRITE_ONCE(n->pprev, LIST_POISON2);
572}
573
574/**
575 * hlist_replace_rcu - replace old entry by new one
576 * @old : the element to be replaced
577 * @new : the new element to insert
578 *
579 * The @old entry will be replaced with the @new entry atomically from
580 * the perspective of concurrent readers. It is the caller's responsibility
581 * to synchronize with concurrent updaters, if any.
582 */
583static inline void hlist_replace_rcu(struct hlist_node *old,
584 struct hlist_node *new)
585{
586 struct hlist_node *next = old->next;
587
588 new->next = next;
589 WRITE_ONCE(new->pprev, old->pprev);
590 rcu_assign_pointer(*(struct hlist_node __rcu **)new->pprev, new);
591 if (next)
592 WRITE_ONCE(new->next->pprev, &new->next);
593 WRITE_ONCE(old->pprev, LIST_POISON2);
594}
595
596/**
597 * hlists_swap_heads_rcu - swap the lists the hlist heads point to
598 * @left: The hlist head on the left
599 * @right: The hlist head on the right
600 *
601 * The lists start out as [@left ][node1 ... ] and
602 * [@right ][node2 ... ]
603 * The lists end up as [@left ][node2 ... ]
604 * [@right ][node1 ... ]
605 */
606static inline void hlists_swap_heads_rcu(struct hlist_head *left, struct hlist_head *right)
607{
608 struct hlist_node *node1 = left->first;
609 struct hlist_node *node2 = right->first;
610
611 rcu_assign_pointer(left->first, node2);
612 rcu_assign_pointer(right->first, node1);
613 WRITE_ONCE(node2->pprev, &left->first);
614 WRITE_ONCE(node1->pprev, &right->first);
615}
616
617/*
618 * return the first or the next element in an RCU protected hlist
619 */
620#define hlist_first_rcu(head) (*((struct hlist_node __rcu **)(&(head)->first)))
621#define hlist_next_rcu(node) (*((struct hlist_node __rcu **)(&(node)->next)))
622#define hlist_pprev_rcu(node) (*((struct hlist_node __rcu **)((node)->pprev)))
623
624/**
625 * hlist_add_head_rcu
626 * @n: the element to add to the hash list.
627 * @h: the list to add to.
628 *
629 * Description:
630 * Adds the specified element to the specified hlist,
631 * while permitting racing traversals.
632 *
633 * The caller must take whatever precautions are necessary
634 * (such as holding appropriate locks) to avoid racing
635 * with another list-mutation primitive, such as hlist_add_head_rcu()
636 * or hlist_del_rcu(), running on this same list.
637 * However, it is perfectly legal to run concurrently with
638 * the _rcu list-traversal primitives, such as
639 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
640 * problems on Alpha CPUs. Regardless of the type of CPU, the
641 * list-traversal primitive must be guarded by rcu_read_lock().
642 */
643static inline void hlist_add_head_rcu(struct hlist_node *n,
644 struct hlist_head *h)
645{
646 struct hlist_node *first = h->first;
647
648 n->next = first;
649 WRITE_ONCE(n->pprev, &h->first);
650 rcu_assign_pointer(hlist_first_rcu(h), n);
651 if (first)
652 WRITE_ONCE(first->pprev, &n->next);
653}
654
655/**
656 * hlist_add_tail_rcu
657 * @n: the element to add to the hash list.
658 * @h: the list to add to.
659 *
660 * Description:
661 * Adds the specified element to the specified hlist,
662 * while permitting racing traversals.
663 *
664 * The caller must take whatever precautions are necessary
665 * (such as holding appropriate locks) to avoid racing
666 * with another list-mutation primitive, such as hlist_add_head_rcu()
667 * or hlist_del_rcu(), running on this same list.
668 * However, it is perfectly legal to run concurrently with
669 * the _rcu list-traversal primitives, such as
670 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
671 * problems on Alpha CPUs. Regardless of the type of CPU, the
672 * list-traversal primitive must be guarded by rcu_read_lock().
673 */
674static inline void hlist_add_tail_rcu(struct hlist_node *n,
675 struct hlist_head *h)
676{
677 struct hlist_node *i, *last = NULL;
678
679 /* Note: write side code, so rcu accessors are not needed. */
680 for (i = h->first; i; i = i->next)
681 last = i;
682
683 if (last) {
684 n->next = last->next;
685 WRITE_ONCE(n->pprev, &last->next);
686 rcu_assign_pointer(hlist_next_rcu(last), n);
687 } else {
688 hlist_add_head_rcu(n, h);
689 }
690}
691
692/**
693 * hlist_add_before_rcu
694 * @n: the new element to add to the hash list.
695 * @next: the existing element to add the new element before.
696 *
697 * Description:
698 * Adds the specified element to the specified hlist
699 * before the specified node while permitting racing traversals.
700 *
701 * The caller must take whatever precautions are necessary
702 * (such as holding appropriate locks) to avoid racing
703 * with another list-mutation primitive, such as hlist_add_head_rcu()
704 * or hlist_del_rcu(), running on this same list.
705 * However, it is perfectly legal to run concurrently with
706 * the _rcu list-traversal primitives, such as
707 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
708 * problems on Alpha CPUs.
709 */
710static inline void hlist_add_before_rcu(struct hlist_node *n,
711 struct hlist_node *next)
712{
713 WRITE_ONCE(n->pprev, next->pprev);
714 n->next = next;
715 rcu_assign_pointer(hlist_pprev_rcu(n), n);
716 WRITE_ONCE(next->pprev, &n->next);
717}
718
719/**
720 * hlist_add_behind_rcu
721 * @n: the new element to add to the hash list.
722 * @prev: the existing element to add the new element after.
723 *
724 * Description:
725 * Adds the specified element to the specified hlist
726 * after the specified node while permitting racing traversals.
727 *
728 * The caller must take whatever precautions are necessary
729 * (such as holding appropriate locks) to avoid racing
730 * with another list-mutation primitive, such as hlist_add_head_rcu()
731 * or hlist_del_rcu(), running on this same list.
732 * However, it is perfectly legal to run concurrently with
733 * the _rcu list-traversal primitives, such as
734 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
735 * problems on Alpha CPUs.
736 */
737static inline void hlist_add_behind_rcu(struct hlist_node *n,
738 struct hlist_node *prev)
739{
740 n->next = prev->next;
741 WRITE_ONCE(n->pprev, &prev->next);
742 rcu_assign_pointer(hlist_next_rcu(prev), n);
743 if (n->next)
744 WRITE_ONCE(n->next->pprev, &n->next);
745}
746
747#define __hlist_for_each_rcu(pos, head) \
748 for (pos = rcu_dereference(hlist_first_rcu(head)); \
749 pos; \
750 pos = rcu_dereference(hlist_next_rcu(pos)))
751
752/**
753 * hlist_for_each_entry_rcu - iterate over rcu list of given type
754 * @pos: the type * to use as a loop cursor.
755 * @head: the head for your list.
756 * @member: the name of the hlist_node within the struct.
757 * @cond: optional lockdep expression if called from non-RCU protection.
758 *
759 * This list-traversal primitive may safely run concurrently with
760 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
761 * as long as the traversal is guarded by rcu_read_lock().
762 */
763#define hlist_for_each_entry_rcu(pos, head, member, cond...) \
764 for (__list_check_rcu(dummy, ## cond, 0), \
765 pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
766 typeof(*(pos)), member); \
767 pos; \
768 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
769 &(pos)->member)), typeof(*(pos)), member))
770
771/**
772 * hlist_for_each_entry_srcu - iterate over rcu list of given type
773 * @pos: the type * to use as a loop cursor.
774 * @head: the head for your list.
775 * @member: the name of the hlist_node within the struct.
776 * @cond: lockdep expression for the lock required to traverse the list.
777 *
778 * This list-traversal primitive may safely run concurrently with
779 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
780 * as long as the traversal is guarded by srcu_read_lock().
781 * The lockdep expression srcu_read_lock_held() can be passed as the
782 * cond argument from read side.
783 */
784#define hlist_for_each_entry_srcu(pos, head, member, cond) \
785 for (__list_check_srcu(cond), \
786 pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
787 typeof(*(pos)), member); \
788 pos; \
789 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
790 &(pos)->member)), typeof(*(pos)), member))
791
792/**
793 * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing)
794 * @pos: the type * to use as a loop cursor.
795 * @head: the head for your list.
796 * @member: the name of the hlist_node within the struct.
797 *
798 * This list-traversal primitive may safely run concurrently with
799 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
800 * as long as the traversal is guarded by rcu_read_lock().
801 *
802 * This is the same as hlist_for_each_entry_rcu() except that it does
803 * not do any RCU debugging or tracing.
804 */
805#define hlist_for_each_entry_rcu_notrace(pos, head, member) \
806 for (pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_first_rcu(head)),\
807 typeof(*(pos)), member); \
808 pos; \
809 pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_next_rcu(\
810 &(pos)->member)), typeof(*(pos)), member))
811
812/**
813 * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type
814 * @pos: the type * to use as a loop cursor.
815 * @head: the head for your list.
816 * @member: the name of the hlist_node within the struct.
817 *
818 * This list-traversal primitive may safely run concurrently with
819 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
820 * as long as the traversal is guarded by rcu_read_lock().
821 */
822#define hlist_for_each_entry_rcu_bh(pos, head, member) \
823 for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_first_rcu(head)),\
824 typeof(*(pos)), member); \
825 pos; \
826 pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(\
827 &(pos)->member)), typeof(*(pos)), member))
828
829/**
830 * hlist_for_each_entry_continue_rcu - iterate over a hlist continuing after current point
831 * @pos: the type * to use as a loop cursor.
832 * @member: the name of the hlist_node within the struct.
833 */
834#define hlist_for_each_entry_continue_rcu(pos, member) \
835 for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
836 &(pos)->member)), typeof(*(pos)), member); \
837 pos; \
838 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
839 &(pos)->member)), typeof(*(pos)), member))
840
841/**
842 * hlist_for_each_entry_continue_rcu_bh - iterate over a hlist continuing after current point
843 * @pos: the type * to use as a loop cursor.
844 * @member: the name of the hlist_node within the struct.
845 */
846#define hlist_for_each_entry_continue_rcu_bh(pos, member) \
847 for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu( \
848 &(pos)->member)), typeof(*(pos)), member); \
849 pos; \
850 pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu( \
851 &(pos)->member)), typeof(*(pos)), member))
852
853/**
854 * hlist_for_each_entry_from_rcu - iterate over a hlist continuing from current point
855 * @pos: the type * to use as a loop cursor.
856 * @member: the name of the hlist_node within the struct.
857 */
858#define hlist_for_each_entry_from_rcu(pos, member) \
859 for (; pos; \
860 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
861 &(pos)->member)), typeof(*(pos)), member))
862
863#endif /* __KERNEL__ */
864#endif
865