Line data Source code
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 : * Why is there no list_empty_rcu()? Because list_empty() serves this
15 : * purpose. The list_empty() function fetches the RCU-protected pointer
16 : * and compares it to the address of the list head, but neither dereferences
17 : * this pointer itself nor provides this pointer to the caller. Therefore,
18 : * it is not necessary to use rcu_dereference(), so that list_empty() can
19 : * be used anywhere you would want to use a list_empty_rcu().
20 : */
21 :
22 : /*
23 : * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers
24 : * @list: list to be initialized
25 : *
26 : * You should instead use INIT_LIST_HEAD() for normal initialization and
27 : * cleanup tasks, when readers have no access to the list being initialized.
28 : * However, if the list being initialized is visible to readers, you
29 : * need to keep the compiler from being too mischievous.
30 : */
31 7 : static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
32 : {
33 7 : WRITE_ONCE(list->next, list);
34 7 : WRITE_ONCE(list->prev, list);
35 : }
36 :
37 : /*
38 : * return the ->next pointer of a list_head in an rcu safe
39 : * way, we must not access it directly
40 : */
41 : #define list_next_rcu(list) (*((struct list_head __rcu **)(&(list)->next)))
42 :
43 : /**
44 : * list_tail_rcu - returns the prev pointer of the head of the list
45 : * @head: the head of the list
46 : *
47 : * Note: This should only be used with the list header, and even then
48 : * only if list_del() and similar primitives are not also used on the
49 : * list header.
50 : */
51 : #define list_tail_rcu(head) (*((struct list_head __rcu **)(&(head)->prev)))
52 :
53 : /*
54 : * Check during list traversal that we are within an RCU reader
55 : */
56 :
57 : #define check_arg_count_one(dummy)
58 :
59 : #ifdef CONFIG_PROVE_RCU_LIST
60 : #define __list_check_rcu(dummy, cond, extra...) \
61 : ({ \
62 : check_arg_count_one(extra); \
63 : RCU_LOCKDEP_WARN(!(cond) && !rcu_read_lock_any_held(), \
64 : "RCU-list traversed in non-reader section!"); \
65 : })
66 :
67 : #define __list_check_srcu(cond) \
68 : ({ \
69 : RCU_LOCKDEP_WARN(!(cond), \
70 : "RCU-list traversed without holding the required lock!");\
71 : })
72 : #else
73 : #define __list_check_rcu(dummy, cond, extra...) \
74 : ({ check_arg_count_one(extra); })
75 :
76 : #define __list_check_srcu(cond) ({ })
77 : #endif
78 :
79 : /*
80 : * Insert a new entry between two known consecutive entries.
81 : *
82 : * This is only for internal list manipulation where we know
83 : * the prev/next entries already!
84 : */
85 729035 : static inline void __list_add_rcu(struct list_head *new,
86 : struct list_head *prev, struct list_head *next)
87 : {
88 729035 : if (!__list_add_valid(new, prev, next))
89 : return;
90 :
91 729035 : new->next = next;
92 728122 : new->prev = prev;
93 728122 : rcu_assign_pointer(list_next_rcu(prev), new);
94 729035 : next->prev = new;
95 : }
96 :
97 : /**
98 : * list_add_rcu - add a new entry to rcu-protected list
99 : * @new: new entry to be added
100 : * @head: list head to add it after
101 : *
102 : * Insert a new entry after the specified head.
103 : * This is good for implementing stacks.
104 : *
105 : * The caller must take whatever precautions are necessary
106 : * (such as holding appropriate locks) to avoid racing
107 : * with another list-mutation primitive, such as list_add_rcu()
108 : * or list_del_rcu(), running on this same list.
109 : * However, it is perfectly legal to run concurrently with
110 : * the _rcu list-traversal primitives, such as
111 : * list_for_each_entry_rcu().
112 : */
113 86 : static inline void list_add_rcu(struct list_head *new, struct list_head *head)
114 : {
115 86 : __list_add_rcu(new, head, head->next);
116 73 : }
117 :
118 : /**
119 : * list_add_tail_rcu - add a new entry to rcu-protected list
120 : * @new: new entry to be added
121 : * @head: list head to add it before
122 : *
123 : * Insert a new entry before the specified head.
124 : * This is useful for implementing queues.
125 : *
126 : * The caller must take whatever precautions are necessary
127 : * (such as holding appropriate locks) to avoid racing
128 : * with another list-mutation primitive, such as list_add_tail_rcu()
129 : * or list_del_rcu(), running on this same list.
130 : * However, it is perfectly legal to run concurrently with
131 : * the _rcu list-traversal primitives, such as
132 : * list_for_each_entry_rcu().
133 : */
134 728036 : static inline void list_add_tail_rcu(struct list_head *new,
135 : struct list_head *head)
136 : {
137 728943 : __list_add_rcu(new, head->prev, head);
138 721513 : }
139 :
140 : /**
141 : * list_del_rcu - deletes entry from list without re-initialization
142 : * @entry: the element to delete from the list.
143 : *
144 : * Note: list_empty() on entry does not return true after this,
145 : * the entry is in an undefined state. It is useful for RCU based
146 : * lockfree traversal.
147 : *
148 : * In particular, it means that we can not poison the forward
149 : * pointers that may still be used for walking the list.
150 : *
151 : * The caller must take whatever precautions are necessary
152 : * (such as holding appropriate locks) to avoid racing
153 : * with another list-mutation primitive, such as list_del_rcu()
154 : * or list_add_rcu(), running on this same list.
155 : * However, it is perfectly legal to run concurrently with
156 : * the _rcu list-traversal primitives, such as
157 : * list_for_each_entry_rcu().
158 : *
159 : * Note that the caller is not permitted to immediately free
160 : * the newly deleted entry. Instead, either synchronize_rcu()
161 : * or call_rcu() must be used to defer freeing until an RCU
162 : * grace period has elapsed.
163 : */
164 641256 : static inline void list_del_rcu(struct list_head *entry)
165 : {
166 641256 : __list_del_entry(entry);
167 641256 : entry->prev = LIST_POISON2;
168 2 : }
169 :
170 : /**
171 : * hlist_del_init_rcu - deletes entry from hash list with re-initialization
172 : * @n: the element to delete from the hash list.
173 : *
174 : * Note: list_unhashed() on the node return true after this. It is
175 : * useful for RCU based read lockfree traversal if the writer side
176 : * must know if the list entry is still hashed or already unhashed.
177 : *
178 : * In particular, it means that we can not poison the forward pointers
179 : * that may still be used for walking the hash list and we can only
180 : * zero the pprev pointer so list_unhashed() will return true after
181 : * this.
182 : *
183 : * The caller must take whatever precautions are necessary (such as
184 : * holding appropriate locks) to avoid racing with another
185 : * list-mutation primitive, such as hlist_add_head_rcu() or
186 : * hlist_del_rcu(), running on this same list. However, it is
187 : * perfectly legal to run concurrently with the _rcu list-traversal
188 : * primitives, such as hlist_for_each_entry_rcu().
189 : */
190 2317 : static inline void hlist_del_init_rcu(struct hlist_node *n)
191 : {
192 2317 : if (!hlist_unhashed(n)) {
193 2086 : __hlist_del(n);
194 2317 : WRITE_ONCE(n->pprev, NULL);
195 : }
196 : }
197 :
198 : /**
199 : * list_replace_rcu - replace old entry by new one
200 : * @old : the element to be replaced
201 : * @new : the new element to insert
202 : *
203 : * The @old entry will be replaced with the @new entry atomically.
204 : * Note: @old should not be empty.
205 : */
206 0 : static inline void list_replace_rcu(struct list_head *old,
207 : struct list_head *new)
208 : {
209 0 : new->next = old->next;
210 0 : new->prev = old->prev;
211 0 : rcu_assign_pointer(list_next_rcu(new->prev), new);
212 0 : new->next->prev = new;
213 0 : old->prev = LIST_POISON2;
214 : }
215 :
216 : /**
217 : * __list_splice_init_rcu - join an RCU-protected list into an existing list.
218 : * @list: the RCU-protected list to splice
219 : * @prev: points to the last element of the existing list
220 : * @next: points to the first element of the existing list
221 : * @sync: synchronize_rcu, synchronize_rcu_expedited, ...
222 : *
223 : * The list pointed to by @prev and @next can be RCU-read traversed
224 : * concurrently with this function.
225 : *
226 : * Note that this function blocks.
227 : *
228 : * Important note: the caller must take whatever action is necessary to prevent
229 : * any other updates to the existing list. In principle, it is possible to
230 : * modify the list as soon as sync() begins execution. If this sort of thing
231 : * becomes necessary, an alternative version based on call_rcu() could be
232 : * created. But only if -really- needed -- there is no shortage of RCU API
233 : * members.
234 : */
235 : static inline void __list_splice_init_rcu(struct list_head *list,
236 : struct list_head *prev,
237 : struct list_head *next,
238 : void (*sync)(void))
239 : {
240 : struct list_head *first = list->next;
241 : struct list_head *last = list->prev;
242 :
243 : /*
244 : * "first" and "last" tracking list, so initialize it. RCU readers
245 : * have access to this list, so we must use INIT_LIST_HEAD_RCU()
246 : * instead of INIT_LIST_HEAD().
247 : */
248 :
249 : INIT_LIST_HEAD_RCU(list);
250 :
251 : /*
252 : * At this point, the list body still points to the source list.
253 : * Wait for any readers to finish using the list before splicing
254 : * the list body into the new list. Any new readers will see
255 : * an empty list.
256 : */
257 :
258 : sync();
259 : ASSERT_EXCLUSIVE_ACCESS(*first);
260 : ASSERT_EXCLUSIVE_ACCESS(*last);
261 :
262 : /*
263 : * Readers are finished with the source list, so perform splice.
264 : * The order is important if the new list is global and accessible
265 : * to concurrent RCU readers. Note that RCU readers are not
266 : * permitted to traverse the prev pointers without excluding
267 : * this function.
268 : */
269 :
270 : last->next = next;
271 : rcu_assign_pointer(list_next_rcu(prev), first);
272 : first->prev = prev;
273 : next->prev = last;
274 : }
275 :
276 : /**
277 : * list_splice_init_rcu - splice an RCU-protected list into an existing list,
278 : * designed for stacks.
279 : * @list: the RCU-protected list to splice
280 : * @head: the place in the existing list to splice the first list into
281 : * @sync: synchronize_rcu, synchronize_rcu_expedited, ...
282 : */
283 : static inline void list_splice_init_rcu(struct list_head *list,
284 : struct list_head *head,
285 : void (*sync)(void))
286 : {
287 : if (!list_empty(list))
288 : __list_splice_init_rcu(list, head, head->next, sync);
289 : }
290 :
291 : /**
292 : * list_splice_tail_init_rcu - splice an RCU-protected list into an existing
293 : * list, designed for queues.
294 : * @list: the RCU-protected list to splice
295 : * @head: the place in the existing list to splice the first list into
296 : * @sync: synchronize_rcu, synchronize_rcu_expedited, ...
297 : */
298 : static inline void list_splice_tail_init_rcu(struct list_head *list,
299 : struct list_head *head,
300 : void (*sync)(void))
301 : {
302 : if (!list_empty(list))
303 : __list_splice_init_rcu(list, head->prev, head, sync);
304 : }
305 :
306 : /**
307 : * list_entry_rcu - get the struct for this entry
308 : * @ptr: the &struct list_head pointer.
309 : * @type: the type of the struct this is embedded in.
310 : * @member: the name of the list_head within the struct.
311 : *
312 : * This primitive may safely run concurrently with the _rcu list-mutation
313 : * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
314 : */
315 : #define list_entry_rcu(ptr, type, member) \
316 : container_of(READ_ONCE(ptr), type, member)
317 :
318 : /*
319 : * Where are list_empty_rcu() and list_first_entry_rcu()?
320 : *
321 : * Implementing those functions following their counterparts list_empty() and
322 : * list_first_entry() is not advisable because they lead to subtle race
323 : * conditions as the following snippet shows:
324 : *
325 : * if (!list_empty_rcu(mylist)) {
326 : * struct foo *bar = list_first_entry_rcu(mylist, struct foo, list_member);
327 : * do_something(bar);
328 : * }
329 : *
330 : * The list may not be empty when list_empty_rcu checks it, but it may be when
331 : * list_first_entry_rcu rereads the ->next pointer.
332 : *
333 : * Rereading the ->next pointer is not a problem for list_empty() and
334 : * list_first_entry() because they would be protected by a lock that blocks
335 : * writers.
336 : *
337 : * See list_first_or_null_rcu for an alternative.
338 : */
339 :
340 : /**
341 : * list_first_or_null_rcu - get the first element from a list
342 : * @ptr: the list head to take the element from.
343 : * @type: the type of the struct this is embedded in.
344 : * @member: the name of the list_head within the struct.
345 : *
346 : * Note that if the list is empty, it returns NULL.
347 : *
348 : * This primitive may safely run concurrently with the _rcu list-mutation
349 : * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
350 : */
351 : #define list_first_or_null_rcu(ptr, type, member) \
352 : ({ \
353 : struct list_head *__ptr = (ptr); \
354 : struct list_head *__next = READ_ONCE(__ptr->next); \
355 : likely(__ptr != __next) ? list_entry_rcu(__next, type, member) : NULL; \
356 : })
357 :
358 : /**
359 : * list_next_or_null_rcu - get the first element from a list
360 : * @head: the head for the list.
361 : * @ptr: the list head to take the next element from.
362 : * @type: the type of the struct this is embedded in.
363 : * @member: the name of the list_head within the struct.
364 : *
365 : * Note that if the ptr is at the end of the list, NULL is returned.
366 : *
367 : * This primitive may safely run concurrently with the _rcu list-mutation
368 : * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
369 : */
370 : #define list_next_or_null_rcu(head, ptr, type, member) \
371 : ({ \
372 : struct list_head *__head = (head); \
373 : struct list_head *__ptr = (ptr); \
374 : struct list_head *__next = READ_ONCE(__ptr->next); \
375 : likely(__next != __head) ? list_entry_rcu(__next, type, \
376 : member) : NULL; \
377 : })
378 :
379 : /**
380 : * list_for_each_entry_rcu - iterate over rcu list of given type
381 : * @pos: the type * to use as a loop cursor.
382 : * @head: the head for your list.
383 : * @member: the name of the list_head within the struct.
384 : * @cond: optional lockdep expression if called from non-RCU protection.
385 : *
386 : * This list-traversal primitive may safely run concurrently with
387 : * the _rcu list-mutation primitives such as list_add_rcu()
388 : * as long as the traversal is guarded by rcu_read_lock().
389 : */
390 : #define list_for_each_entry_rcu(pos, head, member, cond...) \
391 : for (__list_check_rcu(dummy, ## cond, 0), \
392 : pos = list_entry_rcu((head)->next, typeof(*pos), member); \
393 : &pos->member != (head); \
394 : pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
395 :
396 : /**
397 : * list_for_each_entry_srcu - iterate over rcu list of given type
398 : * @pos: the type * to use as a loop cursor.
399 : * @head: the head for your list.
400 : * @member: the name of the list_head within the struct.
401 : * @cond: lockdep expression for the lock required to traverse the list.
402 : *
403 : * This list-traversal primitive may safely run concurrently with
404 : * the _rcu list-mutation primitives such as list_add_rcu()
405 : * as long as the traversal is guarded by srcu_read_lock().
406 : * The lockdep expression srcu_read_lock_held() can be passed as the
407 : * cond argument from read side.
408 : */
409 : #define list_for_each_entry_srcu(pos, head, member, cond) \
410 : for (__list_check_srcu(cond), \
411 : pos = list_entry_rcu((head)->next, typeof(*pos), member); \
412 : &pos->member != (head); \
413 : pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
414 :
415 : /**
416 : * list_entry_lockless - get the struct for this entry
417 : * @ptr: the &struct list_head pointer.
418 : * @type: the type of the struct this is embedded in.
419 : * @member: the name of the list_head within the struct.
420 : *
421 : * This primitive may safely run concurrently with the _rcu
422 : * list-mutation primitives such as list_add_rcu(), but requires some
423 : * implicit RCU read-side guarding. One example is running within a special
424 : * exception-time environment where preemption is disabled and where lockdep
425 : * cannot be invoked. Another example is when items are added to the list,
426 : * but never deleted.
427 : */
428 : #define list_entry_lockless(ptr, type, member) \
429 : container_of((typeof(ptr))READ_ONCE(ptr), type, member)
430 :
431 : /**
432 : * list_for_each_entry_lockless - iterate over rcu list of given type
433 : * @pos: the type * to use as a loop cursor.
434 : * @head: the head for your list.
435 : * @member: the name of the list_struct within the struct.
436 : *
437 : * This primitive may safely run concurrently with the _rcu
438 : * list-mutation primitives such as list_add_rcu(), but requires some
439 : * implicit RCU read-side guarding. One example is running within a special
440 : * exception-time environment where preemption is disabled and where lockdep
441 : * cannot be invoked. Another example is when items are added to the list,
442 : * but never deleted.
443 : */
444 : #define list_for_each_entry_lockless(pos, head, member) \
445 : for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \
446 : &pos->member != (head); \
447 : pos = list_entry_lockless(pos->member.next, typeof(*pos), member))
448 :
449 : /**
450 : * list_for_each_entry_continue_rcu - continue iteration over list of given type
451 : * @pos: the type * to use as a loop cursor.
452 : * @head: the head for your list.
453 : * @member: the name of the list_head within the struct.
454 : *
455 : * Continue to iterate over list of given type, continuing after
456 : * the current position which must have been in the list when the RCU read
457 : * lock was taken.
458 : * This would typically require either that you obtained the node from a
459 : * previous walk of the list in the same RCU read-side critical section, or
460 : * that you held some sort of non-RCU reference (such as a reference count)
461 : * to keep the node alive *and* in the list.
462 : *
463 : * This iterator is similar to list_for_each_entry_from_rcu() except
464 : * this starts after the given position and that one starts at the given
465 : * position.
466 : */
467 : #define list_for_each_entry_continue_rcu(pos, head, member) \
468 : for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
469 : &pos->member != (head); \
470 : pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
471 :
472 : /**
473 : * list_for_each_entry_from_rcu - iterate over a list from current point
474 : * @pos: the type * to use as a loop cursor.
475 : * @head: the head for your list.
476 : * @member: the name of the list_node within the struct.
477 : *
478 : * Iterate over the tail of a list starting from a given position,
479 : * which must have been in the list when the RCU read lock was taken.
480 : * This would typically require either that you obtained the node from a
481 : * previous walk of the list in the same RCU read-side critical section, or
482 : * that you held some sort of non-RCU reference (such as a reference count)
483 : * to keep the node alive *and* in the list.
484 : *
485 : * This iterator is similar to list_for_each_entry_continue_rcu() except
486 : * this starts from the given position and that one starts from the position
487 : * after the given position.
488 : */
489 : #define list_for_each_entry_from_rcu(pos, head, member) \
490 : for (; &(pos)->member != (head); \
491 : pos = list_entry_rcu(pos->member.next, typeof(*(pos)), member))
492 :
493 : /**
494 : * hlist_del_rcu - deletes entry from hash list without re-initialization
495 : * @n: the element to delete from the hash list.
496 : *
497 : * Note: list_unhashed() on entry does not return true after this,
498 : * the entry is in an undefined state. It is useful for RCU based
499 : * lockfree traversal.
500 : *
501 : * In particular, it means that we can not poison the forward
502 : * pointers that may still be used for walking the hash list.
503 : *
504 : * The caller must take whatever precautions are necessary
505 : * (such as holding appropriate locks) to avoid racing
506 : * with another list-mutation primitive, such as hlist_add_head_rcu()
507 : * or hlist_del_rcu(), running on this same list.
508 : * However, it is perfectly legal to run concurrently with
509 : * the _rcu list-traversal primitives, such as
510 : * hlist_for_each_entry().
511 : */
512 3789 : static inline void hlist_del_rcu(struct hlist_node *n)
513 : {
514 3789 : __hlist_del(n);
515 3789 : WRITE_ONCE(n->pprev, LIST_POISON2);
516 0 : }
517 :
518 : /**
519 : * hlist_replace_rcu - replace old entry by new one
520 : * @old : the element to be replaced
521 : * @new : the new element to insert
522 : *
523 : * The @old entry will be replaced with the @new entry atomically.
524 : */
525 0 : static inline void hlist_replace_rcu(struct hlist_node *old,
526 : struct hlist_node *new)
527 : {
528 0 : struct hlist_node *next = old->next;
529 :
530 0 : new->next = next;
531 0 : WRITE_ONCE(new->pprev, old->pprev);
532 0 : rcu_assign_pointer(*(struct hlist_node __rcu **)new->pprev, new);
533 0 : if (next)
534 0 : WRITE_ONCE(new->next->pprev, &new->next);
535 0 : WRITE_ONCE(old->pprev, LIST_POISON2);
536 : }
537 :
538 : /**
539 : * hlists_swap_heads_rcu - swap the lists the hlist heads point to
540 : * @left: The hlist head on the left
541 : * @right: The hlist head on the right
542 : *
543 : * The lists start out as [@left ][node1 ... ] and
544 : * [@right ][node2 ... ]
545 : * The lists end up as [@left ][node2 ... ]
546 : * [@right ][node1 ... ]
547 : */
548 0 : static inline void hlists_swap_heads_rcu(struct hlist_head *left, struct hlist_head *right)
549 : {
550 0 : struct hlist_node *node1 = left->first;
551 0 : struct hlist_node *node2 = right->first;
552 :
553 0 : rcu_assign_pointer(left->first, node2);
554 0 : rcu_assign_pointer(right->first, node1);
555 0 : WRITE_ONCE(node2->pprev, &left->first);
556 0 : WRITE_ONCE(node1->pprev, &right->first);
557 : }
558 :
559 : /*
560 : * return the first or the next element in an RCU protected hlist
561 : */
562 : #define hlist_first_rcu(head) (*((struct hlist_node __rcu **)(&(head)->first)))
563 : #define hlist_next_rcu(node) (*((struct hlist_node __rcu **)(&(node)->next)))
564 : #define hlist_pprev_rcu(node) (*((struct hlist_node __rcu **)((node)->pprev)))
565 :
566 : /**
567 : * hlist_add_head_rcu
568 : * @n: the element to add to the hash list.
569 : * @h: the list to add to.
570 : *
571 : * Description:
572 : * Adds the specified element to the specified hlist,
573 : * while permitting racing traversals.
574 : *
575 : * The caller must take whatever precautions are necessary
576 : * (such as holding appropriate locks) to avoid racing
577 : * with another list-mutation primitive, such as hlist_add_head_rcu()
578 : * or hlist_del_rcu(), running on this same list.
579 : * However, it is perfectly legal to run concurrently with
580 : * the _rcu list-traversal primitives, such as
581 : * hlist_for_each_entry_rcu(), used to prevent memory-consistency
582 : * problems on Alpha CPUs. Regardless of the type of CPU, the
583 : * list-traversal primitive must be guarded by rcu_read_lock().
584 : */
585 21027 : static inline void hlist_add_head_rcu(struct hlist_node *n,
586 : struct hlist_head *h)
587 : {
588 21027 : struct hlist_node *first = h->first;
589 :
590 21027 : n->next = first;
591 21027 : WRITE_ONCE(n->pprev, &h->first);
592 21063 : rcu_assign_pointer(hlist_first_rcu(h), n);
593 21027 : if (first)
594 17861 : WRITE_ONCE(first->pprev, &n->next);
595 : }
596 :
597 : /**
598 : * hlist_add_tail_rcu
599 : * @n: the element to add to the hash list.
600 : * @h: the list to add to.
601 : *
602 : * Description:
603 : * Adds the specified element to the specified hlist,
604 : * while permitting racing traversals.
605 : *
606 : * The caller must take whatever precautions are necessary
607 : * (such as holding appropriate locks) to avoid racing
608 : * with another list-mutation primitive, such as hlist_add_head_rcu()
609 : * or hlist_del_rcu(), running on this same list.
610 : * However, it is perfectly legal to run concurrently with
611 : * the _rcu list-traversal primitives, such as
612 : * hlist_for_each_entry_rcu(), used to prevent memory-consistency
613 : * problems on Alpha CPUs. Regardless of the type of CPU, the
614 : * list-traversal primitive must be guarded by rcu_read_lock().
615 : */
616 38 : static inline void hlist_add_tail_rcu(struct hlist_node *n,
617 : struct hlist_head *h)
618 : {
619 38 : struct hlist_node *i, *last = NULL;
620 :
621 : /* Note: write side code, so rcu accessors are not needed. */
622 40 : for (i = h->first; i; i = i->next)
623 2 : last = i;
624 :
625 38 : if (last) {
626 2 : n->next = last->next;
627 2 : WRITE_ONCE(n->pprev, &last->next);
628 2 : rcu_assign_pointer(hlist_next_rcu(last), n);
629 : } else {
630 36 : hlist_add_head_rcu(n, h);
631 : }
632 38 : }
633 :
634 : /**
635 : * hlist_add_before_rcu
636 : * @n: the new element to add to the hash list.
637 : * @next: the existing element to add the new element before.
638 : *
639 : * Description:
640 : * Adds the specified element to the specified hlist
641 : * before the specified node while permitting racing traversals.
642 : *
643 : * The caller must take whatever precautions are necessary
644 : * (such as holding appropriate locks) to avoid racing
645 : * with another list-mutation primitive, such as hlist_add_head_rcu()
646 : * or hlist_del_rcu(), running on this same list.
647 : * However, it is perfectly legal to run concurrently with
648 : * the _rcu list-traversal primitives, such as
649 : * hlist_for_each_entry_rcu(), used to prevent memory-consistency
650 : * problems on Alpha CPUs.
651 : */
652 8 : static inline void hlist_add_before_rcu(struct hlist_node *n,
653 : struct hlist_node *next)
654 : {
655 8 : WRITE_ONCE(n->pprev, next->pprev);
656 8 : n->next = next;
657 8 : rcu_assign_pointer(hlist_pprev_rcu(n), n);
658 8 : WRITE_ONCE(next->pprev, &n->next);
659 0 : }
660 :
661 : /**
662 : * hlist_add_behind_rcu
663 : * @n: the new element to add to the hash list.
664 : * @prev: the existing element to add the new element after.
665 : *
666 : * Description:
667 : * Adds the specified element to the specified hlist
668 : * after the specified node while permitting racing traversals.
669 : *
670 : * The caller must take whatever precautions are necessary
671 : * (such as holding appropriate locks) to avoid racing
672 : * with another list-mutation primitive, such as hlist_add_head_rcu()
673 : * or hlist_del_rcu(), running on this same list.
674 : * However, it is perfectly legal to run concurrently with
675 : * the _rcu list-traversal primitives, such as
676 : * hlist_for_each_entry_rcu(), used to prevent memory-consistency
677 : * problems on Alpha CPUs.
678 : */
679 5 : static inline void hlist_add_behind_rcu(struct hlist_node *n,
680 : struct hlist_node *prev)
681 : {
682 5 : n->next = prev->next;
683 5 : WRITE_ONCE(n->pprev, &prev->next);
684 5 : rcu_assign_pointer(hlist_next_rcu(prev), n);
685 5 : if (n->next)
686 0 : WRITE_ONCE(n->next->pprev, &n->next);
687 : }
688 :
689 : #define __hlist_for_each_rcu(pos, head) \
690 : for (pos = rcu_dereference(hlist_first_rcu(head)); \
691 : pos; \
692 : pos = rcu_dereference(hlist_next_rcu(pos)))
693 :
694 : /**
695 : * hlist_for_each_entry_rcu - iterate over rcu list of given type
696 : * @pos: the type * to use as a loop cursor.
697 : * @head: the head for your list.
698 : * @member: the name of the hlist_node within the struct.
699 : * @cond: optional lockdep expression if called from non-RCU protection.
700 : *
701 : * This list-traversal primitive may safely run concurrently with
702 : * the _rcu list-mutation primitives such as hlist_add_head_rcu()
703 : * as long as the traversal is guarded by rcu_read_lock().
704 : */
705 : #define hlist_for_each_entry_rcu(pos, head, member, cond...) \
706 : for (__list_check_rcu(dummy, ## cond, 0), \
707 : pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
708 : typeof(*(pos)), member); \
709 : pos; \
710 : pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
711 : &(pos)->member)), typeof(*(pos)), member))
712 :
713 : /**
714 : * hlist_for_each_entry_srcu - iterate over rcu list of given type
715 : * @pos: the type * to use as a loop cursor.
716 : * @head: the head for your list.
717 : * @member: the name of the hlist_node within the struct.
718 : * @cond: lockdep expression for the lock required to traverse the list.
719 : *
720 : * This list-traversal primitive may safely run concurrently with
721 : * the _rcu list-mutation primitives such as hlist_add_head_rcu()
722 : * as long as the traversal is guarded by srcu_read_lock().
723 : * The lockdep expression srcu_read_lock_held() can be passed as the
724 : * cond argument from read side.
725 : */
726 : #define hlist_for_each_entry_srcu(pos, head, member, cond) \
727 : for (__list_check_srcu(cond), \
728 : pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
729 : typeof(*(pos)), member); \
730 : pos; \
731 : pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
732 : &(pos)->member)), typeof(*(pos)), member))
733 :
734 : /**
735 : * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing)
736 : * @pos: the type * to use as a loop cursor.
737 : * @head: the head for your list.
738 : * @member: the name of the hlist_node within the struct.
739 : *
740 : * This list-traversal primitive may safely run concurrently with
741 : * the _rcu list-mutation primitives such as hlist_add_head_rcu()
742 : * as long as the traversal is guarded by rcu_read_lock().
743 : *
744 : * This is the same as hlist_for_each_entry_rcu() except that it does
745 : * not do any RCU debugging or tracing.
746 : */
747 : #define hlist_for_each_entry_rcu_notrace(pos, head, member) \
748 : for (pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_first_rcu(head)),\
749 : typeof(*(pos)), member); \
750 : pos; \
751 : pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_next_rcu(\
752 : &(pos)->member)), typeof(*(pos)), member))
753 :
754 : /**
755 : * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type
756 : * @pos: the type * to use as a loop cursor.
757 : * @head: the head for your list.
758 : * @member: the name of the hlist_node within the struct.
759 : *
760 : * This list-traversal primitive may safely run concurrently with
761 : * the _rcu list-mutation primitives such as hlist_add_head_rcu()
762 : * as long as the traversal is guarded by rcu_read_lock().
763 : */
764 : #define hlist_for_each_entry_rcu_bh(pos, head, member) \
765 : for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_first_rcu(head)),\
766 : typeof(*(pos)), member); \
767 : pos; \
768 : pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(\
769 : &(pos)->member)), typeof(*(pos)), member))
770 :
771 : /**
772 : * hlist_for_each_entry_continue_rcu - iterate over a hlist continuing after current point
773 : * @pos: the type * to use as a loop cursor.
774 : * @member: the name of the hlist_node within the struct.
775 : */
776 : #define hlist_for_each_entry_continue_rcu(pos, member) \
777 : for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
778 : &(pos)->member)), typeof(*(pos)), member); \
779 : pos; \
780 : pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
781 : &(pos)->member)), typeof(*(pos)), member))
782 :
783 : /**
784 : * hlist_for_each_entry_continue_rcu_bh - iterate over a hlist continuing after current point
785 : * @pos: the type * to use as a loop cursor.
786 : * @member: the name of the hlist_node within the struct.
787 : */
788 : #define hlist_for_each_entry_continue_rcu_bh(pos, member) \
789 : for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu( \
790 : &(pos)->member)), typeof(*(pos)), member); \
791 : pos; \
792 : pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu( \
793 : &(pos)->member)), typeof(*(pos)), member))
794 :
795 : /**
796 : * hlist_for_each_entry_from_rcu - iterate over a hlist continuing from current point
797 : * @pos: the type * to use as a loop cursor.
798 : * @member: the name of the hlist_node within the struct.
799 : */
800 : #define hlist_for_each_entry_from_rcu(pos, member) \
801 : for (; pos; \
802 : pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
803 : &(pos)->member)), typeof(*(pos)), member))
804 :
805 : #endif /* __KERNEL__ */
806 : #endif
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