1 #ifndef _LINUX_RCULIST_H
2 #define _LINUX_RCULIST_H
7 * RCU-protected list version
9 #include <linux/list.h>
10 #include <linux/rcupdate.h>
13 * Why is there no list_empty_rcu()? Because list_empty() serves this
14 * purpose. The list_empty() function fetches the RCU-protected pointer
15 * and compares it to the address of the list head, but neither dereferences
16 * this pointer itself nor provides this pointer to the caller. Therefore,
17 * it is not necessary to use rcu_dereference(), so that list_empty() can
18 * be used anywhere you would want to use a list_empty_rcu().
22 * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers
23 * @list: list to be initialized
25 * You should instead use INIT_LIST_HEAD() for normal initialization and
26 * cleanup tasks, when readers have no access to the list being initialized.
27 * However, if the list being initialized is visible to readers, you
28 * need to keep the compiler from being too mischievous.
30 static inline void INIT_LIST_HEAD_RCU(struct list_head
*list
)
32 ACCESS_ONCE(list
->next
) = list
;
33 ACCESS_ONCE(list
->prev
) = list
;
37 * return the ->next pointer of a list_head in an rcu safe
38 * way, we must not access it directly
40 #define list_next_rcu(list) (*((struct list_head __rcu **)(&(list)->next)))
43 * Insert a new entry between two known consecutive entries.
45 * This is only for internal list manipulation where we know
46 * the prev/next entries already!
48 #ifndef CONFIG_DEBUG_LIST
49 static inline void __list_add_rcu(struct list_head
*new,
50 struct list_head
*prev
, struct list_head
*next
)
54 rcu_assign_pointer(list_next_rcu(prev
), new);
58 void __list_add_rcu(struct list_head
*new,
59 struct list_head
*prev
, struct list_head
*next
);
63 * list_add_rcu - add a new entry to rcu-protected list
64 * @new: new entry to be added
65 * @head: list head to add it after
67 * Insert a new entry after the specified head.
68 * This is good for implementing stacks.
70 * The caller must take whatever precautions are necessary
71 * (such as holding appropriate locks) to avoid racing
72 * with another list-mutation primitive, such as list_add_rcu()
73 * or list_del_rcu(), running on this same list.
74 * However, it is perfectly legal to run concurrently with
75 * the _rcu list-traversal primitives, such as
76 * list_for_each_entry_rcu().
78 static inline void list_add_rcu(struct list_head
*new, struct list_head
*head
)
80 __list_add_rcu(new, head
, head
->next
);
84 * list_add_tail_rcu - add a new entry to rcu-protected list
85 * @new: new entry to be added
86 * @head: list head to add it before
88 * Insert a new entry before the specified head.
89 * This is useful for implementing queues.
91 * The caller must take whatever precautions are necessary
92 * (such as holding appropriate locks) to avoid racing
93 * with another list-mutation primitive, such as list_add_tail_rcu()
94 * or list_del_rcu(), running on this same list.
95 * However, it is perfectly legal to run concurrently with
96 * the _rcu list-traversal primitives, such as
97 * list_for_each_entry_rcu().
99 static inline void list_add_tail_rcu(struct list_head
*new,
100 struct list_head
*head
)
102 __list_add_rcu(new, head
->prev
, head
);
106 * list_del_rcu - deletes entry from list without re-initialization
107 * @entry: the element to delete from the list.
109 * Note: list_empty() on entry does not return true after this,
110 * the entry is in an undefined state. It is useful for RCU based
111 * lockfree traversal.
113 * In particular, it means that we can not poison the forward
114 * pointers that may still be used for walking the list.
116 * The caller must take whatever precautions are necessary
117 * (such as holding appropriate locks) to avoid racing
118 * with another list-mutation primitive, such as list_del_rcu()
119 * or list_add_rcu(), running on this same list.
120 * However, it is perfectly legal to run concurrently with
121 * the _rcu list-traversal primitives, such as
122 * list_for_each_entry_rcu().
124 * Note that the caller is not permitted to immediately free
125 * the newly deleted entry. Instead, either synchronize_rcu()
126 * or call_rcu() must be used to defer freeing until an RCU
127 * grace period has elapsed.
129 static inline void list_del_rcu(struct list_head
*entry
)
131 __list_del_entry(entry
);
132 entry
->prev
= LIST_POISON2
;
136 * hlist_del_init_rcu - deletes entry from hash list with re-initialization
137 * @n: the element to delete from the hash list.
139 * Note: list_unhashed() on the node return true after this. It is
140 * useful for RCU based read lockfree traversal if the writer side
141 * must know if the list entry is still hashed or already unhashed.
143 * In particular, it means that we can not poison the forward pointers
144 * that may still be used for walking the hash list and we can only
145 * zero the pprev pointer so list_unhashed() will return true after
148 * The caller must take whatever precautions are necessary (such as
149 * holding appropriate locks) to avoid racing with another
150 * list-mutation primitive, such as hlist_add_head_rcu() or
151 * hlist_del_rcu(), running on this same list. However, it is
152 * perfectly legal to run concurrently with the _rcu list-traversal
153 * primitives, such as hlist_for_each_entry_rcu().
155 static inline void hlist_del_init_rcu(struct hlist_node
*n
)
157 if (!hlist_unhashed(n
)) {
164 * list_replace_rcu - replace old entry by new one
165 * @old : the element to be replaced
166 * @new : the new element to insert
168 * The @old entry will be replaced with the @new entry atomically.
169 * Note: @old should not be empty.
171 static inline void list_replace_rcu(struct list_head
*old
,
172 struct list_head
*new)
174 new->next
= old
->next
;
175 new->prev
= old
->prev
;
176 rcu_assign_pointer(list_next_rcu(new->prev
), new);
177 new->next
->prev
= new;
178 old
->prev
= LIST_POISON2
;
182 * list_splice_init_rcu - splice an RCU-protected list into an existing list.
183 * @list: the RCU-protected list to splice
184 * @head: the place in the list to splice the first list into
185 * @sync: function to sync: synchronize_rcu(), synchronize_sched(), ...
187 * @head can be RCU-read traversed concurrently with this function.
189 * Note that this function blocks.
191 * Important note: the caller must take whatever action is necessary to
192 * prevent any other updates to @head. In principle, it is possible
193 * to modify the list as soon as sync() begins execution.
194 * If this sort of thing becomes necessary, an alternative version
195 * based on call_rcu() could be created. But only if -really-
196 * needed -- there is no shortage of RCU API members.
198 static inline void list_splice_init_rcu(struct list_head
*list
,
199 struct list_head
*head
,
202 struct list_head
*first
= list
->next
;
203 struct list_head
*last
= list
->prev
;
204 struct list_head
*at
= head
->next
;
206 if (list_empty(list
))
210 * "first" and "last" tracking list, so initialize it. RCU readers
211 * have access to this list, so we must use INIT_LIST_HEAD_RCU()
212 * instead of INIT_LIST_HEAD().
215 INIT_LIST_HEAD_RCU(list
);
218 * At this point, the list body still points to the source list.
219 * Wait for any readers to finish using the list before splicing
220 * the list body into the new list. Any new readers will see
227 * Readers are finished with the source list, so perform splice.
228 * The order is important if the new list is global and accessible
229 * to concurrent RCU readers. Note that RCU readers are not
230 * permitted to traverse the prev pointers without excluding
235 rcu_assign_pointer(list_next_rcu(head
), first
);
241 * list_entry_rcu - get the struct for this entry
242 * @ptr: the &struct list_head pointer.
243 * @type: the type of the struct this is embedded in.
244 * @member: the name of the list_head within the struct.
246 * This primitive may safely run concurrently with the _rcu list-mutation
247 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
249 #define list_entry_rcu(ptr, type, member) \
251 typeof(*ptr) __rcu *__ptr = (typeof(*ptr) __rcu __force *)ptr; \
252 container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \
256 * Where are list_empty_rcu() and list_first_entry_rcu()?
258 * Implementing those functions following their counterparts list_empty() and
259 * list_first_entry() is not advisable because they lead to subtle race
260 * conditions as the following snippet shows:
262 * if (!list_empty_rcu(mylist)) {
263 * struct foo *bar = list_first_entry_rcu(mylist, struct foo, list_member);
267 * The list may not be empty when list_empty_rcu checks it, but it may be when
268 * list_first_entry_rcu rereads the ->next pointer.
270 * Rereading the ->next pointer is not a problem for list_empty() and
271 * list_first_entry() because they would be protected by a lock that blocks
274 * See list_first_or_null_rcu for an alternative.
278 * list_first_or_null_rcu - get the first element from a list
279 * @ptr: the list head to take the element from.
280 * @type: the type of the struct this is embedded in.
281 * @member: the name of the list_head within the struct.
283 * Note that if the list is empty, it returns NULL.
285 * This primitive may safely run concurrently with the _rcu list-mutation
286 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
288 #define list_first_or_null_rcu(ptr, type, member) \
290 struct list_head *__ptr = (ptr); \
291 struct list_head *__next = ACCESS_ONCE(__ptr->next); \
292 likely(__ptr != __next) ? list_entry_rcu(__next, type, member) : NULL; \
296 * list_for_each_entry_rcu - iterate over rcu list of given type
297 * @pos: the type * to use as a loop cursor.
298 * @head: the head for your list.
299 * @member: the name of the list_head within the struct.
301 * This list-traversal primitive may safely run concurrently with
302 * the _rcu list-mutation primitives such as list_add_rcu()
303 * as long as the traversal is guarded by rcu_read_lock().
305 #define list_for_each_entry_rcu(pos, head, member) \
306 for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
307 &pos->member != (head); \
308 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
311 * list_for_each_entry_continue_rcu - continue iteration over list of given type
312 * @pos: the type * to use as a loop cursor.
313 * @head: the head for your list.
314 * @member: the name of the list_head within the struct.
316 * Continue to iterate over list of given type, continuing after
317 * the current position.
319 #define list_for_each_entry_continue_rcu(pos, head, member) \
320 for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
321 &pos->member != (head); \
322 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
325 * hlist_del_rcu - deletes entry from hash list without re-initialization
326 * @n: the element to delete from the hash list.
328 * Note: list_unhashed() on entry does not return true after this,
329 * the entry is in an undefined state. It is useful for RCU based
330 * lockfree traversal.
332 * In particular, it means that we can not poison the forward
333 * pointers that may still be used for walking the hash list.
335 * The caller must take whatever precautions are necessary
336 * (such as holding appropriate locks) to avoid racing
337 * with another list-mutation primitive, such as hlist_add_head_rcu()
338 * or hlist_del_rcu(), running on this same list.
339 * However, it is perfectly legal to run concurrently with
340 * the _rcu list-traversal primitives, such as
341 * hlist_for_each_entry().
343 static inline void hlist_del_rcu(struct hlist_node
*n
)
346 n
->pprev
= LIST_POISON2
;
350 * hlist_replace_rcu - replace old entry by new one
351 * @old : the element to be replaced
352 * @new : the new element to insert
354 * The @old entry will be replaced with the @new entry atomically.
356 static inline void hlist_replace_rcu(struct hlist_node
*old
,
357 struct hlist_node
*new)
359 struct hlist_node
*next
= old
->next
;
362 new->pprev
= old
->pprev
;
363 rcu_assign_pointer(*(struct hlist_node __rcu
**)new->pprev
, new);
365 new->next
->pprev
= &new->next
;
366 old
->pprev
= LIST_POISON2
;
370 * return the first or the next element in an RCU protected hlist
372 #define hlist_first_rcu(head) (*((struct hlist_node __rcu **)(&(head)->first)))
373 #define hlist_next_rcu(node) (*((struct hlist_node __rcu **)(&(node)->next)))
374 #define hlist_pprev_rcu(node) (*((struct hlist_node __rcu **)((node)->pprev)))
378 * @n: the element to add to the hash list.
379 * @h: the list to add to.
382 * Adds the specified element to the specified hlist,
383 * while permitting racing traversals.
385 * The caller must take whatever precautions are necessary
386 * (such as holding appropriate locks) to avoid racing
387 * with another list-mutation primitive, such as hlist_add_head_rcu()
388 * or hlist_del_rcu(), running on this same list.
389 * However, it is perfectly legal to run concurrently with
390 * the _rcu list-traversal primitives, such as
391 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
392 * problems on Alpha CPUs. Regardless of the type of CPU, the
393 * list-traversal primitive must be guarded by rcu_read_lock().
395 static inline void hlist_add_head_rcu(struct hlist_node
*n
,
396 struct hlist_head
*h
)
398 struct hlist_node
*first
= h
->first
;
401 n
->pprev
= &h
->first
;
402 rcu_assign_pointer(hlist_first_rcu(h
), n
);
404 first
->pprev
= &n
->next
;
408 * hlist_add_before_rcu
409 * @n: the new element to add to the hash list.
410 * @next: the existing element to add the new element before.
413 * Adds the specified element to the specified hlist
414 * before the specified node while permitting racing traversals.
416 * The caller must take whatever precautions are necessary
417 * (such as holding appropriate locks) to avoid racing
418 * with another list-mutation primitive, such as hlist_add_head_rcu()
419 * or hlist_del_rcu(), running on this same list.
420 * However, it is perfectly legal to run concurrently with
421 * the _rcu list-traversal primitives, such as
422 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
423 * problems on Alpha CPUs.
425 static inline void hlist_add_before_rcu(struct hlist_node
*n
,
426 struct hlist_node
*next
)
428 n
->pprev
= next
->pprev
;
430 rcu_assign_pointer(hlist_pprev_rcu(n
), n
);
431 next
->pprev
= &n
->next
;
435 * hlist_add_behind_rcu
436 * @n: the new element to add to the hash list.
437 * @prev: the existing element to add the new element after.
440 * Adds the specified element to the specified hlist
441 * after the specified node while permitting racing traversals.
443 * The caller must take whatever precautions are necessary
444 * (such as holding appropriate locks) to avoid racing
445 * with another list-mutation primitive, such as hlist_add_head_rcu()
446 * or hlist_del_rcu(), running on this same list.
447 * However, it is perfectly legal to run concurrently with
448 * the _rcu list-traversal primitives, such as
449 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
450 * problems on Alpha CPUs.
452 static inline void hlist_add_behind_rcu(struct hlist_node
*n
,
453 struct hlist_node
*prev
)
455 n
->next
= prev
->next
;
456 n
->pprev
= &prev
->next
;
457 rcu_assign_pointer(hlist_next_rcu(prev
), n
);
459 n
->next
->pprev
= &n
->next
;
462 #define __hlist_for_each_rcu(pos, head) \
463 for (pos = rcu_dereference(hlist_first_rcu(head)); \
465 pos = rcu_dereference(hlist_next_rcu(pos)))
468 * hlist_for_each_entry_rcu - iterate over rcu list of given type
469 * @pos: the type * to use as a loop cursor.
470 * @head: the head for your list.
471 * @member: the name of the hlist_node within the struct.
473 * This list-traversal primitive may safely run concurrently with
474 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
475 * as long as the traversal is guarded by rcu_read_lock().
477 #define hlist_for_each_entry_rcu(pos, head, member) \
478 for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
479 typeof(*(pos)), member); \
481 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
482 &(pos)->member)), typeof(*(pos)), member))
485 * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing)
486 * @pos: the type * to use as a loop cursor.
487 * @head: the head for your list.
488 * @member: the name of the hlist_node within the struct.
490 * This list-traversal primitive may safely run concurrently with
491 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
492 * as long as the traversal is guarded by rcu_read_lock().
494 * This is the same as hlist_for_each_entry_rcu() except that it does
495 * not do any RCU debugging or tracing.
497 #define hlist_for_each_entry_rcu_notrace(pos, head, member) \
498 for (pos = hlist_entry_safe (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\
499 typeof(*(pos)), member); \
501 pos = hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\
502 &(pos)->member)), typeof(*(pos)), member))
505 * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type
506 * @pos: the type * to use as a loop cursor.
507 * @head: the head for your list.
508 * @member: the name of the hlist_node within the struct.
510 * This list-traversal primitive may safely run concurrently with
511 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
512 * as long as the traversal is guarded by rcu_read_lock().
514 #define hlist_for_each_entry_rcu_bh(pos, head, member) \
515 for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_first_rcu(head)),\
516 typeof(*(pos)), member); \
518 pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(\
519 &(pos)->member)), typeof(*(pos)), member))
522 * hlist_for_each_entry_continue_rcu - iterate over a hlist continuing after current point
523 * @pos: the type * to use as a loop cursor.
524 * @member: the name of the hlist_node within the struct.
526 #define hlist_for_each_entry_continue_rcu(pos, member) \
527 for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
528 &(pos)->member)), typeof(*(pos)), member); \
530 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
531 &(pos)->member)), typeof(*(pos)), member))
534 * hlist_for_each_entry_continue_rcu_bh - iterate over a hlist continuing after current point
535 * @pos: the type * to use as a loop cursor.
536 * @member: the name of the hlist_node within the struct.
538 #define hlist_for_each_entry_continue_rcu_bh(pos, member) \
539 for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu( \
540 &(pos)->member)), typeof(*(pos)), member); \
542 pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu( \
543 &(pos)->member)), typeof(*(pos)), member))
546 * hlist_for_each_entry_from_rcu - iterate over a hlist continuing from current point
547 * @pos: the type * to use as a loop cursor.
548 * @member: the name of the hlist_node within the struct.
550 #define hlist_for_each_entry_from_rcu(pos, member) \
552 pos = hlist_entry_safe(rcu_dereference((pos)->member.next),\
553 typeof(*(pos)), member))
555 #endif /* __KERNEL__ */
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