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_struct 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) \
250 ({typeof (*ptr) __rcu *__ptr = (typeof (*ptr) __rcu __force *)ptr; \
251 container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \
255 * Where are list_empty_rcu() and list_first_entry_rcu()?
257 * Implementing those functions following their counterparts list_empty() and
258 * list_first_entry() is not advisable because they lead to subtle race
259 * conditions as the following snippet shows:
261 * if (!list_empty_rcu(mylist)) {
262 * struct foo *bar = list_first_entry_rcu(mylist, struct foo, list_member);
266 * The list may not be empty when list_empty_rcu checks it, but it may be when
267 * list_first_entry_rcu rereads the ->next pointer.
269 * Rereading the ->next pointer is not a problem for list_empty() and
270 * list_first_entry() because they would be protected by a lock that blocks
273 * See list_first_or_null_rcu for an alternative.
277 * list_first_or_null_rcu - get the first element from a list
278 * @ptr: the list head to take the element from.
279 * @type: the type of the struct this is embedded in.
280 * @member: the name of the list_struct within the struct.
282 * Note that if the list is empty, it returns NULL.
284 * This primitive may safely run concurrently with the _rcu list-mutation
285 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
287 #define list_first_or_null_rcu(ptr, type, member) \
288 ({struct list_head *__ptr = (ptr); \
289 struct list_head *__next = ACCESS_ONCE(__ptr->next); \
290 likely(__ptr != __next) ? \
291 list_entry_rcu(__next, type, member) : NULL; \
295 * list_for_each_entry_rcu - iterate over rcu list of given type
296 * @pos: the type * to use as a loop cursor.
297 * @head: the head for your list.
298 * @member: the name of the list_struct within the struct.
300 * This list-traversal primitive may safely run concurrently with
301 * the _rcu list-mutation primitives such as list_add_rcu()
302 * as long as the traversal is guarded by rcu_read_lock().
304 #define list_for_each_entry_rcu(pos, head, member) \
305 for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
306 &pos->member != (head); \
307 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
310 * list_for_each_entry_continue_rcu - continue iteration over list of given type
311 * @pos: the type * to use as a loop cursor.
312 * @head: the head for your list.
313 * @member: the name of the list_struct within the struct.
315 * Continue to iterate over list of given type, continuing after
316 * the current position.
318 #define list_for_each_entry_continue_rcu(pos, head, member) \
319 for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
320 &pos->member != (head); \
321 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
324 * hlist_del_rcu - deletes entry from hash list without re-initialization
325 * @n: the element to delete from the hash list.
327 * Note: list_unhashed() on entry does not return true after this,
328 * the entry is in an undefined state. It is useful for RCU based
329 * lockfree traversal.
331 * In particular, it means that we can not poison the forward
332 * pointers that may still be used for walking the hash list.
334 * The caller must take whatever precautions are necessary
335 * (such as holding appropriate locks) to avoid racing
336 * with another list-mutation primitive, such as hlist_add_head_rcu()
337 * or hlist_del_rcu(), running on this same list.
338 * However, it is perfectly legal to run concurrently with
339 * the _rcu list-traversal primitives, such as
340 * hlist_for_each_entry().
342 static inline void hlist_del_rcu(struct hlist_node
*n
)
345 n
->pprev
= LIST_POISON2
;
349 * hlist_replace_rcu - replace old entry by new one
350 * @old : the element to be replaced
351 * @new : the new element to insert
353 * The @old entry will be replaced with the @new entry atomically.
355 static inline void hlist_replace_rcu(struct hlist_node
*old
,
356 struct hlist_node
*new)
358 struct hlist_node
*next
= old
->next
;
361 new->pprev
= old
->pprev
;
362 rcu_assign_pointer(*(struct hlist_node __rcu
**)new->pprev
, new);
364 new->next
->pprev
= &new->next
;
365 old
->pprev
= LIST_POISON2
;
369 * return the first or the next element in an RCU protected hlist
371 #define hlist_first_rcu(head) (*((struct hlist_node __rcu **)(&(head)->first)))
372 #define hlist_next_rcu(node) (*((struct hlist_node __rcu **)(&(node)->next)))
373 #define hlist_pprev_rcu(node) (*((struct hlist_node __rcu **)((node)->pprev)))
377 * @n: the element to add to the hash list.
378 * @h: the list to add to.
381 * Adds the specified element to the specified hlist,
382 * while permitting racing traversals.
384 * The caller must take whatever precautions are necessary
385 * (such as holding appropriate locks) to avoid racing
386 * with another list-mutation primitive, such as hlist_add_head_rcu()
387 * or hlist_del_rcu(), running on this same list.
388 * However, it is perfectly legal to run concurrently with
389 * the _rcu list-traversal primitives, such as
390 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
391 * problems on Alpha CPUs. Regardless of the type of CPU, the
392 * list-traversal primitive must be guarded by rcu_read_lock().
394 static inline void hlist_add_head_rcu(struct hlist_node
*n
,
395 struct hlist_head
*h
)
397 struct hlist_node
*first
= h
->first
;
400 n
->pprev
= &h
->first
;
401 rcu_assign_pointer(hlist_first_rcu(h
), n
);
403 first
->pprev
= &n
->next
;
407 * hlist_add_before_rcu
408 * @n: the new element to add to the hash list.
409 * @next: the existing element to add the new element before.
412 * Adds the specified element to the specified hlist
413 * before the specified node while permitting racing traversals.
415 * The caller must take whatever precautions are necessary
416 * (such as holding appropriate locks) to avoid racing
417 * with another list-mutation primitive, such as hlist_add_head_rcu()
418 * or hlist_del_rcu(), running on this same list.
419 * However, it is perfectly legal to run concurrently with
420 * the _rcu list-traversal primitives, such as
421 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
422 * problems on Alpha CPUs.
424 static inline void hlist_add_before_rcu(struct hlist_node
*n
,
425 struct hlist_node
*next
)
427 n
->pprev
= next
->pprev
;
429 rcu_assign_pointer(hlist_pprev_rcu(n
), n
);
430 next
->pprev
= &n
->next
;
434 * hlist_add_after_rcu
435 * @prev: the existing element to add the new element after.
436 * @n: the new element to add to the hash list.
439 * Adds the specified element to the specified hlist
440 * after the specified node while permitting racing traversals.
442 * The caller must take whatever precautions are necessary
443 * (such as holding appropriate locks) to avoid racing
444 * with another list-mutation primitive, such as hlist_add_head_rcu()
445 * or hlist_del_rcu(), running on this same list.
446 * However, it is perfectly legal to run concurrently with
447 * the _rcu list-traversal primitives, such as
448 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
449 * problems on Alpha CPUs.
451 static inline void hlist_add_after_rcu(struct hlist_node
*prev
,
452 struct hlist_node
*n
)
454 n
->next
= prev
->next
;
455 n
->pprev
= &prev
->next
;
456 rcu_assign_pointer(hlist_next_rcu(prev
), n
);
458 n
->next
->pprev
= &n
->next
;
461 #define __hlist_for_each_rcu(pos, head) \
462 for (pos = rcu_dereference(hlist_first_rcu(head)); \
464 pos = rcu_dereference(hlist_next_rcu(pos)))
467 * hlist_for_each_entry_rcu - iterate over rcu list of given type
468 * @pos: the type * to use as a loop cursor.
469 * @head: the head for your list.
470 * @member: the name of the hlist_node within the struct.
472 * This list-traversal primitive may safely run concurrently with
473 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
474 * as long as the traversal is guarded by rcu_read_lock().
476 #define hlist_for_each_entry_rcu(pos, head, member) \
477 for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
478 typeof(*(pos)), member); \
480 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
481 &(pos)->member)), typeof(*(pos)), member))
484 * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing)
485 * @pos: the type * to use as a loop cursor.
486 * @head: the head for your list.
487 * @member: the name of the hlist_node within the struct.
489 * This list-traversal primitive may safely run concurrently with
490 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
491 * as long as the traversal is guarded by rcu_read_lock().
493 * This is the same as hlist_for_each_entry_rcu() except that it does
494 * not do any RCU debugging or tracing.
496 #define hlist_for_each_entry_rcu_notrace(pos, head, member) \
497 for (pos = hlist_entry_safe (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\
498 typeof(*(pos)), member); \
500 pos = hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\
501 &(pos)->member)), typeof(*(pos)), member))
504 * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type
505 * @pos: the type * to use as a loop cursor.
506 * @head: the head for your list.
507 * @member: the name of the hlist_node within the struct.
509 * This list-traversal primitive may safely run concurrently with
510 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
511 * as long as the traversal is guarded by rcu_read_lock().
513 #define hlist_for_each_entry_rcu_bh(pos, head, member) \
514 for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_first_rcu(head)),\
515 typeof(*(pos)), member); \
517 pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(\
518 &(pos)->member)), typeof(*(pos)), member))
521 * hlist_for_each_entry_continue_rcu - iterate over a hlist continuing after current point
522 * @pos: the type * to use as a loop cursor.
523 * @member: the name of the hlist_node within the struct.
525 #define hlist_for_each_entry_continue_rcu(pos, member) \
526 for (pos = hlist_entry_safe(rcu_dereference((pos)->member.next),\
527 typeof(*(pos)), member); \
529 pos = hlist_entry_safe(rcu_dereference((pos)->member.next),\
530 typeof(*(pos)), member))
533 * hlist_for_each_entry_continue_rcu_bh - iterate over a hlist continuing after current point
534 * @pos: the type * to use as a loop cursor.
535 * @member: the name of the hlist_node within the struct.
537 #define hlist_for_each_entry_continue_rcu_bh(pos, member) \
538 for (pos = hlist_entry_safe(rcu_dereference_bh((pos)->member.next),\
539 typeof(*(pos)), member); \
541 pos = hlist_entry_safe(rcu_dereference_bh((pos)->member.next),\
542 typeof(*(pos)), member))
545 #endif /* __KERNEL__ */
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