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git.proxmox.com Git - mirror_ubuntu-zesty-kernel.git/blob - include/linux/rculist.h
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 * return the ->next pointer of a list_head in an rcu safe
23 * way, we must not access it directly
25 #define list_next_rcu(list) (*((struct list_head __rcu **)(&(list)->next)))
28 * Insert a new entry between two known consecutive entries.
30 * This is only for internal list manipulation where we know
31 * the prev/next entries already!
33 #ifndef CONFIG_DEBUG_LIST
34 static inline void __list_add_rcu(struct list_head
*new,
35 struct list_head
*prev
, struct list_head
*next
)
39 rcu_assign_pointer(list_next_rcu(prev
), new);
43 extern void __list_add_rcu(struct list_head
*new,
44 struct list_head
*prev
, struct list_head
*next
);
48 * list_add_rcu - add a new entry to rcu-protected list
49 * @new: new entry to be added
50 * @head: list head to add it after
52 * Insert a new entry after the specified head.
53 * This is good for implementing stacks.
55 * The caller must take whatever precautions are necessary
56 * (such as holding appropriate locks) to avoid racing
57 * with another list-mutation primitive, such as list_add_rcu()
58 * or list_del_rcu(), running on this same list.
59 * However, it is perfectly legal to run concurrently with
60 * the _rcu list-traversal primitives, such as
61 * list_for_each_entry_rcu().
63 static inline void list_add_rcu(struct list_head
*new, struct list_head
*head
)
65 __list_add_rcu(new, head
, head
->next
);
69 * list_add_tail_rcu - add a new entry to rcu-protected list
70 * @new: new entry to be added
71 * @head: list head to add it before
73 * Insert a new entry before the specified head.
74 * This is useful for implementing queues.
76 * The caller must take whatever precautions are necessary
77 * (such as holding appropriate locks) to avoid racing
78 * with another list-mutation primitive, such as list_add_tail_rcu()
79 * or list_del_rcu(), running on this same list.
80 * However, it is perfectly legal to run concurrently with
81 * the _rcu list-traversal primitives, such as
82 * list_for_each_entry_rcu().
84 static inline void list_add_tail_rcu(struct list_head
*new,
85 struct list_head
*head
)
87 __list_add_rcu(new, head
->prev
, head
);
91 * list_del_rcu - deletes entry from list without re-initialization
92 * @entry: the element to delete from the list.
94 * Note: list_empty() on entry does not return true after this,
95 * the entry is in an undefined state. It is useful for RCU based
98 * In particular, it means that we can not poison the forward
99 * pointers that may still be used for walking the list.
101 * The caller must take whatever precautions are necessary
102 * (such as holding appropriate locks) to avoid racing
103 * with another list-mutation primitive, such as list_del_rcu()
104 * or list_add_rcu(), running on this same list.
105 * However, it is perfectly legal to run concurrently with
106 * the _rcu list-traversal primitives, such as
107 * list_for_each_entry_rcu().
109 * Note that the caller is not permitted to immediately free
110 * the newly deleted entry. Instead, either synchronize_rcu()
111 * or call_rcu() must be used to defer freeing until an RCU
112 * grace period has elapsed.
114 static inline void list_del_rcu(struct list_head
*entry
)
116 __list_del_entry(entry
);
117 entry
->prev
= LIST_POISON2
;
121 * hlist_del_init_rcu - deletes entry from hash list with re-initialization
122 * @n: the element to delete from the hash list.
124 * Note: list_unhashed() on the node return true after this. It is
125 * useful for RCU based read lockfree traversal if the writer side
126 * must know if the list entry is still hashed or already unhashed.
128 * In particular, it means that we can not poison the forward pointers
129 * that may still be used for walking the hash list and we can only
130 * zero the pprev pointer so list_unhashed() will return true after
133 * The caller must take whatever precautions are necessary (such as
134 * holding appropriate locks) to avoid racing with another
135 * list-mutation primitive, such as hlist_add_head_rcu() or
136 * hlist_del_rcu(), running on this same list. However, it is
137 * perfectly legal to run concurrently with the _rcu list-traversal
138 * primitives, such as hlist_for_each_entry_rcu().
140 static inline void hlist_del_init_rcu(struct hlist_node
*n
)
142 if (!hlist_unhashed(n
)) {
149 * list_replace_rcu - replace old entry by new one
150 * @old : the element to be replaced
151 * @new : the new element to insert
153 * The @old entry will be replaced with the @new entry atomically.
154 * Note: @old should not be empty.
156 static inline void list_replace_rcu(struct list_head
*old
,
157 struct list_head
*new)
159 new->next
= old
->next
;
160 new->prev
= old
->prev
;
161 rcu_assign_pointer(list_next_rcu(new->prev
), new);
162 new->next
->prev
= new;
163 old
->prev
= LIST_POISON2
;
167 * list_splice_init_rcu - splice an RCU-protected list into an existing list.
168 * @list: the RCU-protected list to splice
169 * @head: the place in the list to splice the first list into
170 * @sync: function to sync: synchronize_rcu(), synchronize_sched(), ...
172 * @head can be RCU-read traversed concurrently with this function.
174 * Note that this function blocks.
176 * Important note: the caller must take whatever action is necessary to
177 * prevent any other updates to @head. In principle, it is possible
178 * to modify the list as soon as sync() begins execution.
179 * If this sort of thing becomes necessary, an alternative version
180 * based on call_rcu() could be created. But only if -really-
181 * needed -- there is no shortage of RCU API members.
183 static inline void list_splice_init_rcu(struct list_head
*list
,
184 struct list_head
*head
,
187 struct list_head
*first
= list
->next
;
188 struct list_head
*last
= list
->prev
;
189 struct list_head
*at
= head
->next
;
191 if (list_empty(list
))
194 /* "first" and "last" tracking list, so initialize it. */
196 INIT_LIST_HEAD(list
);
199 * At this point, the list body still points to the source list.
200 * Wait for any readers to finish using the list before splicing
201 * the list body into the new list. Any new readers will see
208 * Readers are finished with the source list, so perform splice.
209 * The order is important if the new list is global and accessible
210 * to concurrent RCU readers. Note that RCU readers are not
211 * permitted to traverse the prev pointers without excluding
216 rcu_assign_pointer(list_next_rcu(head
), first
);
222 * list_entry_rcu - get the struct for this entry
223 * @ptr: the &struct list_head pointer.
224 * @type: the type of the struct this is embedded in.
225 * @member: the name of the list_struct within the struct.
227 * This primitive may safely run concurrently with the _rcu list-mutation
228 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
230 #define list_entry_rcu(ptr, type, member) \
231 ({typeof (*ptr) __rcu *__ptr = (typeof (*ptr) __rcu __force *)ptr; \
232 container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \
236 * Where are list_empty_rcu() and list_first_entry_rcu()?
238 * Implementing those functions following their counterparts list_empty() and
239 * list_first_entry() is not advisable because they lead to subtle race
240 * conditions as the following snippet shows:
242 * if (!list_empty_rcu(mylist)) {
243 * struct foo *bar = list_first_entry_rcu(mylist, struct foo, list_member);
247 * The list may not be empty when list_empty_rcu checks it, but it may be when
248 * list_first_entry_rcu rereads the ->next pointer.
250 * Rereading the ->next pointer is not a problem for list_empty() and
251 * list_first_entry() because they would be protected by a lock that blocks
254 * See list_first_or_null_rcu for an alternative.
258 * list_first_or_null_rcu - get the first element from a list
259 * @ptr: the list head to take the element from.
260 * @type: the type of the struct this is embedded in.
261 * @member: the name of the list_struct within the struct.
263 * Note that if the list is empty, it returns NULL.
265 * This primitive may safely run concurrently with the _rcu list-mutation
266 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
268 #define list_first_or_null_rcu(ptr, type, member) \
269 ({struct list_head *__ptr = (ptr); \
270 struct list_head __rcu *__next = list_next_rcu(__ptr); \
271 likely(__ptr != __next) ? container_of(__next, type, member) : NULL; \
275 * list_for_each_entry_rcu - iterate over rcu list of given type
276 * @pos: the type * to use as a loop cursor.
277 * @head: the head for your list.
278 * @member: the name of the list_struct within the struct.
280 * This list-traversal primitive may safely run concurrently with
281 * the _rcu list-mutation primitives such as list_add_rcu()
282 * as long as the traversal is guarded by rcu_read_lock().
284 #define list_for_each_entry_rcu(pos, head, member) \
285 for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
286 &pos->member != (head); \
287 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
290 * list_for_each_entry_continue_rcu - continue iteration over list of given type
291 * @pos: the type * to use as a loop cursor.
292 * @head: the head for your list.
293 * @member: the name of the list_struct within the struct.
295 * Continue to iterate over list of given type, continuing after
296 * the current position.
298 #define list_for_each_entry_continue_rcu(pos, head, member) \
299 for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
300 &pos->member != (head); \
301 pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
304 * hlist_del_rcu - deletes entry from hash list without re-initialization
305 * @n: the element to delete from the hash list.
307 * Note: list_unhashed() on entry does not return true after this,
308 * the entry is in an undefined state. It is useful for RCU based
309 * lockfree traversal.
311 * In particular, it means that we can not poison the forward
312 * pointers that may still be used for walking the hash list.
314 * The caller must take whatever precautions are necessary
315 * (such as holding appropriate locks) to avoid racing
316 * with another list-mutation primitive, such as hlist_add_head_rcu()
317 * or hlist_del_rcu(), running on this same list.
318 * However, it is perfectly legal to run concurrently with
319 * the _rcu list-traversal primitives, such as
320 * hlist_for_each_entry().
322 static inline void hlist_del_rcu(struct hlist_node
*n
)
325 n
->pprev
= LIST_POISON2
;
329 * hlist_replace_rcu - replace old entry by new one
330 * @old : the element to be replaced
331 * @new : the new element to insert
333 * The @old entry will be replaced with the @new entry atomically.
335 static inline void hlist_replace_rcu(struct hlist_node
*old
,
336 struct hlist_node
*new)
338 struct hlist_node
*next
= old
->next
;
341 new->pprev
= old
->pprev
;
342 rcu_assign_pointer(*(struct hlist_node __rcu
**)new->pprev
, new);
344 new->next
->pprev
= &new->next
;
345 old
->pprev
= LIST_POISON2
;
349 * return the first or the next element in an RCU protected hlist
351 #define hlist_first_rcu(head) (*((struct hlist_node __rcu **)(&(head)->first)))
352 #define hlist_next_rcu(node) (*((struct hlist_node __rcu **)(&(node)->next)))
353 #define hlist_pprev_rcu(node) (*((struct hlist_node __rcu **)((node)->pprev)))
357 * @n: the element to add to the hash list.
358 * @h: the list to add to.
361 * Adds the specified element to the specified hlist,
362 * while permitting racing traversals.
364 * The caller must take whatever precautions are necessary
365 * (such as holding appropriate locks) to avoid racing
366 * with another list-mutation primitive, such as hlist_add_head_rcu()
367 * or hlist_del_rcu(), running on this same list.
368 * However, it is perfectly legal to run concurrently with
369 * the _rcu list-traversal primitives, such as
370 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
371 * problems on Alpha CPUs. Regardless of the type of CPU, the
372 * list-traversal primitive must be guarded by rcu_read_lock().
374 static inline void hlist_add_head_rcu(struct hlist_node
*n
,
375 struct hlist_head
*h
)
377 struct hlist_node
*first
= h
->first
;
380 n
->pprev
= &h
->first
;
381 rcu_assign_pointer(hlist_first_rcu(h
), n
);
383 first
->pprev
= &n
->next
;
387 * hlist_add_before_rcu
388 * @n: the new element to add to the hash list.
389 * @next: the existing element to add the new element before.
392 * Adds the specified element to the specified hlist
393 * before the specified node while permitting racing traversals.
395 * The caller must take whatever precautions are necessary
396 * (such as holding appropriate locks) to avoid racing
397 * with another list-mutation primitive, such as hlist_add_head_rcu()
398 * or hlist_del_rcu(), running on this same list.
399 * However, it is perfectly legal to run concurrently with
400 * the _rcu list-traversal primitives, such as
401 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
402 * problems on Alpha CPUs.
404 static inline void hlist_add_before_rcu(struct hlist_node
*n
,
405 struct hlist_node
*next
)
407 n
->pprev
= next
->pprev
;
409 rcu_assign_pointer(hlist_pprev_rcu(n
), n
);
410 next
->pprev
= &n
->next
;
414 * hlist_add_after_rcu
415 * @prev: the existing element to add the new element after.
416 * @n: the new element to add to the hash list.
419 * Adds the specified element to the specified hlist
420 * after the specified node while permitting racing traversals.
422 * The caller must take whatever precautions are necessary
423 * (such as holding appropriate locks) to avoid racing
424 * with another list-mutation primitive, such as hlist_add_head_rcu()
425 * or hlist_del_rcu(), running on this same list.
426 * However, it is perfectly legal to run concurrently with
427 * the _rcu list-traversal primitives, such as
428 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
429 * problems on Alpha CPUs.
431 static inline void hlist_add_after_rcu(struct hlist_node
*prev
,
432 struct hlist_node
*n
)
434 n
->next
= prev
->next
;
435 n
->pprev
= &prev
->next
;
436 rcu_assign_pointer(hlist_next_rcu(prev
), n
);
438 n
->next
->pprev
= &n
->next
;
441 #define __hlist_for_each_rcu(pos, head) \
442 for (pos = rcu_dereference(hlist_first_rcu(head)); \
444 pos = rcu_dereference(hlist_next_rcu(pos)))
447 * hlist_for_each_entry_rcu - iterate over rcu list of given type
448 * @pos: the type * to use as a loop cursor.
449 * @head: the head for your list.
450 * @member: the name of the hlist_node within the struct.
452 * This list-traversal primitive may safely run concurrently with
453 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
454 * as long as the traversal is guarded by rcu_read_lock().
456 #define hlist_for_each_entry_rcu(pos, head, member) \
457 for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
458 typeof(*(pos)), member); \
460 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
461 &(pos)->member)), typeof(*(pos)), member))
464 * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing)
465 * @pos: the type * to use as a loop cursor.
466 * @head: the head for your list.
467 * @member: the name of the hlist_node within the struct.
469 * This list-traversal primitive may safely run concurrently with
470 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
471 * as long as the traversal is guarded by rcu_read_lock().
473 * This is the same as hlist_for_each_entry_rcu() except that it does
474 * not do any RCU debugging or tracing.
476 #define hlist_for_each_entry_rcu_notrace(pos, head, member) \
477 for (pos = hlist_entry_safe (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\
478 typeof(*(pos)), member); \
480 pos = hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\
481 &(pos)->member)), typeof(*(pos)), member))
484 * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type
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 #define hlist_for_each_entry_rcu_bh(pos, head, member) \
494 for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_first_rcu(head)),\
495 typeof(*(pos)), member); \
497 pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(\
498 &(pos)->member)), typeof(*(pos)), member))
501 * hlist_for_each_entry_continue_rcu - iterate over a hlist continuing after current point
502 * @pos: the type * to use as a loop cursor.
503 * @member: the name of the hlist_node within the struct.
505 #define hlist_for_each_entry_continue_rcu(pos, member) \
506 for (pos = hlist_entry_safe(rcu_dereference((pos)->member.next),\
507 typeof(*(pos)), member); \
509 pos = hlist_entry_safe(rcu_dereference((pos)->member.next),\
510 typeof(*(pos)), member))
513 * hlist_for_each_entry_continue_rcu_bh - iterate over a hlist continuing after current point
514 * @pos: the type * to use as a loop cursor.
515 * @member: the name of the hlist_node within the struct.
517 #define hlist_for_each_entry_continue_rcu_bh(pos, member) \
518 for (pos = hlist_entry_safe(rcu_dereference_bh((pos)->member.next),\
519 typeof(*(pos)), member); \
521 pos = hlist_entry_safe(rcu_dereference_bh((pos)->member.next),\
522 typeof(*(pos)), member))
525 #endif /* __KERNEL__ */