cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
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rculist.h (29242B)


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