include/linux/llist.h - kernel/common - Git at Google

 /* SPDX-License-Identifier: GPL-2.0-only */
 #ifndef LLIST_H
 #define LLIST_H
 /*
  * Lock-less NULL terminated single linked list
  *
  * Cases where locking is not needed:
  * If there are multiple producers and multiple consumers, llist_add can be
  * used in producers and llist_del_all can be used in consumers simultaneously
  * without locking. Also a single consumer can use llist_del_first while
  * multiple producers simultaneously use llist_add, without any locking.
  *
  * Cases where locking is needed:
  * If we have multiple consumers with llist_del_first used in one consumer, and
  * llist_del_first or llist_del_all used in other consumers, then a lock is
  * needed.  This is because llist_del_first depends on list->first->next not
  * changing, but without lock protection, there's no way to be sure about that
  * if a preemption happens in the middle of the delete operation and on being
  * preempted back, the list->first is the same as before causing the cmpxchg in
  * llist_del_first to succeed. For example, while a llist_del_first operation
  * is in progress in one consumer, then a llist_del_first, llist_add,
  * llist_add (or llist_del_all, llist_add, llist_add) sequence in another
  * consumer may cause violations.
  *
  * This can be summarized as follows:
  *
  *           |   add    | del_first |  del_all
  * add       |    -     |     -     |     -
  * del_first |          |     L     |     L
  * del_all   |          |           |     -
  *
  * Where, a particular row's operation can happen concurrently with a column's
  * operation, with "-" being no lock needed, while "L" being lock is needed.
  *
  * The list entries deleted via llist_del_all can be traversed with
  * traversing function such as llist_for_each etc.  But the list
  * entries can not be traversed safely before deleted from the list.
  * The order of deleted entries is from the newest to the oldest added
  * one.  If you want to traverse from the oldest to the newest, you
  * must reverse the order by yourself before traversing.
  *
  * The basic atomic operation of this list is cmpxchg on long.  On
  * architectures that don't have NMI-safe cmpxchg implementation, the
  * list can NOT be used in NMI handlers.  So code that uses the list in
  * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
  *
  * Copyright 2010,2011 Intel Corp.
  *   Author: Huang Ying <ying.huang@intel.com>
  */

 #include <linux/atomic.h>
 #include <linux/container_of.h>
 #include <linux/stddef.h>
 #include <linux/types.h>

 struct llist_head {
 	struct llist_node *first;
 };

 struct llist_node {
 	struct llist_node *next;
 };

 #define LLIST_HEAD_INIT(name)	{ NULL }
 #define LLIST_HEAD(name)	struct llist_head name = LLIST_HEAD_INIT(name)

 /**
  * init_llist_head - initialize lock-less list head
  * @head:	the head for your lock-less list
  */
 static inline void init_llist_head(struct llist_head *list)
 {
 	list->first = NULL;
 }

 /**
  * init_llist_node - initialize lock-less list node
  * @node:	the node to be initialised
  *
  * In cases where there is a need to test if a node is on
  * a list or not, this initialises the node to clearly
  * not be on any list.
  */
 static inline void init_llist_node(struct llist_node *node)
 {
 	node->next = node;
 }

 /**
  * llist_on_list - test if a lock-list list node is on a list
  * @node:	the node to test
  *
  * When a node is on a list the ->next pointer will be NULL or
  * some other node.  It can never point to itself.  We use that
  * in init_llist_node() to record that a node is not on any list,
  * and here to test whether it is on any list.
  */
 static inline bool llist_on_list(const struct llist_node *node)
 {
 	return node->next != node;
 }

 /**
  * llist_entry - get the struct of this entry
  * @ptr:	the &struct llist_node pointer.
  * @type:	the type of the struct this is embedded in.
  * @member:	the name of the llist_node within the struct.
  */
 #define llist_entry(ptr, type, member)		\
 	container_of(ptr, type, member)

 /**
  * member_address_is_nonnull - check whether the member address is not NULL
  * @ptr:	the object pointer (struct type * that contains the llist_node)
  * @member:	the name of the llist_node within the struct.
  *
  * This macro is conceptually the same as
  *	&ptr->member != NULL
  * but it works around the fact that compilers can decide that taking a member
  * address is never a NULL pointer.
  *
  * Real objects that start at a high address and have a member at NULL are
  * unlikely to exist, but such pointers may be returned e.g. by the
  * container_of() macro.
  */
 #define member_address_is_nonnull(ptr, member)	\
 	((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)

 /**
  * llist_for_each - iterate over some deleted entries of a lock-less list
  * @pos:	the &struct llist_node to use as a loop cursor
  * @node:	the first entry of deleted list entries
  *
  * In general, some entries of the lock-less list can be traversed
  * safely only after being deleted from list, so start with an entry
  * instead of list head.
  *
  * If being used on entries deleted from lock-less list directly, the
  * traverse order is from the newest to the oldest added entry.  If
  * you want to traverse from the oldest to the newest, you must
  * reverse the order by yourself before traversing.
  */
 #define llist_for_each(pos, node)			\
 	for ((pos) = (node); pos; (pos) = (pos)->next)

 /**
  * llist_for_each_safe - iterate over some deleted entries of a lock-less list
  *			 safe against removal of list entry
  * @pos:	the &struct llist_node to use as a loop cursor
  * @n:		another &struct llist_node to use as temporary storage
  * @node:	the first entry of deleted list entries
  *
  * In general, some entries of the lock-less list can be traversed
  * safely only after being deleted from list, so start with an entry
  * instead of list head.
  *
  * If being used on entries deleted from lock-less list directly, the
  * traverse order is from the newest to the oldest added entry.  If
  * you want to traverse from the oldest to the newest, you must
  * reverse the order by yourself before traversing.
  */
 #define llist_for_each_safe(pos, n, node)			\
 	for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))

 /**
  * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
  * @pos:	the type * to use as a loop cursor.
  * @node:	the fist entry of deleted list entries.
  * @member:	the name of the llist_node with the struct.
  *
  * In general, some entries of the lock-less list can be traversed
  * safely only after being removed from list, so start with an entry
  * instead of list head.
  *
  * If being used on entries deleted from lock-less list directly, the
  * traverse order is from the newest to the oldest added entry.  If
  * you want to traverse from the oldest to the newest, you must
  * reverse the order by yourself before traversing.
  */
 #define llist_for_each_entry(pos, node, member)				\
 	for ((pos) = llist_entry((node), typeof(*(pos)), member);	\
 	     member_address_is_nonnull(pos, member);			\
 	     (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))

 /**
  * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
  *			       safe against removal of list entry
  * @pos:	the type * to use as a loop cursor.
  * @n:		another type * to use as temporary storage
  * @node:	the first entry of deleted list entries.
  * @member:	the name of the llist_node with the struct.
  *
  * In general, some entries of the lock-less list can be traversed
  * safely only after being removed from list, so start with an entry
  * instead of list head.
  *
  * If being used on entries deleted from lock-less list directly, the
  * traverse order is from the newest to the oldest added entry.  If
  * you want to traverse from the oldest to the newest, you must
  * reverse the order by yourself before traversing.
  */
 #define llist_for_each_entry_safe(pos, n, node, member)			       \
 	for (pos = llist_entry((node), typeof(*pos), member);		       \
 	     member_address_is_nonnull(pos, member) &&			       \
 	        (n = llist_entry(pos->member.next, typeof(*n), member), true); \
 	     pos = n)

 /**
  * llist_empty - tests whether a lock-less list is empty
  * @head:	the list to test
  *
  * Not guaranteed to be accurate or up to date.  Just a quick way to
  * test whether the list is empty without deleting something from the
  * list.
  */
 static inline bool llist_empty(const struct llist_head *head)
 {
 	return READ_ONCE(head->first) == NULL;
 }

 static inline struct llist_node *llist_next(struct llist_node *node)
 {
 	return node->next;
 }

 extern bool llist_add_batch(struct llist_node *new_first,
 			    struct llist_node *new_last,
 			    struct llist_head *head);

 static inline bool __llist_add_batch(struct llist_node *new_first,
 				     struct llist_node *new_last,
 				     struct llist_head *head)
 {
 	new_last->next = head->first;
 	head->first = new_first;
 	return new_last->next == NULL;
 }

 /**
  * llist_add - add a new entry
  * @new:	new entry to be added
  * @head:	the head for your lock-less list
  *
  * Returns true if the list was empty prior to adding this entry.
  */
 static inline bool llist_add(struct llist_node *new, struct llist_head *head)
 {
 	return llist_add_batch(new, new, head);
 }

 static inline bool __llist_add(struct llist_node *new, struct llist_head *head)
 {
 	return __llist_add_batch(new, new, head);
 }

 /**
  * llist_del_all - delete all entries from lock-less list
  * @head:	the head of lock-less list to delete all entries
  *
  * If list is empty, return NULL, otherwise, delete all entries and
  * return the pointer to the first entry.  The order of entries
  * deleted is from the newest to the oldest added one.
  */
 static inline struct llist_node *llist_del_all(struct llist_head *head)
 {
 	return xchg(&head->first, NULL);
 }

 static inline struct llist_node *__llist_del_all(struct llist_head *head)
 {
 	struct llist_node *first = head->first;

 	head->first = NULL;
 	return first;
 }

 extern struct llist_node *llist_del_first(struct llist_head *head);

 /**
  * llist_del_first_init - delete first entry from lock-list and mark is as being off-list
  * @head:	the head of lock-less list to delete from.
  *
  * This behave the same as llist_del_first() except that llist_init_node() is called
  * on the returned node so that llist_on_list() will report false for the node.
  */
 static inline struct llist_node *llist_del_first_init(struct llist_head *head)
 {
 	struct llist_node *n = llist_del_first(head);

 	if (n)
 		init_llist_node(n);
 	return n;
 }

 extern bool llist_del_first_this(struct llist_head *head,
 				 struct llist_node *this);

 struct llist_node *llist_reverse_order(struct llist_node *head);

 #endif /* LLIST_H */
	/* SPDX-License-Identifier: GPL-2.0-only */
	#ifndef LLIST_H
	#define LLIST_H
	/*
	* Lock-less NULL terminated single linked list
	*
	* Cases where locking is not needed:
	* If there are multiple producers and multiple consumers, llist_add can be
	* used in producers and llist_del_all can be used in consumers simultaneously
	* without locking. Also a single consumer can use llist_del_first while
	* multiple producers simultaneously use llist_add, without any locking.
	*
	* Cases where locking is needed:
	* If we have multiple consumers with llist_del_first used in one consumer, and
	* llist_del_first or llist_del_all used in other consumers, then a lock is
	* needed. This is because llist_del_first depends on list->first->next not
	* changing, but without lock protection, there's no way to be sure about that
	* if a preemption happens in the middle of the delete operation and on being
	* preempted back, the list->first is the same as before causing the cmpxchg in
	* llist_del_first to succeed. For example, while a llist_del_first operation
	* is in progress in one consumer, then a llist_del_first, llist_add,
	* llist_add (or llist_del_all, llist_add, llist_add) sequence in another
	* consumer may cause violations.
	*
	* This can be summarized as follows:
	*
	* \| add \| del_first \| del_all
	* add \| - \| - \| -
	* del_first \| \| L \| L
	* del_all \| \| \| -
	*
	* Where, a particular row's operation can happen concurrently with a column's
	* operation, with "-" being no lock needed, while "L" being lock is needed.
	*
	* The list entries deleted via llist_del_all can be traversed with
	* traversing function such as llist_for_each etc. But the list
	* entries can not be traversed safely before deleted from the list.
	* The order of deleted entries is from the newest to the oldest added
	* one. If you want to traverse from the oldest to the newest, you
	* must reverse the order by yourself before traversing.
	*
	* The basic atomic operation of this list is cmpxchg on long. On
	* architectures that don't have NMI-safe cmpxchg implementation, the
	* list can NOT be used in NMI handlers. So code that uses the list in
	* an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
	*
	* Copyright 2010,2011 Intel Corp.
	* Author: Huang Ying <ying.huang@intel.com>
	*/

	#include <linux/atomic.h>
	#include <linux/container_of.h>
	#include <linux/stddef.h>
	#include <linux/types.h>

	struct llist_head {
	struct llist_node *first;
	};

	struct llist_node {
	struct llist_node *next;
	};

	#define LLIST_HEAD_INIT(name) { NULL }
	#define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name)

	/**
	* init_llist_head - initialize lock-less list head
	* @head: the head for your lock-less list
	*/
	static inline void init_llist_head(struct llist_head *list)
	{
	list->first = NULL;
	}

	/**
	* init_llist_node - initialize lock-less list node
	* @node: the node to be initialised
	*
	* In cases where there is a need to test if a node is on
	* a list or not, this initialises the node to clearly
	* not be on any list.
	*/
	static inline void init_llist_node(struct llist_node *node)
	{
	node->next = node;
	}

	/**
	* llist_on_list - test if a lock-list list node is on a list
	* @node: the node to test
	*
	* When a node is on a list the ->next pointer will be NULL or
	* some other node. It can never point to itself. We use that
	* in init_llist_node() to record that a node is not on any list,
	* and here to test whether it is on any list.
	*/
	static inline bool llist_on_list(const struct llist_node *node)
	{
	return node->next != node;
	}

	/**
	* llist_entry - get the struct of this entry
	* @ptr: the &struct llist_node pointer.
	* @type: the type of the struct this is embedded in.
	* @member: the name of the llist_node within the struct.
	*/
	#define llist_entry(ptr, type, member) \
	container_of(ptr, type, member)

	/**
	* member_address_is_nonnull - check whether the member address is not NULL
	* @ptr: the object pointer (struct type * that contains the llist_node)
	* @member: the name of the llist_node within the struct.
	*
	* This macro is conceptually the same as
	* &ptr->member != NULL
	* but it works around the fact that compilers can decide that taking a member
	* address is never a NULL pointer.
	*
	* Real objects that start at a high address and have a member at NULL are
	* unlikely to exist, but such pointers may be returned e.g. by the
	* container_of() macro.
	*/
	#define member_address_is_nonnull(ptr, member) \
	((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)

	/**
	* llist_for_each - iterate over some deleted entries of a lock-less list
	* @pos: the &struct llist_node to use as a loop cursor
	* @node: the first entry of deleted list entries
	*
	* In general, some entries of the lock-less list can be traversed
	* safely only after being deleted from list, so start with an entry
	* instead of list head.
	*
	* If being used on entries deleted from lock-less list directly, the
	* traverse order is from the newest to the oldest added entry. If
	* you want to traverse from the oldest to the newest, you must
	* reverse the order by yourself before traversing.
	*/
	#define llist_for_each(pos, node) \
	for ((pos) = (node); pos; (pos) = (pos)->next)

	/**
	* llist_for_each_safe - iterate over some deleted entries of a lock-less list
	* safe against removal of list entry
	* @pos: the &struct llist_node to use as a loop cursor
	* @n: another &struct llist_node to use as temporary storage
	* @node: the first entry of deleted list entries
	*
	* In general, some entries of the lock-less list can be traversed
	* safely only after being deleted from list, so start with an entry
	* instead of list head.
	*
	* If being used on entries deleted from lock-less list directly, the
	* traverse order is from the newest to the oldest added entry. If
	* you want to traverse from the oldest to the newest, you must
	* reverse the order by yourself before traversing.
	*/
	#define llist_for_each_safe(pos, n, node) \
	for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))

	/**
	* llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
	* @pos: the type * to use as a loop cursor.
	* @node: the fist entry of deleted list entries.
	* @member: the name of the llist_node with the struct.
	*
	* In general, some entries of the lock-less list can be traversed
	* safely only after being removed from list, so start with an entry
	* instead of list head.
	*
	* If being used on entries deleted from lock-less list directly, the
	* traverse order is from the newest to the oldest added entry. If
	* you want to traverse from the oldest to the newest, you must
	* reverse the order by yourself before traversing.
	*/
	#define llist_for_each_entry(pos, node, member) \
	for ((pos) = llist_entry((node), typeof(*(pos)), member); \
	member_address_is_nonnull(pos, member); \
	(pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))

	/**
	* llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
	* safe against removal of list entry
	* @pos: the type * to use as a loop cursor.
	* @n: another type * to use as temporary storage
	* @node: the first entry of deleted list entries.
	* @member: the name of the llist_node with the struct.
	*
	* In general, some entries of the lock-less list can be traversed
	* safely only after being removed from list, so start with an entry
	* instead of list head.
	*
	* If being used on entries deleted from lock-less list directly, the
	* traverse order is from the newest to the oldest added entry. If
	* you want to traverse from the oldest to the newest, you must
	* reverse the order by yourself before traversing.
	*/
	#define llist_for_each_entry_safe(pos, n, node, member) \
	for (pos = llist_entry((node), typeof(*pos), member); \
	member_address_is_nonnull(pos, member) && \
	(n = llist_entry(pos->member.next, typeof(*n), member), true); \
	pos = n)

	/**
	* llist_empty - tests whether a lock-less list is empty
	* @head: the list to test
	*
	* Not guaranteed to be accurate or up to date. Just a quick way to
	* test whether the list is empty without deleting something from the
	* list.
	*/
	static inline bool llist_empty(const struct llist_head *head)
	{
	return READ_ONCE(head->first) == NULL;
	}

	static inline struct llist_node llist_next(struct llist_node node)
	{
	return node->next;
	}

	extern bool llist_add_batch(struct llist_node *new_first,
	struct llist_node *new_last,
	struct llist_head *head);

	static inline bool __llist_add_batch(struct llist_node *new_first,
	struct llist_node *new_last,
	struct llist_head *head)
	{
	new_last->next = head->first;
	head->first = new_first;
	return new_last->next == NULL;
	}

	/**
	* llist_add - add a new entry
	* @new: new entry to be added
	* @head: the head for your lock-less list
	*
	* Returns true if the list was empty prior to adding this entry.
	*/
	static inline bool llist_add(struct llist_node new, struct llist_head head)
	{
	return llist_add_batch(new, new, head);
	}

	static inline bool __llist_add(struct llist_node new, struct llist_head head)
	{
	return __llist_add_batch(new, new, head);
	}

	/**
	* llist_del_all - delete all entries from lock-less list
	* @head: the head of lock-less list to delete all entries
	*
	* If list is empty, return NULL, otherwise, delete all entries and
	* return the pointer to the first entry. The order of entries
	* deleted is from the newest to the oldest added one.
	*/
	static inline struct llist_node llist_del_all(struct llist_head head)
	{
	return xchg(&head->first, NULL);
	}

	static inline struct llist_node __llist_del_all(struct llist_head head)
	{
	struct llist_node *first = head->first;

	head->first = NULL;
	return first;
	}

	extern struct llist_node llist_del_first(struct llist_head head);

	/**
	* llist_del_first_init - delete first entry from lock-list and mark is as being off-list
	* @head: the head of lock-less list to delete from.
	*
	* This behave the same as llist_del_first() except that llist_init_node() is called
	* on the returned node so that llist_on_list() will report false for the node.
	*/
	static inline struct llist_node llist_del_first_init(struct llist_head head)
	{
	struct llist_node *n = llist_del_first(head);

	if (n)
	init_llist_node(n);
	return n;
	}

	extern bool llist_del_first_this(struct llist_head *head,
	struct llist_node *this);

	struct llist_node llist_reverse_order(struct llist_node head);

	#endif /* LLIST_H */