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Diffstat (limited to 'include/linux/llist.h')
| -rw-r--r-- | include/linux/llist.h | 254 |
1 files changed, 254 insertions, 0 deletions
diff --git a/include/linux/llist.h b/include/linux/llist.h new file mode 100644 index 000000000..85bda2d02 --- /dev/null +++ b/include/linux/llist.h @@ -0,0 +1,254 @@ +/* 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; +} + +/** + * 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); + +struct llist_node *llist_reverse_order(struct llist_node *head); + +#endif /* LLIST_H */ |