| /* 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/kernel.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); |
| /** |
| * 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); |
| } |
| |
| /** |
| * 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); |
| } |
| |
| extern struct llist_node *llist_del_first(struct llist_head *head); |
| |
| struct llist_node *llist_reverse_order(struct llist_node *head); |
| |
| #endif /* LLIST_H */ |