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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * Lock-less NULL terminated single linked list4 *5 * The basic atomic operation of this list is cmpxchg on long. On6 * architectures that don't have NMI-safe cmpxchg implementation, the7 * list can NOT be used in NMI handlers. So code that uses the list in8 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.9 *10 * Copyright 2010,2011 Intel Corp.11 * Author: Huang Ying <ying.huang@intel.com>12 */13#include <linux/kernel.h>14#include <linux/export.h>15#include <linux/llist.h>16 17 18/**19 * llist_add_batch - add several linked entries in batch20 * @new_first: first entry in batch to be added21 * @new_last: last entry in batch to be added22 * @head: the head for your lock-less list23 *24 * Return whether list is empty before adding.25 */26bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,27 struct llist_head *head)28{29 struct llist_node *first = READ_ONCE(head->first);30 31 do {32 new_last->next = first;33 } while (!try_cmpxchg(&head->first, &first, new_first));34 35 return !first;36}37EXPORT_SYMBOL_GPL(llist_add_batch);38 39/**40 * llist_del_first - delete the first entry of lock-less list41 * @head: the head for your lock-less list42 *43 * If list is empty, return NULL, otherwise, return the first entry44 * deleted, this is the newest added one.45 *46 * Only one llist_del_first user can be used simultaneously with47 * multiple llist_add users without lock. Because otherwise48 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,49 * llist_add) sequence in another user may change @head->first->next,50 * but keep @head->first. If multiple consumers are needed, please51 * use llist_del_all or use lock between consumers.52 */53struct llist_node *llist_del_first(struct llist_head *head)54{55 struct llist_node *entry, *next;56 57 entry = smp_load_acquire(&head->first);58 do {59 if (entry == NULL)60 return NULL;61 next = READ_ONCE(entry->next);62 } while (!try_cmpxchg(&head->first, &entry, next));63 64 return entry;65}66EXPORT_SYMBOL_GPL(llist_del_first);67 68/**69 * llist_del_first_this - delete given entry of lock-less list if it is first70 * @head: the head for your lock-less list71 * @this: a list entry.72 *73 * If head of the list is given entry, delete and return %true else74 * return %false.75 *76 * Multiple callers can safely call this concurrently with multiple77 * llist_add() callers, providing all the callers offer a different @this.78 */79bool llist_del_first_this(struct llist_head *head,80 struct llist_node *this)81{82 struct llist_node *entry, *next;83 84 /* acquire ensures orderig wrt try_cmpxchg() is llist_del_first() */85 entry = smp_load_acquire(&head->first);86 do {87 if (entry != this)88 return false;89 next = READ_ONCE(entry->next);90 } while (!try_cmpxchg(&head->first, &entry, next));91 92 return true;93}94EXPORT_SYMBOL_GPL(llist_del_first_this);95 96/**97 * llist_reverse_order - reverse order of a llist chain98 * @head: first item of the list to be reversed99 *100 * Reverse the order of a chain of llist entries and return the101 * new first entry.102 */103struct llist_node *llist_reverse_order(struct llist_node *head)104{105 struct llist_node *new_head = NULL;106 107 while (head) {108 struct llist_node *tmp = head;109 head = head->next;110 tmp->next = new_head;111 new_head = tmp;112 }113 114 return new_head;115}116EXPORT_SYMBOL_GPL(llist_reverse_order);117