1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Lock-less NULL terminated single linked list 4 * 5 * The basic atomic operation of this list is cmpxchg on long. On 6 * architectures that don't have NMI-safe cmpxchg implementation, the 7 * list can NOT be used in NMI handlers. So code that uses the list in 8 * 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 batch 20 * @new_first: first entry in batch to be added 21 * @new_last: last entry in batch to be added 22 * @head: the head for your lock-less list 23 * 24 * Return whether list is empty before adding. 25 */ 26 bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, 27 struct llist_head *head) 28 { 29 struct llist_node *first; 30 31 do { 32 new_last->next = first = READ_ONCE(head->first); 33 } while (!try_cmpxchg(&head->first, &first, new_first)); 34 35 return !first; 36 } 37 EXPORT_SYMBOL_GPL(llist_add_batch); 38 39 /** 40 * llist_del_first - delete the first entry of lock-less list 41 * @head: the head for your lock-less list 42 * 43 * If list is empty, return NULL, otherwise, return the first entry 44 * deleted, this is the newest added one. 45 * 46 * Only one llist_del_first user can be used simultaneously with 47 * multiple llist_add users without lock. Because otherwise 48 * 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, please 51 * use llist_del_all or use lock between consumers. 52 */ 53 struct 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 } 66 EXPORT_SYMBOL_GPL(llist_del_first); 67 68 /** 69 * llist_reverse_order - reverse order of a llist chain 70 * @head: first item of the list to be reversed 71 * 72 * Reverse the order of a chain of llist entries and return the 73 * new first entry. 74 */ 75 struct llist_node *llist_reverse_order(struct llist_node *head) 76 { 77 struct llist_node *new_head = NULL; 78 79 while (head) { 80 struct llist_node *tmp = head; 81 head = head->next; 82 tmp->next = new_head; 83 new_head = tmp; 84 } 85 86 return new_head; 87 } 88 EXPORT_SYMBOL_GPL(llist_reverse_order); 89