1 /* 2 * Lock-less NULL terminated single linked list 3 * 4 * The basic atomic operation of this list is cmpxchg on long. On 5 * architectures that don't have NMI-safe cmpxchg implementation, the 6 * list can NOT be used in NMI handlers. So code that uses the list in 7 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG. 8 * 9 * Copyright 2010,2011 Intel Corp. 10 * Author: Huang Ying <ying.huang@intel.com> 11 * 12 * This program is free software; you can redistribute it and/or 13 * modify it under the terms of the GNU General Public License version 14 * 2 as published by the Free Software Foundation; 15 * 16 * This program is distributed in the hope that it will be useful, 17 * but WITHOUT ANY WARRANTY; without even the implied warranty of 18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 19 * GNU General Public License for more details. 20 * 21 * You should have received a copy of the GNU General Public License 22 * along with this program; if not, write to the Free Software 23 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 24 */ 25 #include <linux/kernel.h> 26 #include <linux/export.h> 27 #include <linux/llist.h> 28 29 30 /** 31 * llist_add_batch - add several linked entries in batch 32 * @new_first: first entry in batch to be added 33 * @new_last: last entry in batch to be added 34 * @head: the head for your lock-less list 35 * 36 * Return whether list is empty before adding. 37 */ 38 bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, 39 struct llist_head *head) 40 { 41 struct llist_node *first; 42 43 do { 44 new_last->next = first = READ_ONCE(head->first); 45 } while (cmpxchg(&head->first, first, new_first) != first); 46 47 return !first; 48 } 49 EXPORT_SYMBOL_GPL(llist_add_batch); 50 51 /** 52 * llist_del_first - delete the first entry of lock-less list 53 * @head: the head for your lock-less list 54 * 55 * If list is empty, return NULL, otherwise, return the first entry 56 * deleted, this is the newest added one. 57 * 58 * Only one llist_del_first user can be used simultaneously with 59 * multiple llist_add users without lock. Because otherwise 60 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add, 61 * llist_add) sequence in another user may change @head->first->next, 62 * but keep @head->first. If multiple consumers are needed, please 63 * use llist_del_all or use lock between consumers. 64 */ 65 struct llist_node *llist_del_first(struct llist_head *head) 66 { 67 struct llist_node *entry, *old_entry, *next; 68 69 entry = smp_load_acquire(&head->first); 70 for (;;) { 71 if (entry == NULL) 72 return NULL; 73 old_entry = entry; 74 next = READ_ONCE(entry->next); 75 entry = cmpxchg(&head->first, old_entry, next); 76 if (entry == old_entry) 77 break; 78 } 79 80 return entry; 81 } 82 EXPORT_SYMBOL_GPL(llist_del_first); 83 84 /** 85 * llist_reverse_order - reverse order of a llist chain 86 * @head: first item of the list to be reversed 87 * 88 * Reverse the order of a chain of llist entries and return the 89 * new first entry. 90 */ 91 struct llist_node *llist_reverse_order(struct llist_node *head) 92 { 93 struct llist_node *new_head = NULL; 94 95 while (head) { 96 struct llist_node *tmp = head; 97 head = head->next; 98 tmp->next = new_head; 99 new_head = tmp; 100 } 101 102 return new_head; 103 } 104 EXPORT_SYMBOL_GPL(llist_reverse_order); 105