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/interrupt.h> 28 #include <linux/llist.h> 29 30 31 /** 32 * llist_add_batch - add several linked entries in batch 33 * @new_first: first entry in batch to be added 34 * @new_last: last entry in batch to be added 35 * @head: the head for your lock-less list 36 * 37 * Return whether list is empty before adding. 38 */ 39 bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, 40 struct llist_head *head) 41 { 42 struct llist_node *entry, *old_entry; 43 44 entry = head->first; 45 for (;;) { 46 old_entry = entry; 47 new_last->next = entry; 48 entry = cmpxchg(&head->first, old_entry, new_first); 49 if (entry == old_entry) 50 break; 51 } 52 53 return old_entry == NULL; 54 } 55 EXPORT_SYMBOL_GPL(llist_add_batch); 56 57 /** 58 * llist_del_first - delete the first entry of lock-less list 59 * @head: the head for your lock-less list 60 * 61 * If list is empty, return NULL, otherwise, return the first entry 62 * deleted, this is the newest added one. 63 * 64 * Only one llist_del_first user can be used simultaneously with 65 * multiple llist_add users without lock. Because otherwise 66 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add, 67 * llist_add) sequence in another user may change @head->first->next, 68 * but keep @head->first. If multiple consumers are needed, please 69 * use llist_del_all or use lock between consumers. 70 */ 71 struct llist_node *llist_del_first(struct llist_head *head) 72 { 73 struct llist_node *entry, *old_entry, *next; 74 75 entry = head->first; 76 for (;;) { 77 if (entry == NULL) 78 return NULL; 79 old_entry = entry; 80 next = entry->next; 81 entry = cmpxchg(&head->first, old_entry, next); 82 if (entry == old_entry) 83 break; 84 } 85 86 return entry; 87 } 88 EXPORT_SYMBOL_GPL(llist_del_first); 89