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 * llist_del_first - delete the first entry of lock-less list 19 * @head: the head for your lock-less list 20 * 21 * If list is empty, return NULL, otherwise, return the first entry 22 * deleted, this is the newest added one. 23 * 24 * Only one llist_del_first user can be used simultaneously with 25 * multiple llist_add users without lock. Because otherwise 26 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add, 27 * llist_add) sequence in another user may change @head->first->next, 28 * but keep @head->first. If multiple consumers are needed, please 29 * use llist_del_all or use lock between consumers. 30 */ 31 struct llist_node *llist_del_first(struct llist_head *head) 32 { 33 struct llist_node *entry, *next; 34 35 entry = smp_load_acquire(&head->first); 36 do { 37 if (entry == NULL) 38 return NULL; 39 next = READ_ONCE(entry->next); 40 } while (!try_cmpxchg(&head->first, &entry, next)); 41 42 return entry; 43 } 44 EXPORT_SYMBOL_GPL(llist_del_first); 45 46 /** 47 * llist_del_first_this - delete given entry of lock-less list if it is first 48 * @head: the head for your lock-less list 49 * @this: a list entry. 50 * 51 * If head of the list is given entry, delete and return %true else 52 * return %false. 53 * 54 * Multiple callers can safely call this concurrently with multiple 55 * llist_add() callers, providing all the callers offer a different @this. 56 */ 57 bool llist_del_first_this(struct llist_head *head, 58 struct llist_node *this) 59 { 60 struct llist_node *entry, *next; 61 62 /* acquire ensures orderig wrt try_cmpxchg() is llist_del_first() */ 63 entry = smp_load_acquire(&head->first); 64 do { 65 if (entry != this) 66 return false; 67 next = READ_ONCE(entry->next); 68 } while (!try_cmpxchg(&head->first, &entry, next)); 69 70 return true; 71 } 72 EXPORT_SYMBOL_GPL(llist_del_first_this); 73 74 /** 75 * llist_reverse_order - reverse order of a llist chain 76 * @head: first item of the list to be reversed 77 * 78 * Reverse the order of a chain of llist entries and return the 79 * new first entry. 80 */ 81 struct llist_node *llist_reverse_order(struct llist_node *head) 82 { 83 struct llist_node *new_head = NULL; 84 85 while (head) { 86 struct llist_node *tmp = head; 87 head = head->next; 88 tmp->next = new_head; 89 new_head = tmp; 90 } 91 92 return new_head; 93 } 94 EXPORT_SYMBOL_GPL(llist_reverse_order); 95