1 #ifndef LLIST_H 2 #define LLIST_H 3 /* 4 * Lock-less NULL terminated single linked list 5 * 6 * Cases where locking is not needed: 7 * If there are multiple producers and multiple consumers, llist_add can be 8 * used in producers and llist_del_all can be used in consumers simultaneously 9 * without locking. Also a single consumer can use llist_del_first while 10 * multiple producers simultaneously use llist_add, without any locking. 11 * 12 * Cases where locking is needed: 13 * If we have multiple consumers with llist_del_first used in one consumer, and 14 * llist_del_first or llist_del_all used in other consumers, then a lock is 15 * needed. This is because llist_del_first depends on list->first->next not 16 * changing, but without lock protection, there's no way to be sure about that 17 * if a preemption happens in the middle of the delete operation and on being 18 * preempted back, the list->first is the same as before causing the cmpxchg in 19 * llist_del_first to succeed. For example, while a llist_del_first operation 20 * is in progress in one consumer, then a llist_del_first, llist_add, 21 * llist_add (or llist_del_all, llist_add, llist_add) sequence in another 22 * consumer may cause violations. 23 * 24 * This can be summarized as follows: 25 * 26 * | add | del_first | del_all 27 * add | - | - | - 28 * del_first | | L | L 29 * del_all | | | - 30 * 31 * Where, a particular row's operation can happen concurrently with a column's 32 * operation, with "-" being no lock needed, while "L" being lock is needed. 33 * 34 * The list entries deleted via llist_del_all can be traversed with 35 * traversing function such as llist_for_each etc. But the list 36 * entries can not be traversed safely before deleted from the list. 37 * The order of deleted entries is from the newest to the oldest added 38 * one. If you want to traverse from the oldest to the newest, you 39 * must reverse the order by yourself before traversing. 40 * 41 * The basic atomic operation of this list is cmpxchg on long. On 42 * architectures that don't have NMI-safe cmpxchg implementation, the 43 * list can NOT be used in NMI handlers. So code that uses the list in 44 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG. 45 * 46 * Copyright 2010,2011 Intel Corp. 47 * Author: Huang Ying <ying.huang@intel.com> 48 * 49 * This program is free software; you can redistribute it and/or 50 * modify it under the terms of the GNU General Public License version 51 * 2 as published by the Free Software Foundation; 52 * 53 * This program is distributed in the hope that it will be useful, 54 * but WITHOUT ANY WARRANTY; without even the implied warranty of 55 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 56 * GNU General Public License for more details. 57 * 58 * You should have received a copy of the GNU General Public License 59 * along with this program; if not, write to the Free Software 60 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 61 */ 62 63 #include <linux/atomic.h> 64 #include <linux/kernel.h> 65 66 struct llist_head { 67 struct llist_node *first; 68 }; 69 70 struct llist_node { 71 struct llist_node *next; 72 }; 73 74 #define LLIST_HEAD_INIT(name) { NULL } 75 #define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name) 76 77 /** 78 * init_llist_head - initialize lock-less list head 79 * @head: the head for your lock-less list 80 */ 81 static inline void init_llist_head(struct llist_head *list) 82 { 83 list->first = NULL; 84 } 85 86 /** 87 * llist_entry - get the struct of this entry 88 * @ptr: the &struct llist_node pointer. 89 * @type: the type of the struct this is embedded in. 90 * @member: the name of the llist_node within the struct. 91 */ 92 #define llist_entry(ptr, type, member) \ 93 container_of(ptr, type, member) 94 95 /** 96 * llist_for_each - iterate over some deleted entries of a lock-less list 97 * @pos: the &struct llist_node to use as a loop cursor 98 * @node: the first entry of deleted list entries 99 * 100 * In general, some entries of the lock-less list can be traversed 101 * safely only after being deleted from list, so start with an entry 102 * instead of list head. 103 * 104 * If being used on entries deleted from lock-less list directly, the 105 * traverse order is from the newest to the oldest added entry. If 106 * you want to traverse from the oldest to the newest, you must 107 * reverse the order by yourself before traversing. 108 */ 109 #define llist_for_each(pos, node) \ 110 for ((pos) = (node); pos; (pos) = (pos)->next) 111 112 /** 113 * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type 114 * @pos: the type * to use as a loop cursor. 115 * @node: the fist entry of deleted list entries. 116 * @member: the name of the llist_node with the struct. 117 * 118 * In general, some entries of the lock-less list can be traversed 119 * safely only after being removed from list, so start with an entry 120 * instead of list head. 121 * 122 * If being used on entries deleted from lock-less list directly, the 123 * traverse order is from the newest to the oldest added entry. If 124 * you want to traverse from the oldest to the newest, you must 125 * reverse the order by yourself before traversing. 126 */ 127 #define llist_for_each_entry(pos, node, member) \ 128 for ((pos) = llist_entry((node), typeof(*(pos)), member); \ 129 &(pos)->member != NULL; \ 130 (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member)) 131 132 /** 133 * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type 134 * safe against removal of list entry 135 * @pos: the type * to use as a loop cursor. 136 * @n: another type * to use as temporary storage 137 * @node: the first entry of deleted list entries. 138 * @member: the name of the llist_node with the struct. 139 * 140 * In general, some entries of the lock-less list can be traversed 141 * safely only after being removed from list, so start with an entry 142 * instead of list head. 143 * 144 * If being used on entries deleted from lock-less list directly, the 145 * traverse order is from the newest to the oldest added entry. If 146 * you want to traverse from the oldest to the newest, you must 147 * reverse the order by yourself before traversing. 148 */ 149 #define llist_for_each_entry_safe(pos, n, node, member) \ 150 for (pos = llist_entry((node), typeof(*pos), member); \ 151 &pos->member != NULL && \ 152 (n = llist_entry(pos->member.next, typeof(*n), member), true); \ 153 pos = n) 154 155 /** 156 * llist_empty - tests whether a lock-less list is empty 157 * @head: the list to test 158 * 159 * Not guaranteed to be accurate or up to date. Just a quick way to 160 * test whether the list is empty without deleting something from the 161 * list. 162 */ 163 static inline bool llist_empty(const struct llist_head *head) 164 { 165 return ACCESS_ONCE(head->first) == NULL; 166 } 167 168 static inline struct llist_node *llist_next(struct llist_node *node) 169 { 170 return node->next; 171 } 172 173 extern bool llist_add_batch(struct llist_node *new_first, 174 struct llist_node *new_last, 175 struct llist_head *head); 176 /** 177 * llist_add - add a new entry 178 * @new: new entry to be added 179 * @head: the head for your lock-less list 180 * 181 * Returns true if the list was empty prior to adding this entry. 182 */ 183 static inline bool llist_add(struct llist_node *new, struct llist_head *head) 184 { 185 return llist_add_batch(new, new, head); 186 } 187 188 /** 189 * llist_del_all - delete all entries from lock-less list 190 * @head: the head of lock-less list to delete all entries 191 * 192 * If list is empty, return NULL, otherwise, delete all entries and 193 * return the pointer to the first entry. The order of entries 194 * deleted is from the newest to the oldest added one. 195 */ 196 static inline struct llist_node *llist_del_all(struct llist_head *head) 197 { 198 return xchg(&head->first, NULL); 199 } 200 201 extern struct llist_node *llist_del_first(struct llist_head *head); 202 203 struct llist_node *llist_reverse_order(struct llist_node *head); 204 205 #endif /* LLIST_H */ 206