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 * member_address_is_nonnull - check whether the member address is not NULL 97 * @ptr: the object pointer (struct type * that contains the llist_node) 98 * @member: the name of the llist_node within the struct. 99 * 100 * This macro is conceptually the same as 101 * &ptr->member != NULL 102 * but it works around the fact that compilers can decide that taking a member 103 * address is never a NULL pointer. 104 * 105 * Real objects that start at a high address and have a member at NULL are 106 * unlikely to exist, but such pointers may be returned e.g. by the 107 * container_of() macro. 108 */ 109 #define member_address_is_nonnull(ptr, member) \ 110 ((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0) 111 112 /** 113 * llist_for_each - iterate over some deleted entries of a lock-less list 114 * @pos: the &struct llist_node to use as a loop cursor 115 * @node: the first entry of deleted list entries 116 * 117 * In general, some entries of the lock-less list can be traversed 118 * safely only after being deleted from list, so start with an entry 119 * instead of list head. 120 * 121 * If being used on entries deleted from lock-less list directly, the 122 * traverse order is from the newest to the oldest added entry. If 123 * you want to traverse from the oldest to the newest, you must 124 * reverse the order by yourself before traversing. 125 */ 126 #define llist_for_each(pos, node) \ 127 for ((pos) = (node); pos; (pos) = (pos)->next) 128 129 /** 130 * llist_for_each_safe - iterate over some deleted entries of a lock-less list 131 * safe against removal of list entry 132 * @pos: the &struct llist_node to use as a loop cursor 133 * @n: another &struct llist_node to use as temporary storage 134 * @node: the first entry of deleted list entries 135 * 136 * In general, some entries of the lock-less list can be traversed 137 * safely only after being deleted from list, so start with an entry 138 * instead of list head. 139 * 140 * If being used on entries deleted from lock-less list directly, the 141 * traverse order is from the newest to the oldest added entry. If 142 * you want to traverse from the oldest to the newest, you must 143 * reverse the order by yourself before traversing. 144 */ 145 #define llist_for_each_safe(pos, n, node) \ 146 for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n)) 147 148 /** 149 * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type 150 * @pos: the type * to use as a loop cursor. 151 * @node: the fist entry of deleted list entries. 152 * @member: the name of the llist_node with the struct. 153 * 154 * In general, some entries of the lock-less list can be traversed 155 * safely only after being removed from list, so start with an entry 156 * instead of list head. 157 * 158 * If being used on entries deleted from lock-less list directly, the 159 * traverse order is from the newest to the oldest added entry. If 160 * you want to traverse from the oldest to the newest, you must 161 * reverse the order by yourself before traversing. 162 */ 163 #define llist_for_each_entry(pos, node, member) \ 164 for ((pos) = llist_entry((node), typeof(*(pos)), member); \ 165 member_address_is_nonnull(pos, member); \ 166 (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member)) 167 168 /** 169 * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type 170 * safe against removal of list entry 171 * @pos: the type * to use as a loop cursor. 172 * @n: another type * to use as temporary storage 173 * @node: the first entry of deleted list entries. 174 * @member: the name of the llist_node with the struct. 175 * 176 * In general, some entries of the lock-less list can be traversed 177 * safely only after being removed from list, so start with an entry 178 * instead of list head. 179 * 180 * If being used on entries deleted from lock-less list directly, the 181 * traverse order is from the newest to the oldest added entry. If 182 * you want to traverse from the oldest to the newest, you must 183 * reverse the order by yourself before traversing. 184 */ 185 #define llist_for_each_entry_safe(pos, n, node, member) \ 186 for (pos = llist_entry((node), typeof(*pos), member); \ 187 member_address_is_nonnull(pos, member) && \ 188 (n = llist_entry(pos->member.next, typeof(*n), member), true); \ 189 pos = n) 190 191 /** 192 * llist_empty - tests whether a lock-less list is empty 193 * @head: the list to test 194 * 195 * Not guaranteed to be accurate or up to date. Just a quick way to 196 * test whether the list is empty without deleting something from the 197 * list. 198 */ 199 static inline bool llist_empty(const struct llist_head *head) 200 { 201 return READ_ONCE(head->first) == NULL; 202 } 203 204 static inline struct llist_node *llist_next(struct llist_node *node) 205 { 206 return node->next; 207 } 208 209 extern bool llist_add_batch(struct llist_node *new_first, 210 struct llist_node *new_last, 211 struct llist_head *head); 212 /** 213 * llist_add - add a new entry 214 * @new: new entry to be added 215 * @head: the head for your lock-less list 216 * 217 * Returns true if the list was empty prior to adding this entry. 218 */ 219 static inline bool llist_add(struct llist_node *new, struct llist_head *head) 220 { 221 return llist_add_batch(new, new, head); 222 } 223 224 /** 225 * llist_del_all - delete all entries from lock-less list 226 * @head: the head of lock-less list to delete all entries 227 * 228 * If list is empty, return NULL, otherwise, delete all entries and 229 * return the pointer to the first entry. The order of entries 230 * deleted is from the newest to the oldest added one. 231 */ 232 static inline struct llist_node *llist_del_all(struct llist_head *head) 233 { 234 return xchg(&head->first, NULL); 235 } 236 237 extern struct llist_node *llist_del_first(struct llist_head *head); 238 239 struct llist_node *llist_reverse_order(struct llist_node *head); 240 241 #endif /* LLIST_H */ 242