1 /* SPDX-License-Identifier: GPL-2.0-only */ 2 #ifndef LLIST_H 3 #define LLIST_H 4 /* 5 * Lock-less NULL terminated single linked list 6 * 7 * Cases where locking is not needed: 8 * If there are multiple producers and multiple consumers, llist_add can be 9 * used in producers and llist_del_all can be used in consumers simultaneously 10 * without locking. Also a single consumer can use llist_del_first while 11 * multiple producers simultaneously use llist_add, without any locking. 12 * 13 * Cases where locking is needed: 14 * If we have multiple consumers with llist_del_first used in one consumer, and 15 * llist_del_first or llist_del_all used in other consumers, then a lock is 16 * needed. This is because llist_del_first depends on list->first->next not 17 * changing, but without lock protection, there's no way to be sure about that 18 * if a preemption happens in the middle of the delete operation and on being 19 * preempted back, the list->first is the same as before causing the cmpxchg in 20 * llist_del_first to succeed. For example, while a llist_del_first operation 21 * is in progress in one consumer, then a llist_del_first, llist_add, 22 * llist_add (or llist_del_all, llist_add, llist_add) sequence in another 23 * consumer may cause violations. 24 * 25 * This can be summarized as follows: 26 * 27 * | add | del_first | del_all 28 * add | - | - | - 29 * del_first | | L | L 30 * del_all | | | - 31 * 32 * Where, a particular row's operation can happen concurrently with a column's 33 * operation, with "-" being no lock needed, while "L" being lock is needed. 34 * 35 * The list entries deleted via llist_del_all can be traversed with 36 * traversing function such as llist_for_each etc. But the list 37 * entries can not be traversed safely before deleted from the list. 38 * The order of deleted entries is from the newest to the oldest added 39 * one. If you want to traverse from the oldest to the newest, you 40 * must reverse the order by yourself before traversing. 41 * 42 * The basic atomic operation of this list is cmpxchg on long. On 43 * architectures that don't have NMI-safe cmpxchg implementation, the 44 * list can NOT be used in NMI handlers. So code that uses the list in 45 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG. 46 * 47 * Copyright 2010,2011 Intel Corp. 48 * Author: Huang Ying <ying.huang@intel.com> 49 */ 50 51 #include <linux/atomic.h> 52 #include <linux/container_of.h> 53 #include <linux/stddef.h> 54 #include <linux/types.h> 55 56 struct llist_head { 57 struct llist_node *first; 58 }; 59 60 struct llist_node { 61 struct llist_node *next; 62 }; 63 64 #define LLIST_HEAD_INIT(name) { NULL } 65 #define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name) 66 67 /** 68 * init_llist_head - initialize lock-less list head 69 * @head: the head for your lock-less list 70 */ 71 static inline void init_llist_head(struct llist_head *list) 72 { 73 list->first = NULL; 74 } 75 76 /** 77 * llist_entry - get the struct of this entry 78 * @ptr: the &struct llist_node pointer. 79 * @type: the type of the struct this is embedded in. 80 * @member: the name of the llist_node within the struct. 81 */ 82 #define llist_entry(ptr, type, member) \ 83 container_of(ptr, type, member) 84 85 /** 86 * member_address_is_nonnull - check whether the member address is not NULL 87 * @ptr: the object pointer (struct type * that contains the llist_node) 88 * @member: the name of the llist_node within the struct. 89 * 90 * This macro is conceptually the same as 91 * &ptr->member != NULL 92 * but it works around the fact that compilers can decide that taking a member 93 * address is never a NULL pointer. 94 * 95 * Real objects that start at a high address and have a member at NULL are 96 * unlikely to exist, but such pointers may be returned e.g. by the 97 * container_of() macro. 98 */ 99 #define member_address_is_nonnull(ptr, member) \ 100 ((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0) 101 102 /** 103 * llist_for_each - iterate over some deleted entries of a lock-less list 104 * @pos: the &struct llist_node to use as a loop cursor 105 * @node: the first entry of deleted list entries 106 * 107 * In general, some entries of the lock-less list can be traversed 108 * safely only after being deleted from list, so start with an entry 109 * instead of list head. 110 * 111 * If being used on entries deleted from lock-less list directly, the 112 * traverse order is from the newest to the oldest added entry. If 113 * you want to traverse from the oldest to the newest, you must 114 * reverse the order by yourself before traversing. 115 */ 116 #define llist_for_each(pos, node) \ 117 for ((pos) = (node); pos; (pos) = (pos)->next) 118 119 /** 120 * llist_for_each_safe - iterate over some deleted entries of a lock-less list 121 * safe against removal of list entry 122 * @pos: the &struct llist_node to use as a loop cursor 123 * @n: another &struct llist_node to use as temporary storage 124 * @node: the first entry of deleted list entries 125 * 126 * In general, some entries of the lock-less list can be traversed 127 * safely only after being deleted from list, so start with an entry 128 * instead of list head. 129 * 130 * If being used on entries deleted from lock-less list directly, the 131 * traverse order is from the newest to the oldest added entry. If 132 * you want to traverse from the oldest to the newest, you must 133 * reverse the order by yourself before traversing. 134 */ 135 #define llist_for_each_safe(pos, n, node) \ 136 for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n)) 137 138 /** 139 * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type 140 * @pos: the type * to use as a loop cursor. 141 * @node: the fist entry of deleted list entries. 142 * @member: the name of the llist_node with the struct. 143 * 144 * In general, some entries of the lock-less list can be traversed 145 * safely only after being removed from list, so start with an entry 146 * instead of list head. 147 * 148 * If being used on entries deleted from lock-less list directly, the 149 * traverse order is from the newest to the oldest added entry. If 150 * you want to traverse from the oldest to the newest, you must 151 * reverse the order by yourself before traversing. 152 */ 153 #define llist_for_each_entry(pos, node, member) \ 154 for ((pos) = llist_entry((node), typeof(*(pos)), member); \ 155 member_address_is_nonnull(pos, member); \ 156 (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member)) 157 158 /** 159 * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type 160 * safe against removal of list entry 161 * @pos: the type * to use as a loop cursor. 162 * @n: another type * to use as temporary storage 163 * @node: the first entry of deleted list entries. 164 * @member: the name of the llist_node with the struct. 165 * 166 * In general, some entries of the lock-less list can be traversed 167 * safely only after being removed from list, so start with an entry 168 * instead of list head. 169 * 170 * If being used on entries deleted from lock-less list directly, the 171 * traverse order is from the newest to the oldest added entry. If 172 * you want to traverse from the oldest to the newest, you must 173 * reverse the order by yourself before traversing. 174 */ 175 #define llist_for_each_entry_safe(pos, n, node, member) \ 176 for (pos = llist_entry((node), typeof(*pos), member); \ 177 member_address_is_nonnull(pos, member) && \ 178 (n = llist_entry(pos->member.next, typeof(*n), member), true); \ 179 pos = n) 180 181 /** 182 * llist_empty - tests whether a lock-less list is empty 183 * @head: the list to test 184 * 185 * Not guaranteed to be accurate or up to date. Just a quick way to 186 * test whether the list is empty without deleting something from the 187 * list. 188 */ 189 static inline bool llist_empty(const struct llist_head *head) 190 { 191 return READ_ONCE(head->first) == NULL; 192 } 193 194 static inline struct llist_node *llist_next(struct llist_node *node) 195 { 196 return node->next; 197 } 198 199 extern bool llist_add_batch(struct llist_node *new_first, 200 struct llist_node *new_last, 201 struct llist_head *head); 202 203 static inline bool __llist_add_batch(struct llist_node *new_first, 204 struct llist_node *new_last, 205 struct llist_head *head) 206 { 207 new_last->next = head->first; 208 head->first = new_first; 209 return new_last->next == NULL; 210 } 211 212 /** 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 static inline bool __llist_add(struct llist_node *new, struct llist_head *head) 225 { 226 return __llist_add_batch(new, new, head); 227 } 228 229 /** 230 * llist_del_all - delete all entries from lock-less list 231 * @head: the head of lock-less list to delete all entries 232 * 233 * If list is empty, return NULL, otherwise, delete all entries and 234 * return the pointer to the first entry. The order of entries 235 * deleted is from the newest to the oldest added one. 236 */ 237 static inline struct llist_node *llist_del_all(struct llist_head *head) 238 { 239 return xchg(&head->first, NULL); 240 } 241 242 static inline struct llist_node *__llist_del_all(struct llist_head *head) 243 { 244 struct llist_node *first = head->first; 245 246 head->first = NULL; 247 return first; 248 } 249 250 extern struct llist_node *llist_del_first(struct llist_head *head); 251 252 struct llist_node *llist_reverse_order(struct llist_node *head); 253 254 #endif /* LLIST_H */ 255