xref: /openbmc/linux/include/linux/llist.h (revision 4da722ca)
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_safe - iterate over some deleted entries of a lock-less list
114  *			 safe against removal of list entry
115  * @pos:	the &struct llist_node to use as a loop cursor
116  * @n:		another &struct llist_node to use as temporary storage
117  * @node:	the first entry of deleted list entries
118  *
119  * In general, some entries of the lock-less list can be traversed
120  * safely only after being deleted from list, so start with an entry
121  * instead of list head.
122  *
123  * If being used on entries deleted from lock-less list directly, the
124  * traverse order is from the newest to the oldest added entry.  If
125  * you want to traverse from the oldest to the newest, you must
126  * reverse the order by yourself before traversing.
127  */
128 #define llist_for_each_safe(pos, n, node)			\
129 	for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
130 
131 /**
132  * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
133  * @pos:	the type * to use as a loop cursor.
134  * @node:	the fist entry of deleted list entries.
135  * @member:	the name of the llist_node with the struct.
136  *
137  * In general, some entries of the lock-less list can be traversed
138  * safely only after being removed from list, so start with an entry
139  * instead of list head.
140  *
141  * If being used on entries deleted from lock-less list directly, the
142  * traverse order is from the newest to the oldest added entry.  If
143  * you want to traverse from the oldest to the newest, you must
144  * reverse the order by yourself before traversing.
145  */
146 #define llist_for_each_entry(pos, node, member)				\
147 	for ((pos) = llist_entry((node), typeof(*(pos)), member);	\
148 	     &(pos)->member != NULL;					\
149 	     (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
150 
151 /**
152  * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
153  *			       safe against removal of list entry
154  * @pos:	the type * to use as a loop cursor.
155  * @n:		another type * to use as temporary storage
156  * @node:	the first entry of deleted list entries.
157  * @member:	the name of the llist_node with the struct.
158  *
159  * In general, some entries of the lock-less list can be traversed
160  * safely only after being removed from list, so start with an entry
161  * instead of list head.
162  *
163  * If being used on entries deleted from lock-less list directly, the
164  * traverse order is from the newest to the oldest added entry.  If
165  * you want to traverse from the oldest to the newest, you must
166  * reverse the order by yourself before traversing.
167  */
168 #define llist_for_each_entry_safe(pos, n, node, member)			       \
169 	for (pos = llist_entry((node), typeof(*pos), member);		       \
170 	     &pos->member != NULL &&					       \
171 	        (n = llist_entry(pos->member.next, typeof(*n), member), true); \
172 	     pos = n)
173 
174 /**
175  * llist_empty - tests whether a lock-less list is empty
176  * @head:	the list to test
177  *
178  * Not guaranteed to be accurate or up to date.  Just a quick way to
179  * test whether the list is empty without deleting something from the
180  * list.
181  */
182 static inline bool llist_empty(const struct llist_head *head)
183 {
184 	return ACCESS_ONCE(head->first) == NULL;
185 }
186 
187 static inline struct llist_node *llist_next(struct llist_node *node)
188 {
189 	return node->next;
190 }
191 
192 extern bool llist_add_batch(struct llist_node *new_first,
193 			    struct llist_node *new_last,
194 			    struct llist_head *head);
195 /**
196  * llist_add - add a new entry
197  * @new:	new entry to be added
198  * @head:	the head for your lock-less list
199  *
200  * Returns true if the list was empty prior to adding this entry.
201  */
202 static inline bool llist_add(struct llist_node *new, struct llist_head *head)
203 {
204 	return llist_add_batch(new, new, head);
205 }
206 
207 /**
208  * llist_del_all - delete all entries from lock-less list
209  * @head:	the head of lock-less list to delete all entries
210  *
211  * If list is empty, return NULL, otherwise, delete all entries and
212  * return the pointer to the first entry.  The order of entries
213  * deleted is from the newest to the oldest added one.
214  */
215 static inline struct llist_node *llist_del_all(struct llist_head *head)
216 {
217 	return xchg(&head->first, NULL);
218 }
219 
220 extern struct llist_node *llist_del_first(struct llist_head *head);
221 
222 struct llist_node *llist_reverse_order(struct llist_node *head);
223 
224 #endif /* LLIST_H */
225