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  */
init_llist_head(struct llist_head * list)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  */
llist_empty(const struct llist_head * head)199 static inline bool llist_empty(const struct llist_head *head)
200 {
201 	return READ_ONCE(head->first) == NULL;
202 }
203 
llist_next(struct llist_node * node)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  */
llist_add(struct llist_node * new,struct llist_head * head)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  */
llist_del_all(struct llist_head * head)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