include/linux/llist.h

   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 */