lib/llist.c

   1 /*
   2  * Lock-less NULL terminated single linked list
   3  *
   4  * The basic atomic operation of this list is cmpxchg on long.  On
   5  * architectures that don't have NMI-safe cmpxchg implementation, the
   6  * list can NOT be used in NMI handlers.  So code that uses the list in
   7  * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
   8  *
   9  * Copyright 2010,2011 Intel Corp.
  10  *   Author: Huang Ying <ying.huang@intel.com>
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License version
  14  * 2 as published by the Free Software Foundation;
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  * GNU General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU General Public License
  22  * along with this program; if not, write to the Free Software
  23  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  24  */
  25 #include <linux/kernel.h>
  26 #include <linux/export.h>
  27 #include <linux/llist.h>
  28
  29
  30 /**
  31  * llist_add_batch - add several linked entries in batch
  32  * @new_first:  first entry in batch to be added
  33  * @new_last:   last entry in batch to be added
  34  * @head:       the head for your lock-less list
  35  *
  36  * Return whether list is empty before adding.
  37  */
  38 bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
  39                      struct llist_head *head)
  40 {
  41         struct llist_node *first;
  42
  43         do {
  44                 new_last->next = first = ACCESS_ONCE(head->first);
  45         } while (cmpxchg(&head->first, first, new_first) != first);
  46
  47         return !first;
  48 }
  49 EXPORT_SYMBOL_GPL(llist_add_batch);
  50
  51 /**
  52  * llist_del_first - delete the first entry of lock-less list
  53  * @head:       the head for your lock-less list
  54  *
  55  * If list is empty, return NULL, otherwise, return the first entry
  56  * deleted, this is the newest added one.
  57  *
  58  * Only one llist_del_first user can be used simultaneously with
  59  * multiple llist_add users without lock.  Because otherwise
  60  * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
  61  * llist_add) sequence in another user may change @head->first->next,
  62  * but keep @head->first.  If multiple consumers are needed, please
  63  * use llist_del_all or use lock between consumers.
  64  */
  65 struct llist_node *llist_del_first(struct llist_head *head)
  66 {
  67         struct llist_node *entry, *old_entry, *next;
  68
  69         entry = smp_load_acquire(&head->first);
  70         for (;;) {
  71                 if (entry == NULL)
  72                         return NULL;
  73                 old_entry = entry;
  74                 next = READ_ONCE(entry->next);
  75                 entry = cmpxchg(&head->first, old_entry, next);
  76                 if (entry == old_entry)
  77                         break;
  78         }
  79
  80         return entry;
  81 }
  82 EXPORT_SYMBOL_GPL(llist_del_first);
  83
  84 /**
  85  * llist_reverse_order - reverse order of a llist chain
  86  * @head:       first item of the list to be reversed
  87  *
  88  * Reverse the order of a chain of llist entries and return the
  89  * new first entry.
  90  */
  91 struct llist_node *llist_reverse_order(struct llist_node *head)
  92 {
  93         struct llist_node *new_head = NULL;
  94
  95         while (head) {
  96                 struct llist_node *tmp = head;
  97                 head = head->next;
  98                 tmp->next = new_head;
  99                 new_head = tmp;
 100         }
 101
 102         return new_head;
 103 }
 104 EXPORT_SYMBOL_GPL(llist_reverse_order);