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/interrupt.h>
  28 #include <linux/llist.h>
  29
  30
  31 /**
  32  * llist_add_batch - add several linked entries in batch
  33  * @new_first:  first entry in batch to be added
  34  * @new_last:   last entry in batch to be added
  35  * @head:       the head for your lock-less list
  36  *
  37  * Return whether list is empty before adding.
  38  */
  39 bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
  40                      struct llist_head *head)
  41 {
  42         struct llist_node *first;
  43
  44         do {
  45                 new_last->next = first = ACCESS_ONCE(head->first);
  46         } while (cmpxchg(&head->first, first, new_first) != first);
  47
  48         return !first;
  49 }
  50 EXPORT_SYMBOL_GPL(llist_add_batch);
  51
  52 /**
  53  * llist_del_first - delete the first entry of lock-less list
  54  * @head:       the head for your lock-less list
  55  *
  56  * If list is empty, return NULL, otherwise, return the first entry
  57  * deleted, this is the newest added one.
  58  *
  59  * Only one llist_del_first user can be used simultaneously with
  60  * multiple llist_add users without lock.  Because otherwise
  61  * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
  62  * llist_add) sequence in another user may change @head->first->next,
  63  * but keep @head->first.  If multiple consumers are needed, please
  64  * use llist_del_all or use lock between consumers.
  65  */
  66 struct llist_node *llist_del_first(struct llist_head *head)
  67 {
  68         struct llist_node *entry, *old_entry, *next;
  69
  70         entry = head->first;
  71         for (;;) {
  72                 if (entry == NULL)
  73                         return NULL;
  74                 old_entry = entry;
  75                 next = entry->next;
  76                 entry = cmpxchg(&head->first, old_entry, next);
  77                 if (entry == old_entry)
  78                         break;
  79         }
  80
  81         return entry;
  82 }
  83 EXPORT_SYMBOL_GPL(llist_del_first);