LXR linux/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 */
  39bool 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}
  50EXPORT_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 */
  66struct 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}
  83EXPORT_SYMBOL_GPL(llist_del_first);
  84