linux/lib/llist.c
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   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 handler.  So code uses the list in NMI
   7 * 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/module.h>
  27#include <linux/interrupt.h>
  28#include <linux/llist.h>
  29
  30#include <asm/system.h>
  31
  32/**
  33 * llist_add - add a new entry
  34 * @new:        new entry to be added
  35 * @head:       the head for your lock-less list
  36 */
  37void llist_add(struct llist_node *new, struct llist_head *head)
  38{
  39        struct llist_node *entry, *old_entry;
  40
  41#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
  42        BUG_ON(in_nmi());
  43#endif
  44
  45        entry = head->first;
  46        do {
  47                old_entry = entry;
  48                new->next = entry;
  49                cpu_relax();
  50        } while ((entry = cmpxchg(&head->first, old_entry, new)) != old_entry);
  51}
  52EXPORT_SYMBOL_GPL(llist_add);
  53
  54/**
  55 * llist_add_batch - add several linked entries in batch
  56 * @new_first:  first entry in batch to be added
  57 * @new_last:   last entry in batch to be added
  58 * @head:       the head for your lock-less list
  59 */
  60void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
  61                     struct llist_head *head)
  62{
  63        struct llist_node *entry, *old_entry;
  64
  65#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
  66        BUG_ON(in_nmi());
  67#endif
  68
  69        entry = head->first;
  70        do {
  71                old_entry = entry;
  72                new_last->next = entry;
  73                cpu_relax();
  74        } while ((entry = cmpxchg(&head->first, old_entry, new_first)) != old_entry);
  75}
  76EXPORT_SYMBOL_GPL(llist_add_batch);
  77
  78/**
  79 * llist_del_first - delete the first entry of lock-less list
  80 * @head:       the head for your lock-less list
  81 *
  82 * If list is empty, return NULL, otherwise, return the first entry
  83 * deleted, this is the newest added one.
  84 *
  85 * Only one llist_del_first user can be used simultaneously with
  86 * multiple llist_add users without lock.  Because otherwise
  87 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
  88 * llist_add) sequence in another user may change @head->first->next,
  89 * but keep @head->first.  If multiple consumers are needed, please
  90 * use llist_del_all or use lock between consumers.
  91 */
  92struct llist_node *llist_del_first(struct llist_head *head)
  93{
  94        struct llist_node *entry, *old_entry, *next;
  95
  96#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
  97        BUG_ON(in_nmi());
  98#endif
  99
 100        entry = head->first;
 101        do {
 102                if (entry == NULL)
 103                        return NULL;
 104                old_entry = entry;
 105                next = entry->next;
 106                cpu_relax();
 107        } while ((entry = cmpxchg(&head->first, old_entry, next)) != old_entry);
 108
 109        return entry;
 110}
 111EXPORT_SYMBOL_GPL(llist_del_first);
 112
 113/**
 114 * llist_del_all - delete all entries from lock-less list
 115 * @head:       the head of lock-less list to delete all entries
 116 *
 117 * If list is empty, return NULL, otherwise, delete all entries and
 118 * return the pointer to the first entry.  The order of entries
 119 * deleted is from the newest to the oldest added one.
 120 */
 121struct llist_node *llist_del_all(struct llist_head *head)
 122{
 123#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
 124        BUG_ON(in_nmi());
 125#endif
 126
 127        return xchg(&head->first, NULL);
 128}
 129EXPORT_SYMBOL_GPL(llist_del_all);
 130
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