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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/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);
105 

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