llist.c 3.1 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105
  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. * llist_add_batch - add several linked entries in batch
  31. * @new_first: first entry in batch to be added
  32. * @new_last: last entry in batch to be added
  33. * @head: the head for your lock-less list
  34. *
  35. * Return whether list is empty before adding.
  36. */
  37. bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
  38. struct llist_head *head)
  39. {
  40. struct llist_node *first;
  41. do {
  42. new_last->next = first = ACCESS_ONCE(head->first);
  43. } while (cmpxchg(&head->first, first, new_first) != first);
  44. return !first;
  45. }
  46. EXPORT_SYMBOL_GPL(llist_add_batch);
  47. /**
  48. * llist_del_first - delete the first entry of lock-less list
  49. * @head: the head for your lock-less list
  50. *
  51. * If list is empty, return NULL, otherwise, return the first entry
  52. * deleted, this is the newest added one.
  53. *
  54. * Only one llist_del_first user can be used simultaneously with
  55. * multiple llist_add users without lock. Because otherwise
  56. * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
  57. * llist_add) sequence in another user may change @head->first->next,
  58. * but keep @head->first. If multiple consumers are needed, please
  59. * use llist_del_all or use lock between consumers.
  60. */
  61. struct llist_node *llist_del_first(struct llist_head *head)
  62. {
  63. struct llist_node *entry, *old_entry, *next;
  64. entry = head->first;
  65. for (;;) {
  66. if (entry == NULL)
  67. return NULL;
  68. old_entry = entry;
  69. next = entry->next;
  70. entry = cmpxchg(&head->first, old_entry, next);
  71. if (entry == old_entry)
  72. break;
  73. }
  74. return entry;
  75. }
  76. EXPORT_SYMBOL_GPL(llist_del_first);
  77. /**
  78. * llist_reverse_order - reverse order of a llist chain
  79. * @head: first item of the list to be reversed
  80. *
  81. * Reverse the order of a chain of llist entries and return the
  82. * new first entry.
  83. */
  84. struct llist_node *llist_reverse_order(struct llist_node *head)
  85. {
  86. struct llist_node *new_head = NULL;
  87. while (head) {
  88. struct llist_node *tmp = head;
  89. head = head->next;
  90. tmp->next = new_head;
  91. new_head = tmp;
  92. }
  93. return new_head;
  94. }
  95. EXPORT_SYMBOL_GPL(llist_reverse_order);