iocontext.h 4.6 KB

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  1. /* SPDX-License-Identifier: GPL-2.0 */
  2. #ifndef IOCONTEXT_H
  3. #define IOCONTEXT_H
  4. #include <linux/radix-tree.h>
  5. #include <linux/rcupdate.h>
  6. #include <linux/workqueue.h>
  7. enum {
  8. ICQ_EXITED = 1 << 2,
  9. ICQ_DESTROYED = 1 << 3,
  10. };
  11. /*
  12. * An io_cq (icq) is association between an io_context (ioc) and a
  13. * request_queue (q). This is used by elevators which need to track
  14. * information per ioc - q pair.
  15. *
  16. * Elevator can request use of icq by setting elevator_type->icq_size and
  17. * ->icq_align. Both size and align must be larger than that of struct
  18. * io_cq and elevator can use the tail area for private information. The
  19. * recommended way to do this is defining a struct which contains io_cq as
  20. * the first member followed by private members and using its size and
  21. * align. For example,
  22. *
  23. * struct snail_io_cq {
  24. * struct io_cq icq;
  25. * int poke_snail;
  26. * int feed_snail;
  27. * };
  28. *
  29. * struct elevator_type snail_elv_type {
  30. * .ops = { ... },
  31. * .icq_size = sizeof(struct snail_io_cq),
  32. * .icq_align = __alignof__(struct snail_io_cq),
  33. * ...
  34. * };
  35. *
  36. * If icq_size is set, block core will manage icq's. All requests will
  37. * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
  38. * is called and be holding a reference to the associated io_context.
  39. *
  40. * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
  41. * called and, on destruction, ->elevator_exit_icq_fn(). Both functions
  42. * are called with both the associated io_context and queue locks held.
  43. *
  44. * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
  45. * queue lock but the returned icq is valid only until the queue lock is
  46. * released. Elevators can not and should not try to create or destroy
  47. * icq's.
  48. *
  49. * As icq's are linked from both ioc and q, the locking rules are a bit
  50. * complex.
  51. *
  52. * - ioc lock nests inside q lock.
  53. *
  54. * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
  55. * q->icq_list and icq->q_node by q lock.
  56. *
  57. * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
  58. * itself is protected by q lock. However, both the indexes and icq
  59. * itself are also RCU managed and lookup can be performed holding only
  60. * the q lock.
  61. *
  62. * - icq's are not reference counted. They are destroyed when either the
  63. * ioc or q goes away. Each request with icq set holds an extra
  64. * reference to ioc to ensure it stays until the request is completed.
  65. *
  66. * - Linking and unlinking icq's are performed while holding both ioc and q
  67. * locks. Due to the lock ordering, q exit is simple but ioc exit
  68. * requires reverse-order double lock dance.
  69. */
  70. struct io_cq {
  71. struct request_queue *q;
  72. struct io_context *ioc;
  73. /*
  74. * q_node and ioc_node link io_cq through icq_list of q and ioc
  75. * respectively. Both fields are unused once ioc_exit_icq() is
  76. * called and shared with __rcu_icq_cache and __rcu_head which are
  77. * used for RCU free of io_cq.
  78. */
  79. union {
  80. struct list_head q_node;
  81. struct kmem_cache *__rcu_icq_cache;
  82. };
  83. union {
  84. struct hlist_node ioc_node;
  85. struct rcu_head __rcu_head;
  86. };
  87. unsigned int flags;
  88. };
  89. /*
  90. * I/O subsystem state of the associated processes. It is refcounted
  91. * and kmalloc'ed. These could be shared between processes.
  92. */
  93. struct io_context {
  94. atomic_long_t refcount;
  95. atomic_t active_ref;
  96. atomic_t nr_tasks;
  97. /* all the fields below are protected by this lock */
  98. spinlock_t lock;
  99. unsigned short ioprio;
  100. struct radix_tree_root icq_tree;
  101. struct io_cq __rcu *icq_hint;
  102. struct hlist_head icq_list;
  103. struct work_struct release_work;
  104. };
  105. /**
  106. * get_io_context_active - get active reference on ioc
  107. * @ioc: ioc of interest
  108. *
  109. * Only iocs with active reference can issue new IOs. This function
  110. * acquires an active reference on @ioc. The caller must already have an
  111. * active reference on @ioc.
  112. */
  113. static inline void get_io_context_active(struct io_context *ioc)
  114. {
  115. WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
  116. WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
  117. atomic_long_inc(&ioc->refcount);
  118. atomic_inc(&ioc->active_ref);
  119. }
  120. static inline void ioc_task_link(struct io_context *ioc)
  121. {
  122. get_io_context_active(ioc);
  123. WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
  124. atomic_inc(&ioc->nr_tasks);
  125. }
  126. struct task_struct;
  127. #ifdef CONFIG_BLOCK
  128. void put_io_context(struct io_context *ioc);
  129. void put_io_context_active(struct io_context *ioc);
  130. void exit_io_context(struct task_struct *task);
  131. struct io_context *get_task_io_context(struct task_struct *task,
  132. gfp_t gfp_flags, int node);
  133. #else
  134. struct io_context;
  135. static inline void put_io_context(struct io_context *ioc) { }
  136. static inline void exit_io_context(struct task_struct *task) { }
  137. #endif
  138. #endif