1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef IOCONTEXT_H
3 #define IOCONTEXT_H
4
5 #include <linux/radix-tree.h>
6 #include <linux/rcupdate.h>
7 #include <linux/workqueue.h>
8
9 enum {
10 ICQ_EXITED = 1 << 2,
11 };
12
13 /*
14 * An io_cq (icq) is association between an io_context (ioc) and a
15 * request_queue (q). This is used by elevators which need to track
16 * information per ioc - q pair.
17 *
18 * Elevator can request use of icq by setting elevator_type->icq_size and
19 * ->icq_align. Both size and align must be larger than that of struct
20 * io_cq and elevator can use the tail area for private information. The
21 * recommended way to do this is defining a struct which contains io_cq as
22 * the first member followed by private members and using its size and
23 * align. For example,
24 *
25 * struct snail_io_cq {
26 * struct io_cq icq;
27 * int poke_snail;
28 * int feed_snail;
29 * };
30 *
31 * struct elevator_type snail_elv_type {
32 * .ops = { ... },
33 * .icq_size = sizeof(struct snail_io_cq),
34 * .icq_align = __alignof__(struct snail_io_cq),
35 * ...
36 * };
37 *
38 * If icq_size is set, block core will manage icq's. All requests will
39 * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
40 * is called and be holding a reference to the associated io_context.
41 *
42 * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
43 * called and, on destruction, ->elevator_exit_icq_fn(). Both functions
44 * are called with both the associated io_context and queue locks held.
45 *
46 * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
47 * queue lock but the returned icq is valid only until the queue lock is
48 * released. Elevators can not and should not try to create or destroy
49 * icq's.
50 *
51 * As icq's are linked from both ioc and q, the locking rules are a bit
52 * complex.
53 *
54 * - ioc lock nests inside q lock.
55 *
56 * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
57 * q->icq_list and icq->q_node by q lock.
58 *
59 * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
60 * itself is protected by q lock. However, both the indexes and icq
61 * itself are also RCU managed and lookup can be performed holding only
62 * the q lock.
63 *
64 * - icq's are not reference counted. They are destroyed when either the
65 * ioc or q goes away. Each request with icq set holds an extra
66 * reference to ioc to ensure it stays until the request is completed.
67 *
68 * - Linking and unlinking icq's are performed while holding both ioc and q
69 * locks. Due to the lock ordering, q exit is simple but ioc exit
70 * requires reverse-order double lock dance.
71 */
72 struct io_cq {
73 struct request_queue *q;
74 struct io_context *ioc;
75
76 /*
77 * q_node and ioc_node link io_cq through icq_list of q and ioc
78 * respectively. Both fields are unused once ioc_exit_icq() is
79 * called and shared with __rcu_icq_cache and __rcu_head which are
80 * used for RCU free of io_cq.
81 */
82 union {
83 struct list_head q_node;
84 struct kmem_cache *__rcu_icq_cache;
85 };
86 union {
87 struct hlist_node ioc_node;
88 struct rcu_head __rcu_head;
89 };
90
91 unsigned int flags;
92 };
93
94 /*
95 * I/O subsystem state of the associated processes. It is refcounted
96 * and kmalloc'ed. These could be shared between processes.
97 */
98 struct io_context {
99 atomic_long_t refcount;
100 atomic_t active_ref;
101 atomic_t nr_tasks;
102
103 /* all the fields below are protected by this lock */
104 spinlock_t lock;
105
106 unsigned short ioprio;
107
108 /*
109 * For request batching
110 */
111 int nr_batch_requests; /* Number of requests left in the batch */
112 unsigned long last_waited; /* Time last woken after wait for request */
113
114 struct radix_tree_root icq_tree;
115 struct io_cq __rcu *icq_hint;
116 struct hlist_head icq_list;
117
118 struct work_struct release_work;
119 };
120
121 /**
122 * get_io_context_active - get active reference on ioc
123 * @ioc: ioc of interest
124 *
125 * Only iocs with active reference can issue new IOs. This function
126 * acquires an active reference on @ioc. The caller must already have an
127 * active reference on @ioc.
128 */
get_io_context_active(struct io_context * ioc)129 static inline void get_io_context_active(struct io_context *ioc)
130 {
131 WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
132 WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
133 atomic_long_inc(&ioc->refcount);
134 atomic_inc(&ioc->active_ref);
135 }
136
ioc_task_link(struct io_context * ioc)137 static inline void ioc_task_link(struct io_context *ioc)
138 {
139 get_io_context_active(ioc);
140
141 WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
142 atomic_inc(&ioc->nr_tasks);
143 }
144
145 struct task_struct;
146 #ifdef CONFIG_BLOCK
147 void put_io_context(struct io_context *ioc);
148 void put_io_context_active(struct io_context *ioc);
149 void exit_io_context(struct task_struct *task);
150 struct io_context *get_task_io_context(struct task_struct *task,
151 gfp_t gfp_flags, int node);
152 #else
153 struct io_context;
put_io_context(struct io_context * ioc)154 static inline void put_io_context(struct io_context *ioc) { }
exit_io_context(struct task_struct * task)155 static inline void exit_io_context(struct task_struct *task) { }
156 #endif
157
158 #endif
159
