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