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