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 */ 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 } 131 132 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; 149 static inline void put_io_context(struct io_context *ioc) { } 150 static inline void exit_io_context(struct task_struct *task) { } 151 #endif 152 153 #endif 154