LXR linux/include/linux/iocontext.h

   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
   9enum {
  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 */
  72struct 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 */
  98struct 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 */
 129static 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
 137static 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
 145struct task_struct;
 146#ifdef CONFIG_BLOCK
 147void put_io_context(struct io_context *ioc);
 148void put_io_context_active(struct io_context *ioc);
 149void exit_io_context(struct task_struct *task);
 150struct io_context *get_task_io_context(struct task_struct *task,
 151                                       gfp_t gfp_flags, int node);
 152#else
 153struct io_context;
 154static inline void put_io_context(struct io_context *ioc) { }
 155static inline void exit_io_context(struct task_struct *task) { }
 156#endif
 157
 158#endif
 159