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        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 */
  73struct 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 */
  99struct 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 */
 124static 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
 132static 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
 140struct task_struct;
 141#ifdef CONFIG_BLOCK
 142void put_io_context(struct io_context *ioc);
 143void put_io_context_active(struct io_context *ioc);
 144void exit_io_context(struct task_struct *task);
 145struct io_context *get_task_io_context(struct task_struct *task,
 146                                       gfp_t gfp_flags, int node);
 147#else
 148struct io_context;
 149static inline void put_io_context(struct io_context *ioc) { }
 150static inline void exit_io_context(struct task_struct *task) { }
 151#endif
 152
 153#endif
 154