linux/block/blk-ioc.c
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   1/*
   2 * Functions related to io context handling
   3 */
   4#include <linux/kernel.h>
   5#include <linux/module.h>
   6#include <linux/init.h>
   7#include <linux/bio.h>
   8#include <linux/blkdev.h>
   9#include <linux/bootmem.h>      /* for max_pfn/max_low_pfn */
  10
  11#include "blk.h"
  12
  13/*
  14 * For io context allocations
  15 */
  16static struct kmem_cache *iocontext_cachep;
  17
  18static void cfq_dtor(struct io_context *ioc)
  19{
  20        if (!hlist_empty(&ioc->cic_list)) {
  21                struct cfq_io_context *cic;
  22
  23                cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
  24                                                                cic_list);
  25                cic->dtor(ioc);
  26        }
  27}
  28
  29/*
  30 * IO Context helper functions. put_io_context() returns 1 if there are no
  31 * more users of this io context, 0 otherwise.
  32 */
  33int put_io_context(struct io_context *ioc)
  34{
  35        if (ioc == NULL)
  36                return 1;
  37
  38        BUG_ON(atomic_read(&ioc->refcount) == 0);
  39
  40        if (atomic_dec_and_test(&ioc->refcount)) {
  41                rcu_read_lock();
  42                if (ioc->aic && ioc->aic->dtor)
  43                        ioc->aic->dtor(ioc->aic);
  44                cfq_dtor(ioc);
  45                rcu_read_unlock();
  46
  47                kmem_cache_free(iocontext_cachep, ioc);
  48                return 1;
  49        }
  50        return 0;
  51}
  52EXPORT_SYMBOL(put_io_context);
  53
  54static void cfq_exit(struct io_context *ioc)
  55{
  56        rcu_read_lock();
  57
  58        if (!hlist_empty(&ioc->cic_list)) {
  59                struct cfq_io_context *cic;
  60
  61                cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
  62                                                                cic_list);
  63                cic->exit(ioc);
  64        }
  65        rcu_read_unlock();
  66}
  67
  68/* Called by the exitting task */
  69void exit_io_context(void)
  70{
  71        struct io_context *ioc;
  72
  73        task_lock(current);
  74        ioc = current->io_context;
  75        current->io_context = NULL;
  76        task_unlock(current);
  77
  78        if (atomic_dec_and_test(&ioc->nr_tasks)) {
  79                if (ioc->aic && ioc->aic->exit)
  80                        ioc->aic->exit(ioc->aic);
  81                cfq_exit(ioc);
  82
  83                put_io_context(ioc);
  84        }
  85}
  86
  87struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
  88{
  89        struct io_context *ret;
  90
  91        ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
  92        if (ret) {
  93                atomic_set(&ret->refcount, 1);
  94                atomic_set(&ret->nr_tasks, 1);
  95                spin_lock_init(&ret->lock);
  96                ret->ioprio_changed = 0;
  97                ret->ioprio = 0;
  98                ret->last_waited = jiffies; /* doesn't matter... */
  99                ret->nr_batch_requests = 0; /* because this is 0 */
 100                ret->aic = NULL;
 101                INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH);
 102                INIT_HLIST_HEAD(&ret->cic_list);
 103                ret->ioc_data = NULL;
 104        }
 105
 106        return ret;
 107}
 108
 109/*
 110 * If the current task has no IO context then create one and initialise it.
 111 * Otherwise, return its existing IO context.
 112 *
 113 * This returned IO context doesn't have a specifically elevated refcount,
 114 * but since the current task itself holds a reference, the context can be
 115 * used in general code, so long as it stays within `current` context.
 116 */
 117struct io_context *current_io_context(gfp_t gfp_flags, int node)
 118{
 119        struct task_struct *tsk = current;
 120        struct io_context *ret;
 121
 122        ret = tsk->io_context;
 123        if (likely(ret))
 124                return ret;
 125
 126        ret = alloc_io_context(gfp_flags, node);
 127        if (ret) {
 128                /* make sure set_task_ioprio() sees the settings above */
 129                smp_wmb();
 130                tsk->io_context = ret;
 131        }
 132
 133        return ret;
 134}
 135
 136/*
 137 * If the current task has no IO context then create one and initialise it.
 138 * If it does have a context, take a ref on it.
 139 *
 140 * This is always called in the context of the task which submitted the I/O.
 141 */
 142struct io_context *get_io_context(gfp_t gfp_flags, int node)
 143{
 144        struct io_context *ret = NULL;
 145
 146        /*
 147         * Check for unlikely race with exiting task. ioc ref count is
 148         * zero when ioc is being detached.
 149         */
 150        do {
 151                ret = current_io_context(gfp_flags, node);
 152                if (unlikely(!ret))
 153                        break;
 154        } while (!atomic_inc_not_zero(&ret->refcount));
 155
 156        return ret;
 157}
 158EXPORT_SYMBOL(get_io_context);
 159
 160void copy_io_context(struct io_context **pdst, struct io_context **psrc)
 161{
 162        struct io_context *src = *psrc;
 163        struct io_context *dst = *pdst;
 164
 165        if (src) {
 166                BUG_ON(atomic_read(&src->refcount) == 0);
 167                atomic_inc(&src->refcount);
 168                put_io_context(dst);
 169                *pdst = src;
 170        }
 171}
 172EXPORT_SYMBOL(copy_io_context);
 173
 174static int __init blk_ioc_init(void)
 175{
 176        iocontext_cachep = kmem_cache_create("blkdev_ioc",
 177                        sizeof(struct io_context), 0, SLAB_PANIC, NULL);
 178        return 0;
 179}
 180subsys_initcall(blk_ioc_init);
 181
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