block/blk-ioc.c

   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 #include <linux/slab.h>
  11
  12 #include "blk.h"
  13
  14 /*
  15  * For io context allocations
  16  */
  17 static struct kmem_cache *iocontext_cachep;
  18
  19 /**
  20  * get_io_context - increment reference count to io_context
  21  * @ioc: io_context to get
  22  *
  23  * Increment reference count to @ioc.
  24  */
  25 void get_io_context(struct io_context *ioc)
  26 {
  27         BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
  28         atomic_long_inc(&ioc->refcount);
  29 }
  30 EXPORT_SYMBOL(get_io_context);
  31
  32 static void cfq_dtor(struct io_context *ioc)
  33 {
  34         if (!hlist_empty(&ioc->cic_list)) {
  35                 struct cfq_io_context *cic;
  36
  37                 cic = hlist_entry(ioc->cic_list.first, struct cfq_io_context,
  38                                                                 cic_list);
  39                 cic->dtor(ioc);
  40         }
  41 }
  42
  43 /**
  44  * put_io_context - put a reference of io_context
  45  * @ioc: io_context to put
  46  *
  47  * Decrement reference count of @ioc and release it if the count reaches
  48  * zero.
  49  */
  50 void put_io_context(struct io_context *ioc)
  51 {
  52         if (ioc == NULL)
  53                 return;
  54
  55         BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
  56
  57         if (!atomic_long_dec_and_test(&ioc->refcount))
  58                 return;
  59
  60         rcu_read_lock();
  61         cfq_dtor(ioc);
  62         rcu_read_unlock();
  63
  64         kmem_cache_free(iocontext_cachep, ioc);
  65 }
  66 EXPORT_SYMBOL(put_io_context);
  67
  68 static void cfq_exit(struct io_context *ioc)
  69 {
  70         rcu_read_lock();
  71
  72         if (!hlist_empty(&ioc->cic_list)) {
  73                 struct cfq_io_context *cic;
  74
  75                 cic = hlist_entry(ioc->cic_list.first, struct cfq_io_context,
  76                                                                 cic_list);
  77                 cic->exit(ioc);
  78         }
  79         rcu_read_unlock();
  80 }
  81
  82 /* Called by the exiting task */
  83 void exit_io_context(struct task_struct *task)
  84 {
  85         struct io_context *ioc;
  86
  87         /* PF_EXITING prevents new io_context from being attached to @task */
  88         WARN_ON_ONCE(!(current->flags & PF_EXITING));
  89
  90         task_lock(task);
  91         ioc = task->io_context;
  92         task->io_context = NULL;
  93         task_unlock(task);
  94
  95         if (atomic_dec_and_test(&ioc->nr_tasks))
  96                 cfq_exit(ioc);
  97
  98         put_io_context(ioc);
  99 }
 100
 101 static struct io_context *create_task_io_context(struct task_struct *task,
 102                                                  gfp_t gfp_flags, int node,
 103                                                  bool take_ref)
 104 {
 105         struct io_context *ioc;
 106
 107         ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
 108                                     node);
 109         if (unlikely(!ioc))
 110                 return NULL;
 111
 112         /* initialize */
 113         atomic_long_set(&ioc->refcount, 1);
 114         atomic_set(&ioc->nr_tasks, 1);
 115         spin_lock_init(&ioc->lock);
 116         INIT_RADIX_TREE(&ioc->radix_root, GFP_ATOMIC | __GFP_HIGH);
 117         INIT_HLIST_HEAD(&ioc->cic_list);
 118
 119         /* try to install, somebody might already have beaten us to it */
 120         task_lock(task);
 121
 122         if (!task->io_context && !(task->flags & PF_EXITING)) {
 123                 task->io_context = ioc;
 124         } else {
 125                 kmem_cache_free(iocontext_cachep, ioc);
 126                 ioc = task->io_context;
 127         }
 128
 129         if (ioc && take_ref)
 130                 get_io_context(ioc);
 131
 132         task_unlock(task);
 133         return ioc;
 134 }
 135
 136 /**
 137  * current_io_context - get io_context of %current
 138  * @gfp_flags: allocation flags, used if allocation is necessary
 139  * @node: allocation node, used if allocation is necessary
 140  *
 141  * Return io_context of %current.  If it doesn't exist, it is created with
 142  * @gfp_flags and @node.  The returned io_context does NOT have its
 143  * reference count incremented.  Because io_context is exited only on task
 144  * exit, %current can be sure that the returned io_context is valid and
 145  * alive as long as it is executing.
 146  */
 147 struct io_context *current_io_context(gfp_t gfp_flags, int node)
 148 {
 149         might_sleep_if(gfp_flags & __GFP_WAIT);
 150
 151         if (current->io_context)
 152                 return current->io_context;
 153
 154         return create_task_io_context(current, gfp_flags, node, false);
 155 }
 156 EXPORT_SYMBOL(current_io_context);
 157
 158 /**
 159  * get_task_io_context - get io_context of a task
 160  * @task: task of interest
 161  * @gfp_flags: allocation flags, used if allocation is necessary
 162  * @node: allocation node, used if allocation is necessary
 163  *
 164  * Return io_context of @task.  If it doesn't exist, it is created with
 165  * @gfp_flags and @node.  The returned io_context has its reference count
 166  * incremented.
 167  *
 168  * This function always goes through task_lock() and it's better to use
 169  * current_io_context() + get_io_context() for %current.
 170  */
 171 struct io_context *get_task_io_context(struct task_struct *task,
 172                                        gfp_t gfp_flags, int node)
 173 {
 174         struct io_context *ioc;
 175
 176         might_sleep_if(gfp_flags & __GFP_WAIT);
 177
 178         task_lock(task);
 179         ioc = task->io_context;
 180         if (likely(ioc)) {
 181                 get_io_context(ioc);
 182                 task_unlock(task);
 183                 return ioc;
 184         }
 185         task_unlock(task);
 186
 187         return create_task_io_context(task, gfp_flags, node, true);
 188 }
 189 EXPORT_SYMBOL(get_task_io_context);
 190
 191 static int __init blk_ioc_init(void)
 192 {
 193         iocontext_cachep = kmem_cache_create("blkdev_ioc",
 194                         sizeof(struct io_context), 0, SLAB_PANIC, NULL);
 195         return 0;
 196 }
 197 subsys_initcall(blk_ioc_init);