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#include <linux/slab.h>
  11
  12#include "blk.h"
  13
  14/*
  15 * For io context allocations
  16 */
  17static 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 */
  25void get_io_context(struct io_context *ioc)
  26{
  27        BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
  28        atomic_long_inc(&ioc->refcount);
  29}
  30EXPORT_SYMBOL(get_io_context);
  31
  32static void icq_free_icq_rcu(struct rcu_head *head)
  33{
  34        struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
  35
  36        kmem_cache_free(icq->__rcu_icq_cache, icq);
  37}
  38
  39/* Exit an icq. Called with both ioc and q locked. */
  40static void ioc_exit_icq(struct io_cq *icq)
  41{
  42        struct elevator_type *et = icq->q->elevator->type;
  43
  44        if (icq->flags & ICQ_EXITED)
  45                return;
  46
  47        if (et->ops.elevator_exit_icq_fn)
  48                et->ops.elevator_exit_icq_fn(icq);
  49
  50        icq->flags |= ICQ_EXITED;
  51}
  52
  53/* Release an icq.  Called with both ioc and q locked. */
  54static void ioc_destroy_icq(struct io_cq *icq)
  55{
  56        struct io_context *ioc = icq->ioc;
  57        struct request_queue *q = icq->q;
  58        struct elevator_type *et = q->elevator->type;
  59
  60        lockdep_assert_held(&ioc->lock);
  61        lockdep_assert_held(q->queue_lock);
  62
  63        radix_tree_delete(&ioc->icq_tree, icq->q->id);
  64        hlist_del_init(&icq->ioc_node);
  65        list_del_init(&icq->q_node);
  66
  67        /*
  68         * Both setting lookup hint to and clearing it from @icq are done
  69         * under queue_lock.  If it's not pointing to @icq now, it never
  70         * will.  Hint assignment itself can race safely.
  71         */
  72        if (rcu_dereference_raw(ioc->icq_hint) == icq)
  73                rcu_assign_pointer(ioc->icq_hint, NULL);
  74
  75        ioc_exit_icq(icq);
  76
  77        /*
  78         * @icq->q might have gone away by the time RCU callback runs
  79         * making it impossible to determine icq_cache.  Record it in @icq.
  80         */
  81        icq->__rcu_icq_cache = et->icq_cache;
  82        call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
  83}
  84
  85/*
  86 * Slow path for ioc release in put_io_context().  Performs double-lock
  87 * dancing to unlink all icq's and then frees ioc.
  88 */
  89static void ioc_release_fn(struct work_struct *work)
  90{
  91        struct io_context *ioc = container_of(work, struct io_context,
  92                                              release_work);
  93        unsigned long flags;
  94
  95        /*
  96         * Exiting icq may call into put_io_context() through elevator
  97         * which will trigger lockdep warning.  The ioc's are guaranteed to
  98         * be different, use a different locking subclass here.  Use
  99         * irqsave variant as there's no spin_lock_irq_nested().
 100         */
 101        spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 102
 103        while (!hlist_empty(&ioc->icq_list)) {
 104                struct io_cq *icq = hlist_entry(ioc->icq_list.first,
 105                                                struct io_cq, ioc_node);
 106                struct request_queue *q = icq->q;
 107
 108                if (spin_trylock(q->queue_lock)) {
 109                        ioc_destroy_icq(icq);
 110                        spin_unlock(q->queue_lock);
 111                } else {
 112                        spin_unlock_irqrestore(&ioc->lock, flags);
 113                        cpu_relax();
 114                        spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 115                }
 116        }
 117
 118        spin_unlock_irqrestore(&ioc->lock, flags);
 119
 120        kmem_cache_free(iocontext_cachep, ioc);
 121}
 122
 123/**
 124 * put_io_context - put a reference of io_context
 125 * @ioc: io_context to put
 126 *
 127 * Decrement reference count of @ioc and release it if the count reaches
 128 * zero.
 129 */
 130void put_io_context(struct io_context *ioc)
 131{
 132        unsigned long flags;
 133        bool free_ioc = false;
 134
 135        if (ioc == NULL)
 136                return;
 137
 138        BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
 139
 140        /*
 141         * Releasing ioc requires reverse order double locking and we may
 142         * already be holding a queue_lock.  Do it asynchronously from wq.
 143         */
 144        if (atomic_long_dec_and_test(&ioc->refcount)) {
 145                spin_lock_irqsave(&ioc->lock, flags);
 146                if (!hlist_empty(&ioc->icq_list))
 147                        schedule_work(&ioc->release_work);
 148                else
 149                        free_ioc = true;
 150                spin_unlock_irqrestore(&ioc->lock, flags);
 151        }
 152
 153        if (free_ioc)
 154                kmem_cache_free(iocontext_cachep, ioc);
 155}
 156EXPORT_SYMBOL(put_io_context);
 157
 158/**
 159 * put_io_context_active - put active reference on ioc
 160 * @ioc: ioc of interest
 161 *
 162 * Undo get_io_context_active().  If active reference reaches zero after
 163 * put, @ioc can never issue further IOs and ioscheds are notified.
 164 */
 165void put_io_context_active(struct io_context *ioc)
 166{
 167        unsigned long flags;
 168        struct io_cq *icq;
 169
 170        if (!atomic_dec_and_test(&ioc->active_ref)) {
 171                put_io_context(ioc);
 172                return;
 173        }
 174
 175        /*
 176         * Need ioc lock to walk icq_list and q lock to exit icq.  Perform
 177         * reverse double locking.  Read comment in ioc_release_fn() for
 178         * explanation on the nested locking annotation.
 179         */
 180retry:
 181        spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 182        hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
 183                if (icq->flags & ICQ_EXITED)
 184                        continue;
 185                if (spin_trylock(icq->q->queue_lock)) {
 186                        ioc_exit_icq(icq);
 187                        spin_unlock(icq->q->queue_lock);
 188                } else {
 189                        spin_unlock_irqrestore(&ioc->lock, flags);
 190                        cpu_relax();
 191                        goto retry;
 192                }
 193        }
 194        spin_unlock_irqrestore(&ioc->lock, flags);
 195
 196        put_io_context(ioc);
 197}
 198
 199/* Called by the exiting task */
 200void exit_io_context(struct task_struct *task)
 201{
 202        struct io_context *ioc;
 203
 204        task_lock(task);
 205        ioc = task->io_context;
 206        task->io_context = NULL;
 207        task_unlock(task);
 208
 209        atomic_dec(&ioc->nr_tasks);
 210        put_io_context_active(ioc);
 211}
 212
 213/**
 214 * ioc_clear_queue - break any ioc association with the specified queue
 215 * @q: request_queue being cleared
 216 *
 217 * Walk @q->icq_list and exit all io_cq's.  Must be called with @q locked.
 218 */
 219void ioc_clear_queue(struct request_queue *q)
 220{
 221        lockdep_assert_held(q->queue_lock);
 222
 223        while (!list_empty(&q->icq_list)) {
 224                struct io_cq *icq = list_entry(q->icq_list.next,
 225                                               struct io_cq, q_node);
 226                struct io_context *ioc = icq->ioc;
 227
 228                spin_lock(&ioc->lock);
 229                ioc_destroy_icq(icq);
 230                spin_unlock(&ioc->lock);
 231        }
 232}
 233
 234int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
 235{
 236        struct io_context *ioc;
 237        int ret;
 238
 239        ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
 240                                    node);
 241        if (unlikely(!ioc))
 242                return -ENOMEM;
 243
 244        /* initialize */
 245        atomic_long_set(&ioc->refcount, 1);
 246        atomic_set(&ioc->nr_tasks, 1);
 247        atomic_set(&ioc->active_ref, 1);
 248        spin_lock_init(&ioc->lock);
 249        INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
 250        INIT_HLIST_HEAD(&ioc->icq_list);
 251        INIT_WORK(&ioc->release_work, ioc_release_fn);
 252
 253        /*
 254         * Try to install.  ioc shouldn't be installed if someone else
 255         * already did or @task, which isn't %current, is exiting.  Note
 256         * that we need to allow ioc creation on exiting %current as exit
 257         * path may issue IOs from e.g. exit_files().  The exit path is
 258         * responsible for not issuing IO after exit_io_context().
 259         */
 260        task_lock(task);
 261        if (!task->io_context &&
 262            (task == current || !(task->flags & PF_EXITING)))
 263                task->io_context = ioc;
 264        else
 265                kmem_cache_free(iocontext_cachep, ioc);
 266
 267        ret = task->io_context ? 0 : -EBUSY;
 268
 269        task_unlock(task);
 270
 271        return ret;
 272}
 273
 274/**
 275 * get_task_io_context - get io_context of a task
 276 * @task: task of interest
 277 * @gfp_flags: allocation flags, used if allocation is necessary
 278 * @node: allocation node, used if allocation is necessary
 279 *
 280 * Return io_context of @task.  If it doesn't exist, it is created with
 281 * @gfp_flags and @node.  The returned io_context has its reference count
 282 * incremented.
 283 *
 284 * This function always goes through task_lock() and it's better to use
 285 * %current->io_context + get_io_context() for %current.
 286 */
 287struct io_context *get_task_io_context(struct task_struct *task,
 288                                       gfp_t gfp_flags, int node)
 289{
 290        struct io_context *ioc;
 291
 292        might_sleep_if(gfp_flags & __GFP_WAIT);
 293
 294        do {
 295                task_lock(task);
 296                ioc = task->io_context;
 297                if (likely(ioc)) {
 298                        get_io_context(ioc);
 299                        task_unlock(task);
 300                        return ioc;
 301                }
 302                task_unlock(task);
 303        } while (!create_task_io_context(task, gfp_flags, node));
 304
 305        return NULL;
 306}
 307EXPORT_SYMBOL(get_task_io_context);
 308
 309/**
 310 * ioc_lookup_icq - lookup io_cq from ioc
 311 * @ioc: the associated io_context
 312 * @q: the associated request_queue
 313 *
 314 * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
 315 * with @q->queue_lock held.
 316 */
 317struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
 318{
 319        struct io_cq *icq;
 320
 321        lockdep_assert_held(q->queue_lock);
 322
 323        /*
 324         * icq's are indexed from @ioc using radix tree and hint pointer,
 325         * both of which are protected with RCU.  All removals are done
 326         * holding both q and ioc locks, and we're holding q lock - if we
 327         * find a icq which points to us, it's guaranteed to be valid.
 328         */
 329        rcu_read_lock();
 330        icq = rcu_dereference(ioc->icq_hint);
 331        if (icq && icq->q == q)
 332                goto out;
 333
 334        icq = radix_tree_lookup(&ioc->icq_tree, q->id);
 335        if (icq && icq->q == q)
 336                rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
 337        else
 338                icq = NULL;
 339out:
 340        rcu_read_unlock();
 341        return icq;
 342}
 343EXPORT_SYMBOL(ioc_lookup_icq);
 344
 345/**
 346 * ioc_create_icq - create and link io_cq
 347 * @ioc: io_context of interest
 348 * @q: request_queue of interest
 349 * @gfp_mask: allocation mask
 350 *
 351 * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
 352 * will be created using @gfp_mask.
 353 *
 354 * The caller is responsible for ensuring @ioc won't go away and @q is
 355 * alive and will stay alive until this function returns.
 356 */
 357struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
 358                             gfp_t gfp_mask)
 359{
 360        struct elevator_type *et = q->elevator->type;
 361        struct io_cq *icq;
 362
 363        /* allocate stuff */
 364        icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
 365                                    q->node);
 366        if (!icq)
 367                return NULL;
 368
 369        if (radix_tree_preload(gfp_mask) < 0) {
 370                kmem_cache_free(et->icq_cache, icq);
 371                return NULL;
 372        }
 373
 374        icq->ioc = ioc;
 375        icq->q = q;
 376        INIT_LIST_HEAD(&icq->q_node);
 377        INIT_HLIST_NODE(&icq->ioc_node);
 378
 379        /* lock both q and ioc and try to link @icq */
 380        spin_lock_irq(q->queue_lock);
 381        spin_lock(&ioc->lock);
 382
 383        if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
 384                hlist_add_head(&icq->ioc_node, &ioc->icq_list);
 385                list_add(&icq->q_node, &q->icq_list);
 386                if (et->ops.elevator_init_icq_fn)
 387                        et->ops.elevator_init_icq_fn(icq);
 388        } else {
 389                kmem_cache_free(et->icq_cache, icq);
 390                icq = ioc_lookup_icq(ioc, q);
 391                if (!icq)
 392                        printk(KERN_ERR "cfq: icq link failed!\n");
 393        }
 394
 395        spin_unlock(&ioc->lock);
 396        spin_unlock_irq(q->queue_lock);
 397        radix_tree_preload_end();
 398        return icq;
 399}
 400
 401static int __init blk_ioc_init(void)
 402{
 403        iocontext_cachep = kmem_cache_create("blkdev_ioc",
 404                        sizeof(struct io_context), 0, SLAB_PANIC, NULL);
 405        return 0;
 406}
 407subsys_initcall(blk_ioc_init);
 408
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