linux/block/blk-ioc.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Functions related to io context handling
   4 */
   5#include <linux/kernel.h>
   6#include <linux/module.h>
   7#include <linux/init.h>
   8#include <linux/bio.h>
   9#include <linux/blkdev.h>
  10#include <linux/slab.h>
  11#include <linux/sched/task.h>
  12
  13#include "blk.h"
  14
  15/*
  16 * For io context allocations
  17 */
  18static struct kmem_cache *iocontext_cachep;
  19
  20/**
  21 * get_io_context - increment reference count to io_context
  22 * @ioc: io_context to get
  23 *
  24 * Increment reference count to @ioc.
  25 */
  26void get_io_context(struct io_context *ioc)
  27{
  28        BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
  29        atomic_long_inc(&ioc->refcount);
  30}
  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/*
  40 * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
  41 * and queue locked for legacy.
  42 */
  43static void ioc_exit_icq(struct io_cq *icq)
  44{
  45        struct elevator_type *et = icq->q->elevator->type;
  46
  47        if (icq->flags & ICQ_EXITED)
  48                return;
  49
  50        if (et->ops.exit_icq)
  51                et->ops.exit_icq(icq);
  52
  53        icq->flags |= ICQ_EXITED;
  54}
  55
  56/*
  57 * Release an icq. Called with ioc locked for blk-mq, and with both ioc
  58 * and queue locked for legacy.
  59 */
  60static void ioc_destroy_icq(struct io_cq *icq)
  61{
  62        struct io_context *ioc = icq->ioc;
  63        struct request_queue *q = icq->q;
  64        struct elevator_type *et = q->elevator->type;
  65
  66        lockdep_assert_held(&ioc->lock);
  67
  68        radix_tree_delete(&ioc->icq_tree, icq->q->id);
  69        hlist_del_init(&icq->ioc_node);
  70        list_del_init(&icq->q_node);
  71
  72        /*
  73         * Both setting lookup hint to and clearing it from @icq are done
  74         * under queue_lock.  If it's not pointing to @icq now, it never
  75         * will.  Hint assignment itself can race safely.
  76         */
  77        if (rcu_access_pointer(ioc->icq_hint) == icq)
  78                rcu_assign_pointer(ioc->icq_hint, NULL);
  79
  80        ioc_exit_icq(icq);
  81
  82        /*
  83         * @icq->q might have gone away by the time RCU callback runs
  84         * making it impossible to determine icq_cache.  Record it in @icq.
  85         */
  86        icq->__rcu_icq_cache = et->icq_cache;
  87        icq->flags |= ICQ_DESTROYED;
  88        call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
  89}
  90
  91/*
  92 * Slow path for ioc release in put_io_context().  Performs double-lock
  93 * dancing to unlink all icq's and then frees ioc.
  94 */
  95static void ioc_release_fn(struct work_struct *work)
  96{
  97        struct io_context *ioc = container_of(work, struct io_context,
  98                                              release_work);
  99        spin_lock_irq(&ioc->lock);
 100
 101        while (!hlist_empty(&ioc->icq_list)) {
 102                struct io_cq *icq = hlist_entry(ioc->icq_list.first,
 103                                                struct io_cq, ioc_node);
 104                struct request_queue *q = icq->q;
 105
 106                if (spin_trylock(&q->queue_lock)) {
 107                        ioc_destroy_icq(icq);
 108                        spin_unlock(&q->queue_lock);
 109                } else {
 110                        /* Make sure q and icq cannot be freed. */
 111                        rcu_read_lock();
 112
 113                        /* Re-acquire the locks in the correct order. */
 114                        spin_unlock(&ioc->lock);
 115                        spin_lock(&q->queue_lock);
 116                        spin_lock(&ioc->lock);
 117
 118                        /*
 119                         * The icq may have been destroyed when the ioc lock
 120                         * was released.
 121                         */
 122                        if (!(icq->flags & ICQ_DESTROYED))
 123                                ioc_destroy_icq(icq);
 124
 125                        spin_unlock(&q->queue_lock);
 126                        rcu_read_unlock();
 127                }
 128        }
 129
 130        spin_unlock_irq(&ioc->lock);
 131
 132        kmem_cache_free(iocontext_cachep, ioc);
 133}
 134
 135/**
 136 * put_io_context - put a reference of io_context
 137 * @ioc: io_context to put
 138 *
 139 * Decrement reference count of @ioc and release it if the count reaches
 140 * zero.
 141 */
 142void put_io_context(struct io_context *ioc)
 143{
 144        unsigned long flags;
 145        bool free_ioc = false;
 146
 147        if (ioc == NULL)
 148                return;
 149
 150        BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
 151
 152        /*
 153         * Releasing ioc requires reverse order double locking and we may
 154         * already be holding a queue_lock.  Do it asynchronously from wq.
 155         */
 156        if (atomic_long_dec_and_test(&ioc->refcount)) {
 157                spin_lock_irqsave(&ioc->lock, flags);
 158                if (!hlist_empty(&ioc->icq_list))
 159                        queue_work(system_power_efficient_wq,
 160                                        &ioc->release_work);
 161                else
 162                        free_ioc = true;
 163                spin_unlock_irqrestore(&ioc->lock, flags);
 164        }
 165
 166        if (free_ioc)
 167                kmem_cache_free(iocontext_cachep, ioc);
 168}
 169
 170/**
 171 * put_io_context_active - put active reference on ioc
 172 * @ioc: ioc of interest
 173 *
 174 * Undo get_io_context_active().  If active reference reaches zero after
 175 * put, @ioc can never issue further IOs and ioscheds are notified.
 176 */
 177void put_io_context_active(struct io_context *ioc)
 178{
 179        struct io_cq *icq;
 180
 181        if (!atomic_dec_and_test(&ioc->active_ref)) {
 182                put_io_context(ioc);
 183                return;
 184        }
 185
 186        spin_lock_irq(&ioc->lock);
 187        hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
 188                if (icq->flags & ICQ_EXITED)
 189                        continue;
 190
 191                ioc_exit_icq(icq);
 192        }
 193        spin_unlock_irq(&ioc->lock);
 194
 195        put_io_context(ioc);
 196}
 197
 198/* Called by the exiting task */
 199void exit_io_context(struct task_struct *task)
 200{
 201        struct io_context *ioc;
 202
 203        task_lock(task);
 204        ioc = task->io_context;
 205        task->io_context = NULL;
 206        task_unlock(task);
 207
 208        atomic_dec(&ioc->nr_tasks);
 209        put_io_context_active(ioc);
 210}
 211
 212static void __ioc_clear_queue(struct list_head *icq_list)
 213{
 214        unsigned long flags;
 215
 216        rcu_read_lock();
 217        while (!list_empty(icq_list)) {
 218                struct io_cq *icq = list_entry(icq_list->next,
 219                                                struct io_cq, q_node);
 220                struct io_context *ioc = icq->ioc;
 221
 222                spin_lock_irqsave(&ioc->lock, flags);
 223                if (icq->flags & ICQ_DESTROYED) {
 224                        spin_unlock_irqrestore(&ioc->lock, flags);
 225                        continue;
 226                }
 227                ioc_destroy_icq(icq);
 228                spin_unlock_irqrestore(&ioc->lock, flags);
 229        }
 230        rcu_read_unlock();
 231}
 232
 233/**
 234 * ioc_clear_queue - break any ioc association with the specified queue
 235 * @q: request_queue being cleared
 236 *
 237 * Walk @q->icq_list and exit all io_cq's.
 238 */
 239void ioc_clear_queue(struct request_queue *q)
 240{
 241        LIST_HEAD(icq_list);
 242
 243        spin_lock_irq(&q->queue_lock);
 244        list_splice_init(&q->icq_list, &icq_list);
 245        spin_unlock_irq(&q->queue_lock);
 246
 247        __ioc_clear_queue(&icq_list);
 248}
 249
 250int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
 251{
 252        struct io_context *ioc;
 253        int ret;
 254
 255        ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
 256                                    node);
 257        if (unlikely(!ioc))
 258                return -ENOMEM;
 259
 260        /* initialize */
 261        atomic_long_set(&ioc->refcount, 1);
 262        atomic_set(&ioc->nr_tasks, 1);
 263        atomic_set(&ioc->active_ref, 1);
 264        spin_lock_init(&ioc->lock);
 265        INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
 266        INIT_HLIST_HEAD(&ioc->icq_list);
 267        INIT_WORK(&ioc->release_work, ioc_release_fn);
 268
 269        /*
 270         * Try to install.  ioc shouldn't be installed if someone else
 271         * already did or @task, which isn't %current, is exiting.  Note
 272         * that we need to allow ioc creation on exiting %current as exit
 273         * path may issue IOs from e.g. exit_files().  The exit path is
 274         * responsible for not issuing IO after exit_io_context().
 275         */
 276        task_lock(task);
 277        if (!task->io_context &&
 278            (task == current || !(task->flags & PF_EXITING)))
 279                task->io_context = ioc;
 280        else
 281                kmem_cache_free(iocontext_cachep, ioc);
 282
 283        ret = task->io_context ? 0 : -EBUSY;
 284
 285        task_unlock(task);
 286
 287        return ret;
 288}
 289
 290/**
 291 * get_task_io_context - get io_context of a task
 292 * @task: task of interest
 293 * @gfp_flags: allocation flags, used if allocation is necessary
 294 * @node: allocation node, used if allocation is necessary
 295 *
 296 * Return io_context of @task.  If it doesn't exist, it is created with
 297 * @gfp_flags and @node.  The returned io_context has its reference count
 298 * incremented.
 299 *
 300 * This function always goes through task_lock() and it's better to use
 301 * %current->io_context + get_io_context() for %current.
 302 */
 303struct io_context *get_task_io_context(struct task_struct *task,
 304                                       gfp_t gfp_flags, int node)
 305{
 306        struct io_context *ioc;
 307
 308        might_sleep_if(gfpflags_allow_blocking(gfp_flags));
 309
 310        do {
 311                task_lock(task);
 312                ioc = task->io_context;
 313                if (likely(ioc)) {
 314                        get_io_context(ioc);
 315                        task_unlock(task);
 316                        return ioc;
 317                }
 318                task_unlock(task);
 319        } while (!create_task_io_context(task, gfp_flags, node));
 320
 321        return NULL;
 322}
 323
 324/**
 325 * ioc_lookup_icq - lookup io_cq from ioc
 326 * @ioc: the associated io_context
 327 * @q: the associated request_queue
 328 *
 329 * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
 330 * with @q->queue_lock held.
 331 */
 332struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
 333{
 334        struct io_cq *icq;
 335
 336        lockdep_assert_held(&q->queue_lock);
 337
 338        /*
 339         * icq's are indexed from @ioc using radix tree and hint pointer,
 340         * both of which are protected with RCU.  All removals are done
 341         * holding both q and ioc locks, and we're holding q lock - if we
 342         * find a icq which points to us, it's guaranteed to be valid.
 343         */
 344        rcu_read_lock();
 345        icq = rcu_dereference(ioc->icq_hint);
 346        if (icq && icq->q == q)
 347                goto out;
 348
 349        icq = radix_tree_lookup(&ioc->icq_tree, q->id);
 350        if (icq && icq->q == q)
 351                rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
 352        else
 353                icq = NULL;
 354out:
 355        rcu_read_unlock();
 356        return icq;
 357}
 358EXPORT_SYMBOL(ioc_lookup_icq);
 359
 360/**
 361 * ioc_create_icq - create and link io_cq
 362 * @ioc: io_context of interest
 363 * @q: request_queue of interest
 364 * @gfp_mask: allocation mask
 365 *
 366 * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
 367 * will be created using @gfp_mask.
 368 *
 369 * The caller is responsible for ensuring @ioc won't go away and @q is
 370 * alive and will stay alive until this function returns.
 371 */
 372struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
 373                             gfp_t gfp_mask)
 374{
 375        struct elevator_type *et = q->elevator->type;
 376        struct io_cq *icq;
 377
 378        /* allocate stuff */
 379        icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
 380                                    q->node);
 381        if (!icq)
 382                return NULL;
 383
 384        if (radix_tree_maybe_preload(gfp_mask) < 0) {
 385                kmem_cache_free(et->icq_cache, icq);
 386                return NULL;
 387        }
 388
 389        icq->ioc = ioc;
 390        icq->q = q;
 391        INIT_LIST_HEAD(&icq->q_node);
 392        INIT_HLIST_NODE(&icq->ioc_node);
 393
 394        /* lock both q and ioc and try to link @icq */
 395        spin_lock_irq(&q->queue_lock);
 396        spin_lock(&ioc->lock);
 397
 398        if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
 399                hlist_add_head(&icq->ioc_node, &ioc->icq_list);
 400                list_add(&icq->q_node, &q->icq_list);
 401                if (et->ops.init_icq)
 402                        et->ops.init_icq(icq);
 403        } else {
 404                kmem_cache_free(et->icq_cache, icq);
 405                icq = ioc_lookup_icq(ioc, q);
 406                if (!icq)
 407                        printk(KERN_ERR "cfq: icq link failed!\n");
 408        }
 409
 410        spin_unlock(&ioc->lock);
 411        spin_unlock_irq(&q->queue_lock);
 412        radix_tree_preload_end();
 413        return icq;
 414}
 415
 416static int __init blk_ioc_init(void)
 417{
 418        iocontext_cachep = kmem_cache_create("blkdev_ioc",
 419                        sizeof(struct io_context), 0, SLAB_PANIC, NULL);
 420        return 0;
 421}
 422subsys_initcall(blk_ioc_init);
 423