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.
io_contio_cq" class="sd
struct d="L229" class="line" na3e="L232"> 269         260        icq = ioc-> 241        if (icq &/a> = icq->k == q)
 302                goto icq;
 233
 204        icq = icq">ioc_l_lock" class="sring ">icq">ioc_lntext(&ioc->icq_tree, q->icq &/a> = icq->k == q)
 296                (ioc->icq<       237        else
 228                icq = NULL;
 23goto icy:
 260         271        return icq;
 272}
 247EXPORT_SYMBOL(ioc_lookup_ick);
 304
 325/**
 276crokup_iref">cocks,assk ref">io/**
 277
 278 * @q: request_qtexk of interest
 159 * m * @td if allocamf a task
 310 311 312 * m * valid.
 313 *
 254 255 256 317struct io_cq *crokup_icq" class="sref"ref">crokup_icq(struct io_context *ioc, struct request_queue *k,
 288                        /a>, gfp_t q)
 289{
 290        struct ret = q->q-> 261        struct io_cq *icq;
 322
 323         204        icq = kmem_cache_alloc_node(rec->s | __GFP_ZERO,
 265                               /a>, q->node);
 296   >
request_q9x36"> 296   dc ale stuffelizea>->nlass=n name="L297"> 297 305        return NULL;
 268
 241        if k" class="spreloaioc)) {
 230                kmem_cache_free(rec->icq);
 297 305        return NULL;
="L234"> 272}
 273
 204        icq->io_context = ioc;
 205        icq->, ioc;
 246       K" clef="+code=INIT_HLIST_HEAD" clss="sref">INIT_HLIST_HEAD(&icq->q_node);
 267       D" class="sNODE=INIT_HLIST_HEAD" class="sNODE>INIT_HLIST_HEAD(&icq->ie=kmem_cache_alloc_nodi">kmem_cachsref">q_node);
 268
 323          ref">@9;t  ale stuffelize */
 260       t" class="sra href="+code=ict" class="sra>kmem_cache_free(q->queue_lock);
 321        spin_lock(&ioc->lock);
 322
                if (ioc_lntext(&ioc->icq_tree, q->task,(ioc)) {
 224kmem_>task,hy" cladd_heaINIT_HLIST_HEAD(&icq->ie=kmem_cache_alloc_nodi">kmem_cach, _HLIST_HEAD(&ioc->icq_list);
 295               y" claddef="+code=likely" cladd>INIT_HLIST_HEAD(&icq->q->icq_list);
 296                if (rec->op="+code=gfp_flagop= claef">icq_liste" class=srefsrefcode=ioc_release_fe" class=srefsrefcod296   dc ale stuffelizea>->ock/blk-i3c.c#L287" id="L287" clas3="lin38 name="L297"> 297 295               (rec->op="+code=gfp_flagop= claef">icq_liste" class=srefsrefcode=ioc_release_fe" class=srefsrefcod296<_destroy_icq(icq);
}> 237"sref">ioc)) {
 229                kmem_cache_free(rec->icq);
 230                icq =*iocio_context *(&icq);
 297 296   >
request_q9x36"> 296   dc ale stuffelizea>->ock/blk-i3c.c#L292" id="L292" clas3="lin39 na3e="L233"> 302 230               print href="+code=locprint ">iocio_context KERN_ERRhref="+code=locKERN_ERRass="s323     stonsi">"cfq:39;t ref">failed!\n"le stufs="sref">icq);
 "sref">icq);
 304
 205        spin_unlock(&ioc->lock);
 246       k" class="s"sra href="+code=ict" class="s"sra>kmem_cache_free(q->queue_lock);
 267        " class="spreloa<_enqueue_lock);
 271        return icq;
icq);
 320
gfp_flags, int_"+code=spin_lock_ini_"sref">spp_flags, int
kmem="L2/a>   dc ale stuffelizea>-&g4ock/blk-i4c.c#L302" id="L302" clas4="lin4" namesref">ioc)) {
unlock(&iocos="sref">icq = kmem_323     stonsi">"
__GFP_ZERO,
 224>>>>>>>>sizeof">crokup_icq(struct (& queue_lock);
 305queue_lock);
 306}
 307kme">queue_lock);



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