block/blk-ioc.c

   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  */
  18 static 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  */
  26 void 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
  32 static 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  */
  43 static 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  */
  60 static 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         call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
  88 }
  89
  90 /*
  91  * Slow path for ioc release in put_io_context().  Performs double-lock
  92  * dancing to unlink all icq's and then frees ioc.
  93  */
  94 static void ioc_release_fn(struct work_struct *work)
  95 {
  96         struct io_context *ioc = container_of(work, struct io_context,
  97                                               release_work);
  98         unsigned long flags;
  99
 100         /*
 101          * Exiting icq may call into put_io_context() through elevator
 102          * which will trigger lockdep warning.  The ioc's are guaranteed to
 103          * be different, use a different locking subclass here.  Use
 104          * irqsave variant as there's no spin_lock_irq_nested().
 105          */
 106         spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 107
 108         while (!hlist_empty(&ioc->icq_list)) {
 109                 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
 110                                                 struct io_cq, ioc_node);
 111                 struct request_queue *q = icq->q;
 112
 113                 if (spin_trylock(&q->queue_lock)) {
 114                         ioc_destroy_icq(icq);
 115                         spin_unlock(&q->queue_lock);
 116                 } else {
 117                         spin_unlock_irqrestore(&ioc->lock, flags);
 118                         cpu_relax();
 119                         spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 120                 }
 121         }
 122
 123         spin_unlock_irqrestore(&ioc->lock, flags);
 124
 125         kmem_cache_free(iocontext_cachep, ioc);
 126 }
 127
 128 /**
 129  * put_io_context - put a reference of io_context
 130  * @ioc: io_context to put
 131  *
 132  * Decrement reference count of @ioc and release it if the count reaches
 133  * zero.
 134  */
 135 void put_io_context(struct io_context *ioc)
 136 {
 137         unsigned long flags;
 138         bool free_ioc = false;
 139
 140         if (ioc == NULL)
 141                 return;
 142
 143         BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
 144
 145         /*
 146          * Releasing ioc requires reverse order double locking and we may
 147          * already be holding a queue_lock.  Do it asynchronously from wq.
 148          */
 149         if (atomic_long_dec_and_test(&ioc->refcount)) {
 150                 spin_lock_irqsave(&ioc->lock, flags);
 151                 if (!hlist_empty(&ioc->icq_list))
 152                         queue_work(system_power_efficient_wq,
 153                                         &ioc->release_work);
 154                 else
 155                         free_ioc = true;
 156                 spin_unlock_irqrestore(&ioc->lock, flags);
 157         }
 158
 159         if (free_ioc)
 160                 kmem_cache_free(iocontext_cachep, ioc);
 161 }
 162
 163 /**
 164  * put_io_context_active - put active reference on ioc
 165  * @ioc: ioc of interest
 166  *
 167  * Undo get_io_context_active().  If active reference reaches zero after
 168  * put, @ioc can never issue further IOs and ioscheds are notified.
 169  */
 170 void put_io_context_active(struct io_context *ioc)
 171 {
 172         unsigned long flags;
 173         struct io_cq *icq;
 174
 175         if (!atomic_dec_and_test(&ioc->active_ref)) {
 176                 put_io_context(ioc);
 177                 return;
 178         }
 179
 180         /*
 181          * Need ioc lock to walk icq_list and q lock to exit icq.  Perform
 182          * reverse double locking.  Read comment in ioc_release_fn() for
 183          * explanation on the nested locking annotation.
 184          */
 185         spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 186         hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
 187                 if (icq->flags & ICQ_EXITED)
 188                         continue;
 189
 190                 ioc_exit_icq(icq);
 191         }
 192         spin_unlock_irqrestore(&ioc->lock, flags);
 193
 194         put_io_context(ioc);
 195 }
 196
 197 /* Called by the exiting task */
 198 void exit_io_context(struct task_struct *task)
 199 {
 200         struct io_context *ioc;
 201
 202         task_lock(task);
 203         ioc = task->io_context;
 204         task->io_context = NULL;
 205         task_unlock(task);
 206
 207         atomic_dec(&ioc->nr_tasks);
 208         put_io_context_active(ioc);
 209 }
 210
 211 static void __ioc_clear_queue(struct list_head *icq_list)
 212 {
 213         unsigned long flags;
 214
 215         while (!list_empty(icq_list)) {
 216                 struct io_cq *icq = list_entry(icq_list->next,
 217                                                 struct io_cq, q_node);
 218                 struct io_context *ioc = icq->ioc;
 219
 220                 spin_lock_irqsave(&ioc->lock, flags);
 221                 ioc_destroy_icq(icq);
 222                 spin_unlock_irqrestore(&ioc->lock, flags);
 223         }
 224 }
 225
 226 /**
 227  * ioc_clear_queue - break any ioc association with the specified queue
 228  * @q: request_queue being cleared
 229  *
 230  * Walk @q->icq_list and exit all io_cq's.
 231  */
 232 void ioc_clear_queue(struct request_queue *q)
 233 {
 234         LIST_HEAD(icq_list);
 235
 236         spin_lock_irq(&q->queue_lock);
 237         list_splice_init(&q->icq_list, &icq_list);
 238         spin_unlock_irq(&q->queue_lock);
 239
 240         __ioc_clear_queue(&icq_list);
 241 }
 242
 243 int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
 244 {
 245         struct io_context *ioc;
 246         int ret;
 247
 248         ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
 249                                     node);
 250         if (unlikely(!ioc))
 251                 return -ENOMEM;
 252
 253         /* initialize */
 254         atomic_long_set(&ioc->refcount, 1);
 255         atomic_set(&ioc->nr_tasks, 1);
 256         atomic_set(&ioc->active_ref, 1);
 257         spin_lock_init(&ioc->lock);
 258         INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
 259         INIT_HLIST_HEAD(&ioc->icq_list);
 260         INIT_WORK(&ioc->release_work, ioc_release_fn);
 261
 262         /*
 263          * Try to install.  ioc shouldn't be installed if someone else
 264          * already did or @task, which isn't %current, is exiting.  Note
 265          * that we need to allow ioc creation on exiting %current as exit
 266          * path may issue IOs from e.g. exit_files().  The exit path is
 267          * responsible for not issuing IO after exit_io_context().
 268          */
 269         task_lock(task);
 270         if (!task->io_context &&
 271             (task == current || !(task->flags & PF_EXITING)))
 272                 task->io_context = ioc;
 273         else
 274                 kmem_cache_free(iocontext_cachep, ioc);
 275
 276         ret = task->io_context ? 0 : -EBUSY;
 277
 278         task_unlock(task);
 279
 280         return ret;
 281 }
 282
 283 /**
 284  * get_task_io_context - get io_context of a task
 285  * @task: task of interest
 286  * @gfp_flags: allocation flags, used if allocation is necessary
 287  * @node: allocation node, used if allocation is necessary
 288  *
 289  * Return io_context of @task.  If it doesn't exist, it is created with
 290  * @gfp_flags and @node.  The returned io_context has its reference count
 291  * incremented.
 292  *
 293  * This function always goes through task_lock() and it's better to use
 294  * %current->io_context + get_io_context() for %current.
 295  */
 296 struct io_context *get_task_io_context(struct task_struct *task,
 297                                        gfp_t gfp_flags, int node)
 298 {
 299         struct io_context *ioc;
 300
 301         might_sleep_if(gfpflags_allow_blocking(gfp_flags));
 302
 303         do {
 304                 task_lock(task);
 305                 ioc = task->io_context;
 306                 if (likely(ioc)) {
 307                         get_io_context(ioc);
 308                         task_unlock(task);
 309                         return ioc;
 310                 }
 311                 task_unlock(task);
 312         } while (!create_task_io_context(task, gfp_flags, node));
 313
 314         return NULL;
 315 }
 316
 317 /**
 318  * ioc_lookup_icq - lookup io_cq from ioc
 319  * @ioc: the associated io_context
 320  * @q: the associated request_queue
 321  *
 322  * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
 323  * with @q->queue_lock held.
 324  */
 325 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
 326 {
 327         struct io_cq *icq;
 328
 329         lockdep_assert_held(&q->queue_lock);
 330
 331         /*
 332          * icq's are indexed from @ioc using radix tree and hint pointer,
 333          * both of which are protected with RCU.  All removals are done
 334          * holding both q and ioc locks, and we're holding q lock - if we
 335          * find a icq which points to us, it's guaranteed to be valid.
 336          */
 337         rcu_read_lock();
 338         icq = rcu_dereference(ioc->icq_hint);
 339         if (icq && icq->q == q)
 340                 goto out;
 341
 342         icq = radix_tree_lookup(&ioc->icq_tree, q->id);
 343         if (icq && icq->q == q)
 344                 rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
 345         else
 346                 icq = NULL;
 347 out:
 348         rcu_read_unlock();
 349         return icq;
 350 }
 351 EXPORT_SYMBOL(ioc_lookup_icq);
 352
 353 /**
 354  * ioc_create_icq - create and link io_cq
 355  * @ioc: io_context of interest
 356  * @q: request_queue of interest
 357  * @gfp_mask: allocation mask
 358  *
 359  * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
 360  * will be created using @gfp_mask.
 361  *
 362  * The caller is responsible for ensuring @ioc won't go away and @q is
 363  * alive and will stay alive until this function returns.
 364  */
 365 struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
 366                              gfp_t gfp_mask)
 367 {
 368         struct elevator_type *et = q->elevator->type;
 369         struct io_cq *icq;
 370
 371         /* allocate stuff */
 372         icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
 373                                     q->node);
 374         if (!icq)
 375                 return NULL;
 376
 377         if (radix_tree_maybe_preload(gfp_mask) < 0) {
 378                 kmem_cache_free(et->icq_cache, icq);
 379                 return NULL;
 380         }
 381
 382         icq->ioc = ioc;
 383         icq->q = q;
 384         INIT_LIST_HEAD(&icq->q_node);
 385         INIT_HLIST_NODE(&icq->ioc_node);
 386
 387         /* lock both q and ioc and try to link @icq */
 388         spin_lock_irq(&q->queue_lock);
 389         spin_lock(&ioc->lock);
 390
 391         if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
 392                 hlist_add_head(&icq->ioc_node, &ioc->icq_list);
 393                 list_add(&icq->q_node, &q->icq_list);
 394                 if (et->ops.init_icq)
 395                         et->ops.init_icq(icq);
 396         } else {
 397                 kmem_cache_free(et->icq_cache, icq);
 398                 icq = ioc_lookup_icq(ioc, q);
 399                 if (!icq)
 400                         printk(KERN_ERR "cfq: icq link failed!\n");
 401         }
 402
 403         spin_unlock(&ioc->lock);
 404         spin_unlock_irq(&q->queue_lock);
 405         radix_tree_preload_end();
 406         return icq;
 407 }
 408
 409 static int __init blk_ioc_init(void)
 410 {
 411         iocontext_cachep = kmem_cache_create("blkdev_ioc",
 412                         sizeof(struct io_context), 0, SLAB_PANIC, NULL);
 413         return 0;
 414 }
 415 subsys_initcall(blk_ioc_init);