root/block/blk-ioc.c

DEFINITIONS

1. get_io_context
2. icq_free_icq_rcu
3. ioc_exit_icq
4. ioc_destroy_icq
5. ioc_release_fn
6. put_io_context
7. put_io_context_active
8. exit_io_context
9. __ioc_clear_queue
10. ioc_clear_queue
11. create_task_io_context
12. get_task_io_context
13. ioc_lookup_icq
14. ioc_create_icq
15. blk_ioc_init

   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         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  */
  95 static void ioc_release_fn(struct work_struct *work)
  96 {
  97         struct io_context *ioc = container_of(work, struct io_context,
  98                                               release_work);
  99         unsigned long flags;
 100 
 101         /*
 102          * Exiting icq may call into put_io_context() through elevator
 103          * which will trigger lockdep warning.  The ioc's are guaranteed to
 104          * be different, use a different locking subclass here.  Use
 105          * irqsave variant as there's no spin_lock_irq_nested().
 106          */
 107         spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 108 
 109         while (!hlist_empty(&ioc->icq_list)) {
 110                 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
 111                                                 struct io_cq, ioc_node);
 112                 struct request_queue *q = icq->q;
 113 
 114                 if (spin_trylock(&q->queue_lock)) {
 115                         ioc_destroy_icq(icq);
 116                         spin_unlock(&q->queue_lock);
 117                 } else {
 118                         spin_unlock_irqrestore(&ioc->lock, flags);
 119                         cpu_relax();
 120                         spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 121                 }
 122         }
 123 
 124         spin_unlock_irqrestore(&ioc->lock, flags);
 125 
 126         kmem_cache_free(iocontext_cachep, ioc);
 127 }
 128 
 129 /**
 130  * put_io_context - put a reference of io_context
 131  * @ioc: io_context to put
 132  *
 133  * Decrement reference count of @ioc and release it if the count reaches
 134  * zero.
 135  */
 136 void put_io_context(struct io_context *ioc)
 137 {
 138         unsigned long flags;
 139         bool free_ioc = false;
 140 
 141         if (ioc == NULL)
 142                 return;
 143 
 144         BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
 145 
 146         /*
 147          * Releasing ioc requires reverse order double locking and we may
 148          * already be holding a queue_lock.  Do it asynchronously from wq.
 149          */
 150         if (atomic_long_dec_and_test(&ioc->refcount)) {
 151                 spin_lock_irqsave(&ioc->lock, flags);
 152                 if (!hlist_empty(&ioc->icq_list))
 153                         queue_work(system_power_efficient_wq,
 154                                         &ioc->release_work);
 155                 else
 156                         free_ioc = true;
 157                 spin_unlock_irqrestore(&ioc->lock, flags);
 158         }
 159 
 160         if (free_ioc)
 161                 kmem_cache_free(iocontext_cachep, ioc);
 162 }
 163 
 164 /**
 165  * put_io_context_active - put active reference on ioc
 166  * @ioc: ioc of interest
 167  *
 168  * Undo get_io_context_active().  If active reference reaches zero after
 169  * put, @ioc can never issue further IOs and ioscheds are notified.
 170  */
 171 void put_io_context_active(struct io_context *ioc)
 172 {
 173         unsigned long flags;
 174         struct io_cq *icq;
 175 
 176         if (!atomic_dec_and_test(&ioc->active_ref)) {
 177                 put_io_context(ioc);
 178                 return;
 179         }
 180 
 181         /*
 182          * Need ioc lock to walk icq_list and q lock to exit icq.  Perform
 183          * reverse double locking.  Read comment in ioc_release_fn() for
 184          * explanation on the nested locking annotation.
 185          */
 186         spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 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_irqrestore(&ioc->lock, flags);
 194 
 195         put_io_context(ioc);
 196 }
 197 
 198 /* Called by the exiting task */
 199 void 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 
 212 static 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  */
 239 void 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 
 250 int 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  */
 303 struct 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  */
 332 struct 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;
 354 out:
 355         rcu_read_unlock();
 356         return icq;
 357 }
 358 EXPORT_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  */
 372 struct 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 
 416 static 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 }
 422 subsys_initcall(blk_ioc_init);