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/security.h>
  12 #include <linux/sched/task.h>
  13
  14 #include "blk.h"
  15 #include "blk-mq-sched.h"
  16
  17 /*
  18  * For io context allocations
  19  */
  20 static struct kmem_cache *iocontext_cachep;
  21
  22 #ifdef CONFIG_BLK_ICQ
  23 /**
  24  * get_io_context - increment reference count to io_context
  25  * @ioc: io_context to get
  26  *
  27  * Increment reference count to @ioc.
  28  */
  29 static void get_io_context(struct io_context *ioc)
  30 {
  31         BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
  32         atomic_long_inc(&ioc->refcount);
  33 }
  34
  35 static void icq_free_icq_rcu(struct rcu_head *head)
  36 {
  37         struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
  38
  39         kmem_cache_free(icq->__rcu_icq_cache, icq);
  40 }
  41
  42 /*
  43  * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
  44  * and queue locked for legacy.
  45  */
  46 static void ioc_exit_icq(struct io_cq *icq)
  47 {
  48         struct elevator_type *et = icq->q->elevator->type;
  49
  50         if (icq->flags & ICQ_EXITED)
  51                 return;
  52
  53         if (et->ops.exit_icq)
  54                 et->ops.exit_icq(icq);
  55
  56         icq->flags |= ICQ_EXITED;
  57 }
  58
  59 static void ioc_exit_icqs(struct io_context *ioc)
  60 {
  61         struct io_cq *icq;
  62
  63         spin_lock_irq(&ioc->lock);
  64         hlist_for_each_entry(icq, &ioc->icq_list, ioc_node)
  65                 ioc_exit_icq(icq);
  66         spin_unlock_irq(&ioc->lock);
  67 }
  68
  69 /*
  70  * Release an icq. Called with ioc locked for blk-mq, and with both ioc
  71  * and queue locked for legacy.
  72  */
  73 static void ioc_destroy_icq(struct io_cq *icq)
  74 {
  75         struct io_context *ioc = icq->ioc;
  76         struct request_queue *q = icq->q;
  77         struct elevator_type *et = q->elevator->type;
  78
  79         lockdep_assert_held(&ioc->lock);
  80         lockdep_assert_held(&q->queue_lock);
  81
  82         if (icq->flags & ICQ_DESTROYED)
  83                 return;
  84
  85         radix_tree_delete(&ioc->icq_tree, icq->q->id);
  86         hlist_del_init(&icq->ioc_node);
  87         list_del_init(&icq->q_node);
  88
  89         /*
  90          * Both setting lookup hint to and clearing it from @icq are done
  91          * under queue_lock.  If it's not pointing to @icq now, it never
  92          * will.  Hint assignment itself can race safely.
  93          */
  94         if (rcu_access_pointer(ioc->icq_hint) == icq)
  95                 rcu_assign_pointer(ioc->icq_hint, NULL);
  96
  97         ioc_exit_icq(icq);
  98
  99         /*
 100          * @icq->q might have gone away by the time RCU callback runs
 101          * making it impossible to determine icq_cache.  Record it in @icq.
 102          */
 103         icq->__rcu_icq_cache = et->icq_cache;
 104         icq->flags |= ICQ_DESTROYED;
 105         call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
 106 }
 107
 108 /*
 109  * Slow path for ioc release in put_io_context().  Performs double-lock
 110  * dancing to unlink all icq's and then frees ioc.
 111  */
 112 static void ioc_release_fn(struct work_struct *work)
 113 {
 114         struct io_context *ioc = container_of(work, struct io_context,
 115                                               release_work);
 116         spin_lock_irq(&ioc->lock);
 117
 118         while (!hlist_empty(&ioc->icq_list)) {
 119                 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
 120                                                 struct io_cq, ioc_node);
 121                 struct request_queue *q = icq->q;
 122
 123                 if (spin_trylock(&q->queue_lock)) {
 124                         ioc_destroy_icq(icq);
 125                         spin_unlock(&q->queue_lock);
 126                 } else {
 127                         /* Make sure q and icq cannot be freed. */
 128                         rcu_read_lock();
 129
 130                         /* Re-acquire the locks in the correct order. */
 131                         spin_unlock(&ioc->lock);
 132                         spin_lock(&q->queue_lock);
 133                         spin_lock(&ioc->lock);
 134
 135                         ioc_destroy_icq(icq);
 136
 137                         spin_unlock(&q->queue_lock);
 138                         rcu_read_unlock();
 139                 }
 140         }
 141
 142         spin_unlock_irq(&ioc->lock);
 143
 144         kmem_cache_free(iocontext_cachep, ioc);
 145 }
 146
 147 /*
 148  * Releasing icqs requires reverse order double locking and we may already be
 149  * holding a queue_lock.  Do it asynchronously from a workqueue.
 150  */
 151 static bool ioc_delay_free(struct io_context *ioc)
 152 {
 153         unsigned long flags;
 154
 155         spin_lock_irqsave(&ioc->lock, flags);
 156         if (!hlist_empty(&ioc->icq_list)) {
 157                 queue_work(system_power_efficient_wq, &ioc->release_work);
 158                 spin_unlock_irqrestore(&ioc->lock, flags);
 159                 return true;
 160         }
 161         spin_unlock_irqrestore(&ioc->lock, flags);
 162         return false;
 163 }
 164
 165 /**
 166  * ioc_clear_queue - break any ioc association with the specified queue
 167  * @q: request_queue being cleared
 168  *
 169  * Walk @q->icq_list and exit all io_cq's.
 170  */
 171 void ioc_clear_queue(struct request_queue *q)
 172 {
 173         spin_lock_irq(&q->queue_lock);
 174         while (!list_empty(&q->icq_list)) {
 175                 struct io_cq *icq =
 176                         list_first_entry(&q->icq_list, struct io_cq, q_node);
 177
 178                 /*
 179                  * Other context won't hold ioc lock to wait for queue_lock, see
 180                  * details in ioc_release_fn().
 181                  */
 182                 spin_lock(&icq->ioc->lock);
 183                 ioc_destroy_icq(icq);
 184                 spin_unlock(&icq->ioc->lock);
 185         }
 186         spin_unlock_irq(&q->queue_lock);
 187 }
 188 #else /* CONFIG_BLK_ICQ */
 189 static inline void ioc_exit_icqs(struct io_context *ioc)
 190 {
 191 }
 192 static inline bool ioc_delay_free(struct io_context *ioc)
 193 {
 194         return false;
 195 }
 196 #endif /* CONFIG_BLK_ICQ */
 197
 198 /**
 199  * put_io_context - put a reference of io_context
 200  * @ioc: io_context to put
 201  *
 202  * Decrement reference count of @ioc and release it if the count reaches
 203  * zero.
 204  */
 205 void put_io_context(struct io_context *ioc)
 206 {
 207         BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
 208         if (atomic_long_dec_and_test(&ioc->refcount) && !ioc_delay_free(ioc))
 209                 kmem_cache_free(iocontext_cachep, ioc);
 210 }
 211 EXPORT_SYMBOL_GPL(put_io_context);
 212
 213 /* Called by the exiting task */
 214 void exit_io_context(struct task_struct *task)
 215 {
 216         struct io_context *ioc;
 217
 218         task_lock(task);
 219         ioc = task->io_context;
 220         task->io_context = NULL;
 221         task_unlock(task);
 222
 223         if (atomic_dec_and_test(&ioc->active_ref)) {
 224                 ioc_exit_icqs(ioc);
 225                 put_io_context(ioc);
 226         }
 227 }
 228
 229 static struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
 230 {
 231         struct io_context *ioc;
 232
 233         ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
 234                                     node);
 235         if (unlikely(!ioc))
 236                 return NULL;
 237
 238         atomic_long_set(&ioc->refcount, 1);
 239         atomic_set(&ioc->active_ref, 1);
 240 #ifdef CONFIG_BLK_ICQ
 241         spin_lock_init(&ioc->lock);
 242         INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
 243         INIT_HLIST_HEAD(&ioc->icq_list);
 244         INIT_WORK(&ioc->release_work, ioc_release_fn);
 245 #endif
 246         ioc->ioprio = IOPRIO_DEFAULT;
 247
 248         return ioc;
 249 }
 250
 251 int set_task_ioprio(struct task_struct *task, int ioprio)
 252 {
 253         int err;
 254         const struct cred *cred = current_cred(), *tcred;
 255
 256         rcu_read_lock();
 257         tcred = __task_cred(task);
 258         if (!uid_eq(tcred->uid, cred->euid) &&
 259             !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
 260                 rcu_read_unlock();
 261                 return -EPERM;
 262         }
 263         rcu_read_unlock();
 264
 265         err = security_task_setioprio(task, ioprio);
 266         if (err)
 267                 return err;
 268
 269         task_lock(task);
 270         if (unlikely(!task->io_context)) {
 271                 struct io_context *ioc;
 272
 273                 task_unlock(task);
 274
 275                 ioc = alloc_io_context(GFP_ATOMIC, NUMA_NO_NODE);
 276                 if (!ioc)
 277                         return -ENOMEM;
 278
 279                 task_lock(task);
 280                 if (task->flags & PF_EXITING) {
 281                         kmem_cache_free(iocontext_cachep, ioc);
 282                         goto out;
 283                 }
 284                 if (task->io_context)
 285                         kmem_cache_free(iocontext_cachep, ioc);
 286                 else
 287                         task->io_context = ioc;
 288         }
 289         task->io_context->ioprio = ioprio;
 290 out:
 291         task_unlock(task);
 292         return 0;
 293 }
 294 EXPORT_SYMBOL_GPL(set_task_ioprio);
 295
 296 int __copy_io(unsigned long clone_flags, struct task_struct *tsk)
 297 {
 298         struct io_context *ioc = current->io_context;
 299
 300         /*
 301          * Share io context with parent, if CLONE_IO is set
 302          */
 303         if (clone_flags & CLONE_IO) {
 304                 atomic_inc(&ioc->active_ref);
 305                 tsk->io_context = ioc;
 306         } else if (ioprio_valid(ioc->ioprio)) {
 307                 tsk->io_context = alloc_io_context(GFP_KERNEL, NUMA_NO_NODE);
 308                 if (!tsk->io_context)
 309                         return -ENOMEM;
 310                 tsk->io_context->ioprio = ioc->ioprio;
 311         }
 312
 313         return 0;
 314 }
 315
 316 #ifdef CONFIG_BLK_ICQ
 317 /**
 318  * ioc_lookup_icq - lookup io_cq from ioc
 319  * @q: the associated request_queue
 320  *
 321  * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
 322  * with @q->queue_lock held.
 323  */
 324 struct io_cq *ioc_lookup_icq(struct request_queue *q)
 325 {
 326         struct io_context *ioc = current->io_context;
 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  * @q: request_queue of interest
 356  *
 357  * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
 358  * will be created using @gfp_mask.
 359  *
 360  * The caller is responsible for ensuring @ioc won't go away and @q is
 361  * alive and will stay alive until this function returns.
 362  */
 363 static struct io_cq *ioc_create_icq(struct request_queue *q)
 364 {
 365         struct io_context *ioc = current->io_context;
 366         struct elevator_type *et = q->elevator->type;
 367         struct io_cq *icq;
 368
 369         /* allocate stuff */
 370         icq = kmem_cache_alloc_node(et->icq_cache, GFP_ATOMIC | __GFP_ZERO,
 371                                     q->node);
 372         if (!icq)
 373                 return NULL;
 374
 375         if (radix_tree_maybe_preload(GFP_ATOMIC) < 0) {
 376                 kmem_cache_free(et->icq_cache, icq);
 377                 return NULL;
 378         }
 379
 380         icq->ioc = ioc;
 381         icq->q = q;
 382         INIT_LIST_HEAD(&icq->q_node);
 383         INIT_HLIST_NODE(&icq->ioc_node);
 384
 385         /* lock both q and ioc and try to link @icq */
 386         spin_lock_irq(&q->queue_lock);
 387         spin_lock(&ioc->lock);
 388
 389         if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
 390                 hlist_add_head(&icq->ioc_node, &ioc->icq_list);
 391                 list_add(&icq->q_node, &q->icq_list);
 392                 if (et->ops.init_icq)
 393                         et->ops.init_icq(icq);
 394         } else {
 395                 kmem_cache_free(et->icq_cache, icq);
 396                 icq = ioc_lookup_icq(q);
 397                 if (!icq)
 398                         printk(KERN_ERR "cfq: icq link failed!\n");
 399         }
 400
 401         spin_unlock(&ioc->lock);
 402         spin_unlock_irq(&q->queue_lock);
 403         radix_tree_preload_end();
 404         return icq;
 405 }
 406
 407 struct io_cq *ioc_find_get_icq(struct request_queue *q)
 408 {
 409         struct io_context *ioc = current->io_context;
 410         struct io_cq *icq = NULL;
 411
 412         if (unlikely(!ioc)) {
 413                 ioc = alloc_io_context(GFP_ATOMIC, q->node);
 414                 if (!ioc)
 415                         return NULL;
 416
 417                 task_lock(current);
 418                 if (current->io_context) {
 419                         kmem_cache_free(iocontext_cachep, ioc);
 420                         ioc = current->io_context;
 421                 } else {
 422                         current->io_context = ioc;
 423                 }
 424
 425                 get_io_context(ioc);
 426                 task_unlock(current);
 427         } else {
 428                 get_io_context(ioc);
 429
 430                 spin_lock_irq(&q->queue_lock);
 431                 icq = ioc_lookup_icq(q);
 432                 spin_unlock_irq(&q->queue_lock);
 433         }
 434
 435         if (!icq) {
 436                 icq = ioc_create_icq(q);
 437                 if (!icq) {
 438                         put_io_context(ioc);
 439                         return NULL;
 440                 }
 441         }
 442         return icq;
 443 }
 444 EXPORT_SYMBOL_GPL(ioc_find_get_icq);
 445 #endif /* CONFIG_BLK_ICQ */
 446
 447 static int __init blk_ioc_init(void)
 448 {
 449         iocontext_cachep = kmem_cache_create("blkdev_ioc",
 450                         sizeof(struct io_context), 0, SLAB_PANIC, NULL);
 451         return 0;
 452 }
 453 subsys_initcall(blk_ioc_init);