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 /*
  36  * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
  37  * and queue locked for legacy.
  38  */
  39 static void ioc_exit_icq(struct io_cq *icq)
  40 {
  41         struct elevator_type *et = icq->q->elevator->type;
  42
  43         if (icq->flags & ICQ_EXITED)
  44                 return;
  45
  46         if (et->ops.exit_icq)
  47                 et->ops.exit_icq(icq);
  48
  49         icq->flags |= ICQ_EXITED;
  50 }
  51
  52 static void ioc_exit_icqs(struct io_context *ioc)
  53 {
  54         struct io_cq *icq;
  55
  56         spin_lock_irq(&ioc->lock);
  57         hlist_for_each_entry(icq, &ioc->icq_list, ioc_node)
  58                 ioc_exit_icq(icq);
  59         spin_unlock_irq(&ioc->lock);
  60 }
  61
  62 /*
  63  * Release an icq. Called with ioc locked for blk-mq, and with both ioc
  64  * and queue locked for legacy.
  65  */
  66 static void ioc_destroy_icq(struct io_cq *icq)
  67 {
  68         struct io_context *ioc = icq->ioc;
  69         struct request_queue *q = icq->q;
  70         struct elevator_type *et = q->elevator->type;
  71
  72         lockdep_assert_held(&ioc->lock);
  73         lockdep_assert_held(&q->queue_lock);
  74
  75         if (icq->flags & ICQ_DESTROYED)
  76                 return;
  77
  78         radix_tree_delete(&ioc->icq_tree, icq->q->id);
  79         hlist_del_init(&icq->ioc_node);
  80         list_del_init(&icq->q_node);
  81
  82         /*
  83          * Both setting lookup hint to and clearing it from @icq are done
  84          * under queue_lock.  If it's not pointing to @icq now, it never
  85          * will.  Hint assignment itself can race safely.
  86          */
  87         if (rcu_access_pointer(ioc->icq_hint) == icq)
  88                 rcu_assign_pointer(ioc->icq_hint, NULL);
  89
  90         ioc_exit_icq(icq);
  91
  92         /*
  93          * @icq->q might have gone away by the time RCU callback runs
  94          * making it impossible to determine icq_cache.  Record it in @icq.
  95          */
  96         icq->__rcu_icq_cache = et->icq_cache;
  97         icq->flags |= ICQ_DESTROYED;
  98         kfree_rcu(icq, __rcu_head);
  99 }
 100
 101 /*
 102  * Slow path for ioc release in put_io_context().  Performs double-lock
 103  * dancing to unlink all icq's and then frees ioc.
 104  */
 105 static void ioc_release_fn(struct work_struct *work)
 106 {
 107         struct io_context *ioc = container_of(work, struct io_context,
 108                                               release_work);
 109         spin_lock_irq(&ioc->lock);
 110
 111         while (!hlist_empty(&ioc->icq_list)) {
 112                 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
 113                                                 struct io_cq, ioc_node);
 114                 struct request_queue *q = icq->q;
 115
 116                 if (spin_trylock(&q->queue_lock)) {
 117                         ioc_destroy_icq(icq);
 118                         spin_unlock(&q->queue_lock);
 119                 } else {
 120                         /* Make sure q and icq cannot be freed. */
 121                         rcu_read_lock();
 122
 123                         /* Re-acquire the locks in the correct order. */
 124                         spin_unlock(&ioc->lock);
 125                         spin_lock(&q->queue_lock);
 126                         spin_lock(&ioc->lock);
 127
 128                         ioc_destroy_icq(icq);
 129
 130                         spin_unlock(&q->queue_lock);
 131                         rcu_read_unlock();
 132                 }
 133         }
 134
 135         spin_unlock_irq(&ioc->lock);
 136
 137         kmem_cache_free(iocontext_cachep, ioc);
 138 }
 139
 140 /*
 141  * Releasing icqs requires reverse order double locking and we may already be
 142  * holding a queue_lock.  Do it asynchronously from a workqueue.
 143  */
 144 static bool ioc_delay_free(struct io_context *ioc)
 145 {
 146         unsigned long flags;
 147
 148         spin_lock_irqsave(&ioc->lock, flags);
 149         if (!hlist_empty(&ioc->icq_list)) {
 150                 queue_work(system_power_efficient_wq, &ioc->release_work);
 151                 spin_unlock_irqrestore(&ioc->lock, flags);
 152                 return true;
 153         }
 154         spin_unlock_irqrestore(&ioc->lock, flags);
 155         return false;
 156 }
 157
 158 /**
 159  * ioc_clear_queue - break any ioc association with the specified queue
 160  * @q: request_queue being cleared
 161  *
 162  * Walk @q->icq_list and exit all io_cq's.
 163  */
 164 void ioc_clear_queue(struct request_queue *q)
 165 {
 166         spin_lock_irq(&q->queue_lock);
 167         while (!list_empty(&q->icq_list)) {
 168                 struct io_cq *icq =
 169                         list_first_entry(&q->icq_list, struct io_cq, q_node);
 170
 171                 /*
 172                  * Other context won't hold ioc lock to wait for queue_lock, see
 173                  * details in ioc_release_fn().
 174                  */
 175                 spin_lock(&icq->ioc->lock);
 176                 ioc_destroy_icq(icq);
 177                 spin_unlock(&icq->ioc->lock);
 178         }
 179         spin_unlock_irq(&q->queue_lock);
 180 }
 181 #else /* CONFIG_BLK_ICQ */
 182 static inline void ioc_exit_icqs(struct io_context *ioc)
 183 {
 184 }
 185 static inline bool ioc_delay_free(struct io_context *ioc)
 186 {
 187         return false;
 188 }
 189 #endif /* CONFIG_BLK_ICQ */
 190
 191 /**
 192  * put_io_context - put a reference of io_context
 193  * @ioc: io_context to put
 194  *
 195  * Decrement reference count of @ioc and release it if the count reaches
 196  * zero.
 197  */
 198 void put_io_context(struct io_context *ioc)
 199 {
 200         BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
 201         if (atomic_long_dec_and_test(&ioc->refcount) && !ioc_delay_free(ioc))
 202                 kmem_cache_free(iocontext_cachep, ioc);
 203 }
 204 EXPORT_SYMBOL_GPL(put_io_context);
 205
 206 /* Called by the exiting task */
 207 void exit_io_context(struct task_struct *task)
 208 {
 209         struct io_context *ioc;
 210
 211         task_lock(task);
 212         ioc = task->io_context;
 213         task->io_context = NULL;
 214         task_unlock(task);
 215
 216         if (atomic_dec_and_test(&ioc->active_ref)) {
 217                 ioc_exit_icqs(ioc);
 218                 put_io_context(ioc);
 219         }
 220 }
 221
 222 static struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
 223 {
 224         struct io_context *ioc;
 225
 226         ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
 227                                     node);
 228         if (unlikely(!ioc))
 229                 return NULL;
 230
 231         atomic_long_set(&ioc->refcount, 1);
 232         atomic_set(&ioc->active_ref, 1);
 233 #ifdef CONFIG_BLK_ICQ
 234         spin_lock_init(&ioc->lock);
 235         INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
 236         INIT_HLIST_HEAD(&ioc->icq_list);
 237         INIT_WORK(&ioc->release_work, ioc_release_fn);
 238 #endif
 239         ioc->ioprio = IOPRIO_DEFAULT;
 240
 241         return ioc;
 242 }
 243
 244 int set_task_ioprio(struct task_struct *task, int ioprio)
 245 {
 246         int err;
 247         const struct cred *cred = current_cred(), *tcred;
 248
 249         rcu_read_lock();
 250         tcred = __task_cred(task);
 251         if (!uid_eq(tcred->uid, cred->euid) &&
 252             !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
 253                 rcu_read_unlock();
 254                 return -EPERM;
 255         }
 256         rcu_read_unlock();
 257
 258         err = security_task_setioprio(task, ioprio);
 259         if (err)
 260                 return err;
 261
 262         task_lock(task);
 263         if (unlikely(!task->io_context)) {
 264                 struct io_context *ioc;
 265
 266                 task_unlock(task);
 267
 268                 ioc = alloc_io_context(GFP_ATOMIC, NUMA_NO_NODE);
 269                 if (!ioc)
 270                         return -ENOMEM;
 271
 272                 task_lock(task);
 273                 if (task->flags & PF_EXITING) {
 274                         kmem_cache_free(iocontext_cachep, ioc);
 275                         goto out;
 276                 }
 277                 if (task->io_context)
 278                         kmem_cache_free(iocontext_cachep, ioc);
 279                 else
 280                         task->io_context = ioc;
 281         }
 282         task->io_context->ioprio = ioprio;
 283 out:
 284         task_unlock(task);
 285         return 0;
 286 }
 287 EXPORT_SYMBOL_GPL(set_task_ioprio);
 288
 289 int __copy_io(unsigned long clone_flags, struct task_struct *tsk)
 290 {
 291         struct io_context *ioc = current->io_context;
 292
 293         /*
 294          * Share io context with parent, if CLONE_IO is set
 295          */
 296         if (clone_flags & CLONE_IO) {
 297                 atomic_inc(&ioc->active_ref);
 298                 tsk->io_context = ioc;
 299         } else if (ioprio_valid(ioc->ioprio)) {
 300                 tsk->io_context = alloc_io_context(GFP_KERNEL, NUMA_NO_NODE);
 301                 if (!tsk->io_context)
 302                         return -ENOMEM;
 303                 tsk->io_context->ioprio = ioc->ioprio;
 304         }
 305
 306         return 0;
 307 }
 308
 309 #ifdef CONFIG_BLK_ICQ
 310 /**
 311  * ioc_lookup_icq - lookup io_cq from ioc
 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  */
 317 struct io_cq *ioc_lookup_icq(struct request_queue *q)
 318 {
 319         struct io_context *ioc = current->io_context;
 320         struct io_cq *icq;
 321
 322         lockdep_assert_held(&q->queue_lock);
 323
 324         /*
 325          * icq's are indexed from @ioc using radix tree and hint pointer,
 326          * both of which are protected with RCU.  All removals are done
 327          * holding both q and ioc locks, and we're holding q lock - if we
 328          * find a icq which points to us, it's guaranteed to be valid.
 329          */
 330         rcu_read_lock();
 331         icq = rcu_dereference(ioc->icq_hint);
 332         if (icq && icq->q == q)
 333                 goto out;
 334
 335         icq = radix_tree_lookup(&ioc->icq_tree, q->id);
 336         if (icq && icq->q == q)
 337                 rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
 338         else
 339                 icq = NULL;
 340 out:
 341         rcu_read_unlock();
 342         return icq;
 343 }
 344 EXPORT_SYMBOL(ioc_lookup_icq);
 345
 346 /**
 347  * ioc_create_icq - create and link io_cq
 348  * @q: request_queue of interest
 349  *
 350  * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
 351  * will be created using @gfp_mask.
 352  *
 353  * The caller is responsible for ensuring @ioc won't go away and @q is
 354  * alive and will stay alive until this function returns.
 355  */
 356 static struct io_cq *ioc_create_icq(struct request_queue *q)
 357 {
 358         struct io_context *ioc = current->io_context;
 359         struct elevator_type *et = q->elevator->type;
 360         struct io_cq *icq;
 361
 362         /* allocate stuff */
 363         icq = kmem_cache_alloc_node(et->icq_cache, GFP_ATOMIC | __GFP_ZERO,
 364                                     q->node);
 365         if (!icq)
 366                 return NULL;
 367
 368         if (radix_tree_maybe_preload(GFP_ATOMIC) < 0) {
 369                 kmem_cache_free(et->icq_cache, icq);
 370                 return NULL;
 371         }
 372
 373         icq->ioc = ioc;
 374         icq->q = q;
 375         INIT_LIST_HEAD(&icq->q_node);
 376         INIT_HLIST_NODE(&icq->ioc_node);
 377
 378         /* lock both q and ioc and try to link @icq */
 379         spin_lock_irq(&q->queue_lock);
 380         spin_lock(&ioc->lock);
 381
 382         if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
 383                 hlist_add_head(&icq->ioc_node, &ioc->icq_list);
 384                 list_add(&icq->q_node, &q->icq_list);
 385                 if (et->ops.init_icq)
 386                         et->ops.init_icq(icq);
 387         } else {
 388                 kmem_cache_free(et->icq_cache, icq);
 389                 icq = ioc_lookup_icq(q);
 390                 if (!icq)
 391                         printk(KERN_ERR "cfq: icq link failed!\n");
 392         }
 393
 394         spin_unlock(&ioc->lock);
 395         spin_unlock_irq(&q->queue_lock);
 396         radix_tree_preload_end();
 397         return icq;
 398 }
 399
 400 struct io_cq *ioc_find_get_icq(struct request_queue *q)
 401 {
 402         struct io_context *ioc = current->io_context;
 403         struct io_cq *icq = NULL;
 404
 405         if (unlikely(!ioc)) {
 406                 ioc = alloc_io_context(GFP_ATOMIC, q->node);
 407                 if (!ioc)
 408                         return NULL;
 409
 410                 task_lock(current);
 411                 if (current->io_context) {
 412                         kmem_cache_free(iocontext_cachep, ioc);
 413                         ioc = current->io_context;
 414                 } else {
 415                         current->io_context = ioc;
 416                 }
 417
 418                 get_io_context(ioc);
 419                 task_unlock(current);
 420         } else {
 421                 get_io_context(ioc);
 422
 423                 spin_lock_irq(&q->queue_lock);
 424                 icq = ioc_lookup_icq(q);
 425                 spin_unlock_irq(&q->queue_lock);
 426         }
 427
 428         if (!icq) {
 429                 icq = ioc_create_icq(q);
 430                 if (!icq) {
 431                         put_io_context(ioc);
 432                         return NULL;
 433                 }
 434         }
 435         return icq;
 436 }
 437 EXPORT_SYMBOL_GPL(ioc_find_get_icq);
 438 #endif /* CONFIG_BLK_ICQ */
 439
 440 static int __init blk_ioc_init(void)
 441 {
 442         iocontext_cachep = kmem_cache_create("blkdev_ioc",
 443                         sizeof(struct io_context), 0, SLAB_PANIC, NULL);
 444         return 0;
 445 }
 446 subsys_initcall(blk_ioc_init);