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); 416