1 /* 2 * Functions related to io context handling 3 */ 4 #include <linux/kernel.h> 5 #include <linux/module.h> 6 #include <linux/init.h> 7 #include <linux/bio.h> 8 #include <linux/blkdev.h> 9 #include <linux/bootmem.h> /* for max_pfn/max_low_pfn */ 10 #include <linux/slab.h> 11 12 #include "blk.h" 13 14 /* 15 * For io context allocations 16 */ 17 static struct kmem_cache *iocontext_cachep; 18 19 /** 20 * get_io_context - increment reference count to io_context 21 * @ioc: io_context to get 22 * 23 * Increment reference count to @ioc. 24 */ 25 void get_io_context(struct io_context *ioc) 26 { 27 BUG_ON(atomic_long_read(&ioc->refcount) <= 0); 28 atomic_long_inc(&ioc->refcount); 29 } 30 EXPORT_SYMBOL(get_io_context); 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 and free an icq. Called with both ioc and q locked. 41 */ 42 static void ioc_exit_icq(struct io_cq *icq) 43 { 44 struct io_context *ioc = icq->ioc; 45 struct request_queue *q = icq->q; 46 struct elevator_type *et = q->elevator->type; 47 48 lockdep_assert_held(&ioc->lock); 49 lockdep_assert_held(q->queue_lock); 50 51 radix_tree_delete(&ioc->icq_tree, icq->q->id); 52 hlist_del_init(&icq->ioc_node); 53 list_del_init(&icq->q_node); 54 55 /* 56 * Both setting lookup hint to and clearing it from @icq are done 57 * under queue_lock. If it's not pointing to @icq now, it never 58 * will. Hint assignment itself can race safely. 59 */ 60 if (rcu_dereference_raw(ioc->icq_hint) == icq) 61 rcu_assign_pointer(ioc->icq_hint, NULL); 62 63 if (et->ops.elevator_exit_icq_fn) 64 et->ops.elevator_exit_icq_fn(icq); 65 66 /* 67 * @icq->q might have gone away by the time RCU callback runs 68 * making it impossible to determine icq_cache. Record it in @icq. 69 */ 70 icq->__rcu_icq_cache = et->icq_cache; 71 call_rcu(&icq->__rcu_head, icq_free_icq_rcu); 72 } 73 74 /* 75 * Slow path for ioc release in put_io_context(). Performs double-lock 76 * dancing to unlink all icq's and then frees ioc. 77 */ 78 static void ioc_release_fn(struct work_struct *work) 79 { 80 struct io_context *ioc = container_of(work, struct io_context, 81 release_work); 82 struct request_queue *last_q = NULL; 83 unsigned long flags; 84 85 /* 86 * Exiting icq may call into put_io_context() through elevator 87 * which will trigger lockdep warning. The ioc's are guaranteed to 88 * be different, use a different locking subclass here. Use 89 * irqsave variant as there's no spin_lock_irq_nested(). 90 */ 91 spin_lock_irqsave_nested(&ioc->lock, flags, 1); 92 93 while (!hlist_empty(&ioc->icq_list)) { 94 struct io_cq *icq = hlist_entry(ioc->icq_list.first, 95 struct io_cq, ioc_node); 96 struct request_queue *this_q = icq->q; 97 98 if (this_q != last_q) { 99 /* 100 * Need to switch to @this_q. Once we release 101 * @ioc->lock, it can go away along with @cic. 102 * Hold on to it. 103 */ 104 __blk_get_queue(this_q); 105 106 /* 107 * blk_put_queue() might sleep thanks to kobject 108 * idiocy. Always release both locks, put and 109 * restart. 110 */ 111 if (last_q) { 112 spin_unlock(last_q->queue_lock); 113 spin_unlock_irqrestore(&ioc->lock, flags); 114 blk_put_queue(last_q); 115 } else { 116 spin_unlock_irqrestore(&ioc->lock, flags); 117 } 118 119 last_q = this_q; 120 spin_lock_irqsave(this_q->queue_lock, flags); 121 spin_lock_nested(&ioc->lock, 1); 122 continue; 123 } 124 ioc_exit_icq(icq); 125 } 126 127 if (last_q) { 128 spin_unlock(last_q->queue_lock); 129 spin_unlock_irqrestore(&ioc->lock, flags); 130 blk_put_queue(last_q); 131 } else { 132 spin_unlock_irqrestore(&ioc->lock, flags); 133 } 134 135 kmem_cache_free(iocontext_cachep, ioc); 136 } 137 138 /** 139 * put_io_context - put a reference of io_context 140 * @ioc: io_context to put 141 * 142 * Decrement reference count of @ioc and release it if the count reaches 143 * zero. 144 */ 145 void put_io_context(struct io_context *ioc) 146 { 147 unsigned long flags; 148 149 if (ioc == NULL) 150 return; 151 152 BUG_ON(atomic_long_read(&ioc->refcount) <= 0); 153 154 /* 155 * Releasing ioc requires reverse order double locking and we may 156 * already be holding a queue_lock. Do it asynchronously from wq. 157 */ 158 if (atomic_long_dec_and_test(&ioc->refcount)) { 159 spin_lock_irqsave(&ioc->lock, flags); 160 if (!hlist_empty(&ioc->icq_list)) 161 schedule_work(&ioc->release_work); 162 spin_unlock_irqrestore(&ioc->lock, flags); 163 } 164 } 165 EXPORT_SYMBOL(put_io_context); 166 167 /* Called by the exiting task */ 168 void exit_io_context(struct task_struct *task) 169 { 170 struct io_context *ioc; 171 172 task_lock(task); 173 ioc = task->io_context; 174 task->io_context = NULL; 175 task_unlock(task); 176 177 atomic_dec(&ioc->nr_tasks); 178 put_io_context(ioc); 179 } 180 181 /** 182 * ioc_clear_queue - break any ioc association with the specified queue 183 * @q: request_queue being cleared 184 * 185 * Walk @q->icq_list and exit all io_cq's. Must be called with @q locked. 186 */ 187 void ioc_clear_queue(struct request_queue *q) 188 { 189 lockdep_assert_held(q->queue_lock); 190 191 while (!list_empty(&q->icq_list)) { 192 struct io_cq *icq = list_entry(q->icq_list.next, 193 struct io_cq, q_node); 194 struct io_context *ioc = icq->ioc; 195 196 spin_lock(&ioc->lock); 197 ioc_exit_icq(icq); 198 spin_unlock(&ioc->lock); 199 } 200 } 201 202 void create_io_context_slowpath(struct task_struct *task, gfp_t gfp_flags, 203 int node) 204 { 205 struct io_context *ioc; 206 207 ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO, 208 node); 209 if (unlikely(!ioc)) 210 return; 211 212 /* initialize */ 213 atomic_long_set(&ioc->refcount, 1); 214 atomic_set(&ioc->nr_tasks, 1); 215 spin_lock_init(&ioc->lock); 216 INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH); 217 INIT_HLIST_HEAD(&ioc->icq_list); 218 INIT_WORK(&ioc->release_work, ioc_release_fn); 219 220 /* 221 * Try to install. ioc shouldn't be installed if someone else 222 * already did or @task, which isn't %current, is exiting. Note 223 * that we need to allow ioc creation on exiting %current as exit 224 * path may issue IOs from e.g. exit_files(). The exit path is 225 * responsible for not issuing IO after exit_io_context(). 226 */ 227 task_lock(task); 228 if (!task->io_context && 229 (task == current || !(task->flags & PF_EXITING))) 230 task->io_context = ioc; 231 else 232 kmem_cache_free(iocontext_cachep, ioc); 233 task_unlock(task); 234 } 235 236 /** 237 * get_task_io_context - get io_context of a task 238 * @task: task of interest 239 * @gfp_flags: allocation flags, used if allocation is necessary 240 * @node: allocation node, used if allocation is necessary 241 * 242 * Return io_context of @task. If it doesn't exist, it is created with 243 * @gfp_flags and @node. The returned io_context has its reference count 244 * incremented. 245 * 246 * This function always goes through task_lock() and it's better to use 247 * %current->io_context + get_io_context() for %current. 248 */ 249 struct io_context *get_task_io_context(struct task_struct *task, 250 gfp_t gfp_flags, int node) 251 { 252 struct io_context *ioc; 253 254 might_sleep_if(gfp_flags & __GFP_WAIT); 255 256 do { 257 task_lock(task); 258 ioc = task->io_context; 259 if (likely(ioc)) { 260 get_io_context(ioc); 261 task_unlock(task); 262 return ioc; 263 } 264 task_unlock(task); 265 } while (create_io_context(task, gfp_flags, node)); 266 267 return NULL; 268 } 269 EXPORT_SYMBOL(get_task_io_context); 270 271 /** 272 * ioc_lookup_icq - lookup io_cq from ioc 273 * @ioc: the associated io_context 274 * @q: the associated request_queue 275 * 276 * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called 277 * with @q->queue_lock held. 278 */ 279 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q) 280 { 281 struct io_cq *icq; 282 283 lockdep_assert_held(q->queue_lock); 284 285 /* 286 * icq's are indexed from @ioc using radix tree and hint pointer, 287 * both of which are protected with RCU. All removals are done 288 * holding both q and ioc locks, and we're holding q lock - if we 289 * find a icq which points to us, it's guaranteed to be valid. 290 */ 291 rcu_read_lock(); 292 icq = rcu_dereference(ioc->icq_hint); 293 if (icq && icq->q == q) 294 goto out; 295 296 icq = radix_tree_lookup(&ioc->icq_tree, q->id); 297 if (icq && icq->q == q) 298 rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */ 299 else 300 icq = NULL; 301 out: 302 rcu_read_unlock(); 303 return icq; 304 } 305 EXPORT_SYMBOL(ioc_lookup_icq); 306 307 /** 308 * ioc_create_icq - create and link io_cq 309 * @q: request_queue of interest 310 * @gfp_mask: allocation mask 311 * 312 * Make sure io_cq linking %current->io_context and @q exists. If either 313 * io_context and/or icq don't exist, they will be created using @gfp_mask. 314 * 315 * The caller is responsible for ensuring @ioc won't go away and @q is 316 * alive and will stay alive until this function returns. 317 */ 318 struct io_cq *ioc_create_icq(struct request_queue *q, gfp_t gfp_mask) 319 { 320 struct elevator_type *et = q->elevator->type; 321 struct io_context *ioc; 322 struct io_cq *icq; 323 324 /* allocate stuff */ 325 ioc = create_io_context(current, gfp_mask, q->node); 326 if (!ioc) 327 return NULL; 328 329 icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO, 330 q->node); 331 if (!icq) 332 return NULL; 333 334 if (radix_tree_preload(gfp_mask) < 0) { 335 kmem_cache_free(et->icq_cache, icq); 336 return NULL; 337 } 338 339 icq->ioc = ioc; 340 icq->q = q; 341 INIT_LIST_HEAD(&icq->q_node); 342 INIT_HLIST_NODE(&icq->ioc_node); 343 344 /* lock both q and ioc and try to link @icq */ 345 spin_lock_irq(q->queue_lock); 346 spin_lock(&ioc->lock); 347 348 if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) { 349 hlist_add_head(&icq->ioc_node, &ioc->icq_list); 350 list_add(&icq->q_node, &q->icq_list); 351 if (et->ops.elevator_init_icq_fn) 352 et->ops.elevator_init_icq_fn(icq); 353 } else { 354 kmem_cache_free(et->icq_cache, icq); 355 icq = ioc_lookup_icq(ioc, q); 356 if (!icq) 357 printk(KERN_ERR "cfq: icq link failed!\n"); 358 } 359 360 spin_unlock(&ioc->lock); 361 spin_unlock_irq(q->queue_lock); 362 radix_tree_preload_end(); 363 return icq; 364 } 365 366 void ioc_set_changed(struct io_context *ioc, int which) 367 { 368 struct io_cq *icq; 369 struct hlist_node *n; 370 371 hlist_for_each_entry(icq, n, &ioc->icq_list, ioc_node) 372 set_bit(which, &icq->changed); 373 } 374 375 /** 376 * ioc_ioprio_changed - notify ioprio change 377 * @ioc: io_context of interest 378 * @ioprio: new ioprio 379 * 380 * @ioc's ioprio has changed to @ioprio. Set %ICQ_IOPRIO_CHANGED for all 381 * icq's. iosched is responsible for checking the bit and applying it on 382 * request issue path. 383 */ 384 void ioc_ioprio_changed(struct io_context *ioc, int ioprio) 385 { 386 unsigned long flags; 387 388 spin_lock_irqsave(&ioc->lock, flags); 389 ioc->ioprio = ioprio; 390 ioc_set_changed(ioc, ICQ_IOPRIO_CHANGED); 391 spin_unlock_irqrestore(&ioc->lock, flags); 392 } 393 394 /** 395 * ioc_cgroup_changed - notify cgroup change 396 * @ioc: io_context of interest 397 * 398 * @ioc's cgroup has changed. Set %ICQ_CGROUP_CHANGED for all icq's. 399 * iosched is responsible for checking the bit and applying it on request 400 * issue path. 401 */ 402 void ioc_cgroup_changed(struct io_context *ioc) 403 { 404 unsigned long flags; 405 406 spin_lock_irqsave(&ioc->lock, flags); 407 ioc_set_changed(ioc, ICQ_CGROUP_CHANGED); 408 spin_unlock_irqrestore(&ioc->lock, flags); 409 } 410 EXPORT_SYMBOL(ioc_cgroup_changed); 411 412 static int __init blk_ioc_init(void) 413 { 414 iocontext_cachep = kmem_cache_create("blkdev_ioc", 415 sizeof(struct io_context), 0, SLAB_PANIC, NULL); 416 return 0; 417 } 418 subsys_initcall(blk_ioc_init); 419