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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/slab.h> | |
10 | #include <linux/sched/task.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 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->uses_mq && et->ops.mq.exit_icq) | |
51 | et->ops.mq.exit_icq(icq); | |
52 | else if (!et->uses_mq && et->ops.sq.elevator_exit_icq_fn) | |
53 | et->ops.sq.elevator_exit_icq_fn(icq); | |
54 | ||
55 | icq->flags |= ICQ_EXITED; | |
56 | } | |
57 | ||
58 | /* | |
59 | * Release an icq. Called with ioc locked for blk-mq, and with both ioc | |
60 | * and queue locked for legacy. | |
61 | */ | |
62 | static void ioc_destroy_icq(struct io_cq *icq) | |
63 | { | |
64 | struct io_context *ioc = icq->ioc; | |
65 | struct request_queue *q = icq->q; | |
66 | struct elevator_type *et = q->elevator->type; | |
67 | ||
68 | lockdep_assert_held(&ioc->lock); | |
69 | ||
70 | radix_tree_delete(&ioc->icq_tree, icq->q->id); | |
71 | hlist_del_init(&icq->ioc_node); | |
72 | list_del_init(&icq->q_node); | |
73 | ||
74 | /* | |
75 | * Both setting lookup hint to and clearing it from @icq are done | |
76 | * under queue_lock. If it's not pointing to @icq now, it never | |
77 | * will. Hint assignment itself can race safely. | |
78 | */ | |
79 | if (rcu_access_pointer(ioc->icq_hint) == icq) | |
80 | rcu_assign_pointer(ioc->icq_hint, NULL); | |
81 | ||
82 | ioc_exit_icq(icq); | |
83 | ||
84 | /* | |
85 | * @icq->q might have gone away by the time RCU callback runs | |
86 | * making it impossible to determine icq_cache. Record it in @icq. | |
87 | */ | |
88 | icq->__rcu_icq_cache = et->icq_cache; | |
89 | call_rcu(&icq->__rcu_head, icq_free_icq_rcu); | |
90 | } | |
91 | ||
92 | /* | |
93 | * Slow path for ioc release in put_io_context(). Performs double-lock | |
94 | * dancing to unlink all icq's and then frees ioc. | |
95 | */ | |
96 | static void ioc_release_fn(struct work_struct *work) | |
97 | { | |
98 | struct io_context *ioc = container_of(work, struct io_context, | |
99 | release_work); | |
100 | unsigned long flags; | |
101 | ||
102 | /* | |
103 | * Exiting icq may call into put_io_context() through elevator | |
104 | * which will trigger lockdep warning. The ioc's are guaranteed to | |
105 | * be different, use a different locking subclass here. Use | |
106 | * irqsave variant as there's no spin_lock_irq_nested(). | |
107 | */ | |
108 | spin_lock_irqsave_nested(&ioc->lock, flags, 1); | |
109 | ||
110 | while (!hlist_empty(&ioc->icq_list)) { | |
111 | struct io_cq *icq = hlist_entry(ioc->icq_list.first, | |
112 | struct io_cq, ioc_node); | |
113 | struct request_queue *q = icq->q; | |
114 | ||
115 | if (spin_trylock(q->queue_lock)) { | |
116 | ioc_destroy_icq(icq); | |
117 | spin_unlock(q->queue_lock); | |
118 | } else { | |
119 | spin_unlock_irqrestore(&ioc->lock, flags); | |
120 | cpu_relax(); | |
121 | spin_lock_irqsave_nested(&ioc->lock, flags, 1); | |
122 | } | |
123 | } | |
124 | ||
125 | spin_unlock_irqrestore(&ioc->lock, flags); | |
126 | ||
127 | kmem_cache_free(iocontext_cachep, ioc); | |
128 | } | |
129 | ||
130 | /** | |
131 | * put_io_context - put a reference of io_context | |
132 | * @ioc: io_context to put | |
133 | * | |
134 | * Decrement reference count of @ioc and release it if the count reaches | |
135 | * zero. | |
136 | */ | |
137 | void put_io_context(struct io_context *ioc) | |
138 | { | |
139 | unsigned long flags; | |
140 | bool free_ioc = false; | |
141 | ||
142 | if (ioc == NULL) | |
143 | return; | |
144 | ||
145 | BUG_ON(atomic_long_read(&ioc->refcount) <= 0); | |
146 | ||
147 | /* | |
148 | * Releasing ioc requires reverse order double locking and we may | |
149 | * already be holding a queue_lock. Do it asynchronously from wq. | |
150 | */ | |
151 | if (atomic_long_dec_and_test(&ioc->refcount)) { | |
152 | spin_lock_irqsave(&ioc->lock, flags); | |
153 | if (!hlist_empty(&ioc->icq_list)) | |
154 | queue_work(system_power_efficient_wq, | |
155 | &ioc->release_work); | |
156 | else | |
157 | free_ioc = true; | |
158 | spin_unlock_irqrestore(&ioc->lock, flags); | |
159 | } | |
160 | ||
161 | if (free_ioc) | |
162 | kmem_cache_free(iocontext_cachep, ioc); | |
163 | } | |
164 | EXPORT_SYMBOL(put_io_context); | |
165 | ||
166 | /** | |
167 | * put_io_context_active - put active reference on ioc | |
168 | * @ioc: ioc of interest | |
169 | * | |
170 | * Undo get_io_context_active(). If active reference reaches zero after | |
171 | * put, @ioc can never issue further IOs and ioscheds are notified. | |
172 | */ | |
173 | void put_io_context_active(struct io_context *ioc) | |
174 | { | |
175 | struct elevator_type *et; | |
176 | unsigned long flags; | |
177 | struct io_cq *icq; | |
178 | ||
179 | if (!atomic_dec_and_test(&ioc->active_ref)) { | |
180 | put_io_context(ioc); | |
181 | return; | |
182 | } | |
183 | ||
184 | /* | |
185 | * Need ioc lock to walk icq_list and q lock to exit icq. Perform | |
186 | * reverse double locking. Read comment in ioc_release_fn() for | |
187 | * explanation on the nested locking annotation. | |
188 | */ | |
189 | retry: | |
190 | spin_lock_irqsave_nested(&ioc->lock, flags, 1); | |
191 | hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) { | |
192 | if (icq->flags & ICQ_EXITED) | |
193 | continue; | |
194 | ||
195 | et = icq->q->elevator->type; | |
196 | if (et->uses_mq) { | |
197 | ioc_exit_icq(icq); | |
198 | } else { | |
199 | if (spin_trylock(icq->q->queue_lock)) { | |
200 | ioc_exit_icq(icq); | |
201 | spin_unlock(icq->q->queue_lock); | |
202 | } else { | |
203 | spin_unlock_irqrestore(&ioc->lock, flags); | |
204 | cpu_relax(); | |
205 | goto retry; | |
206 | } | |
207 | } | |
208 | } | |
209 | spin_unlock_irqrestore(&ioc->lock, flags); | |
210 | ||
211 | put_io_context(ioc); | |
212 | } | |
213 | ||
214 | /* Called by the exiting task */ | |
215 | void exit_io_context(struct task_struct *task) | |
216 | { | |
217 | struct io_context *ioc; | |
218 | ||
219 | task_lock(task); | |
220 | ioc = task->io_context; | |
221 | task->io_context = NULL; | |
222 | task_unlock(task); | |
223 | ||
224 | atomic_dec(&ioc->nr_tasks); | |
225 | put_io_context_active(ioc); | |
226 | } | |
227 | ||
228 | static void __ioc_clear_queue(struct list_head *icq_list) | |
229 | { | |
230 | unsigned long flags; | |
231 | ||
232 | while (!list_empty(icq_list)) { | |
233 | struct io_cq *icq = list_entry(icq_list->next, | |
234 | struct io_cq, q_node); | |
235 | struct io_context *ioc = icq->ioc; | |
236 | ||
237 | spin_lock_irqsave(&ioc->lock, flags); | |
238 | ioc_destroy_icq(icq); | |
239 | spin_unlock_irqrestore(&ioc->lock, flags); | |
240 | } | |
241 | } | |
242 | ||
243 | /** | |
244 | * ioc_clear_queue - break any ioc association with the specified queue | |
245 | * @q: request_queue being cleared | |
246 | * | |
247 | * Walk @q->icq_list and exit all io_cq's. | |
248 | */ | |
249 | void ioc_clear_queue(struct request_queue *q) | |
250 | { | |
251 | LIST_HEAD(icq_list); | |
252 | ||
253 | spin_lock_irq(q->queue_lock); | |
254 | list_splice_init(&q->icq_list, &icq_list); | |
255 | ||
256 | if (q->mq_ops) { | |
257 | spin_unlock_irq(q->queue_lock); | |
258 | __ioc_clear_queue(&icq_list); | |
259 | } else { | |
260 | __ioc_clear_queue(&icq_list); | |
261 | spin_unlock_irq(q->queue_lock); | |
262 | } | |
263 | } | |
264 | ||
265 | int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node) | |
266 | { | |
267 | struct io_context *ioc; | |
268 | int ret; | |
269 | ||
270 | ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO, | |
271 | node); | |
272 | if (unlikely(!ioc)) | |
273 | return -ENOMEM; | |
274 | ||
275 | /* initialize */ | |
276 | atomic_long_set(&ioc->refcount, 1); | |
277 | atomic_set(&ioc->nr_tasks, 1); | |
278 | atomic_set(&ioc->active_ref, 1); | |
279 | spin_lock_init(&ioc->lock); | |
280 | INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH); | |
281 | INIT_HLIST_HEAD(&ioc->icq_list); | |
282 | INIT_WORK(&ioc->release_work, ioc_release_fn); | |
283 | ||
284 | /* | |
285 | * Try to install. ioc shouldn't be installed if someone else | |
286 | * already did or @task, which isn't %current, is exiting. Note | |
287 | * that we need to allow ioc creation on exiting %current as exit | |
288 | * path may issue IOs from e.g. exit_files(). The exit path is | |
289 | * responsible for not issuing IO after exit_io_context(). | |
290 | */ | |
291 | task_lock(task); | |
292 | if (!task->io_context && | |
293 | (task == current || !(task->flags & PF_EXITING))) | |
294 | task->io_context = ioc; | |
295 | else | |
296 | kmem_cache_free(iocontext_cachep, ioc); | |
297 | ||
298 | ret = task->io_context ? 0 : -EBUSY; | |
299 | ||
300 | task_unlock(task); | |
301 | ||
302 | return ret; | |
303 | } | |
304 | ||
305 | /** | |
306 | * get_task_io_context - get io_context of a task | |
307 | * @task: task of interest | |
308 | * @gfp_flags: allocation flags, used if allocation is necessary | |
309 | * @node: allocation node, used if allocation is necessary | |
310 | * | |
311 | * Return io_context of @task. If it doesn't exist, it is created with | |
312 | * @gfp_flags and @node. The returned io_context has its reference count | |
313 | * incremented. | |
314 | * | |
315 | * This function always goes through task_lock() and it's better to use | |
316 | * %current->io_context + get_io_context() for %current. | |
317 | */ | |
318 | struct io_context *get_task_io_context(struct task_struct *task, | |
319 | gfp_t gfp_flags, int node) | |
320 | { | |
321 | struct io_context *ioc; | |
322 | ||
323 | might_sleep_if(gfpflags_allow_blocking(gfp_flags)); | |
324 | ||
325 | do { | |
326 | task_lock(task); | |
327 | ioc = task->io_context; | |
328 | if (likely(ioc)) { | |
329 | get_io_context(ioc); | |
330 | task_unlock(task); | |
331 | return ioc; | |
332 | } | |
333 | task_unlock(task); | |
334 | } while (!create_task_io_context(task, gfp_flags, node)); | |
335 | ||
336 | return NULL; | |
337 | } | |
338 | EXPORT_SYMBOL(get_task_io_context); | |
339 | ||
340 | /** | |
341 | * ioc_lookup_icq - lookup io_cq from ioc | |
342 | * @ioc: the associated io_context | |
343 | * @q: the associated request_queue | |
344 | * | |
345 | * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called | |
346 | * with @q->queue_lock held. | |
347 | */ | |
348 | struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q) | |
349 | { | |
350 | struct io_cq *icq; | |
351 | ||
352 | lockdep_assert_held(q->queue_lock); | |
353 | ||
354 | /* | |
355 | * icq's are indexed from @ioc using radix tree and hint pointer, | |
356 | * both of which are protected with RCU. All removals are done | |
357 | * holding both q and ioc locks, and we're holding q lock - if we | |
358 | * find a icq which points to us, it's guaranteed to be valid. | |
359 | */ | |
360 | rcu_read_lock(); | |
361 | icq = rcu_dereference(ioc->icq_hint); | |
362 | if (icq && icq->q == q) | |
363 | goto out; | |
364 | ||
365 | icq = radix_tree_lookup(&ioc->icq_tree, q->id); | |
366 | if (icq && icq->q == q) | |
367 | rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */ | |
368 | else | |
369 | icq = NULL; | |
370 | out: | |
371 | rcu_read_unlock(); | |
372 | return icq; | |
373 | } | |
374 | EXPORT_SYMBOL(ioc_lookup_icq); | |
375 | ||
376 | /** | |
377 | * ioc_create_icq - create and link io_cq | |
378 | * @ioc: io_context of interest | |
379 | * @q: request_queue of interest | |
380 | * @gfp_mask: allocation mask | |
381 | * | |
382 | * Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they | |
383 | * will be created using @gfp_mask. | |
384 | * | |
385 | * The caller is responsible for ensuring @ioc won't go away and @q is | |
386 | * alive and will stay alive until this function returns. | |
387 | */ | |
388 | struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q, | |
389 | gfp_t gfp_mask) | |
390 | { | |
391 | struct elevator_type *et = q->elevator->type; | |
392 | struct io_cq *icq; | |
393 | ||
394 | /* allocate stuff */ | |
395 | icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO, | |
396 | q->node); | |
397 | if (!icq) | |
398 | return NULL; | |
399 | ||
400 | if (radix_tree_maybe_preload(gfp_mask) < 0) { | |
401 | kmem_cache_free(et->icq_cache, icq); | |
402 | return NULL; | |
403 | } | |
404 | ||
405 | icq->ioc = ioc; | |
406 | icq->q = q; | |
407 | INIT_LIST_HEAD(&icq->q_node); | |
408 | INIT_HLIST_NODE(&icq->ioc_node); | |
409 | ||
410 | /* lock both q and ioc and try to link @icq */ | |
411 | spin_lock_irq(q->queue_lock); | |
412 | spin_lock(&ioc->lock); | |
413 | ||
414 | if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) { | |
415 | hlist_add_head(&icq->ioc_node, &ioc->icq_list); | |
416 | list_add(&icq->q_node, &q->icq_list); | |
417 | if (et->uses_mq && et->ops.mq.init_icq) | |
418 | et->ops.mq.init_icq(icq); | |
419 | else if (!et->uses_mq && et->ops.sq.elevator_init_icq_fn) | |
420 | et->ops.sq.elevator_init_icq_fn(icq); | |
421 | } else { | |
422 | kmem_cache_free(et->icq_cache, icq); | |
423 | icq = ioc_lookup_icq(ioc, q); | |
424 | if (!icq) | |
425 | printk(KERN_ERR "cfq: icq link failed!\n"); | |
426 | } | |
427 | ||
428 | spin_unlock(&ioc->lock); | |
429 | spin_unlock_irq(q->queue_lock); | |
430 | radix_tree_preload_end(); | |
431 | return icq; | |
432 | } | |
433 | ||
434 | static int __init blk_ioc_init(void) | |
435 | { | |
436 | iocontext_cachep = kmem_cache_create("blkdev_ioc", | |
437 | sizeof(struct io_context), 0, SLAB_PANIC, NULL); | |
438 | return 0; | |
439 | } | |
440 | subsys_initcall(blk_ioc_init); |