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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 | EXPORT_SYMBOL(get_io_context); | |
32 | ||
33 | static void icq_free_icq_rcu(struct rcu_head *head) | |
34 | { | |
35 | struct io_cq *icq = container_of(head, struct io_cq, __rcu_head); | |
36 | ||
37 | kmem_cache_free(icq->__rcu_icq_cache, icq); | |
38 | } | |
39 | ||
40 | /* | |
41 | * Exit an icq. Called with ioc locked for blk-mq, and with both ioc | |
42 | * and queue locked for legacy. | |
43 | */ | |
44 | static void ioc_exit_icq(struct io_cq *icq) | |
45 | { | |
46 | struct elevator_type *et = icq->q->elevator->type; | |
47 | ||
48 | if (icq->flags & ICQ_EXITED) | |
49 | return; | |
50 | ||
51 | if (et->uses_mq && et->ops.mq.exit_icq) | |
52 | et->ops.mq.exit_icq(icq); | |
53 | else if (!et->uses_mq && et->ops.sq.elevator_exit_icq_fn) | |
54 | et->ops.sq.elevator_exit_icq_fn(icq); | |
55 | ||
56 | icq->flags |= ICQ_EXITED; | |
57 | } | |
58 | ||
59 | /* | |
60 | * Release an icq. Called with ioc locked for blk-mq, and with both ioc | |
61 | * and queue locked for legacy. | |
62 | */ | |
63 | static void ioc_destroy_icq(struct io_cq *icq) | |
64 | { | |
65 | struct io_context *ioc = icq->ioc; | |
66 | struct request_queue *q = icq->q; | |
67 | struct elevator_type *et = q->elevator->type; | |
68 | ||
69 | lockdep_assert_held(&ioc->lock); | |
70 | ||
71 | radix_tree_delete(&ioc->icq_tree, icq->q->id); | |
72 | hlist_del_init(&icq->ioc_node); | |
73 | list_del_init(&icq->q_node); | |
74 | ||
75 | /* | |
76 | * Both setting lookup hint to and clearing it from @icq are done | |
77 | * under queue_lock. If it's not pointing to @icq now, it never | |
78 | * will. Hint assignment itself can race safely. | |
79 | */ | |
80 | if (rcu_access_pointer(ioc->icq_hint) == icq) | |
81 | rcu_assign_pointer(ioc->icq_hint, NULL); | |
82 | ||
83 | ioc_exit_icq(icq); | |
84 | ||
85 | /* | |
86 | * @icq->q might have gone away by the time RCU callback runs | |
87 | * making it impossible to determine icq_cache. Record it in @icq. | |
88 | */ | |
89 | icq->__rcu_icq_cache = et->icq_cache; | |
90 | call_rcu(&icq->__rcu_head, icq_free_icq_rcu); | |
91 | } | |
92 | ||
93 | /* | |
94 | * Slow path for ioc release in put_io_context(). Performs double-lock | |
95 | * dancing to unlink all icq's and then frees ioc. | |
96 | */ | |
97 | static void ioc_release_fn(struct work_struct *work) | |
98 | { | |
99 | struct io_context *ioc = container_of(work, struct io_context, | |
100 | release_work); | |
101 | unsigned long flags; | |
102 | ||
103 | /* | |
104 | * Exiting icq may call into put_io_context() through elevator | |
105 | * which will trigger lockdep warning. The ioc's are guaranteed to | |
106 | * be different, use a different locking subclass here. Use | |
107 | * irqsave variant as there's no spin_lock_irq_nested(). | |
108 | */ | |
109 | spin_lock_irqsave_nested(&ioc->lock, flags, 1); | |
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 | spin_unlock_irqrestore(&ioc->lock, flags); | |
121 | cpu_relax(); | |
122 | spin_lock_irqsave_nested(&ioc->lock, flags, 1); | |
123 | } | |
124 | } | |
125 | ||
126 | spin_unlock_irqrestore(&ioc->lock, flags); | |
127 | ||
128 | kmem_cache_free(iocontext_cachep, ioc); | |
129 | } | |
130 | ||
131 | /** | |
132 | * put_io_context - put a reference of io_context | |
133 | * @ioc: io_context to put | |
134 | * | |
135 | * Decrement reference count of @ioc and release it if the count reaches | |
136 | * zero. | |
137 | */ | |
138 | void put_io_context(struct io_context *ioc) | |
139 | { | |
140 | unsigned long flags; | |
141 | bool free_ioc = false; | |
142 | ||
143 | if (ioc == NULL) | |
144 | return; | |
145 | ||
146 | BUG_ON(atomic_long_read(&ioc->refcount) <= 0); | |
147 | ||
148 | /* | |
149 | * Releasing ioc requires reverse order double locking and we may | |
150 | * already be holding a queue_lock. Do it asynchronously from wq. | |
151 | */ | |
152 | if (atomic_long_dec_and_test(&ioc->refcount)) { | |
153 | spin_lock_irqsave(&ioc->lock, flags); | |
154 | if (!hlist_empty(&ioc->icq_list)) | |
155 | queue_work(system_power_efficient_wq, | |
156 | &ioc->release_work); | |
157 | else | |
158 | free_ioc = true; | |
159 | spin_unlock_irqrestore(&ioc->lock, flags); | |
160 | } | |
161 | ||
162 | if (free_ioc) | |
163 | kmem_cache_free(iocontext_cachep, ioc); | |
164 | } | |
165 | EXPORT_SYMBOL(put_io_context); | |
166 | ||
167 | /** | |
168 | * put_io_context_active - put active reference on ioc | |
169 | * @ioc: ioc of interest | |
170 | * | |
171 | * Undo get_io_context_active(). If active reference reaches zero after | |
172 | * put, @ioc can never issue further IOs and ioscheds are notified. | |
173 | */ | |
174 | void put_io_context_active(struct io_context *ioc) | |
175 | { | |
176 | struct elevator_type *et; | |
177 | unsigned long flags; | |
178 | struct io_cq *icq; | |
179 | ||
180 | if (!atomic_dec_and_test(&ioc->active_ref)) { | |
181 | put_io_context(ioc); | |
182 | return; | |
183 | } | |
184 | ||
185 | /* | |
186 | * Need ioc lock to walk icq_list and q lock to exit icq. Perform | |
187 | * reverse double locking. Read comment in ioc_release_fn() for | |
188 | * explanation on the nested locking annotation. | |
189 | */ | |
190 | retry: | |
191 | spin_lock_irqsave_nested(&ioc->lock, flags, 1); | |
192 | hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) { | |
193 | if (icq->flags & ICQ_EXITED) | |
194 | continue; | |
195 | ||
196 | et = icq->q->elevator->type; | |
197 | if (et->uses_mq) { | |
198 | ioc_exit_icq(icq); | |
199 | } else { | |
200 | if (spin_trylock(icq->q->queue_lock)) { | |
201 | ioc_exit_icq(icq); | |
202 | spin_unlock(icq->q->queue_lock); | |
203 | } else { | |
204 | spin_unlock_irqrestore(&ioc->lock, flags); | |
205 | cpu_relax(); | |
206 | goto retry; | |
207 | } | |
208 | } | |
209 | } | |
210 | spin_unlock_irqrestore(&ioc->lock, flags); | |
211 | ||
212 | put_io_context(ioc); | |
213 | } | |
214 | ||
215 | /* Called by the exiting task */ | |
216 | void exit_io_context(struct task_struct *task) | |
217 | { | |
218 | struct io_context *ioc; | |
219 | ||
220 | task_lock(task); | |
221 | ioc = task->io_context; | |
222 | task->io_context = NULL; | |
223 | task_unlock(task); | |
224 | ||
225 | atomic_dec(&ioc->nr_tasks); | |
226 | put_io_context_active(ioc); | |
227 | } | |
228 | ||
229 | static void __ioc_clear_queue(struct list_head *icq_list) | |
230 | { | |
231 | unsigned long flags; | |
232 | ||
233 | while (!list_empty(icq_list)) { | |
234 | struct io_cq *icq = list_entry(icq_list->next, | |
235 | struct io_cq, q_node); | |
236 | struct io_context *ioc = icq->ioc; | |
237 | ||
238 | spin_lock_irqsave(&ioc->lock, flags); | |
239 | ioc_destroy_icq(icq); | |
240 | spin_unlock_irqrestore(&ioc->lock, flags); | |
241 | } | |
242 | } | |
243 | ||
244 | /** | |
245 | * ioc_clear_queue - break any ioc association with the specified queue | |
246 | * @q: request_queue being cleared | |
247 | * | |
248 | * Walk @q->icq_list and exit all io_cq's. | |
249 | */ | |
250 | void ioc_clear_queue(struct request_queue *q) | |
251 | { | |
252 | LIST_HEAD(icq_list); | |
253 | ||
254 | spin_lock_irq(q->queue_lock); | |
255 | list_splice_init(&q->icq_list, &icq_list); | |
256 | ||
257 | if (q->mq_ops) { | |
258 | spin_unlock_irq(q->queue_lock); | |
259 | __ioc_clear_queue(&icq_list); | |
260 | } else { | |
261 | __ioc_clear_queue(&icq_list); | |
262 | spin_unlock_irq(q->queue_lock); | |
263 | } | |
264 | } | |
265 | ||
266 | int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node) | |
267 | { | |
268 | struct io_context *ioc; | |
269 | int ret; | |
270 | ||
271 | ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO, | |
272 | node); | |
273 | if (unlikely(!ioc)) | |
274 | return -ENOMEM; | |
275 | ||
276 | /* initialize */ | |
277 | atomic_long_set(&ioc->refcount, 1); | |
278 | atomic_set(&ioc->nr_tasks, 1); | |
279 | atomic_set(&ioc->active_ref, 1); | |
280 | spin_lock_init(&ioc->lock); | |
281 | INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH); | |
282 | INIT_HLIST_HEAD(&ioc->icq_list); | |
283 | INIT_WORK(&ioc->release_work, ioc_release_fn); | |
284 | ||
285 | /* | |
286 | * Try to install. ioc shouldn't be installed if someone else | |
287 | * already did or @task, which isn't %current, is exiting. Note | |
288 | * that we need to allow ioc creation on exiting %current as exit | |
289 | * path may issue IOs from e.g. exit_files(). The exit path is | |
290 | * responsible for not issuing IO after exit_io_context(). | |
291 | */ | |
292 | task_lock(task); | |
293 | if (!task->io_context && | |
294 | (task == current || !(task->flags & PF_EXITING))) | |
295 | task->io_context = ioc; | |
296 | else | |
297 | kmem_cache_free(iocontext_cachep, ioc); | |
298 | ||
299 | ret = task->io_context ? 0 : -EBUSY; | |
300 | ||
301 | task_unlock(task); | |
302 | ||
303 | return ret; | |
304 | } | |
305 | ||
306 | /** | |
307 | * get_task_io_context - get io_context of a task | |
308 | * @task: task of interest | |
309 | * @gfp_flags: allocation flags, used if allocation is necessary | |
310 | * @node: allocation node, used if allocation is necessary | |
311 | * | |
312 | * Return io_context of @task. If it doesn't exist, it is created with | |
313 | * @gfp_flags and @node. The returned io_context has its reference count | |
314 | * incremented. | |
315 | * | |
316 | * This function always goes through task_lock() and it's better to use | |
317 | * %current->io_context + get_io_context() for %current. | |
318 | */ | |
319 | struct io_context *get_task_io_context(struct task_struct *task, | |
320 | gfp_t gfp_flags, int node) | |
321 | { | |
322 | struct io_context *ioc; | |
323 | ||
324 | might_sleep_if(gfpflags_allow_blocking(gfp_flags)); | |
325 | ||
326 | do { | |
327 | task_lock(task); | |
328 | ioc = task->io_context; | |
329 | if (likely(ioc)) { | |
330 | get_io_context(ioc); | |
331 | task_unlock(task); | |
332 | return ioc; | |
333 | } | |
334 | task_unlock(task); | |
335 | } while (!create_task_io_context(task, gfp_flags, node)); | |
336 | ||
337 | return NULL; | |
338 | } | |
339 | EXPORT_SYMBOL(get_task_io_context); | |
340 | ||
341 | /** | |
342 | * ioc_lookup_icq - lookup io_cq from ioc | |
343 | * @ioc: the associated io_context | |
344 | * @q: the associated request_queue | |
345 | * | |
346 | * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called | |
347 | * with @q->queue_lock held. | |
348 | */ | |
349 | struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q) | |
350 | { | |
351 | struct io_cq *icq; | |
352 | ||
353 | lockdep_assert_held(q->queue_lock); | |
354 | ||
355 | /* | |
356 | * icq's are indexed from @ioc using radix tree and hint pointer, | |
357 | * both of which are protected with RCU. All removals are done | |
358 | * holding both q and ioc locks, and we're holding q lock - if we | |
359 | * find a icq which points to us, it's guaranteed to be valid. | |
360 | */ | |
361 | rcu_read_lock(); | |
362 | icq = rcu_dereference(ioc->icq_hint); | |
363 | if (icq && icq->q == q) | |
364 | goto out; | |
365 | ||
366 | icq = radix_tree_lookup(&ioc->icq_tree, q->id); | |
367 | if (icq && icq->q == q) | |
368 | rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */ | |
369 | else | |
370 | icq = NULL; | |
371 | out: | |
372 | rcu_read_unlock(); | |
373 | return icq; | |
374 | } | |
375 | EXPORT_SYMBOL(ioc_lookup_icq); | |
376 | ||
377 | /** | |
378 | * ioc_create_icq - create and link io_cq | |
379 | * @ioc: io_context of interest | |
380 | * @q: request_queue of interest | |
381 | * @gfp_mask: allocation mask | |
382 | * | |
383 | * Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they | |
384 | * will be created using @gfp_mask. | |
385 | * | |
386 | * The caller is responsible for ensuring @ioc won't go away and @q is | |
387 | * alive and will stay alive until this function returns. | |
388 | */ | |
389 | struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q, | |
390 | gfp_t gfp_mask) | |
391 | { | |
392 | struct elevator_type *et = q->elevator->type; | |
393 | struct io_cq *icq; | |
394 | ||
395 | /* allocate stuff */ | |
396 | icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO, | |
397 | q->node); | |
398 | if (!icq) | |
399 | return NULL; | |
400 | ||
401 | if (radix_tree_maybe_preload(gfp_mask) < 0) { | |
402 | kmem_cache_free(et->icq_cache, icq); | |
403 | return NULL; | |
404 | } | |
405 | ||
406 | icq->ioc = ioc; | |
407 | icq->q = q; | |
408 | INIT_LIST_HEAD(&icq->q_node); | |
409 | INIT_HLIST_NODE(&icq->ioc_node); | |
410 | ||
411 | /* lock both q and ioc and try to link @icq */ | |
412 | spin_lock_irq(q->queue_lock); | |
413 | spin_lock(&ioc->lock); | |
414 | ||
415 | if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) { | |
416 | hlist_add_head(&icq->ioc_node, &ioc->icq_list); | |
417 | list_add(&icq->q_node, &q->icq_list); | |
418 | if (et->uses_mq && et->ops.mq.init_icq) | |
419 | et->ops.mq.init_icq(icq); | |
420 | else if (!et->uses_mq && et->ops.sq.elevator_init_icq_fn) | |
421 | et->ops.sq.elevator_init_icq_fn(icq); | |
422 | } else { | |
423 | kmem_cache_free(et->icq_cache, icq); | |
424 | icq = ioc_lookup_icq(ioc, q); | |
425 | if (!icq) | |
426 | printk(KERN_ERR "cfq: icq link failed!\n"); | |
427 | } | |
428 | ||
429 | spin_unlock(&ioc->lock); | |
430 | spin_unlock_irq(q->queue_lock); | |
431 | radix_tree_preload_end(); | |
432 | return icq; | |
433 | } | |
434 | ||
435 | static int __init blk_ioc_init(void) | |
436 | { | |
437 | iocontext_cachep = kmem_cache_create("blkdev_ioc", | |
438 | sizeof(struct io_context), 0, SLAB_PANIC, NULL); | |
439 | return 0; | |
440 | } | |
441 | subsys_initcall(blk_ioc_init); |