Line data Source code
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 23 : void get_io_context(struct io_context *ioc)
27 : {
28 23 : BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
29 23 : atomic_long_inc(&ioc->refcount);
30 23 : }
31 :
32 0 : static void icq_free_icq_rcu(struct rcu_head *head)
33 : {
34 0 : struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
35 :
36 0 : kmem_cache_free(icq->__rcu_icq_cache, icq);
37 0 : }
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 0 : static void ioc_exit_icq(struct io_cq *icq)
44 : {
45 0 : struct elevator_type *et = icq->q->elevator->type;
46 :
47 0 : if (icq->flags & ICQ_EXITED)
48 : return;
49 :
50 0 : if (et->ops.exit_icq)
51 0 : et->ops.exit_icq(icq);
52 :
53 0 : 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 0 : static void ioc_destroy_icq(struct io_cq *icq)
61 : {
62 0 : struct io_context *ioc = icq->ioc;
63 0 : struct request_queue *q = icq->q;
64 0 : struct elevator_type *et = q->elevator->type;
65 :
66 0 : lockdep_assert_held(&ioc->lock);
67 :
68 0 : radix_tree_delete(&ioc->icq_tree, icq->q->id);
69 0 : hlist_del_init(&icq->ioc_node);
70 0 : 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 0 : if (rcu_access_pointer(ioc->icq_hint) == icq)
78 0 : rcu_assign_pointer(ioc->icq_hint, NULL);
79 :
80 0 : 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 0 : icq->__rcu_icq_cache = et->icq_cache;
87 0 : icq->flags |= ICQ_DESTROYED;
88 0 : call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
89 0 : }
90 :
91 : /*
92 : * Slow path for ioc release in put_io_context(). Performs double-lock
93 : * dancing to unlink all icq's and then frees ioc.
94 : */
95 0 : static void ioc_release_fn(struct work_struct *work)
96 : {
97 0 : struct io_context *ioc = container_of(work, struct io_context,
98 : release_work);
99 0 : spin_lock_irq(&ioc->lock);
100 :
101 0 : while (!hlist_empty(&ioc->icq_list)) {
102 0 : struct io_cq *icq = hlist_entry(ioc->icq_list.first,
103 : struct io_cq, ioc_node);
104 0 : struct request_queue *q = icq->q;
105 :
106 0 : if (spin_trylock(&q->queue_lock)) {
107 0 : ioc_destroy_icq(icq);
108 0 : spin_unlock(&q->queue_lock);
109 : } else {
110 : /* Make sure q and icq cannot be freed. */
111 0 : rcu_read_lock();
112 :
113 : /* Re-acquire the locks in the correct order. */
114 0 : spin_unlock(&ioc->lock);
115 0 : spin_lock(&q->queue_lock);
116 0 : spin_lock(&ioc->lock);
117 :
118 : /*
119 : * The icq may have been destroyed when the ioc lock
120 : * was released.
121 : */
122 0 : if (!(icq->flags & ICQ_DESTROYED))
123 0 : ioc_destroy_icq(icq);
124 :
125 0 : spin_unlock(&q->queue_lock);
126 0 : rcu_read_unlock();
127 : }
128 : }
129 :
130 0 : spin_unlock_irq(&ioc->lock);
131 :
132 0 : kmem_cache_free(iocontext_cachep, ioc);
133 0 : }
134 :
135 : /**
136 : * put_io_context - put a reference of io_context
137 : * @ioc: io_context to put
138 : *
139 : * Decrement reference count of @ioc and release it if the count reaches
140 : * zero.
141 : */
142 171 : void put_io_context(struct io_context *ioc)
143 : {
144 171 : unsigned long flags;
145 171 : bool free_ioc = false;
146 :
147 171 : if (ioc == NULL)
148 : return;
149 :
150 171 : BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
151 :
152 : /*
153 : * Releasing ioc requires reverse order double locking and we may
154 : * already be holding a queue_lock. Do it asynchronously from wq.
155 : */
156 342 : if (atomic_long_dec_and_test(&ioc->refcount)) {
157 148 : spin_lock_irqsave(&ioc->lock, flags);
158 148 : if (!hlist_empty(&ioc->icq_list))
159 0 : queue_work(system_power_efficient_wq,
160 : &ioc->release_work);
161 : else
162 : free_ioc = true;
163 148 : spin_unlock_irqrestore(&ioc->lock, flags);
164 : }
165 :
166 148 : if (free_ioc)
167 148 : kmem_cache_free(iocontext_cachep, ioc);
168 : }
169 :
170 : /**
171 : * put_io_context_active - put active reference on ioc
172 : * @ioc: ioc of interest
173 : *
174 : * Undo get_io_context_active(). If active reference reaches zero after
175 : * put, @ioc can never issue further IOs and ioscheds are notified.
176 : */
177 148 : void put_io_context_active(struct io_context *ioc)
178 : {
179 148 : struct io_cq *icq;
180 :
181 296 : if (!atomic_dec_and_test(&ioc->active_ref)) {
182 0 : put_io_context(ioc);
183 0 : return;
184 : }
185 :
186 148 : spin_lock_irq(&ioc->lock);
187 296 : hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
188 0 : if (icq->flags & ICQ_EXITED)
189 0 : continue;
190 :
191 0 : ioc_exit_icq(icq);
192 : }
193 148 : spin_unlock_irq(&ioc->lock);
194 :
195 148 : put_io_context(ioc);
196 : }
197 :
198 : /* Called by the exiting task */
199 148 : void exit_io_context(struct task_struct *task)
200 : {
201 148 : struct io_context *ioc;
202 :
203 148 : task_lock(task);
204 148 : ioc = task->io_context;
205 148 : task->io_context = NULL;
206 148 : task_unlock(task);
207 :
208 148 : atomic_dec(&ioc->nr_tasks);
209 148 : put_io_context_active(ioc);
210 148 : }
211 :
212 0 : static void __ioc_clear_queue(struct list_head *icq_list)
213 : {
214 0 : unsigned long flags;
215 :
216 0 : rcu_read_lock();
217 0 : while (!list_empty(icq_list)) {
218 0 : struct io_cq *icq = list_entry(icq_list->next,
219 : struct io_cq, q_node);
220 0 : struct io_context *ioc = icq->ioc;
221 :
222 0 : spin_lock_irqsave(&ioc->lock, flags);
223 0 : if (icq->flags & ICQ_DESTROYED) {
224 0 : spin_unlock_irqrestore(&ioc->lock, flags);
225 0 : continue;
226 : }
227 0 : ioc_destroy_icq(icq);
228 0 : spin_unlock_irqrestore(&ioc->lock, flags);
229 : }
230 0 : rcu_read_unlock();
231 0 : }
232 :
233 : /**
234 : * ioc_clear_queue - break any ioc association with the specified queue
235 : * @q: request_queue being cleared
236 : *
237 : * Walk @q->icq_list and exit all io_cq's.
238 : */
239 0 : void ioc_clear_queue(struct request_queue *q)
240 : {
241 0 : LIST_HEAD(icq_list);
242 :
243 0 : spin_lock_irq(&q->queue_lock);
244 0 : list_splice_init(&q->icq_list, &icq_list);
245 0 : spin_unlock_irq(&q->queue_lock);
246 :
247 0 : __ioc_clear_queue(&icq_list);
248 0 : }
249 :
250 167 : int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
251 : {
252 167 : struct io_context *ioc;
253 167 : int ret;
254 :
255 167 : ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
256 : node);
257 167 : if (unlikely(!ioc))
258 : return -ENOMEM;
259 :
260 : /* initialize */
261 167 : atomic_long_set(&ioc->refcount, 1);
262 167 : atomic_set(&ioc->nr_tasks, 1);
263 167 : atomic_set(&ioc->active_ref, 1);
264 167 : spin_lock_init(&ioc->lock);
265 167 : INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
266 167 : INIT_HLIST_HEAD(&ioc->icq_list);
267 167 : INIT_WORK(&ioc->release_work, ioc_release_fn);
268 :
269 : /*
270 : * Try to install. ioc shouldn't be installed if someone else
271 : * already did or @task, which isn't %current, is exiting. Note
272 : * that we need to allow ioc creation on exiting %current as exit
273 : * path may issue IOs from e.g. exit_files(). The exit path is
274 : * responsible for not issuing IO after exit_io_context().
275 : */
276 167 : task_lock(task);
277 167 : if (!task->io_context &&
278 167 : (task == current || !(task->flags & PF_EXITING)))
279 167 : task->io_context = ioc;
280 : else
281 0 : kmem_cache_free(iocontext_cachep, ioc);
282 :
283 167 : ret = task->io_context ? 0 : -EBUSY;
284 :
285 167 : task_unlock(task);
286 :
287 167 : return ret;
288 : }
289 :
290 : /**
291 : * get_task_io_context - get io_context of a task
292 : * @task: task of interest
293 : * @gfp_flags: allocation flags, used if allocation is necessary
294 : * @node: allocation node, used if allocation is necessary
295 : *
296 : * Return io_context of @task. If it doesn't exist, it is created with
297 : * @gfp_flags and @node. The returned io_context has its reference count
298 : * incremented.
299 : *
300 : * This function always goes through task_lock() and it's better to use
301 : * %current->io_context + get_io_context() for %current.
302 : */
303 23 : struct io_context *get_task_io_context(struct task_struct *task,
304 : gfp_t gfp_flags, int node)
305 : {
306 23 : struct io_context *ioc;
307 :
308 23 : might_sleep_if(gfpflags_allow_blocking(gfp_flags));
309 :
310 45 : do {
311 45 : task_lock(task);
312 45 : ioc = task->io_context;
313 45 : if (likely(ioc)) {
314 23 : get_io_context(ioc);
315 23 : task_unlock(task);
316 23 : return ioc;
317 : }
318 22 : task_unlock(task);
319 22 : } while (!create_task_io_context(task, gfp_flags, node));
320 :
321 : return NULL;
322 : }
323 :
324 : /**
325 : * ioc_lookup_icq - lookup io_cq from ioc
326 : * @ioc: the associated io_context
327 : * @q: the associated request_queue
328 : *
329 : * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
330 : * with @q->queue_lock held.
331 : */
332 0 : struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
333 : {
334 0 : struct io_cq *icq;
335 :
336 0 : lockdep_assert_held(&q->queue_lock);
337 :
338 : /*
339 : * icq's are indexed from @ioc using radix tree and hint pointer,
340 : * both of which are protected with RCU. All removals are done
341 : * holding both q and ioc locks, and we're holding q lock - if we
342 : * find a icq which points to us, it's guaranteed to be valid.
343 : */
344 0 : rcu_read_lock();
345 0 : icq = rcu_dereference(ioc->icq_hint);
346 0 : if (icq && icq->q == q)
347 0 : goto out;
348 :
349 0 : icq = radix_tree_lookup(&ioc->icq_tree, q->id);
350 0 : if (icq && icq->q == q)
351 0 : rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
352 : else
353 : icq = NULL;
354 0 : out:
355 0 : rcu_read_unlock();
356 0 : return icq;
357 : }
358 : EXPORT_SYMBOL(ioc_lookup_icq);
359 :
360 : /**
361 : * ioc_create_icq - create and link io_cq
362 : * @ioc: io_context of interest
363 : * @q: request_queue of interest
364 : * @gfp_mask: allocation mask
365 : *
366 : * Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they
367 : * will be created using @gfp_mask.
368 : *
369 : * The caller is responsible for ensuring @ioc won't go away and @q is
370 : * alive and will stay alive until this function returns.
371 : */
372 0 : struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
373 : gfp_t gfp_mask)
374 : {
375 0 : struct elevator_type *et = q->elevator->type;
376 0 : struct io_cq *icq;
377 :
378 : /* allocate stuff */
379 0 : icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
380 : q->node);
381 0 : if (!icq)
382 : return NULL;
383 :
384 0 : if (radix_tree_maybe_preload(gfp_mask) < 0) {
385 0 : kmem_cache_free(et->icq_cache, icq);
386 0 : return NULL;
387 : }
388 :
389 0 : icq->ioc = ioc;
390 0 : icq->q = q;
391 0 : INIT_LIST_HEAD(&icq->q_node);
392 0 : INIT_HLIST_NODE(&icq->ioc_node);
393 :
394 : /* lock both q and ioc and try to link @icq */
395 0 : spin_lock_irq(&q->queue_lock);
396 0 : spin_lock(&ioc->lock);
397 :
398 0 : if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
399 0 : hlist_add_head(&icq->ioc_node, &ioc->icq_list);
400 0 : list_add(&icq->q_node, &q->icq_list);
401 0 : if (et->ops.init_icq)
402 0 : et->ops.init_icq(icq);
403 : } else {
404 0 : kmem_cache_free(et->icq_cache, icq);
405 0 : icq = ioc_lookup_icq(ioc, q);
406 0 : if (!icq)
407 0 : printk(KERN_ERR "cfq: icq link failed!\n");
408 : }
409 :
410 0 : spin_unlock(&ioc->lock);
411 0 : spin_unlock_irq(&q->queue_lock);
412 0 : radix_tree_preload_end();
413 0 : return icq;
414 : }
415 :
416 1 : static int __init blk_ioc_init(void)
417 : {
418 1 : iocontext_cachep = kmem_cache_create("blkdev_ioc",
419 : sizeof(struct io_context), 0, SLAB_PANIC, NULL);
420 1 : return 0;
421 : }
422 : subsys_initcall(blk_ioc_init);
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