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 */
get_io_context(struct io_context * ioc)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
icq_free_icq_rcu(struct rcu_head * head)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 */
ioc_exit_icq(struct io_cq * icq)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 */
ioc_destroy_icq(struct io_cq * icq)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 */
ioc_release_fn(struct work_struct * work)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 */
put_io_context(struct io_context * ioc)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 */
put_io_context_active(struct io_context * ioc)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 */
exit_io_context(struct task_struct * 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
__ioc_clear_queue(struct list_head * icq_list)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 */
ioc_clear_queue(struct request_queue * q)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
create_task_io_context(struct task_struct * task,gfp_t gfp_flags,int node)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 */
get_task_io_context(struct task_struct * task,gfp_t gfp_flags,int node)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 */
ioc_lookup_icq(struct io_context * ioc,struct request_queue * q)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 */
ioc_create_icq(struct io_context * ioc,struct request_queue * q,gfp_t gfp_mask)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
blk_ioc_init(void)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
