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 	icq->flags |= ICQ_DESTROYED;
88 	call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
89 }
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  */
ioc_release_fn(struct work_struct * work)95 static void ioc_release_fn(struct work_struct *work)
96 {
97 	struct io_context *ioc = container_of(work, struct io_context,
98 					      release_work);
99 	spin_lock_irq(&ioc->lock);
100 
101 	while (!hlist_empty(&ioc->icq_list)) {
102 		struct io_cq *icq = hlist_entry(ioc->icq_list.first,
103 						struct io_cq, ioc_node);
104 		struct request_queue *q = icq->q;
105 
106 		if (spin_trylock(&q->queue_lock)) {
107 			ioc_destroy_icq(icq);
108 			spin_unlock(&q->queue_lock);
109 		} else {
110 			/* Make sure q and icq cannot be freed. */
111 			rcu_read_lock();
112 
113 			/* Re-acquire the locks in the correct order. */
114 			spin_unlock(&ioc->lock);
115 			spin_lock(&q->queue_lock);
116 			spin_lock(&ioc->lock);
117 
118 			/*
119 			 * The icq may have been destroyed when the ioc lock
120 			 * was released.
121 			 */
122 			if (!(icq->flags & ICQ_DESTROYED))
123 				ioc_destroy_icq(icq);
124 
125 			spin_unlock(&q->queue_lock);
126 			rcu_read_unlock();
127 		}
128 	}
129 
130 	spin_unlock_irq(&ioc->lock);
131 
132 	kmem_cache_free(iocontext_cachep, ioc);
133 }
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  */
put_io_context(struct io_context * ioc)142 void put_io_context(struct io_context *ioc)
143 {
144 	unsigned long flags;
145 	bool free_ioc = false;
146 
147 	if (ioc == NULL)
148 		return;
149 
150 	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 	if (atomic_long_dec_and_test(&ioc->refcount)) {
157 		spin_lock_irqsave(&ioc->lock, flags);
158 		if (!hlist_empty(&ioc->icq_list))
159 			queue_work(system_power_efficient_wq,
160 					&ioc->release_work);
161 		else
162 			free_ioc = true;
163 		spin_unlock_irqrestore(&ioc->lock, flags);
164 	}
165 
166 	if (free_ioc)
167 		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  */
put_io_context_active(struct io_context * ioc)177 void put_io_context_active(struct io_context *ioc)
178 {
179 	struct io_cq *icq;
180 
181 	if (!atomic_dec_and_test(&ioc->active_ref)) {
182 		put_io_context(ioc);
183 		return;
184 	}
185 
186 	spin_lock_irq(&ioc->lock);
187 	hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
188 		if (icq->flags & ICQ_EXITED)
189 			continue;
190 
191 		ioc_exit_icq(icq);
192 	}
193 	spin_unlock_irq(&ioc->lock);
194 
195 	put_io_context(ioc);
196 }
197 
198 /* Called by the exiting task */
exit_io_context(struct task_struct * task)199 void exit_io_context(struct task_struct *task)
200 {
201 	struct io_context *ioc;
202 
203 	task_lock(task);
204 	ioc = task->io_context;
205 	task->io_context = NULL;
206 	task_unlock(task);
207 
208 	atomic_dec(&ioc->nr_tasks);
209 	put_io_context_active(ioc);
210 }
211 
__ioc_clear_queue(struct list_head * icq_list)212 static void __ioc_clear_queue(struct list_head *icq_list)
213 {
214 	unsigned long flags;
215 
216 	rcu_read_lock();
217 	while (!list_empty(icq_list)) {
218 		struct io_cq *icq = list_entry(icq_list->next,
219 						struct io_cq, q_node);
220 		struct io_context *ioc = icq->ioc;
221 
222 		spin_lock_irqsave(&ioc->lock, flags);
223 		if (icq->flags & ICQ_DESTROYED) {
224 			spin_unlock_irqrestore(&ioc->lock, flags);
225 			continue;
226 		}
227 		ioc_destroy_icq(icq);
228 		spin_unlock_irqrestore(&ioc->lock, flags);
229 	}
230 	rcu_read_unlock();
231 }
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  */
ioc_clear_queue(struct request_queue * q)239 void ioc_clear_queue(struct request_queue *q)
240 {
241 	LIST_HEAD(icq_list);
242 
243 	spin_lock_irq(&q->queue_lock);
244 	list_splice_init(&q->icq_list, &icq_list);
245 	spin_unlock_irq(&q->queue_lock);
246 
247 	__ioc_clear_queue(&icq_list);
248 }
249 
create_task_io_context(struct task_struct * task,gfp_t gfp_flags,int node)250 int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
251 {
252 	struct io_context *ioc;
253 	int ret;
254 
255 	ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
256 				    node);
257 	if (unlikely(!ioc))
258 		return -ENOMEM;
259 
260 	/* initialize */
261 	atomic_long_set(&ioc->refcount, 1);
262 	atomic_set(&ioc->nr_tasks, 1);
263 	atomic_set(&ioc->active_ref, 1);
264 	spin_lock_init(&ioc->lock);
265 	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
266 	INIT_HLIST_HEAD(&ioc->icq_list);
267 	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 	task_lock(task);
277 	if (!task->io_context &&
278 	    (task == current || !(task->flags & PF_EXITING)))
279 		task->io_context = ioc;
280 	else
281 		kmem_cache_free(iocontext_cachep, ioc);
282 
283 	ret = task->io_context ? 0 : -EBUSY;
284 
285 	task_unlock(task);
286 
287 	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  */
get_task_io_context(struct task_struct * task,gfp_t gfp_flags,int node)303 struct io_context *get_task_io_context(struct task_struct *task,
304 				       gfp_t gfp_flags, int node)
305 {
306 	struct io_context *ioc;
307 
308 	might_sleep_if(gfpflags_allow_blocking(gfp_flags));
309 
310 	do {
311 		task_lock(task);
312 		ioc = task->io_context;
313 		if (likely(ioc)) {
314 			get_io_context(ioc);
315 			task_unlock(task);
316 			return ioc;
317 		}
318 		task_unlock(task);
319 	} 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  */
ioc_lookup_icq(struct io_context * ioc,struct request_queue * q)332 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
333 {
334 	struct io_cq *icq;
335 
336 	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 	rcu_read_lock();
345 	icq = rcu_dereference(ioc->icq_hint);
346 	if (icq && icq->q == q)
347 		goto out;
348 
349 	icq = radix_tree_lookup(&ioc->icq_tree, q->id);
350 	if (icq && icq->q == q)
351 		rcu_assign_pointer(ioc->icq_hint, icq);	/* allowed to race */
352 	else
353 		icq = NULL;
354 out:
355 	rcu_read_unlock();
356 	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  */
ioc_create_icq(struct io_context * ioc,struct request_queue * q,gfp_t gfp_mask)372 struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
373 			     gfp_t gfp_mask)
374 {
375 	struct elevator_type *et = q->elevator->type;
376 	struct io_cq *icq;
377 
378 	/* allocate stuff */
379 	icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
380 				    q->node);
381 	if (!icq)
382 		return NULL;
383 
384 	if (radix_tree_maybe_preload(gfp_mask) < 0) {
385 		kmem_cache_free(et->icq_cache, icq);
386 		return NULL;
387 	}
388 
389 	icq->ioc = ioc;
390 	icq->q = q;
391 	INIT_LIST_HEAD(&icq->q_node);
392 	INIT_HLIST_NODE(&icq->ioc_node);
393 
394 	/* lock both q and ioc and try to link @icq */
395 	spin_lock_irq(&q->queue_lock);
396 	spin_lock(&ioc->lock);
397 
398 	if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
399 		hlist_add_head(&icq->ioc_node, &ioc->icq_list);
400 		list_add(&icq->q_node, &q->icq_list);
401 		if (et->ops.init_icq)
402 			et->ops.init_icq(icq);
403 	} else {
404 		kmem_cache_free(et->icq_cache, icq);
405 		icq = ioc_lookup_icq(ioc, q);
406 		if (!icq)
407 			printk(KERN_ERR "cfq: icq link failed!\n");
408 	}
409 
410 	spin_unlock(&ioc->lock);
411 	spin_unlock_irq(&q->queue_lock);
412 	radix_tree_preload_end();
413 	return icq;
414 }
415 
blk_ioc_init(void)416 static int __init blk_ioc_init(void)
417 {
418 	iocontext_cachep = kmem_cache_create("blkdev_ioc",
419 			sizeof(struct io_context), 0, SLAB_PANIC, NULL);
420 	return 0;
421 }
422 subsys_initcall(blk_ioc_init);
423