xref: /openbmc/linux/block/blk-ioc.c (revision a7cfa0af)
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/security.h>
12 #include <linux/sched/task.h>
13 
14 #include "blk.h"
15 #include "blk-mq-sched.h"
16 
17 /*
18  * For io context allocations
19  */
20 static struct kmem_cache *iocontext_cachep;
21 
22 #ifdef CONFIG_BLK_ICQ
23 /**
24  * get_io_context - increment reference count to io_context
25  * @ioc: io_context to get
26  *
27  * Increment reference count to @ioc.
28  */
get_io_context(struct io_context * ioc)29 static void get_io_context(struct io_context *ioc)
30 {
31 	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
32 	atomic_long_inc(&ioc->refcount);
33 }
34 
icq_free_icq_rcu(struct rcu_head * head)35 static void icq_free_icq_rcu(struct rcu_head *head)
36 {
37 	struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
38 
39 	kmem_cache_free(icq->__rcu_icq_cache, icq);
40 }
41 
42 /*
43  * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
44  * and queue locked for legacy.
45  */
ioc_exit_icq(struct io_cq * icq)46 static void ioc_exit_icq(struct io_cq *icq)
47 {
48 	struct elevator_type *et = icq->q->elevator->type;
49 
50 	if (icq->flags & ICQ_EXITED)
51 		return;
52 
53 	if (et->ops.exit_icq)
54 		et->ops.exit_icq(icq);
55 
56 	icq->flags |= ICQ_EXITED;
57 }
58 
ioc_exit_icqs(struct io_context * ioc)59 static void ioc_exit_icqs(struct io_context *ioc)
60 {
61 	struct io_cq *icq;
62 
63 	spin_lock_irq(&ioc->lock);
64 	hlist_for_each_entry(icq, &ioc->icq_list, ioc_node)
65 		ioc_exit_icq(icq);
66 	spin_unlock_irq(&ioc->lock);
67 }
68 
69 /*
70  * Release an icq. Called with ioc locked for blk-mq, and with both ioc
71  * and queue locked for legacy.
72  */
ioc_destroy_icq(struct io_cq * icq)73 static void ioc_destroy_icq(struct io_cq *icq)
74 {
75 	struct io_context *ioc = icq->ioc;
76 	struct request_queue *q = icq->q;
77 	struct elevator_type *et = q->elevator->type;
78 
79 	lockdep_assert_held(&ioc->lock);
80 	lockdep_assert_held(&q->queue_lock);
81 
82 	if (icq->flags & ICQ_DESTROYED)
83 		return;
84 
85 	radix_tree_delete(&ioc->icq_tree, icq->q->id);
86 	hlist_del_init(&icq->ioc_node);
87 	list_del_init(&icq->q_node);
88 
89 	/*
90 	 * Both setting lookup hint to and clearing it from @icq are done
91 	 * under queue_lock.  If it's not pointing to @icq now, it never
92 	 * will.  Hint assignment itself can race safely.
93 	 */
94 	if (rcu_access_pointer(ioc->icq_hint) == icq)
95 		rcu_assign_pointer(ioc->icq_hint, NULL);
96 
97 	ioc_exit_icq(icq);
98 
99 	/*
100 	 * @icq->q might have gone away by the time RCU callback runs
101 	 * making it impossible to determine icq_cache.  Record it in @icq.
102 	 */
103 	icq->__rcu_icq_cache = et->icq_cache;
104 	icq->flags |= ICQ_DESTROYED;
105 	call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
106 }
107 
108 /*
109  * Slow path for ioc release in put_io_context().  Performs double-lock
110  * dancing to unlink all icq's and then frees ioc.
111  */
ioc_release_fn(struct work_struct * work)112 static void ioc_release_fn(struct work_struct *work)
113 {
114 	struct io_context *ioc = container_of(work, struct io_context,
115 					      release_work);
116 	spin_lock_irq(&ioc->lock);
117 
118 	while (!hlist_empty(&ioc->icq_list)) {
119 		struct io_cq *icq = hlist_entry(ioc->icq_list.first,
120 						struct io_cq, ioc_node);
121 		struct request_queue *q = icq->q;
122 
123 		if (spin_trylock(&q->queue_lock)) {
124 			ioc_destroy_icq(icq);
125 			spin_unlock(&q->queue_lock);
126 		} else {
127 			/* Make sure q and icq cannot be freed. */
128 			rcu_read_lock();
129 
130 			/* Re-acquire the locks in the correct order. */
131 			spin_unlock(&ioc->lock);
132 			spin_lock(&q->queue_lock);
133 			spin_lock(&ioc->lock);
134 
135 			ioc_destroy_icq(icq);
136 
137 			spin_unlock(&q->queue_lock);
138 			rcu_read_unlock();
139 		}
140 	}
141 
142 	spin_unlock_irq(&ioc->lock);
143 
144 	kmem_cache_free(iocontext_cachep, ioc);
145 }
146 
147 /*
148  * Releasing icqs requires reverse order double locking and we may already be
149  * holding a queue_lock.  Do it asynchronously from a workqueue.
150  */
ioc_delay_free(struct io_context * ioc)151 static bool ioc_delay_free(struct io_context *ioc)
152 {
153 	unsigned long flags;
154 
155 	spin_lock_irqsave(&ioc->lock, flags);
156 	if (!hlist_empty(&ioc->icq_list)) {
157 		queue_work(system_power_efficient_wq, &ioc->release_work);
158 		spin_unlock_irqrestore(&ioc->lock, flags);
159 		return true;
160 	}
161 	spin_unlock_irqrestore(&ioc->lock, flags);
162 	return false;
163 }
164 
165 /**
166  * ioc_clear_queue - break any ioc association with the specified queue
167  * @q: request_queue being cleared
168  *
169  * Walk @q->icq_list and exit all io_cq's.
170  */
ioc_clear_queue(struct request_queue * q)171 void ioc_clear_queue(struct request_queue *q)
172 {
173 	spin_lock_irq(&q->queue_lock);
174 	while (!list_empty(&q->icq_list)) {
175 		struct io_cq *icq =
176 			list_first_entry(&q->icq_list, struct io_cq, q_node);
177 
178 		/*
179 		 * Other context won't hold ioc lock to wait for queue_lock, see
180 		 * details in ioc_release_fn().
181 		 */
182 		spin_lock(&icq->ioc->lock);
183 		ioc_destroy_icq(icq);
184 		spin_unlock(&icq->ioc->lock);
185 	}
186 	spin_unlock_irq(&q->queue_lock);
187 }
188 #else /* CONFIG_BLK_ICQ */
ioc_exit_icqs(struct io_context * ioc)189 static inline void ioc_exit_icqs(struct io_context *ioc)
190 {
191 }
ioc_delay_free(struct io_context * ioc)192 static inline bool ioc_delay_free(struct io_context *ioc)
193 {
194 	return false;
195 }
196 #endif /* CONFIG_BLK_ICQ */
197 
198 /**
199  * put_io_context - put a reference of io_context
200  * @ioc: io_context to put
201  *
202  * Decrement reference count of @ioc and release it if the count reaches
203  * zero.
204  */
put_io_context(struct io_context * ioc)205 void put_io_context(struct io_context *ioc)
206 {
207 	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
208 	if (atomic_long_dec_and_test(&ioc->refcount) && !ioc_delay_free(ioc))
209 		kmem_cache_free(iocontext_cachep, ioc);
210 }
211 EXPORT_SYMBOL_GPL(put_io_context);
212 
213 /* Called by the exiting task */
exit_io_context(struct task_struct * task)214 void exit_io_context(struct task_struct *task)
215 {
216 	struct io_context *ioc;
217 
218 	task_lock(task);
219 	ioc = task->io_context;
220 	task->io_context = NULL;
221 	task_unlock(task);
222 
223 	if (atomic_dec_and_test(&ioc->active_ref)) {
224 		ioc_exit_icqs(ioc);
225 		put_io_context(ioc);
226 	}
227 }
228 
alloc_io_context(gfp_t gfp_flags,int node)229 static struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
230 {
231 	struct io_context *ioc;
232 
233 	ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
234 				    node);
235 	if (unlikely(!ioc))
236 		return NULL;
237 
238 	atomic_long_set(&ioc->refcount, 1);
239 	atomic_set(&ioc->active_ref, 1);
240 #ifdef CONFIG_BLK_ICQ
241 	spin_lock_init(&ioc->lock);
242 	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
243 	INIT_HLIST_HEAD(&ioc->icq_list);
244 	INIT_WORK(&ioc->release_work, ioc_release_fn);
245 #endif
246 	ioc->ioprio = IOPRIO_DEFAULT;
247 
248 	return ioc;
249 }
250 
set_task_ioprio(struct task_struct * task,int ioprio)251 int set_task_ioprio(struct task_struct *task, int ioprio)
252 {
253 	int err;
254 	const struct cred *cred = current_cred(), *tcred;
255 
256 	rcu_read_lock();
257 	tcred = __task_cred(task);
258 	if (!uid_eq(tcred->uid, cred->euid) &&
259 	    !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
260 		rcu_read_unlock();
261 		return -EPERM;
262 	}
263 	rcu_read_unlock();
264 
265 	err = security_task_setioprio(task, ioprio);
266 	if (err)
267 		return err;
268 
269 	task_lock(task);
270 	if (unlikely(!task->io_context)) {
271 		struct io_context *ioc;
272 
273 		task_unlock(task);
274 
275 		ioc = alloc_io_context(GFP_ATOMIC, NUMA_NO_NODE);
276 		if (!ioc)
277 			return -ENOMEM;
278 
279 		task_lock(task);
280 		if (task->flags & PF_EXITING) {
281 			kmem_cache_free(iocontext_cachep, ioc);
282 			goto out;
283 		}
284 		if (task->io_context)
285 			kmem_cache_free(iocontext_cachep, ioc);
286 		else
287 			task->io_context = ioc;
288 	}
289 	task->io_context->ioprio = ioprio;
290 out:
291 	task_unlock(task);
292 	return 0;
293 }
294 EXPORT_SYMBOL_GPL(set_task_ioprio);
295 
__copy_io(unsigned long clone_flags,struct task_struct * tsk)296 int __copy_io(unsigned long clone_flags, struct task_struct *tsk)
297 {
298 	struct io_context *ioc = current->io_context;
299 
300 	/*
301 	 * Share io context with parent, if CLONE_IO is set
302 	 */
303 	if (clone_flags & CLONE_IO) {
304 		atomic_inc(&ioc->active_ref);
305 		tsk->io_context = ioc;
306 	} else if (ioprio_valid(ioc->ioprio)) {
307 		tsk->io_context = alloc_io_context(GFP_KERNEL, NUMA_NO_NODE);
308 		if (!tsk->io_context)
309 			return -ENOMEM;
310 		tsk->io_context->ioprio = ioc->ioprio;
311 	}
312 
313 	return 0;
314 }
315 
316 #ifdef CONFIG_BLK_ICQ
317 /**
318  * ioc_lookup_icq - lookup io_cq from ioc
319  * @q: the associated request_queue
320  *
321  * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
322  * with @q->queue_lock held.
323  */
ioc_lookup_icq(struct request_queue * q)324 struct io_cq *ioc_lookup_icq(struct request_queue *q)
325 {
326 	struct io_context *ioc = current->io_context;
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  * @q: request_queue of interest
356  *
357  * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
358  * will be created using @gfp_mask.
359  *
360  * The caller is responsible for ensuring @ioc won't go away and @q is
361  * alive and will stay alive until this function returns.
362  */
ioc_create_icq(struct request_queue * q)363 static struct io_cq *ioc_create_icq(struct request_queue *q)
364 {
365 	struct io_context *ioc = current->io_context;
366 	struct elevator_type *et = q->elevator->type;
367 	struct io_cq *icq;
368 
369 	/* allocate stuff */
370 	icq = kmem_cache_alloc_node(et->icq_cache, GFP_ATOMIC | __GFP_ZERO,
371 				    q->node);
372 	if (!icq)
373 		return NULL;
374 
375 	if (radix_tree_maybe_preload(GFP_ATOMIC) < 0) {
376 		kmem_cache_free(et->icq_cache, icq);
377 		return NULL;
378 	}
379 
380 	icq->ioc = ioc;
381 	icq->q = q;
382 	INIT_LIST_HEAD(&icq->q_node);
383 	INIT_HLIST_NODE(&icq->ioc_node);
384 
385 	/* lock both q and ioc and try to link @icq */
386 	spin_lock_irq(&q->queue_lock);
387 	spin_lock(&ioc->lock);
388 
389 	if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
390 		hlist_add_head(&icq->ioc_node, &ioc->icq_list);
391 		list_add(&icq->q_node, &q->icq_list);
392 		if (et->ops.init_icq)
393 			et->ops.init_icq(icq);
394 	} else {
395 		kmem_cache_free(et->icq_cache, icq);
396 		icq = ioc_lookup_icq(q);
397 		if (!icq)
398 			printk(KERN_ERR "cfq: icq link failed!\n");
399 	}
400 
401 	spin_unlock(&ioc->lock);
402 	spin_unlock_irq(&q->queue_lock);
403 	radix_tree_preload_end();
404 	return icq;
405 }
406 
ioc_find_get_icq(struct request_queue * q)407 struct io_cq *ioc_find_get_icq(struct request_queue *q)
408 {
409 	struct io_context *ioc = current->io_context;
410 	struct io_cq *icq = NULL;
411 
412 	if (unlikely(!ioc)) {
413 		ioc = alloc_io_context(GFP_ATOMIC, q->node);
414 		if (!ioc)
415 			return NULL;
416 
417 		task_lock(current);
418 		if (current->io_context) {
419 			kmem_cache_free(iocontext_cachep, ioc);
420 			ioc = current->io_context;
421 		} else {
422 			current->io_context = ioc;
423 		}
424 
425 		get_io_context(ioc);
426 		task_unlock(current);
427 	} else {
428 		get_io_context(ioc);
429 
430 		spin_lock_irq(&q->queue_lock);
431 		icq = ioc_lookup_icq(q);
432 		spin_unlock_irq(&q->queue_lock);
433 	}
434 
435 	if (!icq) {
436 		icq = ioc_create_icq(q);
437 		if (!icq) {
438 			put_io_context(ioc);
439 			return NULL;
440 		}
441 	}
442 	return icq;
443 }
444 EXPORT_SYMBOL_GPL(ioc_find_get_icq);
445 #endif /* CONFIG_BLK_ICQ */
446 
blk_ioc_init(void)447 static int __init blk_ioc_init(void)
448 {
449 	iocontext_cachep = kmem_cache_create("blkdev_ioc",
450 			sizeof(struct io_context), 0, SLAB_PANIC, NULL);
451 	return 0;
452 }
453 subsys_initcall(blk_ioc_init);
454