summaryrefslogtreecommitdiff
path: root/block/blk-ioc.c
blob: 381cb50a673c33ed86f6f5d597331137f2881ce3 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
/*
 * Functions related to io context handling
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/slab.h>

#include "blk.h"

/*
 * For io context allocations
 */
static struct kmem_cache *iocontext_cachep;

/**
 * get_io_context - increment reference count to io_context
 * @ioc: io_context to get
 *
 * Increment reference count to @ioc.
 */
void get_io_context(struct io_context *ioc)
{
	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
	atomic_long_inc(&ioc->refcount);
}
EXPORT_SYMBOL(get_io_context);

static void icq_free_icq_rcu(struct rcu_head *head)
{
	struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);

	kmem_cache_free(icq->__rcu_icq_cache, icq);
}

/* Exit an icq. Called with both ioc and q locked. */
static void ioc_exit_icq(struct io_cq *icq)
{
	struct elevator_type *et = icq->q->elevator->type;

	if (icq->flags & ICQ_EXITED)
		return;

	if (et->ops.elevator_exit_icq_fn)
		et->ops.elevator_exit_icq_fn(icq);

	icq->flags |= ICQ_EXITED;
}

/* Release an icq.  Called with both ioc and q locked. */
static void ioc_destroy_icq(struct io_cq *icq)
{
	struct io_context *ioc = icq->ioc;
	struct request_queue *q = icq->q;
	struct elevator_type *et = q->elevator->type;

	lockdep_assert_held(&ioc->lock);
	lockdep_assert_held(q->queue_lock);

	radix_tree_delete(&ioc->icq_tree, icq->q->id);
	hlist_del_init(&icq->ioc_node);
	list_del_init(&icq->q_node);

	/*
	 * Both setting lookup hint to and clearing it from @icq are done
	 * under queue_lock.  If it's not pointing to @icq now, it never
	 * will.  Hint assignment itself can race safely.
	 */
	if (rcu_access_pointer(ioc->icq_hint) == icq)
		rcu_assign_pointer(ioc->icq_hint, NULL);

	ioc_exit_icq(icq);

	/*
	 * @icq->q might have gone away by the time RCU callback runs
	 * making it impossible to determine icq_cache.  Record it in @icq.
	 */
	icq->__rcu_icq_cache = et->icq_cache;
	call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
}

/*
 * Slow path for ioc release in put_io_context().  Performs double-lock
 * dancing to unlink all icq's and then frees ioc.
 */
static void ioc_release_fn(struct work_struct *work)
{
	struct io_context *ioc = container_of(work, struct io_context,
					      release_work);
	unsigned long flags;

	/*
	 * Exiting icq may call into put_io_context() through elevator
	 * which will trigger lockdep warning.  The ioc's are guaranteed to
	 * be different, use a different locking subclass here.  Use
	 * irqsave variant as there's no spin_lock_irq_nested().
	 */
	spin_lock_irqsave_nested(&ioc->lock, flags, 1);

	while (!hlist_empty(&ioc->icq_list)) {
		struct io_cq *icq = hlist_entry(ioc->icq_list.first,
						struct io_cq, ioc_node);
		struct request_queue *q = icq->q;

		if (spin_trylock(q->queue_lock)) {
			ioc_destroy_icq(icq);
			spin_unlock(q->queue_lock);
		} else {
			spin_unlock_irqrestore(&ioc->lock, flags);
			cpu_relax();
			spin_lock_irqsave_nested(&ioc->lock, flags, 1);
		}
	}

	spin_unlock_irqrestore(&ioc->lock, flags);

	kmem_cache_free(iocontext_cachep, ioc);
}

/**
 * put_io_context - put a reference of io_context
 * @ioc: io_context to put
 *
 * Decrement reference count of @ioc and release it if the count reaches
 * zero.
 */
void put_io_context(struct io_context *ioc)
{
	unsigned long flags;
	bool free_ioc = false;

	if (ioc == NULL)
		return;

	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);

	/*
	 * Releasing ioc requires reverse order double locking and we may
	 * already be holding a queue_lock.  Do it asynchronously from wq.
	 */
	if (atomic_long_dec_and_test(&ioc->refcount)) {
		spin_lock_irqsave(&ioc->lock, flags);
		if (!hlist_empty(&ioc->icq_list))
			queue_work(system_power_efficient_wq,
					&ioc->release_work);
		else
			free_ioc = true;
		spin_unlock_irqrestore(&ioc->lock, flags);
	}

	if (free_ioc)
		kmem_cache_free(iocontext_cachep, ioc);
}
EXPORT_SYMBOL(put_io_context);

/**
 * put_io_context_active - put active reference on ioc
 * @ioc: ioc of interest
 *
 * Undo get_io_context_active().  If active reference reaches zero after
 * put, @ioc can never issue further IOs and ioscheds are notified.
 */
void put_io_context_active(struct io_context *ioc)
{
	unsigned long flags;
	struct io_cq *icq;

	if (!atomic_dec_and_test(&ioc->active_ref)) {
		put_io_context(ioc);
		return;
	}

	/*
	 * Need ioc lock to walk icq_list and q lock to exit icq.  Perform
	 * reverse double locking.  Read comment in ioc_release_fn() for
	 * explanation on the nested locking annotation.
	 */
retry:
	spin_lock_irqsave_nested(&ioc->lock, flags, 1);
	hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
		if (icq->flags & ICQ_EXITED)
			continue;
		if (spin_trylock(icq->q->queue_lock)) {
			ioc_exit_icq(icq);
			spin_unlock(icq->q->queue_lock);
		} else {
			spin_unlock_irqrestore(&ioc->lock, flags);
			cpu_relax();
			goto retry;
		}
	}
	spin_unlock_irqrestore(&ioc->lock, flags);

	put_io_context(ioc);
}

/* Called by the exiting task */
void exit_io_context(struct task_struct *task)
{
	struct io_context *ioc;

	task_lock(task);
	ioc = task->io_context;
	task->io_context = NULL;
	task_unlock(task);

	atomic_dec(&ioc->nr_tasks);
	put_io_context_active(ioc);
}

/**
 * ioc_clear_queue - break any ioc association with the specified queue
 * @q: request_queue being cleared
 *
 * Walk @q->icq_list and exit all io_cq's.  Must be called with @q locked.
 */
void ioc_clear_queue(struct request_queue *q)
{
	lockdep_assert_held(q->queue_lock);

	while (!list_empty(&q->icq_list)) {
		struct io_cq *icq = list_entry(q->icq_list.next,
					       struct io_cq, q_node);
		struct io_context *ioc = icq->ioc;

		spin_lock(&ioc->lock);
		ioc_destroy_icq(icq);
		spin_unlock(&ioc->lock);
	}
}

int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
{
	struct io_context *ioc;
	int ret;

	ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
				    node);
	if (unlikely(!ioc))
		return -ENOMEM;

	/* initialize */
	atomic_long_set(&ioc->refcount, 1);
	atomic_set(&ioc->nr_tasks, 1);
	atomic_set(&ioc->active_ref, 1);
	spin_lock_init(&ioc->lock);
	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
	INIT_HLIST_HEAD(&ioc->icq_list);
	INIT_WORK(&ioc->release_work, ioc_release_fn);

	/*
	 * Try to install.  ioc shouldn't be installed if someone else
	 * already did or @task, which isn't %current, is exiting.  Note
	 * that we need to allow ioc creation on exiting %current as exit
	 * path may issue IOs from e.g. exit_files().  The exit path is
	 * responsible for not issuing IO after exit_io_context().
	 */
	task_lock(task);
	if (!task->io_context &&
	    (task == current || !(task->flags & PF_EXITING)))
		task->io_context = ioc;
	else
		kmem_cache_free(iocontext_cachep, ioc);

	ret = task->io_context ? 0 : -EBUSY;

	task_unlock(task);

	return ret;
}

/**
 * get_task_io_context - get io_context of a task
 * @task: task of interest
 * @gfp_flags: allocation flags, used if allocation is necessary
 * @node: allocation node, used if allocation is necessary
 *
 * Return io_context of @task.  If it doesn't exist, it is created with
 * @gfp_flags and @node.  The returned io_context has its reference count
 * incremented.
 *
 * This function always goes through task_lock() and it's better to use
 * %current->io_context + get_io_context() for %current.
 */
struct io_context *get_task_io_context(struct task_struct *task,
				       gfp_t gfp_flags, int node)
{
	struct io_context *ioc;

	might_sleep_if(gfpflags_allow_blocking(gfp_flags));

	do {
		task_lock(task);
		ioc = task->io_context;
		if (likely(ioc)) {
			get_io_context(ioc);
			task_unlock(task);
			return ioc;
		}
		task_unlock(task);
	} while (!create_task_io_context(task, gfp_flags, node));

	return NULL;
}
EXPORT_SYMBOL(get_task_io_context);

/**
 * ioc_lookup_icq - lookup io_cq from ioc
 * @ioc: the associated io_context
 * @q: the associated request_queue
 *
 * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
 * with @q->queue_lock held.
 */
struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
{
	struct io_cq *icq;

	lockdep_assert_held(q->queue_lock);

	/*
	 * icq's are indexed from @ioc using radix tree and hint pointer,
	 * both of which are protected with RCU.  All removals are done
	 * holding both q and ioc locks, and we're holding q lock - if we
	 * find a icq which points to us, it's guaranteed to be valid.
	 */
	rcu_read_lock();
	icq = rcu_dereference(ioc->icq_hint);
	if (icq && icq->q == q)
		goto out;

	icq = radix_tree_lookup(&ioc->icq_tree, q->id);
	if (icq && icq->q == q)
		rcu_assign_pointer(ioc->icq_hint, icq);	/* allowed to race */
	else
		icq = NULL;
out:
	rcu_read_unlock();
	return icq;
}
EXPORT_SYMBOL(ioc_lookup_icq);

/**
 * ioc_create_icq - create and link io_cq
 * @ioc: io_context of interest
 * @q: request_queue of interest
 * @gfp_mask: allocation mask
 *
 * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
 * will be created using @gfp_mask.
 *
 * The caller is responsible for ensuring @ioc won't go away and @q is
 * alive and will stay alive until this function returns.
 */
struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
			     gfp_t gfp_mask)
{
	struct elevator_type *et = q->elevator->type;
	struct io_cq *icq;

	/* allocate stuff */
	icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
				    q->node);
	if (!icq)
		return NULL;

	if (radix_tree_maybe_preload(gfp_mask) < 0) {
		kmem_cache_free(et->icq_cache, icq);
		return NULL;
	}

	icq->ioc = ioc;
	icq->q = q;
	INIT_LIST_HEAD(&icq->q_node);
	INIT_HLIST_NODE(&icq->ioc_node);

	/* lock both q and ioc and try to link @icq */
	spin_lock_irq(q->queue_lock);
	spin_lock(&ioc->lock);

	if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
		hlist_add_head(&icq->ioc_node, &ioc->icq_list);
		list_add(&icq->q_node, &q->icq_list);
		if (et->ops.elevator_init_icq_fn)
			et->ops.elevator_init_icq_fn(icq);
	} else {
		kmem_cache_free(et->icq_cache, icq);
		icq = ioc_lookup_icq(ioc, q);
		if (!icq)
			printk(KERN_ERR "cfq: icq link failed!\n");
	}

	spin_unlock(&ioc->lock);
	spin_unlock_irq(q->queue_lock);
	radix_tree_preload_end();
	return icq;
}

static int __init blk_ioc_init(void)
{
	iocontext_cachep = kmem_cache_create("blkdev_ioc",
			sizeof(struct io_context), 0, SLAB_PANIC, NULL);
	return 0;
}
subsys_initcall(blk_ioc_init);