summaryrefslogtreecommitdiff
path: root/kernel/async.c
blob: 6c68fc3fae7b61cb6de52c73db9fcd4874c2cc97 (plain)
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
/*
 * async.c: Asynchronous function calls for boot performance
 *
 * (C) Copyright 2009 Intel Corporation
 * Author: Arjan van de Ven <arjan@linux.intel.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; version 2
 * of the License.
 */


/*

Goals and Theory of Operation

The primary goal of this feature is to reduce the kernel boot time,
by doing various independent hardware delays and discovery operations
decoupled and not strictly serialized.

More specifically, the asynchronous function call concept allows
certain operations (primarily during system boot) to happen
asynchronously, out of order, while these operations still
have their externally visible parts happen sequentially and in-order.
(not unlike how out-of-order CPUs retire their instructions in order)

Key to the asynchronous function call implementation is the concept of
a "sequence cookie" (which, although it has an abstracted type, can be
thought of as a monotonically incrementing number).

The async core will assign each scheduled event such a sequence cookie and
pass this to the called functions.

The asynchronously called function should before doing a globally visible
operation, such as registering device numbers, call the
async_synchronize_cookie() function and pass in its own cookie. The
async_synchronize_cookie() function will make sure that all asynchronous
operations that were scheduled prior to the operation corresponding with the
cookie have completed.

Subsystem/driver initialization code that scheduled asynchronous probe
functions, but which shares global resources with other drivers/subsystems
that do not use the asynchronous call feature, need to do a full
synchronization with the async_synchronize_full() function, before returning
from their init function. This is to maintain strict ordering between the
asynchronous and synchronous parts of the kernel.

*/

#include <linux/async.h>
#include <linux/atomic.h>
#include <linux/ktime.h>
#include <linux/export.h>
#include <linux/wait.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/workqueue.h>

#include "workqueue_internal.h"

static async_cookie_t next_cookie = 1;

#define MAX_WORK	32768

static LIST_HEAD(async_pending);
static ASYNC_DOMAIN(async_running);
static LIST_HEAD(async_domains);
static DEFINE_SPINLOCK(async_lock);
static DEFINE_MUTEX(async_register_mutex);

struct async_entry {
	struct list_head	list;
	struct work_struct	work;
	async_cookie_t		cookie;
	async_func_ptr		*func;
	void			*data;
	struct async_domain	*running;
};

static DECLARE_WAIT_QUEUE_HEAD(async_done);

static atomic_t entry_count;


/*
 * MUST be called with the lock held!
 */
static async_cookie_t  __lowest_in_progress(struct async_domain *running)
{
	async_cookie_t first_running = next_cookie;	/* infinity value */
	async_cookie_t first_pending = next_cookie;	/* ditto */
	struct async_entry *entry;

	/*
	 * Both running and pending lists are sorted but not disjoint.
	 * Take the first cookies from both and return the min.
	 */
	if (!list_empty(&running->domain)) {
		entry = list_first_entry(&running->domain, typeof(*entry), list);
		first_running = entry->cookie;
	}

	list_for_each_entry(entry, &async_pending, list) {
		if (entry->running == running) {
			first_pending = entry->cookie;
			break;
		}
	}

	return min(first_running, first_pending);
}

static async_cookie_t  lowest_in_progress(struct async_domain *running)
{
	unsigned long flags;
	async_cookie_t ret;

	spin_lock_irqsave(&async_lock, flags);
	ret = __lowest_in_progress(running);
	spin_unlock_irqrestore(&async_lock, flags);
	return ret;
}

/*
 * pick the first pending entry and run it
 */
static void async_run_entry_fn(struct work_struct *work)
{
	struct async_entry *entry =
		container_of(work, struct async_entry, work);
	struct async_entry *pos;
	unsigned long flags;
	ktime_t uninitialized_var(calltime), delta, rettime;
	struct async_domain *running = entry->running;

	/* 1) move self to the running queue, make sure it stays sorted */
	spin_lock_irqsave(&async_lock, flags);
	list_for_each_entry_reverse(pos, &running->domain, list)
		if (entry->cookie < pos->cookie)
			break;
	list_move_tail(&entry->list, &pos->list);
	spin_unlock_irqrestore(&async_lock, flags);

	/* 2) run (and print duration) */
	if (initcall_debug && system_state == SYSTEM_BOOTING) {
		printk(KERN_DEBUG "calling  %lli_%pF @ %i\n",
			(long long)entry->cookie,
			entry->func, task_pid_nr(current));
		calltime = ktime_get();
	}
	entry->func(entry->data, entry->cookie);
	if (initcall_debug && system_state == SYSTEM_BOOTING) {
		rettime = ktime_get();
		delta = ktime_sub(rettime, calltime);
		printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
			(long long)entry->cookie,
			entry->func,
			(long long)ktime_to_ns(delta) >> 10);
	}

	/* 3) remove self from the running queue */
	spin_lock_irqsave(&async_lock, flags);
	list_del(&entry->list);
	if (running->registered && --running->count == 0)
		list_del_init(&running->node);

	/* 4) free the entry */
	kfree(entry);
	atomic_dec(&entry_count);

	spin_unlock_irqrestore(&async_lock, flags);

	/* 5) wake up any waiters */
	wake_up(&async_done);
}

static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct async_domain *running)
{
	struct async_entry *entry;
	unsigned long flags;
	async_cookie_t newcookie;

	/* allow irq-off callers */
	entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);

	/*
	 * If we're out of memory or if there's too much work
	 * pending already, we execute synchronously.
	 */
	if (!entry || atomic_read(&entry_count) > MAX_WORK) {
		kfree(entry);
		spin_lock_irqsave(&async_lock, flags);
		newcookie = next_cookie++;
		spin_unlock_irqrestore(&async_lock, flags);

		/* low on memory.. run synchronously */
		ptr(data, newcookie);
		return newcookie;
	}
	INIT_WORK(&entry->work, async_run_entry_fn);
	entry->func = ptr;
	entry->data = data;
	entry->running = running;

	spin_lock_irqsave(&async_lock, flags);
	newcookie = entry->cookie = next_cookie++;
	list_add_tail(&entry->list, &async_pending);
	if (running->registered && running->count++ == 0)
		list_add_tail(&running->node, &async_domains);
	atomic_inc(&entry_count);
	spin_unlock_irqrestore(&async_lock, flags);

	/* mark that this task has queued an async job, used by module init */
	current->flags |= PF_USED_ASYNC;

	/* schedule for execution */
	queue_work(system_unbound_wq, &entry->work);

	return newcookie;
}

/**
 * async_schedule - schedule a function for asynchronous execution
 * @ptr: function to execute asynchronously
 * @data: data pointer to pass to the function
 *
 * Returns an async_cookie_t that may be used for checkpointing later.
 * Note: This function may be called from atomic or non-atomic contexts.
 */
async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
{
	return __async_schedule(ptr, data, &async_running);
}
EXPORT_SYMBOL_GPL(async_schedule);

/**
 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
 * @ptr: function to execute asynchronously
 * @data: data pointer to pass to the function
 * @running: running list for the domain
 *
 * Returns an async_cookie_t that may be used for checkpointing later.
 * @running may be used in the async_synchronize_*_domain() functions
 * to wait within a certain synchronization domain rather than globally.
 * A synchronization domain is specified via the running queue @running to use.
 * Note: This function may be called from atomic or non-atomic contexts.
 */
async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
				     struct async_domain *running)
{
	return __async_schedule(ptr, data, running);
}
EXPORT_SYMBOL_GPL(async_schedule_domain);

/**
 * async_synchronize_full - synchronize all asynchronous function calls
 *
 * This function waits until all asynchronous function calls have been done.
 */
void async_synchronize_full(void)
{
	mutex_lock(&async_register_mutex);
	do {
		struct async_domain *domain = NULL;

		spin_lock_irq(&async_lock);
		if (!list_empty(&async_domains))
			domain = list_first_entry(&async_domains, typeof(*domain), node);
		spin_unlock_irq(&async_lock);

		async_synchronize_cookie_domain(next_cookie, domain);
	} while (!list_empty(&async_domains));
	mutex_unlock(&async_register_mutex);
}
EXPORT_SYMBOL_GPL(async_synchronize_full);

/**
 * async_unregister_domain - ensure no more anonymous waiters on this domain
 * @domain: idle domain to flush out of any async_synchronize_full instances
 *
 * async_synchronize_{cookie|full}_domain() are not flushed since callers
 * of these routines should know the lifetime of @domain
 *
 * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
 */
void async_unregister_domain(struct async_domain *domain)
{
	mutex_lock(&async_register_mutex);
	spin_lock_irq(&async_lock);
	WARN_ON(!domain->registered || !list_empty(&domain->node) ||
		!list_empty(&domain->domain));
	domain->registered = 0;
	spin_unlock_irq(&async_lock);
	mutex_unlock(&async_register_mutex);
}
EXPORT_SYMBOL_GPL(async_unregister_domain);

/**
 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 * @domain: running list to synchronize on
 *
 * This function waits until all asynchronous function calls for the
 * synchronization domain specified by the running list @domain have been done.
 */
void async_synchronize_full_domain(struct async_domain *domain)
{
	async_synchronize_cookie_domain(next_cookie, domain);
}
EXPORT_SYMBOL_GPL(async_synchronize_full_domain);

/**
 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 * @cookie: async_cookie_t to use as checkpoint
 * @running: running list to synchronize on
 *
 * This function waits until all asynchronous function calls for the
 * synchronization domain specified by running list @running submitted
 * prior to @cookie have been done.
 */
void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *running)
{
	ktime_t uninitialized_var(starttime), delta, endtime;

	if (!running)
		return;

	if (initcall_debug && system_state == SYSTEM_BOOTING) {
		printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
		starttime = ktime_get();
	}

	wait_event(async_done, lowest_in_progress(running) >= cookie);

	if (initcall_debug && system_state == SYSTEM_BOOTING) {
		endtime = ktime_get();
		delta = ktime_sub(endtime, starttime);

		printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
			task_pid_nr(current),
			(long long)ktime_to_ns(delta) >> 10);
	}
}
EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);

/**
 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 * @cookie: async_cookie_t to use as checkpoint
 *
 * This function waits until all asynchronous function calls prior to @cookie
 * have been done.
 */
void async_synchronize_cookie(async_cookie_t cookie)
{
	async_synchronize_cookie_domain(cookie, &async_running);
}
EXPORT_SYMBOL_GPL(async_synchronize_cookie);

/**
 * current_is_async - is %current an async worker task?
 *
 * Returns %true if %current is an async worker task.
 */
bool current_is_async(void)
{
	struct worker *worker = current_wq_worker();

	return worker && worker->current_func == async_run_entry_fn;
}