summaryrefslogtreecommitdiff
path: root/drivers/md/bcache/closure.h
blob: 3b9dfc9962ad91404b319c715bf509a8fd52707b (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
370
371
372
373
374
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_CLOSURE_H
#define _LINUX_CLOSURE_H

#include <linux/llist.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/workqueue.h>

/*
 * Closure is perhaps the most overused and abused term in computer science, but
 * since I've been unable to come up with anything better you're stuck with it
 * again.
 *
 * What are closures?
 *
 * They embed a refcount. The basic idea is they count "things that are in
 * progress" - in flight bios, some other thread that's doing something else -
 * anything you might want to wait on.
 *
 * The refcount may be manipulated with closure_get() and closure_put().
 * closure_put() is where many of the interesting things happen, when it causes
 * the refcount to go to 0.
 *
 * Closures can be used to wait on things both synchronously and asynchronously,
 * and synchronous and asynchronous use can be mixed without restriction. To
 * wait synchronously, use closure_sync() - you will sleep until your closure's
 * refcount hits 1.
 *
 * To wait asynchronously, use
 *   continue_at(cl, next_function, workqueue);
 *
 * passing it, as you might expect, the function to run when nothing is pending
 * and the workqueue to run that function out of.
 *
 * continue_at() also, critically, requires a 'return' immediately following the
 * location where this macro is referenced, to return to the calling function.
 * There's good reason for this.
 *
 * To use safely closures asynchronously, they must always have a refcount while
 * they are running owned by the thread that is running them. Otherwise, suppose
 * you submit some bios and wish to have a function run when they all complete:
 *
 * foo_endio(struct bio *bio)
 * {
 *	closure_put(cl);
 * }
 *
 * closure_init(cl);
 *
 * do_stuff();
 * closure_get(cl);
 * bio1->bi_endio = foo_endio;
 * bio_submit(bio1);
 *
 * do_more_stuff();
 * closure_get(cl);
 * bio2->bi_endio = foo_endio;
 * bio_submit(bio2);
 *
 * continue_at(cl, complete_some_read, system_wq);
 *
 * If closure's refcount started at 0, complete_some_read() could run before the
 * second bio was submitted - which is almost always not what you want! More
 * importantly, it wouldn't be possible to say whether the original thread or
 * complete_some_read()'s thread owned the closure - and whatever state it was
 * associated with!
 *
 * So, closure_init() initializes a closure's refcount to 1 - and when a
 * closure_fn is run, the refcount will be reset to 1 first.
 *
 * Then, the rule is - if you got the refcount with closure_get(), release it
 * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount
 * on a closure because you called closure_init() or you were run out of a
 * closure - _always_ use continue_at(). Doing so consistently will help
 * eliminate an entire class of particularly pernicious races.
 *
 * Lastly, you might have a wait list dedicated to a specific event, and have no
 * need for specifying the condition - you just want to wait until someone runs
 * closure_wake_up() on the appropriate wait list. In that case, just use
 * closure_wait(). It will return either true or false, depending on whether the
 * closure was already on a wait list or not - a closure can only be on one wait
 * list at a time.
 *
 * Parents:
 *
 * closure_init() takes two arguments - it takes the closure to initialize, and
 * a (possibly null) parent.
 *
 * If parent is non null, the new closure will have a refcount for its lifetime;
 * a closure is considered to be "finished" when its refcount hits 0 and the
 * function to run is null. Hence
 *
 * continue_at(cl, NULL, NULL);
 *
 * returns up the (spaghetti) stack of closures, precisely like normal return
 * returns up the C stack. continue_at() with non null fn is better thought of
 * as doing a tail call.
 *
 * All this implies that a closure should typically be embedded in a particular
 * struct (which its refcount will normally control the lifetime of), and that
 * struct can very much be thought of as a stack frame.
 */

struct closure;
struct closure_syncer;
typedef void (closure_fn) (struct closure *);

struct closure_waitlist {
	struct llist_head	list;
};

enum closure_state {
	/*
	 * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by
	 * the thread that owns the closure, and cleared by the thread that's
	 * waking up the closure.
	 *
	 * The rest are for debugging and don't affect behaviour:
	 *
	 * CLOSURE_RUNNING: Set when a closure is running (i.e. by
	 * closure_init() and when closure_put() runs then next function), and
	 * must be cleared before remaining hits 0. Primarily to help guard
	 * against incorrect usage and accidentally transferring references.
	 * continue_at() and closure_return() clear it for you, if you're doing
	 * something unusual you can use closure_set_dead() which also helps
	 * annotate where references are being transferred.
	 */

	CLOSURE_BITS_START	= (1U << 26),
	CLOSURE_DESTRUCTOR	= (1U << 26),
	CLOSURE_WAITING		= (1U << 28),
	CLOSURE_RUNNING		= (1U << 30),
};

#define CLOSURE_GUARD_MASK					\
	((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1)

#define CLOSURE_REMAINING_MASK		(CLOSURE_BITS_START - 1)
#define CLOSURE_REMAINING_INITIALIZER	(1|CLOSURE_RUNNING)

struct closure {
	union {
		struct {
			struct workqueue_struct *wq;
			struct closure_syncer	*s;
			struct llist_node	list;
			closure_fn		*fn;
		};
		struct work_struct	work;
	};

	struct closure		*parent;

	atomic_t		remaining;

#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
#define CLOSURE_MAGIC_DEAD	0xc054dead
#define CLOSURE_MAGIC_ALIVE	0xc054a11e

	unsigned		magic;
	struct list_head	all;
	unsigned long		ip;
	unsigned long		waiting_on;
#endif
};

void closure_sub(struct closure *cl, int v);
void closure_put(struct closure *cl);
void __closure_wake_up(struct closure_waitlist *list);
bool closure_wait(struct closure_waitlist *list, struct closure *cl);
void __closure_sync(struct closure *cl);

/**
 * closure_sync - sleep until a closure a closure has nothing left to wait on
 *
 * Sleeps until the refcount hits 1 - the thread that's running the closure owns
 * the last refcount.
 */
static inline void closure_sync(struct closure *cl)
{
	if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1)
		__closure_sync(cl);
}

#ifdef CONFIG_BCACHE_CLOSURES_DEBUG

void closure_debug_init(void);
void closure_debug_create(struct closure *cl);
void closure_debug_destroy(struct closure *cl);

#else

static inline void closure_debug_init(void) {}
static inline void closure_debug_create(struct closure *cl) {}
static inline void closure_debug_destroy(struct closure *cl) {}

#endif

static inline void closure_set_ip(struct closure *cl)
{
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
	cl->ip = _THIS_IP_;
#endif
}

static inline void closure_set_ret_ip(struct closure *cl)
{
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
	cl->ip = _RET_IP_;
#endif
}

static inline void closure_set_waiting(struct closure *cl, unsigned long f)
{
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
	cl->waiting_on = f;
#endif
}

static inline void closure_set_stopped(struct closure *cl)
{
	atomic_sub(CLOSURE_RUNNING, &cl->remaining);
}

static inline void set_closure_fn(struct closure *cl, closure_fn *fn,
				  struct workqueue_struct *wq)
{
	closure_set_ip(cl);
	cl->fn = fn;
	cl->wq = wq;
	/* between atomic_dec() in closure_put() */
	smp_mb__before_atomic();
}

static inline void closure_queue(struct closure *cl)
{
	struct workqueue_struct *wq = cl->wq;
	/**
	 * Changes made to closure, work_struct, or a couple of other structs
	 * may cause work.func not pointing to the right location.
	 */
	BUILD_BUG_ON(offsetof(struct closure, fn)
		     != offsetof(struct work_struct, func));
	if (wq) {
		INIT_WORK(&cl->work, cl->work.func);
		BUG_ON(!queue_work(wq, &cl->work));
	} else
		cl->fn(cl);
}

/**
 * closure_get - increment a closure's refcount
 */
static inline void closure_get(struct closure *cl)
{
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
	BUG_ON((atomic_inc_return(&cl->remaining) &
		CLOSURE_REMAINING_MASK) <= 1);
#else
	atomic_inc(&cl->remaining);
#endif
}

/**
 * closure_init - Initialize a closure, setting the refcount to 1
 * @cl:		closure to initialize
 * @parent:	parent of the new closure. cl will take a refcount on it for its
 *		lifetime; may be NULL.
 */
static inline void closure_init(struct closure *cl, struct closure *parent)
{
	memset(cl, 0, sizeof(struct closure));
	cl->parent = parent;
	if (parent)
		closure_get(parent);

	atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);

	closure_debug_create(cl);
	closure_set_ip(cl);
}

static inline void closure_init_stack(struct closure *cl)
{
	memset(cl, 0, sizeof(struct closure));
	atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
}

/**
 * closure_wake_up - wake up all closures on a wait list.
 */
static inline void closure_wake_up(struct closure_waitlist *list)
{
	smp_mb();
	__closure_wake_up(list);
}

/**
 * continue_at - jump to another function with barrier
 *
 * After @cl is no longer waiting on anything (i.e. all outstanding refs have
 * been dropped with closure_put()), it will resume execution at @fn running out
 * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly).
 *
 * This is because after calling continue_at() you no longer have a ref on @cl,
 * and whatever @cl owns may be freed out from under you - a running closure fn
 * has a ref on its own closure which continue_at() drops.
 *
 * Note you are expected to immediately return after using this macro.
 */
#define continue_at(_cl, _fn, _wq)					\
do {									\
	set_closure_fn(_cl, _fn, _wq);					\
	closure_sub(_cl, CLOSURE_RUNNING + 1);				\
} while (0)

/**
 * closure_return - finish execution of a closure
 *
 * This is used to indicate that @cl is finished: when all outstanding refs on
 * @cl have been dropped @cl's ref on its parent closure (as passed to
 * closure_init()) will be dropped, if one was specified - thus this can be
 * thought of as returning to the parent closure.
 */
#define closure_return(_cl)	continue_at((_cl), NULL, NULL)

/**
 * continue_at_nobarrier - jump to another function without barrier
 *
 * Causes @fn to be executed out of @cl, in @wq context (or called directly if
 * @wq is NULL).
 *
 * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn,
 * thus it's not safe to touch anything protected by @cl after a
 * continue_at_nobarrier().
 */
#define continue_at_nobarrier(_cl, _fn, _wq)				\
do {									\
	set_closure_fn(_cl, _fn, _wq);					\
	closure_queue(_cl);						\
} while (0)

/**
 * closure_return - finish execution of a closure, with destructor
 *
 * Works like closure_return(), except @destructor will be called when all
 * outstanding refs on @cl have been dropped; @destructor may be used to safely
 * free the memory occupied by @cl, and it is called with the ref on the parent
 * closure still held - so @destructor could safely return an item to a
 * freelist protected by @cl's parent.
 */
#define closure_return_with_destructor(_cl, _destructor)		\
do {									\
	set_closure_fn(_cl, _destructor, NULL);				\
	closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1);	\
} while (0)

/**
 * closure_call - execute @fn out of a new, uninitialized closure
 *
 * Typically used when running out of one closure, and we want to run @fn
 * asynchronously out of a new closure - @parent will then wait for @cl to
 * finish.
 */
static inline void closure_call(struct closure *cl, closure_fn fn,
				struct workqueue_struct *wq,
				struct closure *parent)
{
	closure_init(cl, parent);
	continue_at_nobarrier(cl, fn, wq);
}

#endif /* _LINUX_CLOSURE_H */