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b2441318 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
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2 | #ifndef _LINUX_CLOSURE_H |
3 | #define _LINUX_CLOSURE_H | |
4 | ||
5 | #include <linux/llist.h> | |
6 | #include <linux/sched.h> | |
68db0cf1 | 7 | #include <linux/sched/task_stack.h> |
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8 | #include <linux/workqueue.h> |
9 | ||
10 | /* | |
11 | * Closure is perhaps the most overused and abused term in computer science, but | |
12 | * since I've been unable to come up with anything better you're stuck with it | |
13 | * again. | |
14 | * | |
15 | * What are closures? | |
16 | * | |
17 | * They embed a refcount. The basic idea is they count "things that are in | |
18 | * progress" - in flight bios, some other thread that's doing something else - | |
19 | * anything you might want to wait on. | |
20 | * | |
21 | * The refcount may be manipulated with closure_get() and closure_put(). | |
22 | * closure_put() is where many of the interesting things happen, when it causes | |
23 | * the refcount to go to 0. | |
24 | * | |
25 | * Closures can be used to wait on things both synchronously and asynchronously, | |
26 | * and synchronous and asynchronous use can be mixed without restriction. To | |
27 | * wait synchronously, use closure_sync() - you will sleep until your closure's | |
28 | * refcount hits 1. | |
29 | * | |
30 | * To wait asynchronously, use | |
31 | * continue_at(cl, next_function, workqueue); | |
32 | * | |
33 | * passing it, as you might expect, the function to run when nothing is pending | |
34 | * and the workqueue to run that function out of. | |
35 | * | |
7abc70d7 YW |
36 | * continue_at() also, critically, requires a 'return' immediately following the |
37 | * location where this macro is referenced, to return to the calling function. | |
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38 | * There's good reason for this. |
39 | * | |
40 | * To use safely closures asynchronously, they must always have a refcount while | |
41 | * they are running owned by the thread that is running them. Otherwise, suppose | |
42 | * you submit some bios and wish to have a function run when they all complete: | |
43 | * | |
4246a0b6 | 44 | * foo_endio(struct bio *bio) |
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45 | * { |
46 | * closure_put(cl); | |
47 | * } | |
48 | * | |
49 | * closure_init(cl); | |
50 | * | |
51 | * do_stuff(); | |
52 | * closure_get(cl); | |
53 | * bio1->bi_endio = foo_endio; | |
54 | * bio_submit(bio1); | |
55 | * | |
56 | * do_more_stuff(); | |
57 | * closure_get(cl); | |
58 | * bio2->bi_endio = foo_endio; | |
59 | * bio_submit(bio2); | |
60 | * | |
61 | * continue_at(cl, complete_some_read, system_wq); | |
62 | * | |
63 | * If closure's refcount started at 0, complete_some_read() could run before the | |
64 | * second bio was submitted - which is almost always not what you want! More | |
65 | * importantly, it wouldn't be possible to say whether the original thread or | |
66 | * complete_some_read()'s thread owned the closure - and whatever state it was | |
67 | * associated with! | |
68 | * | |
69 | * So, closure_init() initializes a closure's refcount to 1 - and when a | |
70 | * closure_fn is run, the refcount will be reset to 1 first. | |
71 | * | |
72 | * Then, the rule is - if you got the refcount with closure_get(), release it | |
73 | * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount | |
74 | * on a closure because you called closure_init() or you were run out of a | |
75 | * closure - _always_ use continue_at(). Doing so consistently will help | |
76 | * eliminate an entire class of particularly pernicious races. | |
77 | * | |
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78 | * Lastly, you might have a wait list dedicated to a specific event, and have no |
79 | * need for specifying the condition - you just want to wait until someone runs | |
80 | * closure_wake_up() on the appropriate wait list. In that case, just use | |
81 | * closure_wait(). It will return either true or false, depending on whether the | |
82 | * closure was already on a wait list or not - a closure can only be on one wait | |
83 | * list at a time. | |
84 | * | |
85 | * Parents: | |
86 | * | |
87 | * closure_init() takes two arguments - it takes the closure to initialize, and | |
88 | * a (possibly null) parent. | |
89 | * | |
90 | * If parent is non null, the new closure will have a refcount for its lifetime; | |
91 | * a closure is considered to be "finished" when its refcount hits 0 and the | |
92 | * function to run is null. Hence | |
93 | * | |
94 | * continue_at(cl, NULL, NULL); | |
95 | * | |
96 | * returns up the (spaghetti) stack of closures, precisely like normal return | |
97 | * returns up the C stack. continue_at() with non null fn is better thought of | |
98 | * as doing a tail call. | |
99 | * | |
100 | * All this implies that a closure should typically be embedded in a particular | |
101 | * struct (which its refcount will normally control the lifetime of), and that | |
102 | * struct can very much be thought of as a stack frame. | |
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103 | */ |
104 | ||
105 | struct closure; | |
e4bf7919 | 106 | struct closure_syncer; |
d4e3b928 | 107 | typedef void (closure_fn) (struct work_struct *); |
df2b9431 | 108 | extern struct dentry *bcache_debug; |
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109 | |
110 | struct closure_waitlist { | |
111 | struct llist_head list; | |
112 | }; | |
113 | ||
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114 | enum closure_state { |
115 | /* | |
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116 | * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by |
117 | * the thread that owns the closure, and cleared by the thread that's | |
118 | * waking up the closure. | |
119 | * | |
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120 | * The rest are for debugging and don't affect behaviour: |
121 | * | |
122 | * CLOSURE_RUNNING: Set when a closure is running (i.e. by | |
123 | * closure_init() and when closure_put() runs then next function), and | |
124 | * must be cleared before remaining hits 0. Primarily to help guard | |
125 | * against incorrect usage and accidentally transferring references. | |
126 | * continue_at() and closure_return() clear it for you, if you're doing | |
127 | * something unusual you can use closure_set_dead() which also helps | |
128 | * annotate where references are being transferred. | |
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129 | */ |
130 | ||
3609c471 ML |
131 | CLOSURE_BITS_START = (1U << 26), |
132 | CLOSURE_DESTRUCTOR = (1U << 26), | |
133 | CLOSURE_WAITING = (1U << 28), | |
134 | CLOSURE_RUNNING = (1U << 30), | |
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135 | }; |
136 | ||
137 | #define CLOSURE_GUARD_MASK \ | |
e4bf7919 | 138 | ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1) |
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139 | |
140 | #define CLOSURE_REMAINING_MASK (CLOSURE_BITS_START - 1) | |
141 | #define CLOSURE_REMAINING_INITIALIZER (1|CLOSURE_RUNNING) | |
142 | ||
143 | struct closure { | |
144 | union { | |
145 | struct { | |
146 | struct workqueue_struct *wq; | |
e4bf7919 | 147 | struct closure_syncer *s; |
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148 | struct llist_node list; |
149 | closure_fn *fn; | |
150 | }; | |
151 | struct work_struct work; | |
152 | }; | |
153 | ||
154 | struct closure *parent; | |
155 | ||
156 | atomic_t remaining; | |
ee526b88 | 157 | bool closure_get_happened; |
cafe5635 | 158 | |
8c8d2d96 | 159 | #ifdef CONFIG_DEBUG_CLOSURES |
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160 | #define CLOSURE_MAGIC_DEAD 0xc054dead |
161 | #define CLOSURE_MAGIC_ALIVE 0xc054a11e | |
162 | ||
6f10f7d1 | 163 | unsigned int magic; |
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164 | struct list_head all; |
165 | unsigned long ip; | |
166 | unsigned long waiting_on; | |
167 | #endif | |
168 | }; | |
169 | ||
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170 | void closure_sub(struct closure *cl, int v); |
171 | void closure_put(struct closure *cl); | |
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172 | void __closure_wake_up(struct closure_waitlist *list); |
173 | bool closure_wait(struct closure_waitlist *list, struct closure *cl); | |
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174 | void __closure_sync(struct closure *cl); |
175 | ||
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176 | static inline unsigned closure_nr_remaining(struct closure *cl) |
177 | { | |
178 | return atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK; | |
179 | } | |
180 | ||
e4bf7919 KO |
181 | /** |
182 | * closure_sync - sleep until a closure a closure has nothing left to wait on | |
183 | * | |
184 | * Sleeps until the refcount hits 1 - the thread that's running the closure owns | |
185 | * the last refcount. | |
186 | */ | |
187 | static inline void closure_sync(struct closure *cl) | |
188 | { | |
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189 | #ifdef CONFIG_DEBUG_CLOSURES |
190 | BUG_ON(closure_nr_remaining(cl) != 1 && !cl->closure_get_happened); | |
191 | #endif | |
192 | ||
193 | if (cl->closure_get_happened) | |
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194 | __closure_sync(cl); |
195 | } | |
cafe5635 | 196 | |
8c8d2d96 | 197 | #ifdef CONFIG_DEBUG_CLOSURES |
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198 | |
199 | void closure_debug_create(struct closure *cl); | |
200 | void closure_debug_destroy(struct closure *cl); | |
201 | ||
202 | #else | |
203 | ||
204 | static inline void closure_debug_create(struct closure *cl) {} | |
205 | static inline void closure_debug_destroy(struct closure *cl) {} | |
206 | ||
207 | #endif | |
208 | ||
209 | static inline void closure_set_ip(struct closure *cl) | |
210 | { | |
8c8d2d96 | 211 | #ifdef CONFIG_DEBUG_CLOSURES |
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212 | cl->ip = _THIS_IP_; |
213 | #endif | |
214 | } | |
215 | ||
216 | static inline void closure_set_ret_ip(struct closure *cl) | |
217 | { | |
8c8d2d96 | 218 | #ifdef CONFIG_DEBUG_CLOSURES |
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219 | cl->ip = _RET_IP_; |
220 | #endif | |
221 | } | |
222 | ||
1dd13c8d | 223 | static inline void closure_set_waiting(struct closure *cl, unsigned long f) |
cafe5635 | 224 | { |
8c8d2d96 | 225 | #ifdef CONFIG_DEBUG_CLOSURES |
1dd13c8d | 226 | cl->waiting_on = f; |
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227 | #endif |
228 | } | |
229 | ||
230 | static inline void closure_set_stopped(struct closure *cl) | |
231 | { | |
232 | atomic_sub(CLOSURE_RUNNING, &cl->remaining); | |
233 | } | |
234 | ||
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235 | static inline void set_closure_fn(struct closure *cl, closure_fn *fn, |
236 | struct workqueue_struct *wq) | |
cafe5635 | 237 | { |
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238 | closure_set_ip(cl); |
239 | cl->fn = fn; | |
240 | cl->wq = wq; | |
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241 | } |
242 | ||
1dd13c8d | 243 | static inline void closure_queue(struct closure *cl) |
cafe5635 | 244 | { |
1dd13c8d | 245 | struct workqueue_struct *wq = cl->wq; |
6446c684 LC |
246 | /** |
247 | * Changes made to closure, work_struct, or a couple of other structs | |
248 | * may cause work.func not pointing to the right location. | |
249 | */ | |
250 | BUILD_BUG_ON(offsetof(struct closure, fn) | |
251 | != offsetof(struct work_struct, func)); | |
8c8d2d96 | 252 | |
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253 | if (wq) { |
254 | INIT_WORK(&cl->work, cl->work.func); | |
255 | BUG_ON(!queue_work(wq, &cl->work)); | |
cafe5635 | 256 | } else |
d4e3b928 | 257 | cl->fn(&cl->work); |
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258 | } |
259 | ||
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260 | /** |
261 | * closure_get - increment a closure's refcount | |
cafe5635 | 262 | */ |
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263 | static inline void closure_get(struct closure *cl) |
264 | { | |
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265 | cl->closure_get_happened = true; |
266 | ||
8c8d2d96 | 267 | #ifdef CONFIG_DEBUG_CLOSURES |
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268 | BUG_ON((atomic_inc_return(&cl->remaining) & |
269 | CLOSURE_REMAINING_MASK) <= 1); | |
270 | #else | |
271 | atomic_inc(&cl->remaining); | |
272 | #endif | |
273 | } | |
cafe5635 | 274 | |
cafe5635 | 275 | /** |
1dd13c8d | 276 | * closure_init - Initialize a closure, setting the refcount to 1 |
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277 | * @cl: closure to initialize |
278 | * @parent: parent of the new closure. cl will take a refcount on it for its | |
279 | * lifetime; may be NULL. | |
280 | */ | |
1dd13c8d | 281 | static inline void closure_init(struct closure *cl, struct closure *parent) |
cafe5635 | 282 | { |
8c8d2d96 | 283 | cl->fn = NULL; |
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284 | cl->parent = parent; |
285 | if (parent) | |
286 | closure_get(parent); | |
cafe5635 | 287 | |
1dd13c8d | 288 | atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); |
ee526b88 | 289 | cl->closure_get_happened = false; |
cafe5635 | 290 | |
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291 | closure_debug_create(cl); |
292 | closure_set_ip(cl); | |
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293 | } |
294 | ||
1dd13c8d | 295 | static inline void closure_init_stack(struct closure *cl) |
cafe5635 | 296 | { |
1dd13c8d | 297 | memset(cl, 0, sizeof(struct closure)); |
e4bf7919 | 298 | atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); |
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299 | } |
300 | ||
cafe5635 | 301 | /** |
eb2b3d03 CL |
302 | * closure_wake_up - wake up all closures on a wait list, |
303 | * with memory barrier | |
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304 | */ |
305 | static inline void closure_wake_up(struct closure_waitlist *list) | |
306 | { | |
eb2b3d03 | 307 | /* Memory barrier for the wait list */ |
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308 | smp_mb(); |
309 | __closure_wake_up(list); | |
310 | } | |
311 | ||
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312 | #define CLOSURE_CALLBACK(name) void name(struct work_struct *ws) |
313 | #define closure_type(name, type, member) \ | |
314 | struct closure *cl = container_of(ws, struct closure, work); \ | |
315 | type *name = container_of(cl, type, member) | |
316 | ||
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317 | /** |
318 | * continue_at - jump to another function with barrier | |
319 | * | |
320 | * After @cl is no longer waiting on anything (i.e. all outstanding refs have | |
321 | * been dropped with closure_put()), it will resume execution at @fn running out | |
322 | * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly). | |
323 | * | |
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324 | * This is because after calling continue_at() you no longer have a ref on @cl, |
325 | * and whatever @cl owns may be freed out from under you - a running closure fn | |
326 | * has a ref on its own closure which continue_at() drops. | |
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327 | * |
328 | * Note you are expected to immediately return after using this macro. | |
cafe5635 | 329 | */ |
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330 | #define continue_at(_cl, _fn, _wq) \ |
331 | do { \ | |
332 | set_closure_fn(_cl, _fn, _wq); \ | |
333 | closure_sub(_cl, CLOSURE_RUNNING + 1); \ | |
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334 | } while (0) |
335 | ||
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336 | /** |
337 | * closure_return - finish execution of a closure | |
338 | * | |
339 | * This is used to indicate that @cl is finished: when all outstanding refs on | |
340 | * @cl have been dropped @cl's ref on its parent closure (as passed to | |
341 | * closure_init()) will be dropped, if one was specified - thus this can be | |
342 | * thought of as returning to the parent closure. | |
343 | */ | |
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344 | #define closure_return(_cl) continue_at((_cl), NULL, NULL) |
345 | ||
1dd13c8d KO |
346 | /** |
347 | * continue_at_nobarrier - jump to another function without barrier | |
348 | * | |
349 | * Causes @fn to be executed out of @cl, in @wq context (or called directly if | |
350 | * @wq is NULL). | |
351 | * | |
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352 | * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn, |
353 | * thus it's not safe to touch anything protected by @cl after a | |
354 | * continue_at_nobarrier(). | |
355 | */ | |
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356 | #define continue_at_nobarrier(_cl, _fn, _wq) \ |
357 | do { \ | |
358 | set_closure_fn(_cl, _fn, _wq); \ | |
a34a8bfd | 359 | closure_queue(_cl); \ |
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360 | } while (0) |
361 | ||
1dd13c8d | 362 | /** |
4516da42 CL |
363 | * closure_return_with_destructor - finish execution of a closure, |
364 | * with destructor | |
1dd13c8d KO |
365 | * |
366 | * Works like closure_return(), except @destructor will be called when all | |
367 | * outstanding refs on @cl have been dropped; @destructor may be used to safely | |
368 | * free the memory occupied by @cl, and it is called with the ref on the parent | |
369 | * closure still held - so @destructor could safely return an item to a | |
370 | * freelist protected by @cl's parent. | |
371 | */ | |
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372 | #define closure_return_with_destructor(_cl, _destructor) \ |
373 | do { \ | |
374 | set_closure_fn(_cl, _destructor, NULL); \ | |
375 | closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \ | |
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376 | } while (0) |
377 | ||
1dd13c8d KO |
378 | /** |
379 | * closure_call - execute @fn out of a new, uninitialized closure | |
380 | * | |
381 | * Typically used when running out of one closure, and we want to run @fn | |
382 | * asynchronously out of a new closure - @parent will then wait for @cl to | |
383 | * finish. | |
384 | */ | |
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385 | static inline void closure_call(struct closure *cl, closure_fn fn, |
386 | struct workqueue_struct *wq, | |
387 | struct closure *parent) | |
388 | { | |
389 | closure_init(cl, parent); | |
390 | continue_at_nobarrier(cl, fn, wq); | |
391 | } | |
392 | ||
ced58fc7 KO |
393 | #define __closure_wait_event(waitlist, _cond) \ |
394 | do { \ | |
395 | struct closure cl; \ | |
396 | \ | |
397 | closure_init_stack(&cl); \ | |
398 | \ | |
399 | while (1) { \ | |
400 | closure_wait(waitlist, &cl); \ | |
401 | if (_cond) \ | |
402 | break; \ | |
403 | closure_sync(&cl); \ | |
404 | } \ | |
405 | closure_wake_up(waitlist); \ | |
406 | closure_sync(&cl); \ | |
407 | } while (0) | |
408 | ||
409 | #define closure_wait_event(waitlist, _cond) \ | |
410 | do { \ | |
411 | if (!(_cond)) \ | |
412 | __closure_wait_event(waitlist, _cond); \ | |
413 | } while (0) | |
414 | ||
cafe5635 | 415 | #endif /* _LINUX_CLOSURE_H */ |