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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 | * | |
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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; |
cafe5635 | 107 | typedef void (closure_fn) (struct closure *); |
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 | ||
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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; | |
157 | ||
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158 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG |
159 | #define CLOSURE_MAGIC_DEAD 0xc054dead | |
160 | #define CLOSURE_MAGIC_ALIVE 0xc054a11e | |
161 | ||
162 | unsigned magic; | |
163 | struct list_head all; | |
164 | unsigned long ip; | |
165 | unsigned long waiting_on; | |
166 | #endif | |
167 | }; | |
168 | ||
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169 | void closure_sub(struct closure *cl, int v); |
170 | void closure_put(struct closure *cl); | |
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171 | void __closure_wake_up(struct closure_waitlist *list); |
172 | bool closure_wait(struct closure_waitlist *list, struct closure *cl); | |
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173 | void __closure_sync(struct closure *cl); |
174 | ||
175 | /** | |
176 | * closure_sync - sleep until a closure a closure has nothing left to wait on | |
177 | * | |
178 | * Sleeps until the refcount hits 1 - the thread that's running the closure owns | |
179 | * the last refcount. | |
180 | */ | |
181 | static inline void closure_sync(struct closure *cl) | |
182 | { | |
183 | if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1) | |
184 | __closure_sync(cl); | |
185 | } | |
cafe5635 | 186 | |
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187 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG |
188 | ||
78ac2107 | 189 | void closure_debug_init(void); |
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190 | void closure_debug_create(struct closure *cl); |
191 | void closure_debug_destroy(struct closure *cl); | |
192 | ||
193 | #else | |
194 | ||
78ac2107 | 195 | static inline void closure_debug_init(void) {} |
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196 | static inline void closure_debug_create(struct closure *cl) {} |
197 | static inline void closure_debug_destroy(struct closure *cl) {} | |
198 | ||
199 | #endif | |
200 | ||
201 | static inline void closure_set_ip(struct closure *cl) | |
202 | { | |
203 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG | |
204 | cl->ip = _THIS_IP_; | |
205 | #endif | |
206 | } | |
207 | ||
208 | static inline void closure_set_ret_ip(struct closure *cl) | |
209 | { | |
210 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG | |
211 | cl->ip = _RET_IP_; | |
212 | #endif | |
213 | } | |
214 | ||
1dd13c8d | 215 | static inline void closure_set_waiting(struct closure *cl, unsigned long f) |
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216 | { |
217 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG | |
1dd13c8d | 218 | cl->waiting_on = f; |
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219 | #endif |
220 | } | |
221 | ||
222 | static inline void closure_set_stopped(struct closure *cl) | |
223 | { | |
224 | atomic_sub(CLOSURE_RUNNING, &cl->remaining); | |
225 | } | |
226 | ||
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227 | static inline void set_closure_fn(struct closure *cl, closure_fn *fn, |
228 | struct workqueue_struct *wq) | |
cafe5635 | 229 | { |
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230 | closure_set_ip(cl); |
231 | cl->fn = fn; | |
232 | cl->wq = wq; | |
233 | /* between atomic_dec() in closure_put() */ | |
4e857c58 | 234 | smp_mb__before_atomic(); |
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235 | } |
236 | ||
1dd13c8d | 237 | static inline void closure_queue(struct closure *cl) |
cafe5635 | 238 | { |
1dd13c8d | 239 | struct workqueue_struct *wq = cl->wq; |
6446c684 LC |
240 | /** |
241 | * Changes made to closure, work_struct, or a couple of other structs | |
242 | * may cause work.func not pointing to the right location. | |
243 | */ | |
244 | BUILD_BUG_ON(offsetof(struct closure, fn) | |
245 | != offsetof(struct work_struct, func)); | |
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246 | if (wq) { |
247 | INIT_WORK(&cl->work, cl->work.func); | |
248 | BUG_ON(!queue_work(wq, &cl->work)); | |
cafe5635 | 249 | } else |
1dd13c8d | 250 | cl->fn(cl); |
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251 | } |
252 | ||
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253 | /** |
254 | * closure_get - increment a closure's refcount | |
cafe5635 | 255 | */ |
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256 | static inline void closure_get(struct closure *cl) |
257 | { | |
258 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG | |
259 | BUG_ON((atomic_inc_return(&cl->remaining) & | |
260 | CLOSURE_REMAINING_MASK) <= 1); | |
261 | #else | |
262 | atomic_inc(&cl->remaining); | |
263 | #endif | |
264 | } | |
cafe5635 | 265 | |
cafe5635 | 266 | /** |
1dd13c8d | 267 | * closure_init - Initialize a closure, setting the refcount to 1 |
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268 | * @cl: closure to initialize |
269 | * @parent: parent of the new closure. cl will take a refcount on it for its | |
270 | * lifetime; may be NULL. | |
271 | */ | |
1dd13c8d | 272 | static inline void closure_init(struct closure *cl, struct closure *parent) |
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273 | { |
274 | memset(cl, 0, sizeof(struct closure)); | |
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275 | cl->parent = parent; |
276 | if (parent) | |
277 | closure_get(parent); | |
cafe5635 | 278 | |
1dd13c8d | 279 | atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); |
cafe5635 | 280 | |
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281 | closure_debug_create(cl); |
282 | closure_set_ip(cl); | |
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283 | } |
284 | ||
1dd13c8d | 285 | static inline void closure_init_stack(struct closure *cl) |
cafe5635 | 286 | { |
1dd13c8d | 287 | memset(cl, 0, sizeof(struct closure)); |
e4bf7919 | 288 | atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); |
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289 | } |
290 | ||
cafe5635 | 291 | /** |
1dd13c8d | 292 | * closure_wake_up - wake up all closures on a wait list. |
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293 | */ |
294 | static inline void closure_wake_up(struct closure_waitlist *list) | |
295 | { | |
296 | smp_mb(); | |
297 | __closure_wake_up(list); | |
298 | } | |
299 | ||
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300 | /** |
301 | * continue_at - jump to another function with barrier | |
302 | * | |
303 | * After @cl is no longer waiting on anything (i.e. all outstanding refs have | |
304 | * been dropped with closure_put()), it will resume execution at @fn running out | |
305 | * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly). | |
306 | * | |
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307 | * This is because after calling continue_at() you no longer have a ref on @cl, |
308 | * and whatever @cl owns may be freed out from under you - a running closure fn | |
309 | * has a ref on its own closure which continue_at() drops. | |
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310 | * |
311 | * Note you are expected to immediately return after using this macro. | |
cafe5635 | 312 | */ |
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313 | #define continue_at(_cl, _fn, _wq) \ |
314 | do { \ | |
315 | set_closure_fn(_cl, _fn, _wq); \ | |
316 | closure_sub(_cl, CLOSURE_RUNNING + 1); \ | |
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317 | } while (0) |
318 | ||
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319 | /** |
320 | * closure_return - finish execution of a closure | |
321 | * | |
322 | * This is used to indicate that @cl is finished: when all outstanding refs on | |
323 | * @cl have been dropped @cl's ref on its parent closure (as passed to | |
324 | * closure_init()) will be dropped, if one was specified - thus this can be | |
325 | * thought of as returning to the parent closure. | |
326 | */ | |
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327 | #define closure_return(_cl) continue_at((_cl), NULL, NULL) |
328 | ||
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329 | /** |
330 | * continue_at_nobarrier - jump to another function without barrier | |
331 | * | |
332 | * Causes @fn to be executed out of @cl, in @wq context (or called directly if | |
333 | * @wq is NULL). | |
334 | * | |
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335 | * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn, |
336 | * thus it's not safe to touch anything protected by @cl after a | |
337 | * continue_at_nobarrier(). | |
338 | */ | |
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339 | #define continue_at_nobarrier(_cl, _fn, _wq) \ |
340 | do { \ | |
341 | set_closure_fn(_cl, _fn, _wq); \ | |
a34a8bfd | 342 | closure_queue(_cl); \ |
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343 | } while (0) |
344 | ||
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345 | /** |
346 | * closure_return - finish execution of a closure, with destructor | |
347 | * | |
348 | * Works like closure_return(), except @destructor will be called when all | |
349 | * outstanding refs on @cl have been dropped; @destructor may be used to safely | |
350 | * free the memory occupied by @cl, and it is called with the ref on the parent | |
351 | * closure still held - so @destructor could safely return an item to a | |
352 | * freelist protected by @cl's parent. | |
353 | */ | |
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354 | #define closure_return_with_destructor(_cl, _destructor) \ |
355 | do { \ | |
356 | set_closure_fn(_cl, _destructor, NULL); \ | |
357 | closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \ | |
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358 | } while (0) |
359 | ||
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360 | /** |
361 | * closure_call - execute @fn out of a new, uninitialized closure | |
362 | * | |
363 | * Typically used when running out of one closure, and we want to run @fn | |
364 | * asynchronously out of a new closure - @parent will then wait for @cl to | |
365 | * finish. | |
366 | */ | |
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367 | static inline void closure_call(struct closure *cl, closure_fn fn, |
368 | struct workqueue_struct *wq, | |
369 | struct closure *parent) | |
370 | { | |
371 | closure_init(cl, parent); | |
372 | continue_at_nobarrier(cl, fn, wq); | |
373 | } | |
374 | ||
cafe5635 | 375 | #endif /* _LINUX_CLOSURE_H */ |