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1 | #ifndef _LINUX_CLOSURE_H |
2 | #define _LINUX_CLOSURE_H | |
3 | ||
4 | #include <linux/llist.h> | |
5 | #include <linux/sched.h> | |
6 | #include <linux/workqueue.h> | |
7 | ||
8 | /* | |
9 | * Closure is perhaps the most overused and abused term in computer science, but | |
10 | * since I've been unable to come up with anything better you're stuck with it | |
11 | * again. | |
12 | * | |
13 | * What are closures? | |
14 | * | |
15 | * They embed a refcount. The basic idea is they count "things that are in | |
16 | * progress" - in flight bios, some other thread that's doing something else - | |
17 | * anything you might want to wait on. | |
18 | * | |
19 | * The refcount may be manipulated with closure_get() and closure_put(). | |
20 | * closure_put() is where many of the interesting things happen, when it causes | |
21 | * the refcount to go to 0. | |
22 | * | |
23 | * Closures can be used to wait on things both synchronously and asynchronously, | |
24 | * and synchronous and asynchronous use can be mixed without restriction. To | |
25 | * wait synchronously, use closure_sync() - you will sleep until your closure's | |
26 | * refcount hits 1. | |
27 | * | |
28 | * To wait asynchronously, use | |
29 | * continue_at(cl, next_function, workqueue); | |
30 | * | |
31 | * passing it, as you might expect, the function to run when nothing is pending | |
32 | * and the workqueue to run that function out of. | |
33 | * | |
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34 | * continue_at() also, critically, requires a 'return' immediately following the |
35 | * location where this macro is referenced, to return to the calling function. | |
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36 | * There's good reason for this. |
37 | * | |
38 | * To use safely closures asynchronously, they must always have a refcount while | |
39 | * they are running owned by the thread that is running them. Otherwise, suppose | |
40 | * you submit some bios and wish to have a function run when they all complete: | |
41 | * | |
4246a0b6 | 42 | * foo_endio(struct bio *bio) |
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43 | * { |
44 | * closure_put(cl); | |
45 | * } | |
46 | * | |
47 | * closure_init(cl); | |
48 | * | |
49 | * do_stuff(); | |
50 | * closure_get(cl); | |
51 | * bio1->bi_endio = foo_endio; | |
52 | * bio_submit(bio1); | |
53 | * | |
54 | * do_more_stuff(); | |
55 | * closure_get(cl); | |
56 | * bio2->bi_endio = foo_endio; | |
57 | * bio_submit(bio2); | |
58 | * | |
59 | * continue_at(cl, complete_some_read, system_wq); | |
60 | * | |
61 | * If closure's refcount started at 0, complete_some_read() could run before the | |
62 | * second bio was submitted - which is almost always not what you want! More | |
63 | * importantly, it wouldn't be possible to say whether the original thread or | |
64 | * complete_some_read()'s thread owned the closure - and whatever state it was | |
65 | * associated with! | |
66 | * | |
67 | * So, closure_init() initializes a closure's refcount to 1 - and when a | |
68 | * closure_fn is run, the refcount will be reset to 1 first. | |
69 | * | |
70 | * Then, the rule is - if you got the refcount with closure_get(), release it | |
71 | * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount | |
72 | * on a closure because you called closure_init() or you were run out of a | |
73 | * closure - _always_ use continue_at(). Doing so consistently will help | |
74 | * eliminate an entire class of particularly pernicious races. | |
75 | * | |
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76 | * Lastly, you might have a wait list dedicated to a specific event, and have no |
77 | * need for specifying the condition - you just want to wait until someone runs | |
78 | * closure_wake_up() on the appropriate wait list. In that case, just use | |
79 | * closure_wait(). It will return either true or false, depending on whether the | |
80 | * closure was already on a wait list or not - a closure can only be on one wait | |
81 | * list at a time. | |
82 | * | |
83 | * Parents: | |
84 | * | |
85 | * closure_init() takes two arguments - it takes the closure to initialize, and | |
86 | * a (possibly null) parent. | |
87 | * | |
88 | * If parent is non null, the new closure will have a refcount for its lifetime; | |
89 | * a closure is considered to be "finished" when its refcount hits 0 and the | |
90 | * function to run is null. Hence | |
91 | * | |
92 | * continue_at(cl, NULL, NULL); | |
93 | * | |
94 | * returns up the (spaghetti) stack of closures, precisely like normal return | |
95 | * returns up the C stack. continue_at() with non null fn is better thought of | |
96 | * as doing a tail call. | |
97 | * | |
98 | * All this implies that a closure should typically be embedded in a particular | |
99 | * struct (which its refcount will normally control the lifetime of), and that | |
100 | * struct can very much be thought of as a stack frame. | |
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101 | */ |
102 | ||
103 | struct closure; | |
104 | typedef void (closure_fn) (struct closure *); | |
105 | ||
106 | struct closure_waitlist { | |
107 | struct llist_head list; | |
108 | }; | |
109 | ||
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110 | enum closure_state { |
111 | /* | |
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112 | * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by |
113 | * the thread that owns the closure, and cleared by the thread that's | |
114 | * waking up the closure. | |
115 | * | |
116 | * CLOSURE_SLEEPING: Must be set before a thread uses a closure to sleep | |
117 | * - indicates that cl->task is valid and closure_put() may wake it up. | |
118 | * Only set or cleared by the thread that owns 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. | |
129 | * | |
130 | * CLOSURE_STACK: Sanity check - remaining should never hit 0 on a | |
131 | * closure with this flag set | |
132 | */ | |
133 | ||
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134 | CLOSURE_BITS_START = (1 << 23), |
135 | CLOSURE_DESTRUCTOR = (1 << 23), | |
136 | CLOSURE_WAITING = (1 << 25), | |
137 | CLOSURE_SLEEPING = (1 << 27), | |
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138 | CLOSURE_RUNNING = (1 << 29), |
139 | CLOSURE_STACK = (1 << 31), | |
140 | }; | |
141 | ||
142 | #define CLOSURE_GUARD_MASK \ | |
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143 | ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_SLEEPING| \ |
144 | CLOSURE_RUNNING|CLOSURE_STACK) << 1) | |
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145 | |
146 | #define CLOSURE_REMAINING_MASK (CLOSURE_BITS_START - 1) | |
147 | #define CLOSURE_REMAINING_INITIALIZER (1|CLOSURE_RUNNING) | |
148 | ||
149 | struct closure { | |
150 | union { | |
151 | struct { | |
152 | struct workqueue_struct *wq; | |
153 | struct task_struct *task; | |
154 | struct llist_node list; | |
155 | closure_fn *fn; | |
156 | }; | |
157 | struct work_struct work; | |
158 | }; | |
159 | ||
160 | struct closure *parent; | |
161 | ||
162 | atomic_t remaining; | |
163 | ||
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164 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG |
165 | #define CLOSURE_MAGIC_DEAD 0xc054dead | |
166 | #define CLOSURE_MAGIC_ALIVE 0xc054a11e | |
167 | ||
168 | unsigned magic; | |
169 | struct list_head all; | |
170 | unsigned long ip; | |
171 | unsigned long waiting_on; | |
172 | #endif | |
173 | }; | |
174 | ||
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175 | void closure_sub(struct closure *cl, int v); |
176 | void closure_put(struct closure *cl); | |
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177 | void __closure_wake_up(struct closure_waitlist *list); |
178 | bool closure_wait(struct closure_waitlist *list, struct closure *cl); | |
179 | void closure_sync(struct closure *cl); | |
180 | ||
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181 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG |
182 | ||
07e86ccb | 183 | void closure_debug_init(void); |
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184 | void closure_debug_create(struct closure *cl); |
185 | void closure_debug_destroy(struct closure *cl); | |
186 | ||
187 | #else | |
188 | ||
07e86ccb | 189 | static inline void closure_debug_init(void) {} |
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190 | static inline void closure_debug_create(struct closure *cl) {} |
191 | static inline void closure_debug_destroy(struct closure *cl) {} | |
192 | ||
193 | #endif | |
194 | ||
195 | static inline void closure_set_ip(struct closure *cl) | |
196 | { | |
197 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG | |
198 | cl->ip = _THIS_IP_; | |
199 | #endif | |
200 | } | |
201 | ||
202 | static inline void closure_set_ret_ip(struct closure *cl) | |
203 | { | |
204 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG | |
205 | cl->ip = _RET_IP_; | |
206 | #endif | |
207 | } | |
208 | ||
1dd13c8d | 209 | static inline void closure_set_waiting(struct closure *cl, unsigned long f) |
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210 | { |
211 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG | |
1dd13c8d | 212 | cl->waiting_on = f; |
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213 | #endif |
214 | } | |
215 | ||
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216 | static inline void __closure_end_sleep(struct closure *cl) |
217 | { | |
218 | __set_current_state(TASK_RUNNING); | |
219 | ||
220 | if (atomic_read(&cl->remaining) & CLOSURE_SLEEPING) | |
221 | atomic_sub(CLOSURE_SLEEPING, &cl->remaining); | |
222 | } | |
223 | ||
224 | static inline void __closure_start_sleep(struct closure *cl) | |
225 | { | |
226 | closure_set_ip(cl); | |
227 | cl->task = current; | |
228 | set_current_state(TASK_UNINTERRUPTIBLE); | |
229 | ||
230 | if (!(atomic_read(&cl->remaining) & CLOSURE_SLEEPING)) | |
231 | atomic_add(CLOSURE_SLEEPING, &cl->remaining); | |
232 | } | |
233 | ||
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234 | static inline void closure_set_stopped(struct closure *cl) |
235 | { | |
236 | atomic_sub(CLOSURE_RUNNING, &cl->remaining); | |
237 | } | |
238 | ||
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239 | static inline void set_closure_fn(struct closure *cl, closure_fn *fn, |
240 | struct workqueue_struct *wq) | |
cafe5635 | 241 | { |
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242 | BUG_ON(object_is_on_stack(cl)); |
243 | closure_set_ip(cl); | |
244 | cl->fn = fn; | |
245 | cl->wq = wq; | |
246 | /* between atomic_dec() in closure_put() */ | |
4e857c58 | 247 | smp_mb__before_atomic(); |
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248 | } |
249 | ||
1dd13c8d | 250 | static inline void closure_queue(struct closure *cl) |
cafe5635 | 251 | { |
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252 | struct workqueue_struct *wq = cl->wq; |
253 | if (wq) { | |
254 | INIT_WORK(&cl->work, cl->work.func); | |
255 | BUG_ON(!queue_work(wq, &cl->work)); | |
cafe5635 | 256 | } else |
1dd13c8d | 257 | cl->fn(cl); |
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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 | { | |
265 | #ifdef CONFIG_BCACHE_CLOSURES_DEBUG | |
266 | BUG_ON((atomic_inc_return(&cl->remaining) & | |
267 | CLOSURE_REMAINING_MASK) <= 1); | |
268 | #else | |
269 | atomic_inc(&cl->remaining); | |
270 | #endif | |
271 | } | |
cafe5635 | 272 | |
cafe5635 | 273 | /** |
1dd13c8d | 274 | * closure_init - Initialize a closure, setting the refcount to 1 |
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275 | * @cl: closure to initialize |
276 | * @parent: parent of the new closure. cl will take a refcount on it for its | |
277 | * lifetime; may be NULL. | |
278 | */ | |
1dd13c8d | 279 | static inline void closure_init(struct closure *cl, struct closure *parent) |
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280 | { |
281 | memset(cl, 0, sizeof(struct closure)); | |
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282 | cl->parent = parent; |
283 | if (parent) | |
284 | closure_get(parent); | |
cafe5635 | 285 | |
1dd13c8d | 286 | atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); |
cafe5635 | 287 | |
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288 | closure_debug_create(cl); |
289 | closure_set_ip(cl); | |
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290 | } |
291 | ||
1dd13c8d | 292 | static inline void closure_init_stack(struct closure *cl) |
cafe5635 | 293 | { |
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294 | memset(cl, 0, sizeof(struct closure)); |
295 | atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER|CLOSURE_STACK); | |
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296 | } |
297 | ||
cafe5635 | 298 | /** |
1dd13c8d | 299 | * closure_wake_up - wake up all closures on a wait list. |
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300 | */ |
301 | static inline void closure_wake_up(struct closure_waitlist *list) | |
302 | { | |
303 | smp_mb(); | |
304 | __closure_wake_up(list); | |
305 | } | |
306 | ||
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307 | /** |
308 | * continue_at - jump to another function with barrier | |
309 | * | |
310 | * After @cl is no longer waiting on anything (i.e. all outstanding refs have | |
311 | * been dropped with closure_put()), it will resume execution at @fn running out | |
312 | * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly). | |
313 | * | |
314 | * NOTE: This macro expands to a return in the calling function! | |
315 | * | |
316 | * This is because after calling continue_at() you no longer have a ref on @cl, | |
317 | * and whatever @cl owns may be freed out from under you - a running closure fn | |
318 | * has a ref on its own closure which continue_at() drops. | |
cafe5635 | 319 | */ |
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320 | #define continue_at(_cl, _fn, _wq) \ |
321 | do { \ | |
322 | set_closure_fn(_cl, _fn, _wq); \ | |
323 | closure_sub(_cl, CLOSURE_RUNNING + 1); \ | |
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324 | } while (0) |
325 | ||
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326 | /** |
327 | * closure_return - finish execution of a closure | |
328 | * | |
329 | * This is used to indicate that @cl is finished: when all outstanding refs on | |
330 | * @cl have been dropped @cl's ref on its parent closure (as passed to | |
331 | * closure_init()) will be dropped, if one was specified - thus this can be | |
332 | * thought of as returning to the parent closure. | |
333 | */ | |
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334 | #define closure_return(_cl) continue_at((_cl), NULL, NULL) |
335 | ||
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336 | /** |
337 | * continue_at_nobarrier - jump to another function without barrier | |
338 | * | |
339 | * Causes @fn to be executed out of @cl, in @wq context (or called directly if | |
340 | * @wq is NULL). | |
341 | * | |
342 | * NOTE: like continue_at(), this macro expands to a return in the caller! | |
343 | * | |
344 | * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn, | |
345 | * thus it's not safe to touch anything protected by @cl after a | |
346 | * continue_at_nobarrier(). | |
347 | */ | |
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348 | #define continue_at_nobarrier(_cl, _fn, _wq) \ |
349 | do { \ | |
350 | set_closure_fn(_cl, _fn, _wq); \ | |
a34a8bfd | 351 | closure_queue(_cl); \ |
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352 | } while (0) |
353 | ||
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354 | /** |
355 | * closure_return - finish execution of a closure, with destructor | |
356 | * | |
357 | * Works like closure_return(), except @destructor will be called when all | |
358 | * outstanding refs on @cl have been dropped; @destructor may be used to safely | |
359 | * free the memory occupied by @cl, and it is called with the ref on the parent | |
360 | * closure still held - so @destructor could safely return an item to a | |
361 | * freelist protected by @cl's parent. | |
362 | */ | |
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363 | #define closure_return_with_destructor(_cl, _destructor) \ |
364 | do { \ | |
365 | set_closure_fn(_cl, _destructor, NULL); \ | |
366 | closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \ | |
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367 | } while (0) |
368 | ||
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369 | /** |
370 | * closure_call - execute @fn out of a new, uninitialized closure | |
371 | * | |
372 | * Typically used when running out of one closure, and we want to run @fn | |
373 | * asynchronously out of a new closure - @parent will then wait for @cl to | |
374 | * finish. | |
375 | */ | |
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376 | static inline void closure_call(struct closure *cl, closure_fn fn, |
377 | struct workqueue_struct *wq, | |
378 | struct closure *parent) | |
379 | { | |
380 | closure_init(cl, parent); | |
381 | continue_at_nobarrier(cl, fn, wq); | |
382 | } | |
383 | ||
cafe5635 | 384 | #endif /* _LINUX_CLOSURE_H */ |