1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_CLOSURE_H 3 #define _LINUX_CLOSURE_H 4 5 #include <linux/llist.h> 6 #include <linux/sched.h> 7 #include <linux/sched/task_stack.h> 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 * 36 * continue_at() also, critically, requires a 'return' immediately following the 37 * location where this macro is referenced, to return to the calling function. 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 * 44 * foo_endio(struct bio *bio) 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 * 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. 103 */ 104 105 struct closure; 106 struct closure_syncer; 107 typedef void (closure_fn) (struct work_struct *); 108 extern struct dentry *bcache_debug; 109 110 struct closure_waitlist { 111 struct llist_head list; 112 }; 113 114 enum closure_state { 115 /* 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 * 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 */ 130 131 CLOSURE_BITS_START = (1U << 26), 132 CLOSURE_DESTRUCTOR = (1U << 26), 133 CLOSURE_WAITING = (1U << 28), 134 CLOSURE_RUNNING = (1U << 30), 135 }; 136 137 #define CLOSURE_GUARD_MASK \ 138 ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1) 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; 147 struct closure_syncer *s; 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 bool closure_get_happened; 158 159 #ifdef CONFIG_DEBUG_CLOSURES 160 #define CLOSURE_MAGIC_DEAD 0xc054dead 161 #define CLOSURE_MAGIC_ALIVE 0xc054a11e 162 163 unsigned int magic; 164 struct list_head all; 165 unsigned long ip; 166 unsigned long waiting_on; 167 #endif 168 }; 169 170 void closure_sub(struct closure *cl, int v); 171 void closure_put(struct closure *cl); 172 void __closure_wake_up(struct closure_waitlist *list); 173 bool closure_wait(struct closure_waitlist *list, struct closure *cl); 174 void __closure_sync(struct closure *cl); 175 176 static inline unsigned closure_nr_remaining(struct closure *cl) 177 { 178 return atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK; 179 } 180 181 /** 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 { 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) 194 __closure_sync(cl); 195 } 196 197 #ifdef CONFIG_DEBUG_CLOSURES 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 { 211 #ifdef CONFIG_DEBUG_CLOSURES 212 cl->ip = _THIS_IP_; 213 #endif 214 } 215 216 static inline void closure_set_ret_ip(struct closure *cl) 217 { 218 #ifdef CONFIG_DEBUG_CLOSURES 219 cl->ip = _RET_IP_; 220 #endif 221 } 222 223 static inline void closure_set_waiting(struct closure *cl, unsigned long f) 224 { 225 #ifdef CONFIG_DEBUG_CLOSURES 226 cl->waiting_on = f; 227 #endif 228 } 229 230 static inline void closure_set_stopped(struct closure *cl) 231 { 232 atomic_sub(CLOSURE_RUNNING, &cl->remaining); 233 } 234 235 static inline void set_closure_fn(struct closure *cl, closure_fn *fn, 236 struct workqueue_struct *wq) 237 { 238 closure_set_ip(cl); 239 cl->fn = fn; 240 cl->wq = wq; 241 } 242 243 static inline void closure_queue(struct closure *cl) 244 { 245 struct workqueue_struct *wq = cl->wq; 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)); 252 253 if (wq) { 254 INIT_WORK(&cl->work, cl->work.func); 255 BUG_ON(!queue_work(wq, &cl->work)); 256 } else 257 cl->fn(&cl->work); 258 } 259 260 /** 261 * closure_get - increment a closure's refcount 262 */ 263 static inline void closure_get(struct closure *cl) 264 { 265 cl->closure_get_happened = true; 266 267 #ifdef CONFIG_DEBUG_CLOSURES 268 BUG_ON((atomic_inc_return(&cl->remaining) & 269 CLOSURE_REMAINING_MASK) <= 1); 270 #else 271 atomic_inc(&cl->remaining); 272 #endif 273 } 274 275 /** 276 * closure_init - Initialize a closure, setting the refcount to 1 277 * @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 */ 281 static inline void closure_init(struct closure *cl, struct closure *parent) 282 { 283 cl->fn = NULL; 284 cl->parent = parent; 285 if (parent) 286 closure_get(parent); 287 288 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); 289 cl->closure_get_happened = false; 290 291 closure_debug_create(cl); 292 closure_set_ip(cl); 293 } 294 295 static inline void closure_init_stack(struct closure *cl) 296 { 297 memset(cl, 0, sizeof(struct closure)); 298 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); 299 } 300 301 /** 302 * closure_wake_up - wake up all closures on a wait list, 303 * with memory barrier 304 */ 305 static inline void closure_wake_up(struct closure_waitlist *list) 306 { 307 /* Memory barrier for the wait list */ 308 smp_mb(); 309 __closure_wake_up(list); 310 } 311 312 #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) 316 317 /** 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 * 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. 327 * 328 * Note you are expected to immediately return after using this macro. 329 */ 330 #define continue_at(_cl, _fn, _wq) \ 331 do { \ 332 set_closure_fn(_cl, _fn, _wq); \ 333 closure_sub(_cl, CLOSURE_RUNNING + 1); \ 334 } while (0) 335 336 /** 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 */ 344 #define closure_return(_cl) continue_at((_cl), NULL, NULL) 345 346 /** 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 * 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 */ 356 #define continue_at_nobarrier(_cl, _fn, _wq) \ 357 do { \ 358 set_closure_fn(_cl, _fn, _wq); \ 359 closure_queue(_cl); \ 360 } while (0) 361 362 /** 363 * closure_return_with_destructor - finish execution of a closure, 364 * with destructor 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 */ 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); \ 376 } while (0) 377 378 /** 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 */ 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 } 392 393 #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) 414 415 #endif /* _LINUX_CLOSURE_H */ 416