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 int __closure_sync_timeout(struct closure *cl, unsigned long timeout); 198 199 static inline int closure_sync_timeout(struct closure *cl, unsigned long timeout) 200 { 201 #ifdef CONFIG_DEBUG_CLOSURES 202 BUG_ON(closure_nr_remaining(cl) != 1 && !cl->closure_get_happened); 203 #endif 204 return cl->closure_get_happened 205 ? __closure_sync_timeout(cl, timeout) 206 : 0; 207 } 208 209 #ifdef CONFIG_DEBUG_CLOSURES 210 211 void closure_debug_create(struct closure *cl); 212 void closure_debug_destroy(struct closure *cl); 213 214 #else 215 216 static inline void closure_debug_create(struct closure *cl) {} 217 static inline void closure_debug_destroy(struct closure *cl) {} 218 219 #endif 220 221 static inline void closure_set_ip(struct closure *cl) 222 { 223 #ifdef CONFIG_DEBUG_CLOSURES 224 cl->ip = _THIS_IP_; 225 #endif 226 } 227 228 static inline void closure_set_ret_ip(struct closure *cl) 229 { 230 #ifdef CONFIG_DEBUG_CLOSURES 231 cl->ip = _RET_IP_; 232 #endif 233 } 234 235 static inline void closure_set_waiting(struct closure *cl, unsigned long f) 236 { 237 #ifdef CONFIG_DEBUG_CLOSURES 238 cl->waiting_on = f; 239 #endif 240 } 241 242 static inline void closure_set_stopped(struct closure *cl) 243 { 244 atomic_sub(CLOSURE_RUNNING, &cl->remaining); 245 } 246 247 static inline void set_closure_fn(struct closure *cl, closure_fn *fn, 248 struct workqueue_struct *wq) 249 { 250 closure_set_ip(cl); 251 cl->fn = fn; 252 cl->wq = wq; 253 } 254 255 static inline void closure_queue(struct closure *cl) 256 { 257 struct workqueue_struct *wq = cl->wq; 258 /** 259 * Changes made to closure, work_struct, or a couple of other structs 260 * may cause work.func not pointing to the right location. 261 */ 262 BUILD_BUG_ON(offsetof(struct closure, fn) 263 != offsetof(struct work_struct, func)); 264 265 if (wq) { 266 INIT_WORK(&cl->work, cl->work.func); 267 BUG_ON(!queue_work(wq, &cl->work)); 268 } else 269 cl->fn(&cl->work); 270 } 271 272 /** 273 * closure_get - increment a closure's refcount 274 */ 275 static inline void closure_get(struct closure *cl) 276 { 277 cl->closure_get_happened = true; 278 279 #ifdef CONFIG_DEBUG_CLOSURES 280 BUG_ON((atomic_inc_return(&cl->remaining) & 281 CLOSURE_REMAINING_MASK) <= 1); 282 #else 283 atomic_inc(&cl->remaining); 284 #endif 285 } 286 287 /** 288 * closure_get_not_zero 289 */ 290 static inline bool closure_get_not_zero(struct closure *cl) 291 { 292 unsigned old = atomic_read(&cl->remaining); 293 do { 294 if (!(old & CLOSURE_REMAINING_MASK)) 295 return false; 296 297 } while (!atomic_try_cmpxchg_acquire(&cl->remaining, &old, old + 1)); 298 299 return true; 300 } 301 302 /** 303 * closure_init - Initialize a closure, setting the refcount to 1 304 * @cl: closure to initialize 305 * @parent: parent of the new closure. cl will take a refcount on it for its 306 * lifetime; may be NULL. 307 */ 308 static inline void closure_init(struct closure *cl, struct closure *parent) 309 { 310 cl->fn = NULL; 311 cl->parent = parent; 312 if (parent) 313 closure_get(parent); 314 315 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); 316 cl->closure_get_happened = false; 317 318 closure_debug_create(cl); 319 closure_set_ip(cl); 320 } 321 322 static inline void closure_init_stack(struct closure *cl) 323 { 324 memset(cl, 0, sizeof(struct closure)); 325 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); 326 } 327 328 static inline void closure_init_stack_release(struct closure *cl) 329 { 330 memset(cl, 0, sizeof(struct closure)); 331 atomic_set_release(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); 332 } 333 334 /** 335 * closure_wake_up - wake up all closures on a wait list, 336 * with memory barrier 337 */ 338 static inline void closure_wake_up(struct closure_waitlist *list) 339 { 340 /* Memory barrier for the wait list */ 341 smp_mb(); 342 __closure_wake_up(list); 343 } 344 345 #define CLOSURE_CALLBACK(name) void name(struct work_struct *ws) 346 #define closure_type(name, type, member) \ 347 struct closure *cl = container_of(ws, struct closure, work); \ 348 type *name = container_of(cl, type, member) 349 350 /** 351 * continue_at - jump to another function with barrier 352 * 353 * After @cl is no longer waiting on anything (i.e. all outstanding refs have 354 * been dropped with closure_put()), it will resume execution at @fn running out 355 * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly). 356 * 357 * This is because after calling continue_at() you no longer have a ref on @cl, 358 * and whatever @cl owns may be freed out from under you - a running closure fn 359 * has a ref on its own closure which continue_at() drops. 360 * 361 * Note you are expected to immediately return after using this macro. 362 */ 363 #define continue_at(_cl, _fn, _wq) \ 364 do { \ 365 set_closure_fn(_cl, _fn, _wq); \ 366 closure_sub(_cl, CLOSURE_RUNNING + 1); \ 367 } while (0) 368 369 /** 370 * closure_return - finish execution of a closure 371 * 372 * This is used to indicate that @cl is finished: when all outstanding refs on 373 * @cl have been dropped @cl's ref on its parent closure (as passed to 374 * closure_init()) will be dropped, if one was specified - thus this can be 375 * thought of as returning to the parent closure. 376 */ 377 #define closure_return(_cl) continue_at((_cl), NULL, NULL) 378 379 void closure_return_sync(struct closure *cl); 380 381 /** 382 * continue_at_nobarrier - jump to another function without barrier 383 * 384 * Causes @fn to be executed out of @cl, in @wq context (or called directly if 385 * @wq is NULL). 386 * 387 * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn, 388 * thus it's not safe to touch anything protected by @cl after a 389 * continue_at_nobarrier(). 390 */ 391 #define continue_at_nobarrier(_cl, _fn, _wq) \ 392 do { \ 393 set_closure_fn(_cl, _fn, _wq); \ 394 closure_queue(_cl); \ 395 } while (0) 396 397 /** 398 * closure_return_with_destructor - finish execution of a closure, 399 * with destructor 400 * 401 * Works like closure_return(), except @destructor will be called when all 402 * outstanding refs on @cl have been dropped; @destructor may be used to safely 403 * free the memory occupied by @cl, and it is called with the ref on the parent 404 * closure still held - so @destructor could safely return an item to a 405 * freelist protected by @cl's parent. 406 */ 407 #define closure_return_with_destructor(_cl, _destructor) \ 408 do { \ 409 set_closure_fn(_cl, _destructor, NULL); \ 410 closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \ 411 } while (0) 412 413 /** 414 * closure_call - execute @fn out of a new, uninitialized closure 415 * 416 * Typically used when running out of one closure, and we want to run @fn 417 * asynchronously out of a new closure - @parent will then wait for @cl to 418 * finish. 419 */ 420 static inline void closure_call(struct closure *cl, closure_fn fn, 421 struct workqueue_struct *wq, 422 struct closure *parent) 423 { 424 closure_init(cl, parent); 425 continue_at_nobarrier(cl, fn, wq); 426 } 427 428 #define __closure_wait_event(waitlist, _cond) \ 429 do { \ 430 struct closure cl; \ 431 \ 432 closure_init_stack(&cl); \ 433 \ 434 while (1) { \ 435 closure_wait(waitlist, &cl); \ 436 if (_cond) \ 437 break; \ 438 closure_sync(&cl); \ 439 } \ 440 closure_wake_up(waitlist); \ 441 closure_sync(&cl); \ 442 } while (0) 443 444 #define closure_wait_event(waitlist, _cond) \ 445 do { \ 446 if (!(_cond)) \ 447 __closure_wait_event(waitlist, _cond); \ 448 } while (0) 449 450 #endif /* _LINUX_CLOSURE_H */ 451