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 * 34 * continue_at() also, critically, is a macro that returns the calling function. 35 * There's good reason for this. 36 * 37 * To use safely closures asynchronously, they must always have a refcount while 38 * they are running owned by the thread that is running them. Otherwise, suppose 39 * you submit some bios and wish to have a function run when they all complete: 40 * 41 * foo_endio(struct bio *bio) 42 * { 43 * closure_put(cl); 44 * } 45 * 46 * closure_init(cl); 47 * 48 * do_stuff(); 49 * closure_get(cl); 50 * bio1->bi_endio = foo_endio; 51 * bio_submit(bio1); 52 * 53 * do_more_stuff(); 54 * closure_get(cl); 55 * bio2->bi_endio = foo_endio; 56 * bio_submit(bio2); 57 * 58 * continue_at(cl, complete_some_read, system_wq); 59 * 60 * If closure's refcount started at 0, complete_some_read() could run before the 61 * second bio was submitted - which is almost always not what you want! More 62 * importantly, it wouldn't be possible to say whether the original thread or 63 * complete_some_read()'s thread owned the closure - and whatever state it was 64 * associated with! 65 * 66 * So, closure_init() initializes a closure's refcount to 1 - and when a 67 * closure_fn is run, the refcount will be reset to 1 first. 68 * 69 * Then, the rule is - if you got the refcount with closure_get(), release it 70 * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount 71 * on a closure because you called closure_init() or you were run out of a 72 * closure - _always_ use continue_at(). Doing so consistently will help 73 * eliminate an entire class of particularly pernicious races. 74 * 75 * Lastly, you might have a wait list dedicated to a specific event, and have no 76 * need for specifying the condition - you just want to wait until someone runs 77 * closure_wake_up() on the appropriate wait list. In that case, just use 78 * closure_wait(). It will return either true or false, depending on whether the 79 * closure was already on a wait list or not - a closure can only be on one wait 80 * list at a time. 81 * 82 * Parents: 83 * 84 * closure_init() takes two arguments - it takes the closure to initialize, and 85 * a (possibly null) parent. 86 * 87 * If parent is non null, the new closure will have a refcount for its lifetime; 88 * a closure is considered to be "finished" when its refcount hits 0 and the 89 * function to run is null. Hence 90 * 91 * continue_at(cl, NULL, NULL); 92 * 93 * returns up the (spaghetti) stack of closures, precisely like normal return 94 * returns up the C stack. continue_at() with non null fn is better thought of 95 * as doing a tail call. 96 * 97 * All this implies that a closure should typically be embedded in a particular 98 * struct (which its refcount will normally control the lifetime of), and that 99 * struct can very much be thought of as a stack frame. 100 */ 101 102 struct closure; 103 typedef void (closure_fn) (struct closure *); 104 105 struct closure_waitlist { 106 struct llist_head list; 107 }; 108 109 enum closure_state { 110 /* 111 * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by 112 * the thread that owns the closure, and cleared by the thread that's 113 * waking up the closure. 114 * 115 * CLOSURE_SLEEPING: Must be set before a thread uses a closure to sleep 116 * - indicates that cl->task is valid and closure_put() may wake it up. 117 * Only set or cleared by the thread that owns the closure. 118 * 119 * The rest are for debugging and don't affect behaviour: 120 * 121 * CLOSURE_RUNNING: Set when a closure is running (i.e. by 122 * closure_init() and when closure_put() runs then next function), and 123 * must be cleared before remaining hits 0. Primarily to help guard 124 * against incorrect usage and accidentally transferring references. 125 * continue_at() and closure_return() clear it for you, if you're doing 126 * something unusual you can use closure_set_dead() which also helps 127 * annotate where references are being transferred. 128 * 129 * CLOSURE_STACK: Sanity check - remaining should never hit 0 on a 130 * closure with this flag set 131 */ 132 133 CLOSURE_BITS_START = (1 << 23), 134 CLOSURE_DESTRUCTOR = (1 << 23), 135 CLOSURE_WAITING = (1 << 25), 136 CLOSURE_SLEEPING = (1 << 27), 137 CLOSURE_RUNNING = (1 << 29), 138 CLOSURE_STACK = (1 << 31), 139 }; 140 141 #define CLOSURE_GUARD_MASK \ 142 ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_SLEEPING| \ 143 CLOSURE_RUNNING|CLOSURE_STACK) << 1) 144 145 #define CLOSURE_REMAINING_MASK (CLOSURE_BITS_START - 1) 146 #define CLOSURE_REMAINING_INITIALIZER (1|CLOSURE_RUNNING) 147 148 struct closure { 149 union { 150 struct { 151 struct workqueue_struct *wq; 152 struct task_struct *task; 153 struct llist_node list; 154 closure_fn *fn; 155 }; 156 struct work_struct work; 157 }; 158 159 struct closure *parent; 160 161 atomic_t remaining; 162 163 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 164 #define CLOSURE_MAGIC_DEAD 0xc054dead 165 #define CLOSURE_MAGIC_ALIVE 0xc054a11e 166 167 unsigned magic; 168 struct list_head all; 169 unsigned long ip; 170 unsigned long waiting_on; 171 #endif 172 }; 173 174 void closure_sub(struct closure *cl, int v); 175 void closure_put(struct closure *cl); 176 void __closure_wake_up(struct closure_waitlist *list); 177 bool closure_wait(struct closure_waitlist *list, struct closure *cl); 178 void closure_sync(struct closure *cl); 179 180 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 181 182 void closure_debug_init(void); 183 void closure_debug_create(struct closure *cl); 184 void closure_debug_destroy(struct closure *cl); 185 186 #else 187 188 static inline void closure_debug_init(void) {} 189 static inline void closure_debug_create(struct closure *cl) {} 190 static inline void closure_debug_destroy(struct closure *cl) {} 191 192 #endif 193 194 static inline void closure_set_ip(struct closure *cl) 195 { 196 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 197 cl->ip = _THIS_IP_; 198 #endif 199 } 200 201 static inline void closure_set_ret_ip(struct closure *cl) 202 { 203 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 204 cl->ip = _RET_IP_; 205 #endif 206 } 207 208 static inline void closure_set_waiting(struct closure *cl, unsigned long f) 209 { 210 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 211 cl->waiting_on = f; 212 #endif 213 } 214 215 static inline void __closure_end_sleep(struct closure *cl) 216 { 217 __set_current_state(TASK_RUNNING); 218 219 if (atomic_read(&cl->remaining) & CLOSURE_SLEEPING) 220 atomic_sub(CLOSURE_SLEEPING, &cl->remaining); 221 } 222 223 static inline void __closure_start_sleep(struct closure *cl) 224 { 225 closure_set_ip(cl); 226 cl->task = current; 227 set_current_state(TASK_UNINTERRUPTIBLE); 228 229 if (!(atomic_read(&cl->remaining) & CLOSURE_SLEEPING)) 230 atomic_add(CLOSURE_SLEEPING, &cl->remaining); 231 } 232 233 static inline void closure_set_stopped(struct closure *cl) 234 { 235 atomic_sub(CLOSURE_RUNNING, &cl->remaining); 236 } 237 238 static inline void set_closure_fn(struct closure *cl, closure_fn *fn, 239 struct workqueue_struct *wq) 240 { 241 BUG_ON(object_is_on_stack(cl)); 242 closure_set_ip(cl); 243 cl->fn = fn; 244 cl->wq = wq; 245 /* between atomic_dec() in closure_put() */ 246 smp_mb__before_atomic(); 247 } 248 249 static inline void closure_queue(struct closure *cl) 250 { 251 struct workqueue_struct *wq = cl->wq; 252 if (wq) { 253 INIT_WORK(&cl->work, cl->work.func); 254 BUG_ON(!queue_work(wq, &cl->work)); 255 } else 256 cl->fn(cl); 257 } 258 259 /** 260 * closure_get - increment a closure's refcount 261 */ 262 static inline void closure_get(struct closure *cl) 263 { 264 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 265 BUG_ON((atomic_inc_return(&cl->remaining) & 266 CLOSURE_REMAINING_MASK) <= 1); 267 #else 268 atomic_inc(&cl->remaining); 269 #endif 270 } 271 272 /** 273 * closure_init - Initialize a closure, setting the refcount to 1 274 * @cl: closure to initialize 275 * @parent: parent of the new closure. cl will take a refcount on it for its 276 * lifetime; may be NULL. 277 */ 278 static inline void closure_init(struct closure *cl, struct closure *parent) 279 { 280 memset(cl, 0, sizeof(struct closure)); 281 cl->parent = parent; 282 if (parent) 283 closure_get(parent); 284 285 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); 286 287 closure_debug_create(cl); 288 closure_set_ip(cl); 289 } 290 291 static inline void closure_init_stack(struct closure *cl) 292 { 293 memset(cl, 0, sizeof(struct closure)); 294 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER|CLOSURE_STACK); 295 } 296 297 /** 298 * closure_wake_up - wake up all closures on a wait list. 299 */ 300 static inline void closure_wake_up(struct closure_waitlist *list) 301 { 302 smp_mb(); 303 __closure_wake_up(list); 304 } 305 306 /** 307 * continue_at - jump to another function with barrier 308 * 309 * After @cl is no longer waiting on anything (i.e. all outstanding refs have 310 * been dropped with closure_put()), it will resume execution at @fn running out 311 * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly). 312 * 313 * NOTE: This macro expands to a return in the calling function! 314 * 315 * This is because after calling continue_at() you no longer have a ref on @cl, 316 * and whatever @cl owns may be freed out from under you - a running closure fn 317 * has a ref on its own closure which continue_at() drops. 318 */ 319 #define continue_at(_cl, _fn, _wq) \ 320 do { \ 321 set_closure_fn(_cl, _fn, _wq); \ 322 closure_sub(_cl, CLOSURE_RUNNING + 1); \ 323 } while (0) 324 325 /** 326 * closure_return - finish execution of a closure 327 * 328 * This is used to indicate that @cl is finished: when all outstanding refs on 329 * @cl have been dropped @cl's ref on its parent closure (as passed to 330 * closure_init()) will be dropped, if one was specified - thus this can be 331 * thought of as returning to the parent closure. 332 */ 333 #define closure_return(_cl) continue_at((_cl), NULL, NULL) 334 335 /** 336 * continue_at_nobarrier - jump to another function without barrier 337 * 338 * Causes @fn to be executed out of @cl, in @wq context (or called directly if 339 * @wq is NULL). 340 * 341 * NOTE: like continue_at(), this macro expands to a return in the caller! 342 * 343 * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn, 344 * thus it's not safe to touch anything protected by @cl after a 345 * continue_at_nobarrier(). 346 */ 347 #define continue_at_nobarrier(_cl, _fn, _wq) \ 348 do { \ 349 set_closure_fn(_cl, _fn, _wq); \ 350 closure_queue(_cl); \ 351 } while (0) 352 353 /** 354 * closure_return - finish execution of a closure, with destructor 355 * 356 * Works like closure_return(), except @destructor will be called when all 357 * outstanding refs on @cl have been dropped; @destructor may be used to safely 358 * free the memory occupied by @cl, and it is called with the ref on the parent 359 * closure still held - so @destructor could safely return an item to a 360 * freelist protected by @cl's parent. 361 */ 362 #define closure_return_with_destructor(_cl, _destructor) \ 363 do { \ 364 set_closure_fn(_cl, _destructor, NULL); \ 365 closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \ 366 } while (0) 367 368 /** 369 * closure_call - execute @fn out of a new, uninitialized closure 370 * 371 * Typically used when running out of one closure, and we want to run @fn 372 * asynchronously out of a new closure - @parent will then wait for @cl to 373 * finish. 374 */ 375 static inline void closure_call(struct closure *cl, closure_fn fn, 376 struct workqueue_struct *wq, 377 struct closure *parent) 378 { 379 closure_init(cl, parent); 380 continue_at_nobarrier(cl, fn, wq); 381 } 382 383 #endif /* _LINUX_CLOSURE_H */ 384