1 #ifndef _LINUX_CLOSURE_H 2 #define _LINUX_CLOSURE_H 3 4 #include <linux/llist.h> 5 #include <linux/sched.h> 6 #include <linux/sched/task_stack.h> 7 #include <linux/workqueue.h> 8 9 /* 10 * Closure is perhaps the most overused and abused term in computer science, but 11 * since I've been unable to come up with anything better you're stuck with it 12 * again. 13 * 14 * What are closures? 15 * 16 * They embed a refcount. The basic idea is they count "things that are in 17 * progress" - in flight bios, some other thread that's doing something else - 18 * anything you might want to wait on. 19 * 20 * The refcount may be manipulated with closure_get() and closure_put(). 21 * closure_put() is where many of the interesting things happen, when it causes 22 * the refcount to go to 0. 23 * 24 * Closures can be used to wait on things both synchronously and asynchronously, 25 * and synchronous and asynchronous use can be mixed without restriction. To 26 * wait synchronously, use closure_sync() - you will sleep until your closure's 27 * refcount hits 1. 28 * 29 * To wait asynchronously, use 30 * continue_at(cl, next_function, workqueue); 31 * 32 * passing it, as you might expect, the function to run when nothing is pending 33 * and the workqueue to run that function out of. 34 * 35 * continue_at() also, critically, requires a 'return' immediately following the 36 * location where this macro is referenced, to return to the calling function. 37 * There's good reason for this. 38 * 39 * To use safely closures asynchronously, they must always have a refcount while 40 * they are running owned by the thread that is running them. Otherwise, suppose 41 * you submit some bios and wish to have a function run when they all complete: 42 * 43 * foo_endio(struct bio *bio) 44 * { 45 * closure_put(cl); 46 * } 47 * 48 * closure_init(cl); 49 * 50 * do_stuff(); 51 * closure_get(cl); 52 * bio1->bi_endio = foo_endio; 53 * bio_submit(bio1); 54 * 55 * do_more_stuff(); 56 * closure_get(cl); 57 * bio2->bi_endio = foo_endio; 58 * bio_submit(bio2); 59 * 60 * continue_at(cl, complete_some_read, system_wq); 61 * 62 * If closure's refcount started at 0, complete_some_read() could run before the 63 * second bio was submitted - which is almost always not what you want! More 64 * importantly, it wouldn't be possible to say whether the original thread or 65 * complete_some_read()'s thread owned the closure - and whatever state it was 66 * associated with! 67 * 68 * So, closure_init() initializes a closure's refcount to 1 - and when a 69 * closure_fn is run, the refcount will be reset to 1 first. 70 * 71 * Then, the rule is - if you got the refcount with closure_get(), release it 72 * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount 73 * on a closure because you called closure_init() or you were run out of a 74 * closure - _always_ use continue_at(). Doing so consistently will help 75 * eliminate an entire class of particularly pernicious races. 76 * 77 * Lastly, you might have a wait list dedicated to a specific event, and have no 78 * need for specifying the condition - you just want to wait until someone runs 79 * closure_wake_up() on the appropriate wait list. In that case, just use 80 * closure_wait(). It will return either true or false, depending on whether the 81 * closure was already on a wait list or not - a closure can only be on one wait 82 * list at a time. 83 * 84 * Parents: 85 * 86 * closure_init() takes two arguments - it takes the closure to initialize, and 87 * a (possibly null) parent. 88 * 89 * If parent is non null, the new closure will have a refcount for its lifetime; 90 * a closure is considered to be "finished" when its refcount hits 0 and the 91 * function to run is null. Hence 92 * 93 * continue_at(cl, NULL, NULL); 94 * 95 * returns up the (spaghetti) stack of closures, precisely like normal return 96 * returns up the C stack. continue_at() with non null fn is better thought of 97 * as doing a tail call. 98 * 99 * All this implies that a closure should typically be embedded in a particular 100 * struct (which its refcount will normally control the lifetime of), and that 101 * struct can very much be thought of as a stack frame. 102 */ 103 104 struct closure; 105 typedef void (closure_fn) (struct closure *); 106 107 struct closure_waitlist { 108 struct llist_head list; 109 }; 110 111 enum closure_state { 112 /* 113 * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by 114 * the thread that owns the closure, and cleared by the thread that's 115 * waking up the closure. 116 * 117 * CLOSURE_SLEEPING: Must be set before a thread uses a closure to sleep 118 * - indicates that cl->task is valid and closure_put() may wake it up. 119 * Only set or cleared by the thread that owns the closure. 120 * 121 * The rest are for debugging and don't affect behaviour: 122 * 123 * CLOSURE_RUNNING: Set when a closure is running (i.e. by 124 * closure_init() and when closure_put() runs then next function), and 125 * must be cleared before remaining hits 0. Primarily to help guard 126 * against incorrect usage and accidentally transferring references. 127 * continue_at() and closure_return() clear it for you, if you're doing 128 * something unusual you can use closure_set_dead() which also helps 129 * annotate where references are being transferred. 130 * 131 * CLOSURE_STACK: Sanity check - remaining should never hit 0 on a 132 * closure with this flag set 133 */ 134 135 CLOSURE_BITS_START = (1 << 23), 136 CLOSURE_DESTRUCTOR = (1 << 23), 137 CLOSURE_WAITING = (1 << 25), 138 CLOSURE_SLEEPING = (1 << 27), 139 CLOSURE_RUNNING = (1 << 29), 140 CLOSURE_STACK = (1 << 31), 141 }; 142 143 #define CLOSURE_GUARD_MASK \ 144 ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_SLEEPING| \ 145 CLOSURE_RUNNING|CLOSURE_STACK) << 1) 146 147 #define CLOSURE_REMAINING_MASK (CLOSURE_BITS_START - 1) 148 #define CLOSURE_REMAINING_INITIALIZER (1|CLOSURE_RUNNING) 149 150 struct closure { 151 union { 152 struct { 153 struct workqueue_struct *wq; 154 struct task_struct *task; 155 struct llist_node list; 156 closure_fn *fn; 157 }; 158 struct work_struct work; 159 }; 160 161 struct closure *parent; 162 163 atomic_t remaining; 164 165 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 166 #define CLOSURE_MAGIC_DEAD 0xc054dead 167 #define CLOSURE_MAGIC_ALIVE 0xc054a11e 168 169 unsigned magic; 170 struct list_head all; 171 unsigned long ip; 172 unsigned long waiting_on; 173 #endif 174 }; 175 176 void closure_sub(struct closure *cl, int v); 177 void closure_put(struct closure *cl); 178 void __closure_wake_up(struct closure_waitlist *list); 179 bool closure_wait(struct closure_waitlist *list, struct closure *cl); 180 void closure_sync(struct closure *cl); 181 182 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 183 184 void closure_debug_init(void); 185 void closure_debug_create(struct closure *cl); 186 void closure_debug_destroy(struct closure *cl); 187 188 #else 189 190 static inline void closure_debug_init(void) {} 191 static inline void closure_debug_create(struct closure *cl) {} 192 static inline void closure_debug_destroy(struct closure *cl) {} 193 194 #endif 195 196 static inline void closure_set_ip(struct closure *cl) 197 { 198 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 199 cl->ip = _THIS_IP_; 200 #endif 201 } 202 203 static inline void closure_set_ret_ip(struct closure *cl) 204 { 205 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 206 cl->ip = _RET_IP_; 207 #endif 208 } 209 210 static inline void closure_set_waiting(struct closure *cl, unsigned long f) 211 { 212 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 213 cl->waiting_on = f; 214 #endif 215 } 216 217 static inline void __closure_end_sleep(struct closure *cl) 218 { 219 __set_current_state(TASK_RUNNING); 220 221 if (atomic_read(&cl->remaining) & CLOSURE_SLEEPING) 222 atomic_sub(CLOSURE_SLEEPING, &cl->remaining); 223 } 224 225 static inline void __closure_start_sleep(struct closure *cl) 226 { 227 closure_set_ip(cl); 228 cl->task = current; 229 set_current_state(TASK_UNINTERRUPTIBLE); 230 231 if (!(atomic_read(&cl->remaining) & CLOSURE_SLEEPING)) 232 atomic_add(CLOSURE_SLEEPING, &cl->remaining); 233 } 234 235 static inline void closure_set_stopped(struct closure *cl) 236 { 237 atomic_sub(CLOSURE_RUNNING, &cl->remaining); 238 } 239 240 static inline void set_closure_fn(struct closure *cl, closure_fn *fn, 241 struct workqueue_struct *wq) 242 { 243 BUG_ON(object_is_on_stack(cl)); 244 closure_set_ip(cl); 245 cl->fn = fn; 246 cl->wq = wq; 247 /* between atomic_dec() in closure_put() */ 248 smp_mb__before_atomic(); 249 } 250 251 static inline void closure_queue(struct closure *cl) 252 { 253 struct workqueue_struct *wq = cl->wq; 254 if (wq) { 255 INIT_WORK(&cl->work, cl->work.func); 256 BUG_ON(!queue_work(wq, &cl->work)); 257 } else 258 cl->fn(cl); 259 } 260 261 /** 262 * closure_get - increment a closure's refcount 263 */ 264 static inline void closure_get(struct closure *cl) 265 { 266 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG 267 BUG_ON((atomic_inc_return(&cl->remaining) & 268 CLOSURE_REMAINING_MASK) <= 1); 269 #else 270 atomic_inc(&cl->remaining); 271 #endif 272 } 273 274 /** 275 * closure_init - Initialize a closure, setting the refcount to 1 276 * @cl: closure to initialize 277 * @parent: parent of the new closure. cl will take a refcount on it for its 278 * lifetime; may be NULL. 279 */ 280 static inline void closure_init(struct closure *cl, struct closure *parent) 281 { 282 memset(cl, 0, sizeof(struct closure)); 283 cl->parent = parent; 284 if (parent) 285 closure_get(parent); 286 287 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); 288 289 closure_debug_create(cl); 290 closure_set_ip(cl); 291 } 292 293 static inline void closure_init_stack(struct closure *cl) 294 { 295 memset(cl, 0, sizeof(struct closure)); 296 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER|CLOSURE_STACK); 297 } 298 299 /** 300 * closure_wake_up - wake up all closures on a wait list. 301 */ 302 static inline void closure_wake_up(struct closure_waitlist *list) 303 { 304 smp_mb(); 305 __closure_wake_up(list); 306 } 307 308 /** 309 * continue_at - jump to another function with barrier 310 * 311 * After @cl is no longer waiting on anything (i.e. all outstanding refs have 312 * been dropped with closure_put()), it will resume execution at @fn running out 313 * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly). 314 * 315 * NOTE: This macro expands to a return in the calling function! 316 * 317 * This is because after calling continue_at() you no longer have a ref on @cl, 318 * and whatever @cl owns may be freed out from under you - a running closure fn 319 * has a ref on its own closure which continue_at() drops. 320 */ 321 #define continue_at(_cl, _fn, _wq) \ 322 do { \ 323 set_closure_fn(_cl, _fn, _wq); \ 324 closure_sub(_cl, CLOSURE_RUNNING + 1); \ 325 } while (0) 326 327 /** 328 * closure_return - finish execution of a closure 329 * 330 * This is used to indicate that @cl is finished: when all outstanding refs on 331 * @cl have been dropped @cl's ref on its parent closure (as passed to 332 * closure_init()) will be dropped, if one was specified - thus this can be 333 * thought of as returning to the parent closure. 334 */ 335 #define closure_return(_cl) continue_at((_cl), NULL, NULL) 336 337 /** 338 * continue_at_nobarrier - jump to another function without barrier 339 * 340 * Causes @fn to be executed out of @cl, in @wq context (or called directly if 341 * @wq is NULL). 342 * 343 * NOTE: like continue_at(), this macro expands to a return in the caller! 344 * 345 * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn, 346 * thus it's not safe to touch anything protected by @cl after a 347 * continue_at_nobarrier(). 348 */ 349 #define continue_at_nobarrier(_cl, _fn, _wq) \ 350 do { \ 351 set_closure_fn(_cl, _fn, _wq); \ 352 closure_queue(_cl); \ 353 } while (0) 354 355 /** 356 * closure_return - finish execution of a closure, with destructor 357 * 358 * Works like closure_return(), except @destructor will be called when all 359 * outstanding refs on @cl have been dropped; @destructor may be used to safely 360 * free the memory occupied by @cl, and it is called with the ref on the parent 361 * closure still held - so @destructor could safely return an item to a 362 * freelist protected by @cl's parent. 363 */ 364 #define closure_return_with_destructor(_cl, _destructor) \ 365 do { \ 366 set_closure_fn(_cl, _destructor, NULL); \ 367 closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \ 368 } while (0) 369 370 /** 371 * closure_call - execute @fn out of a new, uninitialized closure 372 * 373 * Typically used when running out of one closure, and we want to run @fn 374 * asynchronously out of a new closure - @parent will then wait for @cl to 375 * finish. 376 */ 377 static inline void closure_call(struct closure *cl, closure_fn fn, 378 struct workqueue_struct *wq, 379 struct closure *parent) 380 { 381 closure_init(cl, parent); 382 continue_at_nobarrier(cl, fn, wq); 383 } 384 385 #endif /* _LINUX_CLOSURE_H */ 386