1// SPDX-License-Identifier: GPL-2.0-only 2/* 3 * Generic waiting primitives. 4 * 5 * (C) 2004 Nadia Yvette Chambers, Oracle 6 */ 7 8void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key) 9{ 10 spin_lock_init(&wq_head->lock); 11 lockdep_set_class_and_name(&wq_head->lock, key, name); 12 INIT_LIST_HEAD(&wq_head->head); 13} 14 15EXPORT_SYMBOL(__init_waitqueue_head); 16 17void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) 18{ 19 unsigned long flags; 20 21 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; 22 spin_lock_irqsave(&wq_head->lock, flags); 23 __add_wait_queue(wq_head, wq_entry); 24 spin_unlock_irqrestore(&wq_head->lock, flags); 25} 26EXPORT_SYMBOL(add_wait_queue); 27 28void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) 29{ 30 unsigned long flags; 31 32 wq_entry->flags |= WQ_FLAG_EXCLUSIVE; 33 spin_lock_irqsave(&wq_head->lock, flags); 34 __add_wait_queue_entry_tail(wq_head, wq_entry); 35 spin_unlock_irqrestore(&wq_head->lock, flags); 36} 37EXPORT_SYMBOL(add_wait_queue_exclusive); 38 39void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) 40{ 41 unsigned long flags; 42 43 wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY; 44 spin_lock_irqsave(&wq_head->lock, flags); 45 __add_wait_queue(wq_head, wq_entry); 46 spin_unlock_irqrestore(&wq_head->lock, flags); 47} 48EXPORT_SYMBOL_GPL(add_wait_queue_priority); 49 50void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) 51{ 52 unsigned long flags; 53 54 spin_lock_irqsave(&wq_head->lock, flags); 55 __remove_wait_queue(wq_head, wq_entry); 56 spin_unlock_irqrestore(&wq_head->lock, flags); 57} 58EXPORT_SYMBOL(remove_wait_queue); 59 60/* 61 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just 62 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve 63 * number) then we wake that number of exclusive tasks, and potentially all 64 * the non-exclusive tasks. Normally, exclusive tasks will be at the end of 65 * the list and any non-exclusive tasks will be woken first. A priority task 66 * may be at the head of the list, and can consume the event without any other 67 * tasks being woken. 68 * 69 * There are circumstances in which we can try to wake a task which has already 70 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns 71 * zero in this (rare) case, and we handle it by continuing to scan the queue. 72 */ 73static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode, 74 int nr_exclusive, int wake_flags, void *key) 75{ 76 wait_queue_entry_t *curr, *next; 77 78 lockdep_assert_held(&wq_head->lock); 79 80 curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry); 81 82 if (&curr->entry == &wq_head->head) 83 return nr_exclusive; 84 85 list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) { 86 unsigned flags = curr->flags; 87 int ret; 88 89 ret = curr->func(curr, mode, wake_flags, key); 90 if (ret < 0) 91 break; 92 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) 93 break; 94 } 95 96 return nr_exclusive; 97} 98 99static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode, 100 int nr_exclusive, int wake_flags, void *key) 101{ 102 unsigned long flags; 103 int remaining; 104 105 spin_lock_irqsave(&wq_head->lock, flags); 106 remaining = __wake_up_common(wq_head, mode, nr_exclusive, wake_flags, 107 key); 108 spin_unlock_irqrestore(&wq_head->lock, flags); 109 110 return nr_exclusive - remaining; 111} 112 113/** 114 * __wake_up - wake up threads blocked on a waitqueue. 115 * @wq_head: the waitqueue 116 * @mode: which threads 117 * @nr_exclusive: how many wake-one or wake-many threads to wake up 118 * @key: is directly passed to the wakeup function 119 * 120 * If this function wakes up a task, it executes a full memory barrier 121 * before accessing the task state. Returns the number of exclusive 122 * tasks that were awaken. 123 */ 124int __wake_up(struct wait_queue_head *wq_head, unsigned int mode, 125 int nr_exclusive, void *key) 126{ 127 return __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key); 128} 129EXPORT_SYMBOL(__wake_up); 130 131void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, void *key) 132{ 133 __wake_up_common_lock(wq_head, mode, 1, WF_CURRENT_CPU, key); 134} 135 136/* 137 * Same as __wake_up but called with the spinlock in wait_queue_head_t held. 138 */ 139void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr) 140{ 141 __wake_up_common(wq_head, mode, nr, 0, NULL); 142} 143EXPORT_SYMBOL_GPL(__wake_up_locked); 144 145void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key) 146{ 147 __wake_up_common(wq_head, mode, 1, 0, key); 148} 149EXPORT_SYMBOL_GPL(__wake_up_locked_key); 150 151/** 152 * __wake_up_sync_key - wake up threads blocked on a waitqueue. 153 * @wq_head: the waitqueue 154 * @mode: which threads 155 * @key: opaque value to be passed to wakeup targets 156 * 157 * The sync wakeup differs that the waker knows that it will schedule 158 * away soon, so while the target thread will be woken up, it will not 159 * be migrated to another CPU - ie. the two threads are 'synchronized' 160 * with each other. This can prevent needless bouncing between CPUs. 161 * 162 * On UP it can prevent extra preemption. 163 * 164 * If this function wakes up a task, it executes a full memory barrier before 165 * accessing the task state. 166 */ 167void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, 168 void *key) 169{ 170 if (unlikely(!wq_head)) 171 return; 172 173 __wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key); 174} 175EXPORT_SYMBOL_GPL(__wake_up_sync_key); 176 177/** 178 * __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue. 179 * @wq_head: the waitqueue 180 * @mode: which threads 181 * @key: opaque value to be passed to wakeup targets 182 * 183 * The sync wakeup differs in that the waker knows that it will schedule 184 * away soon, so while the target thread will be woken up, it will not 185 * be migrated to another CPU - ie. the two threads are 'synchronized' 186 * with each other. This can prevent needless bouncing between CPUs. 187 * 188 * On UP it can prevent extra preemption. 189 * 190 * If this function wakes up a task, it executes a full memory barrier before 191 * accessing the task state. 192 */ 193void __wake_up_locked_sync_key(struct wait_queue_head *wq_head, 194 unsigned int mode, void *key) 195{ 196 __wake_up_common(wq_head, mode, 1, WF_SYNC, key); 197} 198EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key); 199 200/* 201 * __wake_up_sync - see __wake_up_sync_key() 202 */ 203void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode) 204{ 205 __wake_up_sync_key(wq_head, mode, NULL); 206} 207EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */ 208 209void __wake_up_pollfree(struct wait_queue_head *wq_head) 210{ 211 __wake_up(wq_head, TASK_NORMAL, 0, poll_to_key(EPOLLHUP | POLLFREE)); 212 /* POLLFREE must have cleared the queue. */ 213 WARN_ON_ONCE(waitqueue_active(wq_head)); 214} 215 216/* 217 * Note: we use "set_current_state()" _after_ the wait-queue add, 218 * because we need a memory barrier there on SMP, so that any 219 * wake-function that tests for the wait-queue being active 220 * will be guaranteed to see waitqueue addition _or_ subsequent 221 * tests in this thread will see the wakeup having taken place. 222 * 223 * The spin_unlock() itself is semi-permeable and only protects 224 * one way (it only protects stuff inside the critical region and 225 * stops them from bleeding out - it would still allow subsequent 226 * loads to move into the critical region). 227 */ 228void 229prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) 230{ 231 unsigned long flags; 232 233 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; 234 spin_lock_irqsave(&wq_head->lock, flags); 235 if (list_empty(&wq_entry->entry)) 236 __add_wait_queue(wq_head, wq_entry); 237 set_current_state(state); 238 spin_unlock_irqrestore(&wq_head->lock, flags); 239} 240EXPORT_SYMBOL(prepare_to_wait); 241 242/* Returns true if we are the first waiter in the queue, false otherwise. */ 243bool 244prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) 245{ 246 unsigned long flags; 247 bool was_empty = false; 248 249 wq_entry->flags |= WQ_FLAG_EXCLUSIVE; 250 spin_lock_irqsave(&wq_head->lock, flags); 251 if (list_empty(&wq_entry->entry)) { 252 was_empty = list_empty(&wq_head->head); 253 __add_wait_queue_entry_tail(wq_head, wq_entry); 254 } 255 set_current_state(state); 256 spin_unlock_irqrestore(&wq_head->lock, flags); 257 return was_empty; 258} 259EXPORT_SYMBOL(prepare_to_wait_exclusive); 260 261void init_wait_entry(struct wait_queue_entry *wq_entry, int flags) 262{ 263 wq_entry->flags = flags; 264 wq_entry->private = current; 265 wq_entry->func = autoremove_wake_function; 266 INIT_LIST_HEAD(&wq_entry->entry); 267} 268EXPORT_SYMBOL(init_wait_entry); 269 270long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) 271{ 272 unsigned long flags; 273 long ret = 0; 274 275 spin_lock_irqsave(&wq_head->lock, flags); 276 if (signal_pending_state(state, current)) { 277 /* 278 * Exclusive waiter must not fail if it was selected by wakeup, 279 * it should "consume" the condition we were waiting for. 280 * 281 * The caller will recheck the condition and return success if 282 * we were already woken up, we can not miss the event because 283 * wakeup locks/unlocks the same wq_head->lock. 284 * 285 * But we need to ensure that set-condition + wakeup after that 286 * can't see us, it should wake up another exclusive waiter if 287 * we fail. 288 */ 289 list_del_init(&wq_entry->entry); 290 ret = -ERESTARTSYS; 291 } else { 292 if (list_empty(&wq_entry->entry)) { 293 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE) 294 __add_wait_queue_entry_tail(wq_head, wq_entry); 295 else 296 __add_wait_queue(wq_head, wq_entry); 297 } 298 set_current_state(state); 299 } 300 spin_unlock_irqrestore(&wq_head->lock, flags); 301 302 return ret; 303} 304EXPORT_SYMBOL(prepare_to_wait_event); 305 306/* 307 * Note! These two wait functions are entered with the 308 * wait-queue lock held (and interrupts off in the _irq 309 * case), so there is no race with testing the wakeup 310 * condition in the caller before they add the wait 311 * entry to the wake queue. 312 */ 313int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait) 314{ 315 if (likely(list_empty(&wait->entry))) 316 __add_wait_queue_entry_tail(wq, wait); 317 318 set_current_state(TASK_INTERRUPTIBLE); 319 if (signal_pending(current)) 320 return -ERESTARTSYS; 321 322 spin_unlock(&wq->lock); 323 schedule(); 324 spin_lock(&wq->lock); 325 326 return 0; 327} 328EXPORT_SYMBOL(do_wait_intr); 329 330int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait) 331{ 332 if (likely(list_empty(&wait->entry))) 333 __add_wait_queue_entry_tail(wq, wait); 334 335 set_current_state(TASK_INTERRUPTIBLE); 336 if (signal_pending(current)) 337 return -ERESTARTSYS; 338 339 spin_unlock_irq(&wq->lock); 340 schedule(); 341 spin_lock_irq(&wq->lock); 342 343 return 0; 344} 345EXPORT_SYMBOL(do_wait_intr_irq); 346 347/** 348 * finish_wait - clean up after waiting in a queue 349 * @wq_head: waitqueue waited on 350 * @wq_entry: wait descriptor 351 * 352 * Sets current thread back to running state and removes 353 * the wait descriptor from the given waitqueue if still 354 * queued. 355 */ 356void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) 357{ 358 unsigned long flags; 359 360 __set_current_state(TASK_RUNNING); 361 /* 362 * We can check for list emptiness outside the lock 363 * IFF: 364 * - we use the "careful" check that verifies both 365 * the next and prev pointers, so that there cannot 366 * be any half-pending updates in progress on other 367 * CPU's that we haven't seen yet (and that might 368 * still change the stack area. 369 * and 370 * - all other users take the lock (ie we can only 371 * have _one_ other CPU that looks at or modifies 372 * the list). 373 */ 374 if (!list_empty_careful(&wq_entry->entry)) { 375 spin_lock_irqsave(&wq_head->lock, flags); 376 list_del_init(&wq_entry->entry); 377 spin_unlock_irqrestore(&wq_head->lock, flags); 378 } 379} 380EXPORT_SYMBOL(finish_wait); 381 382int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key) 383{ 384 int ret = default_wake_function(wq_entry, mode, sync, key); 385 386 if (ret) 387 list_del_init_careful(&wq_entry->entry); 388 389 return ret; 390} 391EXPORT_SYMBOL(autoremove_wake_function); 392 393/* 394 * DEFINE_WAIT_FUNC(wait, woken_wake_func); 395 * 396 * add_wait_queue(&wq_head, &wait); 397 * for (;;) { 398 * if (condition) 399 * break; 400 * 401 * // in wait_woken() // in woken_wake_function() 402 * 403 * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN; 404 * smp_mb(); // A try_to_wake_up(): 405 * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier> 406 * schedule() if (p->state & mode) 407 * p->state = TASK_RUNNING; p->state = TASK_RUNNING; 408 * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~ 409 * smp_mb(); // B condition = true; 410 * } smp_mb(); // C 411 * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN; 412 */ 413long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout) 414{ 415 /* 416 * The below executes an smp_mb(), which matches with the full barrier 417 * executed by the try_to_wake_up() in woken_wake_function() such that 418 * either we see the store to wq_entry->flags in woken_wake_function() 419 * or woken_wake_function() sees our store to current->state. 420 */ 421 set_current_state(mode); /* A */ 422 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !kthread_should_stop_or_park()) 423 timeout = schedule_timeout(timeout); 424 __set_current_state(TASK_RUNNING); 425 426 /* 427 * The below executes an smp_mb(), which matches with the smp_mb() (C) 428 * in woken_wake_function() such that either we see the wait condition 429 * being true or the store to wq_entry->flags in woken_wake_function() 430 * follows ours in the coherence order. 431 */ 432 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */ 433 434 return timeout; 435} 436EXPORT_SYMBOL(wait_woken); 437 438int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key) 439{ 440 /* Pairs with the smp_store_mb() in wait_woken(). */ 441 smp_mb(); /* C */ 442 wq_entry->flags |= WQ_FLAG_WOKEN; 443 444 return default_wake_function(wq_entry, mode, sync, key); 445} 446EXPORT_SYMBOL(woken_wake_function); 447