1 /* 2 * Generic wait-for-completion handler; 3 * 4 * It differs from semaphores in that their default case is the opposite, 5 * wait_for_completion default blocks whereas semaphore default non-block. The 6 * interface also makes it easy to 'complete' multiple waiting threads, 7 * something which isn't entirely natural for semaphores. 8 * 9 * But more importantly, the primitive documents the usage. Semaphores would 10 * typically be used for exclusion which gives rise to priority inversion. 11 * Waiting for completion is a typically sync point, but not an exclusion point. 12 */ 13 14 #include <linux/sched.h> 15 #include <linux/completion.h> 16 17 /** 18 * complete: - signals a single thread waiting on this completion 19 * @x: holds the state of this particular completion 20 * 21 * This will wake up a single thread waiting on this completion. Threads will be 22 * awakened in the same order in which they were queued. 23 * 24 * See also complete_all(), wait_for_completion() and related routines. 25 * 26 * It may be assumed that this function implies a write memory barrier before 27 * changing the task state if and only if any tasks are woken up. 28 */ 29 void complete(struct completion *x) 30 { 31 unsigned long flags; 32 33 spin_lock_irqsave(&x->wait.lock, flags); 34 x->done++; 35 __wake_up_locked(&x->wait, TASK_NORMAL, 1); 36 spin_unlock_irqrestore(&x->wait.lock, flags); 37 } 38 EXPORT_SYMBOL(complete); 39 40 /** 41 * complete_all: - signals all threads waiting on this completion 42 * @x: holds the state of this particular completion 43 * 44 * This will wake up all threads waiting on this particular completion event. 45 * 46 * It may be assumed that this function implies a write memory barrier before 47 * changing the task state if and only if any tasks are woken up. 48 */ 49 void complete_all(struct completion *x) 50 { 51 unsigned long flags; 52 53 spin_lock_irqsave(&x->wait.lock, flags); 54 x->done += UINT_MAX/2; 55 __wake_up_locked(&x->wait, TASK_NORMAL, 0); 56 spin_unlock_irqrestore(&x->wait.lock, flags); 57 } 58 EXPORT_SYMBOL(complete_all); 59 60 static inline long __sched 61 do_wait_for_common(struct completion *x, 62 long (*action)(long), long timeout, int state) 63 { 64 if (!x->done) { 65 DECLARE_WAITQUEUE(wait, current); 66 67 __add_wait_queue_tail_exclusive(&x->wait, &wait); 68 do { 69 if (signal_pending_state(state, current)) { 70 timeout = -ERESTARTSYS; 71 break; 72 } 73 __set_current_state(state); 74 spin_unlock_irq(&x->wait.lock); 75 timeout = action(timeout); 76 spin_lock_irq(&x->wait.lock); 77 } while (!x->done && timeout); 78 __remove_wait_queue(&x->wait, &wait); 79 if (!x->done) 80 return timeout; 81 } 82 x->done--; 83 return timeout ?: 1; 84 } 85 86 static inline long __sched 87 __wait_for_common(struct completion *x, 88 long (*action)(long), long timeout, int state) 89 { 90 might_sleep(); 91 92 spin_lock_irq(&x->wait.lock); 93 timeout = do_wait_for_common(x, action, timeout, state); 94 spin_unlock_irq(&x->wait.lock); 95 return timeout; 96 } 97 98 static long __sched 99 wait_for_common(struct completion *x, long timeout, int state) 100 { 101 return __wait_for_common(x, schedule_timeout, timeout, state); 102 } 103 104 static long __sched 105 wait_for_common_io(struct completion *x, long timeout, int state) 106 { 107 return __wait_for_common(x, io_schedule_timeout, timeout, state); 108 } 109 110 /** 111 * wait_for_completion: - waits for completion of a task 112 * @x: holds the state of this particular completion 113 * 114 * This waits to be signaled for completion of a specific task. It is NOT 115 * interruptible and there is no timeout. 116 * 117 * See also similar routines (i.e. wait_for_completion_timeout()) with timeout 118 * and interrupt capability. Also see complete(). 119 */ 120 void __sched wait_for_completion(struct completion *x) 121 { 122 wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE); 123 } 124 EXPORT_SYMBOL(wait_for_completion); 125 126 /** 127 * wait_for_completion_timeout: - waits for completion of a task (w/timeout) 128 * @x: holds the state of this particular completion 129 * @timeout: timeout value in jiffies 130 * 131 * This waits for either a completion of a specific task to be signaled or for a 132 * specified timeout to expire. The timeout is in jiffies. It is not 133 * interruptible. 134 * 135 * Return: 0 if timed out, and positive (at least 1, or number of jiffies left 136 * till timeout) if completed. 137 */ 138 unsigned long __sched 139 wait_for_completion_timeout(struct completion *x, unsigned long timeout) 140 { 141 return wait_for_common(x, timeout, TASK_UNINTERRUPTIBLE); 142 } 143 EXPORT_SYMBOL(wait_for_completion_timeout); 144 145 /** 146 * wait_for_completion_io: - waits for completion of a task 147 * @x: holds the state of this particular completion 148 * 149 * This waits to be signaled for completion of a specific task. It is NOT 150 * interruptible and there is no timeout. The caller is accounted as waiting 151 * for IO (which traditionally means blkio only). 152 */ 153 void __sched wait_for_completion_io(struct completion *x) 154 { 155 wait_for_common_io(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE); 156 } 157 EXPORT_SYMBOL(wait_for_completion_io); 158 159 /** 160 * wait_for_completion_io_timeout: - waits for completion of a task (w/timeout) 161 * @x: holds the state of this particular completion 162 * @timeout: timeout value in jiffies 163 * 164 * This waits for either a completion of a specific task to be signaled or for a 165 * specified timeout to expire. The timeout is in jiffies. It is not 166 * interruptible. The caller is accounted as waiting for IO (which traditionally 167 * means blkio only). 168 * 169 * Return: 0 if timed out, and positive (at least 1, or number of jiffies left 170 * till timeout) if completed. 171 */ 172 unsigned long __sched 173 wait_for_completion_io_timeout(struct completion *x, unsigned long timeout) 174 { 175 return wait_for_common_io(x, timeout, TASK_UNINTERRUPTIBLE); 176 } 177 EXPORT_SYMBOL(wait_for_completion_io_timeout); 178 179 /** 180 * wait_for_completion_interruptible: - waits for completion of a task (w/intr) 181 * @x: holds the state of this particular completion 182 * 183 * This waits for completion of a specific task to be signaled. It is 184 * interruptible. 185 * 186 * Return: -ERESTARTSYS if interrupted, 0 if completed. 187 */ 188 int __sched wait_for_completion_interruptible(struct completion *x) 189 { 190 long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE); 191 if (t == -ERESTARTSYS) 192 return t; 193 return 0; 194 } 195 EXPORT_SYMBOL(wait_for_completion_interruptible); 196 197 /** 198 * wait_for_completion_interruptible_timeout: - waits for completion (w/(to,intr)) 199 * @x: holds the state of this particular completion 200 * @timeout: timeout value in jiffies 201 * 202 * This waits for either a completion of a specific task to be signaled or for a 203 * specified timeout to expire. It is interruptible. The timeout is in jiffies. 204 * 205 * Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1, 206 * or number of jiffies left till timeout) if completed. 207 */ 208 long __sched 209 wait_for_completion_interruptible_timeout(struct completion *x, 210 unsigned long timeout) 211 { 212 return wait_for_common(x, timeout, TASK_INTERRUPTIBLE); 213 } 214 EXPORT_SYMBOL(wait_for_completion_interruptible_timeout); 215 216 /** 217 * wait_for_completion_killable: - waits for completion of a task (killable) 218 * @x: holds the state of this particular completion 219 * 220 * This waits to be signaled for completion of a specific task. It can be 221 * interrupted by a kill signal. 222 * 223 * Return: -ERESTARTSYS if interrupted, 0 if completed. 224 */ 225 int __sched wait_for_completion_killable(struct completion *x) 226 { 227 long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_KILLABLE); 228 if (t == -ERESTARTSYS) 229 return t; 230 return 0; 231 } 232 EXPORT_SYMBOL(wait_for_completion_killable); 233 234 /** 235 * wait_for_completion_killable_timeout: - waits for completion of a task (w/(to,killable)) 236 * @x: holds the state of this particular completion 237 * @timeout: timeout value in jiffies 238 * 239 * This waits for either a completion of a specific task to be 240 * signaled or for a specified timeout to expire. It can be 241 * interrupted by a kill signal. The timeout is in jiffies. 242 * 243 * Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1, 244 * or number of jiffies left till timeout) if completed. 245 */ 246 long __sched 247 wait_for_completion_killable_timeout(struct completion *x, 248 unsigned long timeout) 249 { 250 return wait_for_common(x, timeout, TASK_KILLABLE); 251 } 252 EXPORT_SYMBOL(wait_for_completion_killable_timeout); 253 254 /** 255 * try_wait_for_completion - try to decrement a completion without blocking 256 * @x: completion structure 257 * 258 * Return: 0 if a decrement cannot be done without blocking 259 * 1 if a decrement succeeded. 260 * 261 * If a completion is being used as a counting completion, 262 * attempt to decrement the counter without blocking. This 263 * enables us to avoid waiting if the resource the completion 264 * is protecting is not available. 265 */ 266 bool try_wait_for_completion(struct completion *x) 267 { 268 unsigned long flags; 269 int ret = 1; 270 271 /* 272 * Since x->done will need to be locked only 273 * in the non-blocking case, we check x->done 274 * first without taking the lock so we can 275 * return early in the blocking case. 276 */ 277 if (!READ_ONCE(x->done)) 278 return 0; 279 280 spin_lock_irqsave(&x->wait.lock, flags); 281 if (!x->done) 282 ret = 0; 283 else 284 x->done--; 285 spin_unlock_irqrestore(&x->wait.lock, flags); 286 return ret; 287 } 288 EXPORT_SYMBOL(try_wait_for_completion); 289 290 /** 291 * completion_done - Test to see if a completion has any waiters 292 * @x: completion structure 293 * 294 * Return: 0 if there are waiters (wait_for_completion() in progress) 295 * 1 if there are no waiters. 296 * 297 */ 298 bool completion_done(struct completion *x) 299 { 300 if (!READ_ONCE(x->done)) 301 return false; 302 303 /* 304 * If ->done, we need to wait for complete() to release ->wait.lock 305 * otherwise we can end up freeing the completion before complete() 306 * is done referencing it. 307 * 308 * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders 309 * the loads of ->done and ->wait.lock such that we cannot observe 310 * the lock before complete() acquires it while observing the ->done 311 * after it's acquired the lock. 312 */ 313 smp_rmb(); 314 spin_unlock_wait(&x->wait.lock); 315 return true; 316 } 317 EXPORT_SYMBOL(completion_done); 318