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       1                 :            : // SPDX-License-Identifier: GPL-2.0
       2                 :            : /*
       3                 :            :  * Generic wait-for-completion handler;
       4                 :            :  *
       5                 :            :  * It differs from semaphores in that their default case is the opposite,
       6                 :            :  * wait_for_completion default blocks whereas semaphore default non-block. The
       7                 :            :  * interface also makes it easy to 'complete' multiple waiting threads,
       8                 :            :  * something which isn't entirely natural for semaphores.
       9                 :            :  *
      10                 :            :  * But more importantly, the primitive documents the usage. Semaphores would
      11                 :            :  * typically be used for exclusion which gives rise to priority inversion.
      12                 :            :  * Waiting for completion is a typically sync point, but not an exclusion point.
      13                 :            :  */
      14                 :            : #include "sched.h"
      15                 :            : 
      16                 :            : /**
      17                 :            :  * complete: - signals a single thread waiting on this completion
      18                 :            :  * @x:  holds the state of this particular completion
      19                 :            :  *
      20                 :            :  * This will wake up a single thread waiting on this completion. Threads will be
      21                 :            :  * awakened in the same order in which they were queued.
      22                 :            :  *
      23                 :            :  * See also complete_all(), wait_for_completion() and related routines.
      24                 :            :  *
      25                 :            :  * If this function wakes up a task, it executes a full memory barrier before
      26                 :            :  * accessing the task state.
      27                 :            :  */
      28                 :          3 : void complete(struct completion *x)
      29                 :            : {
      30                 :            :         unsigned long flags;
      31                 :            : 
      32                 :          3 :         spin_lock_irqsave(&x->wait.lock, flags);
      33                 :            : 
      34                 :          3 :         if (x->done != UINT_MAX)
      35                 :          3 :                 x->done++;
      36                 :          3 :         __wake_up_locked(&x->wait, TASK_NORMAL, 1);
      37                 :            :         spin_unlock_irqrestore(&x->wait.lock, flags);
      38                 :          3 : }
      39                 :            : EXPORT_SYMBOL(complete);
      40                 :            : 
      41                 :            : /**
      42                 :            :  * complete_all: - signals all threads waiting on this completion
      43                 :            :  * @x:  holds the state of this particular completion
      44                 :            :  *
      45                 :            :  * This will wake up all threads waiting on this particular completion event.
      46                 :            :  *
      47                 :            :  * If this function wakes up a task, it executes a full memory barrier before
      48                 :            :  * accessing the task state.
      49                 :            :  *
      50                 :            :  * Since complete_all() sets the completion of @x permanently to done
      51                 :            :  * to allow multiple waiters to finish, a call to reinit_completion()
      52                 :            :  * must be used on @x if @x is to be used again. The code must make
      53                 :            :  * sure that all waiters have woken and finished before reinitializing
      54                 :            :  * @x. Also note that the function completion_done() can not be used
      55                 :            :  * to know if there are still waiters after complete_all() has been called.
      56                 :            :  */
      57                 :          3 : void complete_all(struct completion *x)
      58                 :            : {
      59                 :            :         unsigned long flags;
      60                 :            : 
      61                 :          3 :         spin_lock_irqsave(&x->wait.lock, flags);
      62                 :          3 :         x->done = UINT_MAX;
      63                 :          3 :         __wake_up_locked(&x->wait, TASK_NORMAL, 0);
      64                 :            :         spin_unlock_irqrestore(&x->wait.lock, flags);
      65                 :          3 : }
      66                 :            : EXPORT_SYMBOL(complete_all);
      67                 :            : 
      68                 :            : static inline long __sched
      69                 :          3 : do_wait_for_common(struct completion *x,
      70                 :            :                    long (*action)(long), long timeout, int state)
      71                 :            : {
      72                 :          3 :         if (!x->done) {
      73                 :          3 :                 DECLARE_WAITQUEUE(wait, current);
      74                 :            : 
      75                 :            :                 __add_wait_queue_entry_tail_exclusive(&x->wait, &wait);
      76                 :            :                 do {
      77                 :          3 :                         if (signal_pending_state(state, current)) {
      78                 :            :                                 timeout = -ERESTARTSYS;
      79                 :            :                                 break;
      80                 :            :                         }
      81                 :          3 :                         __set_current_state(state);
      82                 :            :                         spin_unlock_irq(&x->wait.lock);
      83                 :          3 :                         timeout = action(timeout);
      84                 :            :                         spin_lock_irq(&x->wait.lock);
      85                 :          3 :                 } while (!x->done && timeout);
      86                 :            :                 __remove_wait_queue(&x->wait, &wait);
      87                 :          3 :                 if (!x->done)
      88                 :          0 :                         return timeout;
      89                 :            :         }
      90                 :          3 :         if (x->done != UINT_MAX)
      91                 :          3 :                 x->done--;
      92                 :          3 :         return timeout ?: 1;
      93                 :            : }
      94                 :            : 
      95                 :            : static inline long __sched
      96                 :          3 : __wait_for_common(struct completion *x,
      97                 :            :                   long (*action)(long), long timeout, int state)
      98                 :            : {
      99                 :          3 :         might_sleep();
     100                 :            : 
     101                 :            :         complete_acquire(x);
     102                 :            : 
     103                 :            :         spin_lock_irq(&x->wait.lock);
     104                 :          3 :         timeout = do_wait_for_common(x, action, timeout, state);
     105                 :            :         spin_unlock_irq(&x->wait.lock);
     106                 :            : 
     107                 :            :         complete_release(x);
     108                 :            : 
     109                 :          3 :         return timeout;
     110                 :            : }
     111                 :            : 
     112                 :            : static long __sched
     113                 :            : wait_for_common(struct completion *x, long timeout, int state)
     114                 :            : {
     115                 :          3 :         return __wait_for_common(x, schedule_timeout, timeout, state);
     116                 :            : }
     117                 :            : 
     118                 :            : static long __sched
     119                 :            : wait_for_common_io(struct completion *x, long timeout, int state)
     120                 :            : {
     121                 :          3 :         return __wait_for_common(x, io_schedule_timeout, timeout, state);
     122                 :            : }
     123                 :            : 
     124                 :            : /**
     125                 :            :  * wait_for_completion: - waits for completion of a task
     126                 :            :  * @x:  holds the state of this particular completion
     127                 :            :  *
     128                 :            :  * This waits to be signaled for completion of a specific task. It is NOT
     129                 :            :  * interruptible and there is no timeout.
     130                 :            :  *
     131                 :            :  * See also similar routines (i.e. wait_for_completion_timeout()) with timeout
     132                 :            :  * and interrupt capability. Also see complete().
     133                 :            :  */
     134                 :          3 : void __sched wait_for_completion(struct completion *x)
     135                 :            : {
     136                 :            :         wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
     137                 :          3 : }
     138                 :            : EXPORT_SYMBOL(wait_for_completion);
     139                 :            : 
     140                 :            : /**
     141                 :            :  * wait_for_completion_timeout: - waits for completion of a task (w/timeout)
     142                 :            :  * @x:  holds the state of this particular completion
     143                 :            :  * @timeout:  timeout value in jiffies
     144                 :            :  *
     145                 :            :  * This waits for either a completion of a specific task to be signaled or for a
     146                 :            :  * specified timeout to expire. The timeout is in jiffies. It is not
     147                 :            :  * interruptible.
     148                 :            :  *
     149                 :            :  * Return: 0 if timed out, and positive (at least 1, or number of jiffies left
     150                 :            :  * till timeout) if completed.
     151                 :            :  */
     152                 :            : unsigned long __sched
     153                 :          3 : wait_for_completion_timeout(struct completion *x, unsigned long timeout)
     154                 :            : {
     155                 :          3 :         return wait_for_common(x, timeout, TASK_UNINTERRUPTIBLE);
     156                 :            : }
     157                 :            : EXPORT_SYMBOL(wait_for_completion_timeout);
     158                 :            : 
     159                 :            : /**
     160                 :            :  * wait_for_completion_io: - waits for completion of a task
     161                 :            :  * @x:  holds the state of this particular completion
     162                 :            :  *
     163                 :            :  * This waits to be signaled for completion of a specific task. It is NOT
     164                 :            :  * interruptible and there is no timeout. The caller is accounted as waiting
     165                 :            :  * for IO (which traditionally means blkio only).
     166                 :            :  */
     167                 :          3 : void __sched wait_for_completion_io(struct completion *x)
     168                 :            : {
     169                 :            :         wait_for_common_io(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
     170                 :          3 : }
     171                 :            : EXPORT_SYMBOL(wait_for_completion_io);
     172                 :            : 
     173                 :            : /**
     174                 :            :  * wait_for_completion_io_timeout: - waits for completion of a task (w/timeout)
     175                 :            :  * @x:  holds the state of this particular completion
     176                 :            :  * @timeout:  timeout value in jiffies
     177                 :            :  *
     178                 :            :  * This waits for either a completion of a specific task to be signaled or for a
     179                 :            :  * specified timeout to expire. The timeout is in jiffies. It is not
     180                 :            :  * interruptible. The caller is accounted as waiting for IO (which traditionally
     181                 :            :  * means blkio only).
     182                 :            :  *
     183                 :            :  * Return: 0 if timed out, and positive (at least 1, or number of jiffies left
     184                 :            :  * till timeout) if completed.
     185                 :            :  */
     186                 :            : unsigned long __sched
     187                 :          0 : wait_for_completion_io_timeout(struct completion *x, unsigned long timeout)
     188                 :            : {
     189                 :          0 :         return wait_for_common_io(x, timeout, TASK_UNINTERRUPTIBLE);
     190                 :            : }
     191                 :            : EXPORT_SYMBOL(wait_for_completion_io_timeout);
     192                 :            : 
     193                 :            : /**
     194                 :            :  * wait_for_completion_interruptible: - waits for completion of a task (w/intr)
     195                 :            :  * @x:  holds the state of this particular completion
     196                 :            :  *
     197                 :            :  * This waits for completion of a specific task to be signaled. It is
     198                 :            :  * interruptible.
     199                 :            :  *
     200                 :            :  * Return: -ERESTARTSYS if interrupted, 0 if completed.
     201                 :            :  */
     202                 :          2 : int __sched wait_for_completion_interruptible(struct completion *x)
     203                 :            : {
     204                 :            :         long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE);
     205                 :          2 :         if (t == -ERESTARTSYS)
     206                 :          0 :                 return t;
     207                 :            :         return 0;
     208                 :            : }
     209                 :            : EXPORT_SYMBOL(wait_for_completion_interruptible);
     210                 :            : 
     211                 :            : /**
     212                 :            :  * wait_for_completion_interruptible_timeout: - waits for completion (w/(to,intr))
     213                 :            :  * @x:  holds the state of this particular completion
     214                 :            :  * @timeout:  timeout value in jiffies
     215                 :            :  *
     216                 :            :  * This waits for either a completion of a specific task to be signaled or for a
     217                 :            :  * specified timeout to expire. It is interruptible. The timeout is in jiffies.
     218                 :            :  *
     219                 :            :  * Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1,
     220                 :            :  * or number of jiffies left till timeout) if completed.
     221                 :            :  */
     222                 :            : long __sched
     223                 :          0 : wait_for_completion_interruptible_timeout(struct completion *x,
     224                 :            :                                           unsigned long timeout)
     225                 :            : {
     226                 :          0 :         return wait_for_common(x, timeout, TASK_INTERRUPTIBLE);
     227                 :            : }
     228                 :            : EXPORT_SYMBOL(wait_for_completion_interruptible_timeout);
     229                 :            : 
     230                 :            : /**
     231                 :            :  * wait_for_completion_killable: - waits for completion of a task (killable)
     232                 :            :  * @x:  holds the state of this particular completion
     233                 :            :  *
     234                 :            :  * This waits to be signaled for completion of a specific task. It can be
     235                 :            :  * interrupted by a kill signal.
     236                 :            :  *
     237                 :            :  * Return: -ERESTARTSYS if interrupted, 0 if completed.
     238                 :            :  */
     239                 :          3 : int __sched wait_for_completion_killable(struct completion *x)
     240                 :            : {
     241                 :            :         long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_KILLABLE);
     242                 :          3 :         if (t == -ERESTARTSYS)
     243                 :          0 :                 return t;
     244                 :            :         return 0;
     245                 :            : }
     246                 :            : EXPORT_SYMBOL(wait_for_completion_killable);
     247                 :            : 
     248                 :            : /**
     249                 :            :  * wait_for_completion_killable_timeout: - waits for completion of a task (w/(to,killable))
     250                 :            :  * @x:  holds the state of this particular completion
     251                 :            :  * @timeout:  timeout value in jiffies
     252                 :            :  *
     253                 :            :  * This waits for either a completion of a specific task to be
     254                 :            :  * signaled or for a specified timeout to expire. It can be
     255                 :            :  * interrupted by a kill signal. The timeout is in jiffies.
     256                 :            :  *
     257                 :            :  * Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1,
     258                 :            :  * or number of jiffies left till timeout) if completed.
     259                 :            :  */
     260                 :            : long __sched
     261                 :          3 : wait_for_completion_killable_timeout(struct completion *x,
     262                 :            :                                      unsigned long timeout)
     263                 :            : {
     264                 :          3 :         return wait_for_common(x, timeout, TASK_KILLABLE);
     265                 :            : }
     266                 :            : EXPORT_SYMBOL(wait_for_completion_killable_timeout);
     267                 :            : 
     268                 :            : /**
     269                 :            :  *      try_wait_for_completion - try to decrement a completion without blocking
     270                 :            :  *      @x:     completion structure
     271                 :            :  *
     272                 :            :  *      Return: 0 if a decrement cannot be done without blocking
     273                 :            :  *               1 if a decrement succeeded.
     274                 :            :  *
     275                 :            :  *      If a completion is being used as a counting completion,
     276                 :            :  *      attempt to decrement the counter without blocking. This
     277                 :            :  *      enables us to avoid waiting if the resource the completion
     278                 :            :  *      is protecting is not available.
     279                 :            :  */
     280                 :          2 : bool try_wait_for_completion(struct completion *x)
     281                 :            : {
     282                 :            :         unsigned long flags;
     283                 :            :         bool ret = true;
     284                 :            : 
     285                 :            :         /*
     286                 :            :          * Since x->done will need to be locked only
     287                 :            :          * in the non-blocking case, we check x->done
     288                 :            :          * first without taking the lock so we can
     289                 :            :          * return early in the blocking case.
     290                 :            :          */
     291                 :          2 :         if (!READ_ONCE(x->done))
     292                 :            :                 return false;
     293                 :            : 
     294                 :          2 :         spin_lock_irqsave(&x->wait.lock, flags);
     295                 :          2 :         if (!x->done)
     296                 :            :                 ret = false;
     297                 :          2 :         else if (x->done != UINT_MAX)
     298                 :          2 :                 x->done--;
     299                 :            :         spin_unlock_irqrestore(&x->wait.lock, flags);
     300                 :          2 :         return ret;
     301                 :            : }
     302                 :            : EXPORT_SYMBOL(try_wait_for_completion);
     303                 :            : 
     304                 :            : /**
     305                 :            :  *      completion_done - Test to see if a completion has any waiters
     306                 :            :  *      @x:     completion structure
     307                 :            :  *
     308                 :            :  *      Return: 0 if there are waiters (wait_for_completion() in progress)
     309                 :            :  *               1 if there are no waiters.
     310                 :            :  *
     311                 :            :  *      Note, this will always return true if complete_all() was called on @X.
     312                 :            :  */
     313                 :          0 : bool completion_done(struct completion *x)
     314                 :            : {
     315                 :            :         unsigned long flags;
     316                 :            : 
     317                 :          0 :         if (!READ_ONCE(x->done))
     318                 :            :                 return false;
     319                 :            : 
     320                 :            :         /*
     321                 :            :          * If ->done, we need to wait for complete() to release ->wait.lock
     322                 :            :          * otherwise we can end up freeing the completion before complete()
     323                 :            :          * is done referencing it.
     324                 :            :          */
     325                 :          0 :         spin_lock_irqsave(&x->wait.lock, flags);
     326                 :            :         spin_unlock_irqrestore(&x->wait.lock, flags);
     327                 :          0 :         return true;
     328                 :            : }
     329                 :            : EXPORT_SYMBOL(completion_done);