LCOV - code coverage report
Current view: top level - kernel/sched - wait.c (source / functions) Hit Total Coverage
Test: Real Lines: 100 121 82.6 %
Date: 2020-10-17 15:46:16 Functions: 1 23 4.3 %
Legend: Neither, QEMU, Real, Both Branches: 0 0 -

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

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