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  1. /*
  2.  * Copyright (C) 2001-2004 Jakub Jermar
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  *
  9.  * - Redistributions of source code must retain the above copyright
  10.  *   notice, this list of conditions and the following disclaimer.
  11.  * - Redistributions in binary form must reproduce the above copyright
  12.  *   notice, this list of conditions and the following disclaimer in the
  13.  *   documentation and/or other materials provided with the distribution.
  14.  * - The name of the author may not be used to endorse or promote products
  15.  *   derived from this software without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18.  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20.  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23.  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24.  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25.  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26.  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27.  */
  28.  
  29.  /** @addtogroup sync
  30.  * @{
  31.  */
  32.  
  33. /**
  34.  * @file
  35.  * @brief   Wait queue.
  36.  *
  37.  * Wait queue is the basic synchronization primitive upon which all
  38.  * other synchronization primitives build.
  39.  *
  40.  * It allows threads to wait for an event in first-come, first-served
  41.  * fashion. Conditional operation as well as timeouts and interruptions
  42.  * are supported.
  43.  */
  44.  
  45. #include <synch/waitq.h>
  46. #include <synch/synch.h>
  47. #include <synch/spinlock.h>
  48. #include <proc/thread.h>
  49. #include <proc/scheduler.h>
  50. #include <arch/asm.h>
  51. #include <arch/types.h>
  52. #include <typedefs.h>
  53. #include <time/timeout.h>
  54. #include <arch.h>
  55. #include <context.h>
  56. #include <adt/list.h>
  57.  
  58. static void waitq_timeouted_sleep(void *data);
  59.  
  60. /** Initialize wait queue
  61.  *
  62.  * Initialize wait queue.
  63.  *
  64.  * @param wq Pointer to wait queue to be initialized.
  65.  */
  66. void waitq_initialize(waitq_t *wq)
  67. {
  68.     spinlock_initialize(&wq->lock, "waitq_lock");
  69.     list_initialize(&wq->head);
  70.     wq->missed_wakeups = 0;
  71. }
  72.  
  73. /** Handle timeout during waitq_sleep_timeout() call
  74.  *
  75.  * This routine is called when waitq_sleep_timeout() timeouts.
  76.  * Interrupts are disabled.
  77.  *
  78.  * It is supposed to try to remove 'its' thread from the wait queue;
  79.  * it can eventually fail to achieve this goal when these two events
  80.  * overlap. In that case it behaves just as though there was no
  81.  * timeout at all.
  82.  *
  83.  * @param data Pointer to the thread that called waitq_sleep_timeout().
  84.  */
  85. void waitq_timeouted_sleep(void *data)
  86. {
  87.     thread_t *t = (thread_t *) data;
  88.     waitq_t *wq;
  89.     bool do_wakeup = false;
  90.  
  91.     spinlock_lock(&threads_lock);
  92.     if (!thread_exists(t))
  93.         goto out;
  94.  
  95. grab_locks:
  96.     spinlock_lock(&t->lock);
  97.     if ((wq = t->sleep_queue)) {        /* assignment */
  98.         if (!spinlock_trylock(&wq->lock)) {
  99.             spinlock_unlock(&t->lock);
  100.             goto grab_locks;    /* avoid deadlock */
  101.         }
  102.  
  103.         list_remove(&t->wq_link);
  104.         t->saved_context = t->sleep_timeout_context;
  105.         do_wakeup = true;
  106.         t->sleep_queue = NULL;
  107.         spinlock_unlock(&wq->lock);
  108.     }
  109.    
  110.     t->timeout_pending = false;
  111.     spinlock_unlock(&t->lock);
  112.    
  113.     if (do_wakeup)
  114.         thread_ready(t);
  115.  
  116. out:
  117.     spinlock_unlock(&threads_lock);
  118. }
  119.  
  120. /** Interrupt sleeping thread.
  121.  *
  122.  * This routine attempts to interrupt a thread from its sleep in a waitqueue.
  123.  * If the thread is not found sleeping, no action is taken.
  124.  *
  125.  * @param t Thread to be interrupted.
  126.  */
  127. void waitq_interrupt_sleep(thread_t *t)
  128. {
  129.     waitq_t *wq;
  130.     bool do_wakeup = false;
  131.     ipl_t ipl;
  132.  
  133.     ipl = interrupts_disable();
  134.     spinlock_lock(&threads_lock);
  135.     if (!thread_exists(t))
  136.         goto out;
  137.  
  138. grab_locks:
  139.     spinlock_lock(&t->lock);
  140.     if ((wq = t->sleep_queue)) {        /* assignment */
  141.         if (!(t->sleep_interruptible)) {
  142.             /*
  143.              * The sleep cannot be interrupted.
  144.              */
  145.             spinlock_unlock(&t->lock);
  146.             goto out;
  147.         }
  148.            
  149.         if (!spinlock_trylock(&wq->lock)) {
  150.             spinlock_unlock(&t->lock);
  151.             goto grab_locks;    /* avoid deadlock */
  152.         }
  153.  
  154.         if (t->timeout_pending && timeout_unregister(&t->sleep_timeout))
  155.             t->timeout_pending = false;
  156.  
  157.         list_remove(&t->wq_link);
  158.         t->saved_context = t->sleep_interruption_context;
  159.         do_wakeup = true;
  160.         t->sleep_queue = NULL;
  161.         spinlock_unlock(&wq->lock);
  162.     }
  163.     spinlock_unlock(&t->lock);
  164.  
  165.     if (do_wakeup)
  166.         thread_ready(t);
  167.  
  168. out:
  169.     spinlock_unlock(&threads_lock);
  170.     interrupts_restore(ipl);
  171. }
  172.  
  173. /** Sleep until either wakeup, timeout or interruption occurs
  174.  *
  175.  * This is a sleep implementation which allows itself to time out or to be
  176.  * interrupted from the sleep, restoring a failover context.
  177.  *
  178.  * Sleepers are organised in a FIFO fashion in a structure called wait queue.
  179.  *
  180.  * This function is really basic in that other functions as waitq_sleep()
  181.  * and all the *_timeout() functions use it.
  182.  *
  183.  * @param wq Pointer to wait queue.
  184.  * @param usec Timeout in microseconds.
  185.  * @param flags Specify mode of the sleep.
  186.  *
  187.  * The sleep can be interrupted only if the
  188.  * SYNCH_FLAGS_INTERRUPTIBLE bit is specified in flags.
  189.  
  190.  * If usec is greater than zero, regardless of the value of the
  191.  * SYNCH_FLAGS_NON_BLOCKING bit in flags, the call will not return until either timeout,
  192.  * interruption or wakeup comes.
  193.  *
  194.  * If usec is zero and the SYNCH_FLAGS_NON_BLOCKING bit is not set in flags, the call
  195.  * will not return until wakeup or interruption comes.
  196.  *
  197.  * If usec is zero and the SYNCH_FLAGS_NON_BLOCKING bit is set in flags, the call will
  198.  * immediately return, reporting either success or failure.
  199.  *
  200.  * @return  Returns one of: ESYNCH_WOULD_BLOCK, ESYNCH_TIMEOUT, ESYNCH_INTERRUPTED,
  201.  *          ESYNCH_OK_ATOMIC, ESYNCH_OK_BLOCKED.
  202.  *
  203.  * @li ESYNCH_WOULD_BLOCK means that the sleep failed because at the time
  204.  * of the call there was no pending wakeup.
  205.  *
  206.  * @li ESYNCH_TIMEOUT means that the sleep timed out.
  207.  *
  208.  * @li ESYNCH_INTERRUPTED means that somebody interrupted the sleeping thread.
  209.  *
  210.  * @li ESYNCH_OK_ATOMIC means that the sleep succeeded and that there was
  211.  * a pending wakeup at the time of the call. The caller was not put
  212.  * asleep at all.
  213.  *
  214.  * @li ESYNCH_OK_BLOCKED means that the sleep succeeded; the full sleep was
  215.  * attempted.
  216.  */
  217. int waitq_sleep_timeout(waitq_t *wq, __u32 usec, int flags)
  218. {
  219.     ipl_t ipl;
  220.     int rc;
  221.    
  222.     ipl = waitq_sleep_prepare(wq);
  223.     rc = waitq_sleep_timeout_unsafe(wq, usec, flags);
  224.     waitq_sleep_finish(wq, rc, ipl);
  225.     return rc;
  226. }
  227.  
  228. /** Prepare to sleep in a waitq.
  229.  *
  230.  * This function will return holding the lock of the wait queue
  231.  * and interrupts disabled.
  232.  *
  233.  * @param wq Wait queue.
  234.  *
  235.  * @return Interrupt level as it existed on entry to this function.
  236.  */
  237. ipl_t waitq_sleep_prepare(waitq_t *wq)
  238. {
  239.     ipl_t ipl;
  240.    
  241. restart:
  242.     ipl = interrupts_disable();
  243.  
  244.     if (THREAD) {   /* needed during system initiailzation */
  245.         /*
  246.          * Busy waiting for a delayed timeout.
  247.          * This is an important fix for the race condition between
  248.          * a delayed timeout and a next call to waitq_sleep_timeout().
  249.          * Simply, the thread is not allowed to go to sleep if
  250.          * there are timeouts in progress.
  251.          */
  252.         spinlock_lock(&THREAD->lock);
  253.         if (THREAD->timeout_pending) {
  254.             spinlock_unlock(&THREAD->lock);
  255.             interrupts_restore(ipl);
  256.             goto restart;
  257.         }
  258.         spinlock_unlock(&THREAD->lock);
  259.     }
  260.                                                    
  261.     spinlock_lock(&wq->lock);
  262.     return ipl;
  263. }
  264.  
  265. /** Finish waiting in a wait queue.
  266.  *
  267.  * This function restores interrupts to the state that existed prior
  268.  * to the call to waitq_sleep_prepare(). If necessary, the wait queue
  269.  * lock is released.
  270.  *
  271.  * @param wq Wait queue.
  272.  * @param rc Return code of waitq_sleep_timeout_unsafe().
  273.  * @param ipl Interrupt level returned by waitq_sleep_prepare().
  274.  */
  275. void waitq_sleep_finish(waitq_t *wq, int rc, ipl_t ipl)
  276. {
  277.     switch (rc) {
  278.     case ESYNCH_WOULD_BLOCK:
  279.     case ESYNCH_OK_ATOMIC:
  280.         spinlock_unlock(&wq->lock);
  281.         break;
  282.     default:
  283.         break;
  284.     }
  285.     interrupts_restore(ipl);
  286. }
  287.  
  288. /** Internal implementation of waitq_sleep_timeout().
  289.  *
  290.  * This function implements logic of sleeping in a wait queue.
  291.  * This call must be preceeded by a call to waitq_sleep_prepare()
  292.  * and followed by a call to waitq_slee_finish().
  293.  *
  294.  * @param wq See waitq_sleep_timeout().
  295.  * @param usec See waitq_sleep_timeout().
  296.  * @param flags See waitq_sleep_timeout().
  297.  *
  298.  * @return See waitq_sleep_timeout().
  299.  */
  300. int waitq_sleep_timeout_unsafe(waitq_t *wq, __u32 usec, int flags)
  301. {
  302.     /* checks whether to go to sleep at all */
  303.     if (wq->missed_wakeups) {
  304.         wq->missed_wakeups--;
  305.         return ESYNCH_OK_ATOMIC;
  306.     }
  307.     else {
  308.         if ((flags & SYNCH_FLAGS_NON_BLOCKING) && (usec == 0)) {
  309.             /* return immediatelly instead of going to sleep */
  310.             return ESYNCH_WOULD_BLOCK;
  311.         }
  312.     }
  313.    
  314.     /*
  315.      * Now we are firmly decided to go to sleep.
  316.      */
  317.     spinlock_lock(&THREAD->lock);
  318.  
  319.     if (flags & SYNCH_FLAGS_INTERRUPTIBLE) {
  320.  
  321.         /*
  322.          * If the thread was already interrupted,
  323.          * don't go to sleep at all.
  324.          */
  325.         if (THREAD->interrupted) {
  326.             spinlock_unlock(&THREAD->lock);
  327.             spinlock_unlock(&wq->lock);
  328.             return ESYNCH_INTERRUPTED;
  329.         }
  330.  
  331.         /*
  332.          * Set context that will be restored if the sleep
  333.          * of this thread is ever interrupted.
  334.          */
  335.         THREAD->sleep_interruptible = true;
  336.         if (!context_save(&THREAD->sleep_interruption_context)) {
  337.             /* Short emulation of scheduler() return code. */
  338.             spinlock_unlock(&THREAD->lock);
  339.             return ESYNCH_INTERRUPTED;
  340.         }
  341.  
  342.     } else {
  343.         THREAD->sleep_interruptible = false;
  344.     }
  345.  
  346.     if (usec) {
  347.         /* We use the timeout variant. */
  348.         if (!context_save(&THREAD->sleep_timeout_context)) {
  349.             /* Short emulation of scheduler() return code. */
  350.             spinlock_unlock(&THREAD->lock);
  351.             return ESYNCH_TIMEOUT;
  352.         }
  353.         THREAD->timeout_pending = true;
  354.         timeout_register(&THREAD->sleep_timeout, (__u64) usec, waitq_timeouted_sleep, THREAD);
  355.     }
  356.  
  357.     list_append(&THREAD->wq_link, &wq->head);
  358.  
  359.     /*
  360.      * Suspend execution.
  361.      */
  362.     THREAD->state = Sleeping;
  363.     THREAD->sleep_queue = wq;
  364.  
  365.     spinlock_unlock(&THREAD->lock);
  366.  
  367.     scheduler();    /* wq->lock is released in scheduler_separated_stack() */
  368.    
  369.     return ESYNCH_OK_BLOCKED;
  370. }
  371.  
  372.  
  373. /** Wake up first thread sleeping in a wait queue
  374.  *
  375.  * Wake up first thread sleeping in a wait queue.
  376.  * This is the SMP- and IRQ-safe wrapper meant for
  377.  * general use.
  378.  *
  379.  * Besides its 'normal' wakeup operation, it attempts
  380.  * to unregister possible timeout.
  381.  *
  382.  * @param wq Pointer to wait queue.
  383.  * @param all If this is non-zero, all sleeping threads
  384.  *        will be woken up and missed count will be zeroed.
  385.  */
  386. void waitq_wakeup(waitq_t *wq, bool all)
  387. {
  388.     ipl_t ipl;
  389.  
  390.     ipl = interrupts_disable();
  391.     spinlock_lock(&wq->lock);
  392.  
  393.     _waitq_wakeup_unsafe(wq, all);
  394.  
  395.     spinlock_unlock(&wq->lock);
  396.     interrupts_restore(ipl);   
  397. }
  398.  
  399. /** Internal SMP- and IRQ-unsafe version of waitq_wakeup()
  400.  *
  401.  * This is the internal SMP- and IRQ-unsafe version
  402.  * of waitq_wakeup(). It assumes wq->lock is already
  403.  * locked and interrupts are already disabled.
  404.  *
  405.  * @param wq Pointer to wait queue.
  406.  * @param all If this is non-zero, all sleeping threads
  407.  *        will be woken up and missed count will be zeroed.
  408.  */
  409. void _waitq_wakeup_unsafe(waitq_t *wq, bool all)
  410. {
  411.     thread_t *t;
  412.  
  413. loop:  
  414.     if (list_empty(&wq->head)) {
  415.         wq->missed_wakeups++;
  416.         if (all)
  417.             wq->missed_wakeups = 0;
  418.         return;
  419.     }
  420.  
  421.     t = list_get_instance(wq->head.next, thread_t, wq_link);
  422.    
  423.     /*
  424.      * Lock the thread prior to removing it from the wq.
  425.      * This is not necessary because of mutual exclusion
  426.      * (the link belongs to the wait queue), but because
  427.      * of synchronization with waitq_timeouted_sleep()
  428.      * and waitq_interrupt_sleep().
  429.      *
  430.      * In order for these two functions to work, the following
  431.      * invariant must hold:
  432.      *
  433.      * t->sleep_queue != NULL <=> t sleeps in a wait queue
  434.      *
  435.      * For an observer who locks the thread, the invariant
  436.      * holds only when the lock is held prior to removing
  437.      * it from the wait queue.
  438.      */
  439.     spinlock_lock(&t->lock);
  440.     list_remove(&t->wq_link);
  441.    
  442.     if (t->timeout_pending && timeout_unregister(&t->sleep_timeout))
  443.         t->timeout_pending = false;
  444.     t->sleep_queue = NULL;
  445.     spinlock_unlock(&t->lock);
  446.  
  447.     thread_ready(t);
  448.  
  449.     if (all)
  450.         goto loop;
  451. }
  452.  
  453.  /** @}
  454.  */
  455.  
  456.