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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. /**
  30.  * @file    waitq.c
  31.  * @brief   Wait queue.
  32.  *
  33.  * Wait queue is the basic synchronization primitive upon which all
  34.  * other synchronization primitives build.
  35.  *
  36.  * It allows threads to wait for an event in first-come, first-served
  37.  * fashion. Conditional operation as well as timeouts and interruptions
  38.  * are supported.
  39.  */
  40.  
  41. #include <synch/waitq.h>
  42. #include <synch/synch.h>
  43. #include <synch/spinlock.h>
  44. #include <proc/thread.h>
  45. #include <proc/scheduler.h>
  46. #include <arch/asm.h>
  47. #include <arch/types.h>
  48. #include <typedefs.h>
  49. #include <time/timeout.h>
  50. #include <arch.h>
  51. #include <context.h>
  52. #include <adt/list.h>
  53.  
  54. static void waitq_timeouted_sleep(void *data);
  55.  
  56. /** Initialize wait queue
  57.  *
  58.  * Initialize wait queue.
  59.  *
  60.  * @param wq Pointer to wait queue to be initialized.
  61.  */
  62. void waitq_initialize(waitq_t *wq)
  63. {
  64.     spinlock_initialize(&wq->lock, "waitq_lock");
  65.     list_initialize(&wq->head);
  66.     wq->missed_wakeups = 0;
  67. }
  68.  
  69. /** Handle timeout during waitq_sleep_timeout() call
  70.  *
  71.  * This routine is called when waitq_sleep_timeout() timeouts.
  72.  * Interrupts are disabled.
  73.  *
  74.  * It is supposed to try to remove 'its' thread from the wait queue;
  75.  * it can eventually fail to achieve this goal when these two events
  76.  * overlap. In that case it behaves just as though there was no
  77.  * timeout at all.
  78.  *
  79.  * @param data Pointer to the thread that called waitq_sleep_timeout().
  80.  */
  81. void waitq_timeouted_sleep(void *data)
  82. {
  83.     thread_t *t = (thread_t *) data;
  84.     waitq_t *wq;
  85.     bool do_wakeup = false;
  86.  
  87.     spinlock_lock(&threads_lock);
  88.     if (!thread_exists(t))
  89.         goto out;
  90.  
  91. grab_locks:
  92.     spinlock_lock(&t->lock);
  93.     if ((wq = t->sleep_queue)) {        /* assignment */
  94.         if (!spinlock_trylock(&wq->lock)) {
  95.             spinlock_unlock(&t->lock);
  96.             goto grab_locks;    /* avoid deadlock */
  97.         }
  98.  
  99.         list_remove(&t->wq_link);
  100.         t->saved_context = t->sleep_timeout_context;
  101.         do_wakeup = true;
  102.        
  103.         spinlock_unlock(&wq->lock);
  104.         t->sleep_queue = NULL;
  105.     }
  106.    
  107.     t->timeout_pending = false;
  108.     spinlock_unlock(&t->lock);
  109.    
  110.     if (do_wakeup)
  111.         thread_ready(t);
  112.  
  113. out:
  114.     spinlock_unlock(&threads_lock);
  115. }
  116.  
  117. /** Interrupt sleeping thread.
  118.  *
  119.  * This routine attempts to interrupt a thread from its sleep in a waitqueue.
  120.  * If the thread is not found sleeping, no action is taken.
  121.  *
  122.  * @param t Thread to be interrupted.
  123.  */
  124. void waitq_interrupt_sleep(thread_t *t)
  125. {
  126.     waitq_t *wq;
  127.     bool do_wakeup = false;
  128.     ipl_t ipl;
  129.  
  130.     ipl = interrupts_disable();
  131.     spinlock_lock(&threads_lock);
  132.     if (!thread_exists(t))
  133.         goto out;
  134.  
  135. grab_locks:
  136.     spinlock_lock(&t->lock);
  137.     if ((wq = t->sleep_queue)) {        /* assignment */
  138.         if (!spinlock_trylock(&wq->lock)) {
  139.             spinlock_unlock(&t->lock);
  140.             goto grab_locks;    /* avoid deadlock */
  141.         }
  142.  
  143.         list_remove(&t->wq_link);
  144.         t->saved_context = t->sleep_interruption_context;
  145.         do_wakeup = true;
  146.        
  147.         spinlock_unlock(&wq->lock);
  148.         t->sleep_queue = NULL;
  149.     }
  150.     spinlock_unlock(&t->lock);
  151.  
  152.     if (do_wakeup)
  153.         thread_ready(t);
  154.  
  155. out:
  156.     spinlock_unlock(&threads_lock);
  157.     interrupts_restore(ipl);
  158. }
  159.  
  160. /** Sleep until either wakeup, timeout or interruption occurs
  161.  *
  162.  * This is a sleep implementation which allows itself to be
  163.  * interrupted from the sleep, restoring a failover context.
  164.  *
  165.  * Sleepers are organised in a FIFO fashion in a structure called wait queue.
  166.  *
  167.  * This function is really basic in that other functions as waitq_sleep()
  168.  * and all the *_timeout() functions use it.
  169.  *
  170.  * @param wq Pointer to wait queue.
  171.  * @param usec Timeout in microseconds.
  172.  * @param nonblocking Blocking vs. non-blocking operation mode switch.
  173.  *
  174.  * If usec is greater than zero, regardless of the value of nonblocking,
  175.  * the call will not return until either timeout or wakeup comes.
  176.  *
  177.  * If usec is zero and @nonblocking is zero (false), the call
  178.  * will not return until wakeup comes.
  179.  *
  180.  * If usec is zero and nonblocking is non-zero (true), the call will
  181.  * immediately return, reporting either success or failure.
  182.  *
  183.  * @return  Returns one of: ESYNCH_WOULD_BLOCK, ESYNCH_TIMEOUT,
  184.  *          ESYNCH_OK_ATOMIC, ESYNCH_OK_BLOCKED.
  185.  *
  186.  * @li ESYNCH_WOULD_BLOCK means that the sleep failed because at the time
  187.  * of the call there was no pending wakeup.
  188.  *
  189.  * @li ESYNCH_TIMEOUT means that the sleep timed out.
  190.  *
  191.  * @li ESYNCH_INTERRUPTED means that somebody interrupted the sleeping thread.
  192.  *
  193.  * @li ESYNCH_OK_ATOMIC means that the sleep succeeded and that there was
  194.  * a pending wakeup at the time of the call. The caller was not put
  195.  * asleep at all.
  196.  *
  197.  * @li ESYNCH_OK_BLOCKED means that the sleep succeeded; the full sleep was
  198.  * attempted.
  199.  */
  200. int waitq_sleep_timeout(waitq_t *wq, __u32 usec, int nonblocking)
  201. {
  202.     ipl_t ipl;
  203.     int rc;
  204.    
  205.     ipl = waitq_sleep_prepare(wq);
  206.     rc = waitq_sleep_timeout_unsafe(wq, usec, nonblocking);
  207.     waitq_sleep_finish(wq, rc, ipl);
  208.     return rc;
  209. }
  210.  
  211. /** Prepare to sleep in a waitq.
  212.  *
  213.  * This function will return holding the lock of the wait queue
  214.  * and interrupts disabled.
  215.  *
  216.  * @param wq Wait queue.
  217.  *
  218.  * @return Interrupt level as it existed on entry to this function.
  219.  */
  220. ipl_t waitq_sleep_prepare(waitq_t *wq)
  221. {
  222.     ipl_t ipl;
  223.    
  224. restart:
  225.     ipl = interrupts_disable();
  226.  
  227.     if (THREAD) {   /* needed during system initiailzation */
  228.         /*
  229.          * Busy waiting for a delayed timeout.
  230.          * This is an important fix for the race condition between
  231.          * a delayed timeout and a next call to waitq_sleep_timeout().
  232.          * Simply, the thread is not allowed to go to sleep if
  233.          * there are timeouts in progress.
  234.          */
  235.         spinlock_lock(&THREAD->lock);
  236.         if (THREAD->timeout_pending) {
  237.             spinlock_unlock(&THREAD->lock);
  238.             interrupts_restore(ipl);
  239.             goto restart;
  240.         }
  241.         spinlock_unlock(&THREAD->lock);
  242.     }
  243.                                                    
  244.     spinlock_lock(&wq->lock);
  245.     return ipl;
  246. }
  247.  
  248. /** Finish waiting in a wait queue.
  249.  *
  250.  * This function restores interrupts to the state that existed prior
  251.  * to the call to waitq_sleep_prepare(). If necessary, the wait queue
  252.  * lock is released.
  253.  *
  254.  * @param wq Wait queue.
  255.  * @param rc Return code of waitq_sleep_timeout_unsafe().
  256.  * @param ipl Interrupt level returned by waitq_sleep_prepare().
  257.  */
  258. void waitq_sleep_finish(waitq_t *wq, int rc, ipl_t ipl)
  259. {
  260.     switch (rc) {
  261.     case ESYNCH_WOULD_BLOCK:
  262.     case ESYNCH_OK_ATOMIC:
  263.         spinlock_unlock(&wq->lock);
  264.         break;
  265.     default:
  266.         break;
  267.     }
  268.     interrupts_restore(ipl);
  269. }
  270.  
  271. /** Internal implementation of waitq_sleep_timeout().
  272.  *
  273.  * This function implements logic of sleeping in a wait queue.
  274.  * This call must be preceeded by a call to waitq_sleep_prepare()
  275.  * and followed by a call to waitq_slee_finish().
  276.  *
  277.  * @param wq See waitq_sleep_timeout().
  278.  * @param usec See waitq_sleep_timeout().
  279.  * @param nonblocking See waitq_sleep_timeout().
  280.  *
  281.  * @return See waitq_sleep_timeout().
  282.  */
  283. int waitq_sleep_timeout_unsafe(waitq_t *wq, __u32 usec, int nonblocking)
  284. {
  285.     /* checks whether to go to sleep at all */
  286.     if (wq->missed_wakeups) {
  287.         wq->missed_wakeups--;
  288.         return ESYNCH_OK_ATOMIC;
  289.     }
  290.     else {
  291.         if (nonblocking && (usec == 0)) {
  292.             /* return immediatelly instead of going to sleep */
  293.             return ESYNCH_WOULD_BLOCK;
  294.         }
  295.     }
  296.    
  297.     /*
  298.      * Now we are firmly decided to go to sleep.
  299.      */
  300.     spinlock_lock(&THREAD->lock);
  301.  
  302.     /*
  303.      * Set context that will be restored if the sleep
  304.      * of this thread is ever interrupted.
  305.      */
  306.     if (!context_save(&THREAD->sleep_interruption_context)) {
  307.         /* Short emulation of scheduler() return code. */
  308.         spinlock_unlock(&THREAD->lock);
  309.         return ESYNCH_INTERRUPTED;
  310.     }
  311.  
  312.     if (usec) {
  313.         /* We use the timeout variant. */
  314.         if (!context_save(&THREAD->sleep_timeout_context)) {
  315.             /* Short emulation of scheduler() return code. */
  316.             spinlock_unlock(&THREAD->lock);
  317.             return ESYNCH_TIMEOUT;
  318.         }
  319.         THREAD->timeout_pending = true;
  320.         timeout_register(&THREAD->sleep_timeout, (__u64) usec, waitq_timeouted_sleep, THREAD);
  321.     }
  322.  
  323.     list_append(&THREAD->wq_link, &wq->head);
  324.  
  325.     /*
  326.      * Suspend execution.
  327.      */
  328.     THREAD->state = Sleeping;
  329.     THREAD->sleep_queue = wq;
  330.  
  331.     spinlock_unlock(&THREAD->lock);
  332.  
  333.     scheduler();    /* wq->lock is released in scheduler_separated_stack() */
  334.    
  335.     return ESYNCH_OK_BLOCKED;
  336. }
  337.  
  338.  
  339. /** Wake up first thread sleeping in a wait queue
  340.  *
  341.  * Wake up first thread sleeping in a wait queue.
  342.  * This is the SMP- and IRQ-safe wrapper meant for
  343.  * general use.
  344.  *
  345.  * Besides its 'normal' wakeup operation, it attempts
  346.  * to unregister possible timeout.
  347.  *
  348.  * @param wq Pointer to wait queue.
  349.  * @param all If this is non-zero, all sleeping threads
  350.  *        will be woken up and missed count will be zeroed.
  351.  */
  352. void waitq_wakeup(waitq_t *wq, bool all)
  353. {
  354.     ipl_t ipl;
  355.  
  356.     ipl = interrupts_disable();
  357.     spinlock_lock(&wq->lock);
  358.  
  359.     _waitq_wakeup_unsafe(wq, all);
  360.  
  361.     spinlock_unlock(&wq->lock);
  362.     interrupts_restore(ipl);   
  363. }
  364.  
  365. /** Internal SMP- and IRQ-unsafe version of waitq_wakeup()
  366.  *
  367.  * This is the internal SMP- and IRQ-unsafe version
  368.  * of waitq_wakeup(). It assumes wq->lock is already
  369.  * locked and interrupts are already disabled.
  370.  *
  371.  * @param wq Pointer to wait queue.
  372.  * @param all If this is non-zero, all sleeping threads
  373.  *        will be woken up and missed count will be zeroed.
  374.  */
  375. void _waitq_wakeup_unsafe(waitq_t *wq, bool all)
  376. {
  377.     thread_t *t;
  378.  
  379. loop:  
  380.     if (list_empty(&wq->head)) {
  381.         wq->missed_wakeups++;
  382.         if (all)
  383.             wq->missed_wakeups = 0;
  384.         return;
  385.     }
  386.  
  387.     t = list_get_instance(wq->head.next, thread_t, wq_link);
  388.    
  389.     list_remove(&t->wq_link);
  390.     spinlock_lock(&t->lock);
  391.     if (t->timeout_pending && timeout_unregister(&t->sleep_timeout))
  392.         t->timeout_pending = false;
  393.     t->sleep_queue = NULL;
  394.     spinlock_unlock(&t->lock);
  395.  
  396.     thread_ready(t);
  397.  
  398.     if (all)
  399.         goto loop;
  400. }
  401.