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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. #include <synch/waitq.h>
  30. #include <synch/synch.h>
  31. #include <synch/spinlock.h>
  32. #include <proc/thread.h>
  33. #include <proc/scheduler.h>
  34. #include <arch/asm.h>
  35. #include <arch/types.h>
  36. #include <time/timeout.h>
  37. #include <arch.h>
  38. #include <context.h>
  39. #include <list.h>
  40.  
  41. /** Initialize wait queue
  42.  *
  43.  * Initialize wait queue.
  44.  *
  45.  * @param wq Pointer to wait queue to be initialized.
  46.  */
  47. void waitq_initialize(waitq_t *wq)
  48. {
  49.     spinlock_initialize(&wq->lock);
  50.     list_initialize(&wq->head);
  51.     wq->missed_wakeups = 0;
  52. }
  53.  
  54. /** Handle timeout during waitq_sleep_timeout() call
  55.  *
  56.  * This routine is called when waitq_sleep_timeout() timeouts.
  57.  * Interrupts are disabled.
  58.  *
  59.  * It is supposed to try to remove 'its' thread from the wait queue;
  60.  * it can eventually fail to achieve this goal when these two events
  61.  * overlap. In that case it behaves just as though there was no
  62.  * timeout at all.
  63.  *
  64.  * @param data Pointer to the thread that called waitq_sleep_timeout().
  65.  */
  66. void waitq_interrupted_sleep(void *data)
  67. {
  68.     thread_t *t = (thread_t *) data;
  69.     waitq_t *wq;
  70.     int do_wakeup = 0;
  71.  
  72.     spinlock_lock(&threads_lock);
  73.     if (!list_member(&t->threads_link, &threads_head))
  74.         goto out;
  75.  
  76. grab_locks:
  77.     spinlock_lock(&t->lock);
  78.     if (wq = t->sleep_queue) {
  79.         if (!spinlock_trylock(&wq->lock)) {
  80.             spinlock_unlock(&t->lock);
  81.             goto grab_locks; /* avoid deadlock */
  82.         }
  83.  
  84.         list_remove(&t->wq_link);
  85.         t->saved_context = t->sleep_timeout_context;
  86.         do_wakeup = 1;
  87.        
  88.         spinlock_unlock(&wq->lock);
  89.         t->sleep_queue = NULL;
  90.     }
  91.    
  92.     t->timeout_pending = 0;
  93.     spinlock_unlock(&t->lock);
  94.    
  95.     if (do_wakeup) thread_ready(t);
  96.  
  97. out:
  98.     spinlock_unlock(&threads_lock);
  99. }
  100.  
  101. /** Sleep until either wakeup or timeout occurs
  102.  *
  103.  * This is a sleep implementation which allows itself to be
  104.  * interrupted from the sleep, restoring a failover context.
  105.  *
  106.  * Sleepers are organised in FIFO fashion in a structure called wait queue.
  107.  *
  108.  * This function is really basic in that other functions as waitq_sleep()
  109.  * and all the *_timeout() functions use it.
  110.  *
  111.  * @param wq Pointer to wait queue.
  112.  * @param usec Timeout in microseconds.
  113.  * @param nonblocking Blocking vs. non-blocking operation mode switch.
  114.  *
  115.  * If usec is greater than zero, regardless of the value of nonblocking,
  116.  * the call will not return until either timeout or wakeup comes.
  117.  *
  118.  * If usec is zero and nonblocking is zero (false), the call
  119.  * will not return until wakeup comes.
  120.  *
  121.  * If usec is zero and nonblocking is non-zero (true), the call will
  122.  * immediately return, reporting either success or failure.
  123.  *
  124.  * @return Returns one of: ESYNCH_WOULD_BLOCK, ESYNCH_TIMEOUT,
  125.  *         ESYNCH_OK_ATOMIC, ESYNCH_OK_BLOCKED.
  126.  *
  127.  * ESYNCH_WOULD_BLOCK means that the sleep failed because at the time
  128.  * of the call there was no pending wakeup.
  129.  *
  130.  * ESYNCH_TIMEOUT means that the sleep timed out.
  131.  *
  132.  * ESYNCH_OK_ATOMIC means that the sleep succeeded and that there was
  133.  * a pending wakeup at the time of the call. The caller was not put
  134.  * asleep at all.
  135.  *
  136.  * ESYNCH_OK_BLOCKED means that the sleep succeeded; the full sleep was
  137.  * attempted.
  138.  */
  139. int waitq_sleep_timeout(waitq_t *wq, __u32 usec, int nonblocking)
  140. {
  141.     volatile ipl_t ipl; /* must be live after context_restore() */
  142.    
  143.    
  144. restart:
  145.     ipl = interrupts_disable();
  146.    
  147.     /*
  148.      * Busy waiting for a delayed timeout.
  149.      * This is an important fix for the race condition between
  150.      * a delayed timeout and a next call to waitq_sleep_timeout().
  151.      * Simply, the thread is not allowed to go to sleep if
  152.      * there are timeouts in progress.
  153.      */
  154.     spinlock_lock(&THREAD->lock);
  155.     if (THREAD->timeout_pending) {
  156.         spinlock_unlock(&THREAD->lock);
  157.         interrupts_restore(ipl);       
  158.         goto restart;
  159.     }
  160.     spinlock_unlock(&THREAD->lock);
  161.    
  162.     spinlock_lock(&wq->lock);
  163.    
  164.     /* checks whether to go to sleep at all */
  165.     if (wq->missed_wakeups) {
  166.         wq->missed_wakeups--;
  167.         spinlock_unlock(&wq->lock);
  168.         interrupts_restore(ipl);
  169.         return ESYNCH_OK_ATOMIC;
  170.     }
  171.     else {
  172.         if (nonblocking && (usec == 0)) {
  173.             /* return immediatelly instead of going to sleep */
  174.             spinlock_unlock(&wq->lock);
  175.             interrupts_restore(ipl);
  176.             return ESYNCH_WOULD_BLOCK;
  177.         }
  178.     }
  179.  
  180.    
  181.     /*
  182.      * Now we are firmly decided to go to sleep.
  183.      */
  184.     spinlock_lock(&THREAD->lock);
  185.     if (usec) {
  186.         /* We use the timeout variant. */
  187.         if (!context_save(&THREAD->sleep_timeout_context)) {
  188.             /*
  189.              * Short emulation of scheduler() return code.
  190.              */
  191.             before_thread_runs();
  192.             spinlock_unlock(&THREAD->lock);
  193.             interrupts_restore(ipl);
  194.             return ESYNCH_TIMEOUT;
  195.         }
  196.         THREAD->timeout_pending = 1;
  197.         timeout_register(&THREAD->sleep_timeout, (__u64) usec, waitq_interrupted_sleep, THREAD);
  198.     }
  199.  
  200.     list_append(&THREAD->wq_link, &wq->head);
  201.  
  202.     /*
  203.      * Suspend execution.
  204.      */
  205.     THREAD->state = Sleeping;
  206.     THREAD->sleep_queue = wq;
  207.  
  208.     spinlock_unlock(&THREAD->lock);
  209.  
  210.     scheduler();    /* wq->lock is released in scheduler_separated_stack() */
  211.     interrupts_restore(ipl);
  212.    
  213.     return ESYNCH_OK_BLOCKED;
  214. }
  215.  
  216.  
  217. /** Wake up first thread sleeping in a wait queue
  218.  *
  219.  * Wake up first thread sleeping in a wait queue.
  220.  * This is the SMP- and IRQ-safe wrapper meant for
  221.  * general use.
  222.  *
  223.  * Besides its 'normal' wakeup operation, it attempts
  224.  * to unregister possible timeout.
  225.  *
  226.  * @param wq Pointer to wait queue.
  227.  * @param all If this is non-zero, all sleeping threads
  228.  *        will be woken up and missed count will be zeroed.
  229.  */
  230. void waitq_wakeup(waitq_t *wq, int all)
  231. {
  232.     ipl_t ipl;
  233.  
  234.     ipl = interrupts_disable();
  235.     spinlock_lock(&wq->lock);
  236.  
  237.     _waitq_wakeup_unsafe(wq, all);
  238.  
  239.     spinlock_unlock(&wq->lock);
  240.     interrupts_restore(ipl);   
  241. }
  242.  
  243. /** Internal SMP- and IRQ-unsafe version of waitq_wakeup()
  244.  *
  245.  * This is the internal SMP- and IRQ-unsafe version
  246.  * of waitq_wakeup(). It assumes wq->lock is already
  247.  * locked and interrupts are already disabled.
  248.  *
  249.  * @param wq Pointer to wait queue.
  250.  * @param all If this is non-zero, all sleeping threads
  251.  *        will be woken up and missed count will be zeroed.
  252.  */
  253. void _waitq_wakeup_unsafe(waitq_t *wq, int all)
  254. {
  255.     thread_t *t;
  256.  
  257. loop:  
  258.     if (list_empty(&wq->head)) {
  259.         wq->missed_wakeups++;
  260.         if (all) wq->missed_wakeups = 0;
  261.         return;
  262.     }
  263.  
  264.     t = list_get_instance(wq->head.next, thread_t, wq_link);
  265.    
  266.     list_remove(&t->wq_link);
  267.     spinlock_lock(&t->lock);
  268.     if (t->timeout_pending && timeout_unregister(&t->sleep_timeout))
  269.         t->timeout_pending = 0;
  270.     t->sleep_queue = NULL;
  271.     spinlock_unlock(&t->lock);
  272.  
  273.     thread_ready(t);
  274.  
  275.     if (all) goto loop;
  276. }
  277.