source: rtems/cpukit/rtems/src/eventsurrender.c @ b84a51c

Last change on this file since b84a51c was b84a51c, checked in by Sebastian Huber <sebastian.huber@…>, on Nov 10, 2015 at 4:23:12 PM

score: Fix race condition on SMP

We must ensure that the Thread_Control::Wait information update is
visible to the target thread before we update its wait flags, otherwise
we may return out of date events or a wrong status.

  • Property mode set to 100644
File size: 3.3 KB
Line 
1/**
2 *  @file
3 *
4 *  @brief Surrender Event
5 *  @ingroup ClassicEvent
6 */
7
8/*
9 *  COPYRIGHT (c) 1989-2008.
10 *  On-Line Applications Research Corporation (OAR).
11 *
12 *  The license and distribution terms for this file may be
13 *  found in the file LICENSE in this distribution or at
14 *  http://www.rtems.org/license/LICENSE.
15 */
16
17#if HAVE_CONFIG_H
18  #include "config.h"
19#endif
20
21#include <rtems/rtems/eventimpl.h>
22#include <rtems/rtems/optionsimpl.h>
23#include <rtems/score/threadimpl.h>
24#include <rtems/score/watchdogimpl.h>
25
26static void _Event_Satisfy(
27  Thread_Control  *the_thread,
28  Event_Control   *event,
29  rtems_event_set  pending_events,
30  rtems_event_set  seized_events
31)
32{
33  event->pending_events = _Event_sets_Clear( pending_events, seized_events );
34  *(rtems_event_set *) the_thread->Wait.return_argument = seized_events;
35}
36
37static bool _Event_Is_blocking_on_event(
38  const Thread_Control *the_thread,
39  Thread_Wait_flags     wait_class
40)
41{
42  Thread_Wait_flags wait_flags;
43  Thread_Wait_flags wait_mask;
44
45  wait_flags = _Thread_Wait_flags_get( the_thread );
46  wait_mask = THREAD_WAIT_CLASS_MASK | THREAD_WAIT_STATE_READY_AGAIN;
47
48  return ( wait_flags & wait_mask ) == wait_class;
49}
50
51static bool _Event_Is_satisfied(
52  const Thread_Control *the_thread,
53  rtems_event_set       pending_events,
54  rtems_event_set      *seized_events
55)
56{
57  rtems_option    option_set;
58  rtems_event_set event_condition;
59
60  option_set = the_thread->Wait.option;
61  event_condition = the_thread->Wait.count;
62  *seized_events = _Event_sets_Get( pending_events, event_condition );
63
64  return !_Event_sets_Is_empty( *seized_events )
65    && ( *seized_events == event_condition || _Options_Is_any( option_set ) );
66}
67
68void _Event_Surrender(
69  Thread_Control    *the_thread,
70  rtems_event_set    event_in,
71  Event_Control     *event,
72  Thread_Wait_flags  wait_class,
73  ISR_lock_Context  *lock_context
74)
75{
76  rtems_event_set pending_events;
77  rtems_event_set seized_events;
78  bool            unblock;
79
80  _Thread_Lock_acquire_default_critical( the_thread, lock_context );
81
82  _Event_sets_Post( event_in, &event->pending_events );
83  pending_events = event->pending_events;
84
85  if (
86    _Event_Is_blocking_on_event( the_thread, wait_class )
87      && _Event_Is_satisfied( the_thread, pending_events, &seized_events )
88  ) {
89    Thread_Wait_flags ready_again;
90    bool              success;
91
92    _Event_Satisfy( the_thread, event, pending_events, seized_events );
93
94    /* See _Event_Seize() */
95    _Atomic_Fence( ATOMIC_ORDER_RELEASE );
96
97    ready_again = wait_class | THREAD_WAIT_STATE_READY_AGAIN;
98    success = _Thread_Wait_flags_try_change_critical(
99      the_thread,
100      wait_class | THREAD_WAIT_STATE_INTEND_TO_BLOCK,
101      ready_again
102    );
103
104    if ( success ) {
105      unblock = false;
106    } else {
107      _Assert(
108        _Thread_Wait_flags_get( the_thread )
109          == wait_class | THREAD_WAIT_STATE_BLOCKED
110      );
111      _Thread_Wait_flags_set( the_thread, ready_again );
112      unblock = true;
113    }
114  } else {
115    unblock = false;
116  }
117
118  if ( unblock ) {
119    Per_CPU_Control *cpu_self;
120
121    cpu_self = _Thread_Dispatch_disable_critical( lock_context );
122    _Thread_Lock_release_default( the_thread, lock_context );
123
124    _Watchdog_Remove_ticks( &the_thread->Timer );
125    _Thread_Unblock( the_thread );
126
127    _Thread_Dispatch_enable( cpu_self );
128  } else {
129    _Thread_Lock_release_default( the_thread, lock_context );
130  }
131}
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