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author | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2015-11-10 17:23:12 +0100 |
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committer | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2015-11-17 07:47:48 +0100 |
commit | 72857659c1f8fc71da4a30833caab583a2cfac6d (patch) | |
tree | 43998ecf8c46c6f4fed92acc227d58bb8c8a42dd /cpukit/rtems/src/eventsurrender.c | |
parent | Fix interrupt epilogue for ARMv7-AR and PowerPC (diff) | |
download | rtems-72857659c1f8fc71da4a30833caab583a2cfac6d.tar.bz2 |
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we may return out of date events or a wrong status.
Close #2471.
Diffstat (limited to 'cpukit/rtems/src/eventsurrender.c')
-rw-r--r-- | cpukit/rtems/src/eventsurrender.c | 55 |
1 files changed, 33 insertions, 22 deletions
diff --git a/cpukit/rtems/src/eventsurrender.c b/cpukit/rtems/src/eventsurrender.c index 156586023d..6a14467b7d 100644 --- a/cpukit/rtems/src/eventsurrender.c +++ b/cpukit/rtems/src/eventsurrender.c @@ -34,6 +34,20 @@ static void _Event_Satisfy( *(rtems_event_set *) the_thread->Wait.return_argument = seized_events; } +static bool _Event_Is_blocking_on_event( + const Thread_Control *the_thread, + Thread_Wait_flags wait_class +) +{ + Thread_Wait_flags wait_flags; + Thread_Wait_flags wait_mask; + + wait_flags = _Thread_Wait_flags_get( the_thread ); + wait_mask = THREAD_WAIT_CLASS_MASK | THREAD_WAIT_STATE_READY_AGAIN; + + return ( wait_flags & wait_mask ) == wait_class; +} + static bool _Event_Is_satisfied( const Thread_Control *the_thread, rtems_event_set pending_events, @@ -59,46 +73,43 @@ void _Event_Surrender( ISR_lock_Context *lock_context ) { - rtems_event_set pending_events; - rtems_event_set seized_events; - Thread_Wait_flags wait_flags; - bool unblock; + rtems_event_set pending_events; + rtems_event_set seized_events; + bool unblock; _Thread_Lock_acquire_default_critical( the_thread, lock_context ); _Event_sets_Post( event_in, &event->pending_events ); pending_events = event->pending_events; - wait_flags = _Thread_Wait_flags_get( the_thread ); - if ( - ( wait_flags & THREAD_WAIT_CLASS_MASK ) == wait_class + _Event_Is_blocking_on_event( the_thread, wait_class ) && _Event_Is_satisfied( the_thread, pending_events, &seized_events ) ) { - Thread_Wait_flags intend_to_block; - Thread_Wait_flags blocked; - bool success; + Thread_Wait_flags ready_again; + bool success; + + _Event_Satisfy( the_thread, event, pending_events, seized_events ); - intend_to_block = wait_class | THREAD_WAIT_STATE_INTEND_TO_BLOCK; - blocked = wait_class | THREAD_WAIT_STATE_BLOCKED; + /* See _Event_Seize() */ + _Atomic_Fence( ATOMIC_ORDER_RELEASE ); + ready_again = wait_class | THREAD_WAIT_STATE_READY_AGAIN; success = _Thread_Wait_flags_try_change_critical( the_thread, - intend_to_block, - wait_class | THREAD_WAIT_STATE_READY_AGAIN + wait_class | THREAD_WAIT_STATE_INTEND_TO_BLOCK, + ready_again ); + if ( success ) { - _Event_Satisfy( the_thread, event, pending_events, seized_events ); unblock = false; - } else if ( _Thread_Wait_flags_get( the_thread ) == blocked ) { - _Event_Satisfy( the_thread, event, pending_events, seized_events ); - _Thread_Wait_flags_set( - the_thread, - wait_class | THREAD_WAIT_STATE_READY_AGAIN + } else { + _Assert( + _Thread_Wait_flags_get( the_thread ) + == wait_class | THREAD_WAIT_STATE_BLOCKED ); + _Thread_Wait_flags_set( the_thread, ready_again ); unblock = true; - } else { - unblock = false; } } else { unblock = false; |