forked from Imagelibrary/rtems
9b83a66546
The changes in _Thread_Dispatch() of commitsdad36c52b8andd4dc7c8196introduced a severe bug which destroys the real-time properties of RTEMS completely. Consider the following scenario. We have three tasks L (lowest priority), M (middle priority), and H (highest priority). Now let a thread dispatch from M to L happen. An interrupt occurs in _Thread_Dispatch() here: void _Thread_Dispatch( void ) { [...] post_switch: _ISR_Enable( level ); <-- INTERRUPT <-- AFTER INTERRUPT _Thread_Unnest_dispatch(); _API_extensions_Run_postswitch(); } The interrupt event makes task H ready. The interrupt code will see _Thread_Dispatch_disable_level > 0 and thus doesn't perform a _Thread_Dispatch(). Now we return to position "AFTER INTERRUPT". This means task L executes now although task H is ready! Task H will execute once someone calls _Thread_Dispatch().