Changeset 10b51ae in rtems

score: Critical section change in _Thread_Dispatch

If we enter _Thread_Dispatch() then _Thread_Dispatch_disable_level must
be zero. Single processor RTEMS assumes that stores of non-zero values
to _Thread_Dispatch_disable_level are observed by interrupts as non-zero values.

Move the _Thread_Dispatch_set_disable_level( 1 ) out of the first ISR
disabled critical section. In case interrupts happen between the
_Thread_Dispatch_set_disable_level( 1 ) and _ISR_Disable( level ) then
the interrupt will observe a non-zero _Thread_Dispatch_disable_level and
will not issue a _Thread_Dispatch() and we can enter the ISR disabled
section directly after interrupt processing.

This change leads to symmetry between the single processor and SMP
configuration.