Many problems come from the interaction between process signals and thread signals.
RTLinux V3.0 uses the concept of process signals to provide an interface to hard interrupt handlers. If act is non-null, the new action for signal signum is installed from act . If oldact is non-null, the previous action is saved in oldact . In V3 and prior RTLinux these flags have no effect. Furthermore, when a signal handler for a hard interrupt is entered all interrupts are blocked by default.