Dear Johannes, Commit cd01672d64a3 ("um: Enable preemption in UML") changes the select in arch/um/Kconfig from selecting ARCH_NO_PREEMPT to selecting the non-existing config ARCH_NO_PREEMPT_DYNAMIC.
As I do not fully understand the change, I do not know exactly if the change in this line was just an accident or if it intends to select HAVE_PREEMPT_DYNAMIC. Maybe you could have another look at this? At the moment, this select command is without effect, as the current config does not exist. Best regards, Lukas