I hope the change in arch/um/kernel/skas/MMU.c isn't the cause of all this trouble!No it is not, but it is one that needs refinement. Fix coming up in 10 minutes or so, I was just cleaning up the patches for submission. The issue is reentrancy of the core interrupt logic which the code in unblock_signals is supposed to prevent, but it fails (for some reason) to do so.