This is a form of pre-emptive scheduling. It doesn't happen when the stack size needs to increase, it causes the stack check to fail. A bit of classic Dmitry cleverness: https://docs.google.com/document/d/1ETuA2IOmnaQ4j81AtTGT40Y4... http://golang.org/doc/go1.2#preemption

Anyway, I was just offering this scenario up as a bit of curious humour where somebody might think they are providing an escape hatch but the compiler in-lines their call foiling their plans :)

Curious humor == Classic too clever by half.