quoted

Nothing, but I also don't see how to prevent that.

You can test for current->flags & PF_KTHREAD following the check for
in_interrupt() and return true, it's what you were trying to do with the
check for !current->mm.

am I right to believe that if not in interrupt context - already ruled 
out - and !(current->flags & PF_KTHREAD), I am guaranteed to have a mm 
context, and thus, don't need to test against it ?