Yes, it is a bit, umm, innovative.  If it is going to be kept, even if 
just for devel logging, you should disable interrupts around it.  
Changing segments is not a normal thing to do.

Actually that wouldn't be needed because interrupts are not allowed to do any 
user accesses. And contrary to the name it doesn't actually change
the segment registers, only state used by *_user.

-Andi