> Is it safe to sleep on a userland address? It seems safe to me, but I'd
> like to have a confirmation.

safe -- for now, but questionable.

BTW, all code calling sleep() or its successors should always be
prepared for spurious wakeups -- i.e., always use sleep() in a loop.
They are rare, but happen in the vicinity of things like signals and
the like.

				- Bill