Calling tsleep(9) with interrupts disabled

[Ian Lepore]

I just realized that I've accidentally coded a sequence similar to this
in a driver:

   s = intr_disable();
   // do stuff here
   tsleep(sc, 0, "twird", hz / 4);
   // more stuff
   intr_restore(s);

Much to my surpise this works, including waking up due to wakeup(sc)
being called from an interrupt handler.  So apparently tsleep() results
in interrupts being re-enabled during the sleep, although nothing in the
manpage says that will happen.

Can I safely rely on this behavior, or is it working by accident?

(Please no lectures on the evils of disabling interrupts...  This is not
a multi-GHz multi-core Xeon, it's a 180mhz embedded SoC with buggy
builtin devices that will drop or corrupt data if an interrupt happens
during the "do stuff here" part of the code.)

-- Ian