Thanks to Andi Kleen for the idea, answering my questions, fixing
my mistakes, filling content, etc. Philipp Rumpf for more spelling
and clarity fixes, and some excellent non-obvious points. Werner
Almesberger for giving me a great summary of
disable_irq(), and Jes Sorensen and Andrea
Arcangeli added caveats. Michael Elizabeth Chastain for checking
and adding to the Configure section. Telsa Gwynne for teaching me DocBook.