[zozbot234]

You could use CAS loops throughout to make your locks "less than one byte" in size, i.e. one byte, or perhaps one machine word, but using the free bits in that byte/word to store arbitrary data. (This is because a CAS loop can implement any read-modify-write operation on atomically sized data. But CAS will be somewhat slower than special-cased hardware atomics, so this is a bad idea for locks that are performance-sensitive.)

[gpderetta]

Single bit spin locks to protect things like linked list nodes are not unheard of.