Yes, we do depend on this. All the RCU stuff (and in general *anything*
that depends on memory ordering as opposed to full locking, and we have
quite a lot of it) is very fundamentally dependent on the fact that things
like pointers get read and written atomically.
HOWEVER, it is worth pointing out that it's generally true in a
"different" sense than the actual atomic accesses. For example, if you
test a single bit of a word, it's still quite possible that gcc will have
turned that "atomic" read into a single byte read, so it's not necessarily
the case that we'll actually even read the whole word.
(Writes are different: if you do things like bitwise updates they simply
*will*not* be atomic, but that's simply not what we depend on anyway).
So in that sense, the atomicity guarantees are a lot weaker than the ones
we do for IO accesses, but that's all fine. Memory isn't IO, and doesn't
have side effects.
Linus
--
