From: Luck, Tony
Sent: 13 June 2022 17:27
It's listed in Documentation/atomic_bitops.txt.
Oh, so my memory was actually correct that I saw it in the docs
somewhere.
WDYT, should I mention this here in the code (block comment) as well
that it's atomic and must not lose `volatile` as Andy suggested or
it's sufficient to have it in the docs (+ it's not underscored)?
I think a comment that the "volatile" is required to prevent re-ordering
is enough.
But maybe others are sufficiently clear on the meaning? I once wasted
time looking for the non-atomic __test_bit() version (to use in some code
that was already protected by a spin lock, so didn't need the overhead
of an "atomic" version) before realizing there wasn't a non-atomic one.
Does it make any sense for 'test bit' to be atomic?
I'm not even sure is needs any ordering constraints either.
The result is always stale - the value can be changed by
another cpu at any time.
The set/clear atomic bit-ops require a RMW bus cycle - which has
to be locked (or similar) to avoid corruption.
The atomic 'test and set' (etc) are RMW and return a valid state.
David
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