Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 13 Dec 2021 10:11:28 -0800 | Subject | Re: [PATCH v2 8/9] atomic,x86: Alternative atomic_*_overflow() scheme |
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On Mon, Dec 13, 2021 at 8:43 AM Peter Zijlstra <peterz@infradead.org> wrote: > > So Marco was expressing doubt about this exact interface for the > atomic_*_overflow() functions, since it's extremely easy to get the > whole ATOMIC_OVERFLOW_OFFSET thing wrong.
I missed that discussion (maybe it was on irc? Or maybe I just get too much email).
Anyway, my preferred solution would simply be to make the ref-counting atomics use a different type.
Voilà, problem solved. You can't really misuse them by mistake, because you can't access it by mistake.
Sure, it could be a wrapper around 'atomic_t' on architectures that end up using the generic fallback, so it might be as simple as
typedef atomic_t atomic_ref_t;
in some asm-generic implementation, although I suspect that you'd want type safety even there, and do
typedef struct { atomic_t atomic_val; } atomic_ref_t;
But then on x86 - and other architectures that might prefer to use that offset trick because they have flags - I'm not sure it even makes sense to have anything to do with 'atomic_t' at all, since there would basically be zero overlap with the regular atomic operations (partly due to the offset, but partly simply because the 'ref' operations are simply different).
(Wrt naming: I do think this is more about the "ref" part than the "overflow" part - thus I'd suggest the "atomic_ref_t" rather than your ofl naming).
Linus
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