On Tue, Jan 31, 2017 at 1:32 PM, Linus Torvalds
<[email protected]> wrote:
>
> I've pulled this, but I really think it's papering over the real
> issue. Adding "linux-arch" mailing list to ask architecture
> maintainers to check their implementation of the atomic ops that
> return a truth value.
For example, looking at the x86-32 version, I see this:
static inline int atomic64_add_unless(atomic64_t *v, long long a, long long u)
...
return (int)a;
which looks really horribly wrong, but the assembly implementation
actually returns 0/1 in %eax so it ends up being right - just
confusingly so.
Also, to make things more confusing, the underscore version
(__atomic_add_unless()) actually returns the old value, not the truth
value of the comparison.
So this area definitely is messy. The x86-64 versions actually look
fairly clean and return nice boolean values.
Linus
