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SubjectRe: [PATCH] x86: Code atomic(64)_read and atomic(64)_set in C not CPP [was Re: FRV: Implement atomic64_t]

* Paul Mackerras <> wrote:

> Occasionally we get bugs where atomic_read or atomic_set are used
> on atomic64_t variables or vice versa. These bugs don't generate
> warnings on x86 because atomic_read and atomic_set are coded as
> macros rather than C functions, so we don't get any type-checking
> on their arguments; similarly for atomic64_read and atomic64_set
> in 64-bit kernels.
> This converts them to C functions so that the arguments are
> type-checked and bugs like this will get caught more easily. It
> also converts atomic_cmpxchg and atomic_xchg, and atomic64_cmpxchg
> and atomic64_xchg on 64-bit, so we get type-checking on their
> arguments too.
> Compiling a typical 64-bit x86 config, this generates no new
> warnings, and the vmlinux text is 86 bytes smaller.
> Signed-off-by: Paul Mackerras <>

Thanks Paul!

> ---
> Linus Torvalds writes:
> > Btw, Ingo: I looked at the x86-32 versions to be sure, and noticed a
> > couple of buglets:
> >
> > - atomic64_xchg uses "atomic_read()". Sure, it happens to work, since
> > the "atomic_read()" is not type-safe, and gets a non-atomic 64-bit
> > read, but that looks really really bogus.
> >
> > It _should_ use __atomic64_read(), and the 64-bit versions should use a
> > different counter name ("counter64"?) or we should use an inline
> > function for atomic_read(), so that the type safety issue gets fixed.
> I did this patch a few weeks ago (before the merge window) and
> sent it to Ingo, Thomas & Peter, but it seems to have got lost.

Yeah, as i noted back then off-list i didnt take it due to it
causing a criss-cross merge:

| > Acked-by: Peter Zijlstra <>
| Nice - could someone please remind us later in the merge window to
| have a look at this again? Right now this needs to go into
| perfcounters/core - but i'd like to avoid having to do too many
| cross-changes there.

Linus reminded us ;-)


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