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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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