Re: [PATCH -v2 14/33] locking,m68k: Implement atomic_fetch_{add,sub,and,or,xor}()

[Geert Uytterhoeven]

Hi Peter,

On Tue, May 31, 2016 at 12:19 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> Implement FETCH-OP atomic primitives, these are very similar to the
> existing OP-RETURN primitives we already have, except they return the
> value of the atomic variable _before_ modification.
>
> This is especially useful for irreversible operations -- such as
> bitops (because it becomes impossible to reconstruct the state prior
> to modification).
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  arch/m68k/include/asm/atomic.h |   53 +++++++++++++++++++++++++++++++++++++----
>  1 file changed, 49 insertions(+), 4 deletions(-)
>
> --- a/arch/m68k/include/asm/atomic.h
> +++ b/arch/m68k/include/asm/atomic.h
> @@ -38,6 +38,13 @@ static inline void atomic_##op(int i, at
>
>  #ifdef CONFIG_RMW_INSNS
>
> +/*
> + * Am I reading these CAS loops right in that %2 is the old value and the first
> + * iteration uses an uninitialized value?
> + *
> + * Would it not make sense to add: tmp = atomic_read(v); to avoid this?
> + */
> +
>  #define ATOMIC_OP_RETURN(op, c_op, asm_op)                             \
>  static inline int atomic_##op##_return(int i, atomic_t *v)             \
>  {                                                                      \

Do we want the above comment in the code?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds